12 Modern Homo sapiens
Beth Shook; Ph.D.; Lara Braff; Katie Nelson; Kelsie Aguilera; and M.A.
Keith Chan, Ph.D., Grossmont-Cuyamaca Community College District and MiraCosta College
This chapter is a revision from “Chapter 12: Modern Homo sapiens” by Keith Chan. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Identify the skeletal and behavioral traits that represent modern Homo sapiens.
- Critically evaluate different types of evidence for the origin of our species in Africa and our expansion around the world.
- Understand how the human lifestyle changed when people transitioned from foraging to agriculture.
- Hypothesize how human evolutionary trends may continue into the future.
The walls of a pink limestone cave in the hillside of Jebel Irhoud jutted out of the otherwise barren landscape of the Moroccan desert (Figure 12.1). Miners had excavated the cave in the 1960s, revealing some fossils. In 2007, a re-excavation of the site became a momentous occasion for science. A fossil cranium unearthed by a team of researchers was barely visible to the untrained eye. Just the fossil’s robust brows were peering out of the rock. This research team from the Max Planck Institute for Evolutionary Anthropology was the latest to explore the ancient human presence in this part of North Africa after a find by miners in 1960. Excavating near the first discovery, the researchers wanted to learn more about how Homo sapiens lived far from East Africa, where we thought our species originated.

The scientists were surprised when they analyzed the cranium, named Irhoud 10, and other fossils. Statistical comparisons with other human crania concluded that the Irhoud face shapes were typical of recent modern humans while the braincases matched ancient modern humans. Based on the findings of other scientists, the team expected these modern Homo sapiens fossils to be around 200,000 years old. Instead, dating revealed that the cranium had been buried for around 315,000 years.
Together, the modern-looking facial dimensions and the older date reshaped the interpretation of our species: modern Homo sapiens. Some key evolutionary changes from the archaic Homo sapiens (described in Chapter 11) to our species today happened 100,000 years earlier than we had thought and across the vast African continent rather than concentrated in its eastern region.
This revelation in the study of modern Homo sapiens is just one of the latest in this continually advancing area of biological anthropology. Researchers today are still discovering amazing fossils and ingenious ways to collect data and test hypotheses about our past. Through the collective work of many scientists, we are building an overall theory of modern human origins. In this chapter, we will first cover the skeletal changes from archaic Homo sapiens to modern Homo sapiens. Next, we will track how modern Homo sapiens expanded around the world. Lastly, we will cover the development of agriculture and how it changed human culture.
Defining Modernity
What defines modern Homo sapiens when compared to archaic Homo sapiens? Modern humans, like you and me, have a set of derived traits that are not seen in archaic humans or any other hominin. As with other transitions in hominin evolution, such as increasing brain size and bipedal ability, modern traits do not appear fully formed or all at once. In other words, the first modern Homo sapiens was not just born one day from archaic parents. The traits common to modern Homo sapiens appeared in a mosaic manner: gradually and out of sync with one another. There are two areas to consider when tracking the complex evolution of modern human traits. One is the physical change in the skeleton. The other is behavior inferred from the size and shape of the cranium and material culture evidence.
Skeletal Traits
The skeleton of modern Homo sapiens is less robust than that of archaic Homo sapiens. In other words, the modern skeleton is gracile, meaning that the structures are thinner and smoother. Differences related to gracility in the cranium are seen in the braincase, the face, and the mandible. There are also broad differences in the rest of the skeleton.
Cranial Traits

Several elements of the braincase differ between modern and archaic Homo sapiens. Overall, the shape is much rounder, or more globular, on a modern skull (Lieberman, McBratney, and Krovitz 2002; Neubauer, Hublin, and Gunz 2018; Pearson 2008; Figure 12.2). You can feel the globularity of your own modern human skull. Feel the height of your forehead with the palm of your hand. Viewed from the side, the tall vertical forehead of a modern Homo sapiens stands out when compared to the sloping archaic version. This is because the frontal lobe of the modern human brain is larger than the one in archaic humans, and the skull has to accommodate the expansion. The vertical forehead reduces a trait that is common to all other hominins: the brow ridge or supraorbital torus. The parietal lobes of the brain and the matching parietal bones on either side of the skull both bulge outward more in modern humans. At the back of the skull, the archaic occipital bun is no longer present. Instead, the occipital region of the modern human cranium has a derived tall and smooth curve, again reflecting the globular brain inside.
The trend of shrinking face size across hominins reaches its extreme with our species as well. The facial bones of a modern Homo sapiens are extremely gracile compared to all other hominins (Lieberman, McBratney, and Krovitz 2002). Continuing a trend in hominin evolution, technological innovations kept reducing the importance of teeth in reproductive success (Lucas 2007). As natural selection favored smaller and smaller teeth, the surrounding bone holding these teeth also shrank.
Related to smaller teeth, the mandible is also gracile in modern humans when compared to archaic humans and other hominins. Interestingly, our mandibles have pulled back so far from the prognathism of earlier hominins that we gained an extra structure at the most anterior point, called the mental eminence. You know this structure as the chin. At the skeletal level, it resembles an upside-down “T” at the centerline of the mandible (Pearson 2008). Looking back at archaic humans, you will see that they all lack a chin. Instead, their mandibles curve straight back without a forward point. What is the chin for and how did it develop? Flora Gröning and colleagues (2011) found evidence of the chin’s importance by simulating physical forces on computer models of different mandible shapes. Their results showed that the chin acts as structural support to withstand strain on the otherwise gracile mandible.
Postcranial Gracility

The rest of the modern human skeleton is also more gracile than its archaic counterpart. The differences are clear when comparing a modern Homo sapiens with a cold-adapted Neanderthal (Sawyer and Maley 2005), but the trends are still present when comparing modern and archaic humans within Africa (Pearson 2000). Overall, a modern Homo sapiens postcranial skeleton has thinner cortical bone, smoother features, and more slender shapes when compared to archaic Homo sapiens (Figure 12.3). Comparing whole skeletons, modern humans have longer limb proportions relative to the length and width of the torso, giving us lankier outlines.
Why is our skeleton so gracile compared to those of other hominins? Natural selection can drive the gracilization of skeletons in several ways (Lieberman 2015). A slender frame is adapted for the efficient long-distance running ability that started with Homo erectus. Furthermore, slenderness is a genetic adaptation for cooling an active body in hotter climates, which aligns with the ample evidence that Africa was the home continent of our species.
Behavioral Modernity
Aside from physical differences in the skeleton, researchers have also uncovered evidence of behavioral changes associated with increased cultural complexity from archaic to modern humans. How did cultural complexity develop? Two investigations into this question are archaeology and the analysis of reconstructed brains.
Archaeology tells us much about the behavioral complexity of past humans by interpreting the significance of material culture. In terms of advanced culture, items created with an artistic flair, or as decoration, speak of abstract thought processes (Figure 12.4). The demonstration of difficult artistic techniques and technological complexity hints at social learning and cooperation as well. According to paleoanthropologist John Shea (2011), one way to track the complexity of past behavior through artifacts is by measuring the variety of tools found together. The more types of tools constructed with different techniques and for different purposes, the more modern the behavior. Researchers are still working on an archaeological way to measure cultural complexity that is useful across time and place.

The interpretation of brain anatomy is another promising approach to studying the evolution of human behavior. When looking at investigations on this topic in modern Homo sapiens brains, researchers found a weak association between brain size and test-measured intelligence (Pietschnig et al. 2015). Additionally, they found no association between intelligence and biological sex. These findings mean that there are more significant factors that affect tested intelligence than just brain size. Since the sheer size of the brain is not useful for weighing intelligence within a species, paleoanthropologists are instead investigating the differences in certain brain structures. The differences in organization between modern Homo sapiens brains and archaic Homo sapiens brains may reflect different cognitive priorities that account for modern human culture. As with the archaeological approach, new discoveries will refine what we know about the human brain and apply that knowledge to studying the distant past.
Taken together, the cognitive abilities in modern humans may have translated into an adept use of tools to enhance survival. Researchers Patrick Roberts and Brian A. Stewart (2018) call this concept the generalist-specialist niche: our species is an expert at living in a wide array of environments, with populations culturally specializing in their own particular surroundings. The next section tracks how far around the world these skeletal and behavioral traits have taken us.
First Africa, Then the World
What enabled modern Homo sapiens to expand its range further in 300,000 years than Homo erectus did in 1.5 million years? The key is the set of derived biological traits from the last section. The gracile frame and neurological anatomy allowed modern humans to survive and even flourish in the vastly different environments they encountered. Based on multiple types of evidence, the source of all of these modern humans was Africa. Instead of originating from just one location, evidence shows that modern Homo sapiens evolution occurred in a complex gene flow network across Africa, a concept called African multiregionalism (Scerri et al. 2018).
This section traces the origin of modern Homo sapiens and the massive expansion of our species across all of the continents (except Antarctica) by 12,000 years ago. While modern Homo sapiens first shared geography with archaic humans, modern humans eventually spread into lands where no human had gone before. Figure 12.5 shows the broad routes that our species took expanding around the world. I encourage you to make your own timeline with the dates in this part to see the overall trends.

Modern Homo sapiens Biology and Culture in Africa
We start with the ample fossil evidence supporting the theory that modern humans originated in Africa during the Middle Pleistocene, having evolved from African archaic Homo sapiens. The earliest dated fossils considered to be modern actually have a mosaic of archaic and modern traits, showing the complex changes from one type to the other. Experts have various names for these transitional fossils, such as Early Modern Homo sapiens or Early Anatomically Modern Humans. However they are labeled, the presence of some modern traits means that they illustrate the origin of the modern type. Three particularly informative sites with fossils of the earliest modern Homo sapiens are Jebel Irhoud, Omo, and Herto.

Recall from the start of the chapter that the most recent finds at Jebel Irhoud are now the oldest dated fossils that exhibit some facial traits of modern Homo sapiens. Besides Irhoud 10, the cranium that was dated to 315,000 years ago (Hublin et al. 2017; Richter et al. 2017), there were other fossils found in the same deposit that we now know are from the same time period. In total there are at least five individuals, representing life stages from childhood to adulthood. These fossils form an image of high variation in skeletal traits. For example, the skull named Irhoud 1 has a primitive brow ridge, while Irhoud 2 and Irhoud 10 do not (Figure 12.6). The braincases are lower than what is seen in the modern humans of today but higher than in archaic Homo sapiens. The teeth also have a mix of archaic and modern traits that defy clear categorization into either group.
Research separated by nearly four decades uncovered fossils and artifacts from the Kibish Formation in the Lower Omo Valley in Ethiopia. These Omo Kibish hominins were represented by braincases and fragmented postcranial bones of three individuals found kilometers apart, dating back to around 233,000 years ago (Day 1969; McDougall, Brown, and Fleagle 2005; Vidal et al. 2022). One interesting finding was the variation in braincase size between the two more-complete specimens: while the individual named Omo I had a more globular dome, Omo II had an archaic-style long and low cranium.
Also in Ethiopia, a team led by Tim White (2003) excavated numerous fossils at Herto. There were fossilized crania of two adults and a child, along with fragments of more individuals. The dates ranged between 160,000 and 154,000 years ago. The skeletal traits and stone-tool assemblage were both intermediate between the archaic and modern types. Features reminiscent of modern humans included a tall braincase and thinner zygomatic (cheek) bones than those of archaic humans (Figure 12.7). Still, some archaic traits persisted in the Herto fossils, such as the supraorbital tori. Statistical analysis by other research teams concluded that at least some cranial measurements fit just within the modern human range (McCarthy and Lucas 2014), favoring categorization with our own species.

The timeline of material culture suggests a long period of relying on similar tools before a noticeable diversification of artifacts types. Researchers label the time of stable technology shared with archaic types the Middle Stone Age, while the subsequent time of diversification in material culture is called the Later Stone Age.
In the Middle Stone Age, the sites of Jebel Irhoud, Omo, and Herto all bore tools of the same flaked style as archaic assemblages, even though they were separated by almost 150,000 years. The consistency in technology may be evidence that behavioral modernity was not so developed. No clear signs of art dating back this far have been found either. Other hypotheses not related to behavioral modernity could explain these observations. The tool set may have been suitable for thriving in Africa without further innovation. Maybe works of art from that time were made with media that deteriorated or perhaps such art was removed by later humans.
Evidence of what Homo sapiens did in Africa from the end of the Middle Stone Age to the Later Stone Age is concentrated in South African cave sites that reveal the complexity of human behavior at the time. For example, Blombos Cave, located along the present shore of the Cape of Africa facing the Indian Ocean, is notable for having a wide variety of artifacts. The material culture shows that toolmaking and artistry were more complex than previously thought for the Middle Stone Age. In a layer dated to 100,000 years ago, researchers found two intact ochre-processing kits made of abalone shells and grinding stones (Henshilwood et al. 2011). Marine snail shell beads from 75,000 years ago were also excavated (Figure 12.8; d’Errico et al. 2005). Together, the evidence shows that the Middle Stone Age occupation at Blombos Cave incorporated resources from a variety of local environments into their culture, from caves (ochre), open land (animal bones and fat), and the sea (abalone and snail shells). This complexity shows a deep knowledge of the region’s resources and their use—not just for survival but also for symbolic purposes.

On the eastern coast of South Africa, Border Cave shows new African cultural developments at the start of the Later Stone Age. Paola Villa and colleagues (2012) identified several changes in technology around 43,000 years ago. Stone-tool production transitioned from a slower process to one that was faster and made many microliths, small and precise stone tools. Changes in decorations were also found across the Later Stone Age transition. Beads were made from a new resource: fragments of ostrich eggs shaped into circular forms resembling present-day breakfast cereal O’s (d’Errico et al. 2012). These beads show a higher level of altering one’s own surroundings and a move from the natural to the abstract in terms of design.
Summary of Modern H. sapiens in Africa
The combined fossil evidence paints a picture of diversity in geography and traits. Instead of evolving in just East Africa, the Jebel Irhoud find revealed that early modern Homo sapiens had a wide range across Middle Pleistocene Africa. Supporting this explanation, fossils have different mosaics of archaic and modern traits in different places and even within the same area. The high level of diversity from just these fossils shows that the modern traits took separate paths toward the set we have today. The connections were convoluted, involving fluctuating gene flow among small groups of regional nomadic foragers across a large continent over a long time.
African culture experienced a long constant phase called the Middle Stone Age until a faster burst of change produced innovation and new styles. The change was not one moment but rather an escalation in development. Later Stone Age culture introduced elements seen across many regions, including the construction of composite tools and even the use of strung decorations such as beads. These developments appear in the Later Stone Age of other regions, such as Europe. Based on the early date of the African artifacts, Later Stone Age culture may have originated in Africa and passed from person to person and region to region, with people adapting the general technique to their local resources and viewing the meaning in their own way.
Expansion into the Middle East and Asia
While modern Homo sapiens lived across Africa, some members eventually left the continent. These pioneers could have used two connections to the Middle East or West Asia. From North Africa, they could have crossed the Sinai Peninsula and moved north to the Levant, or eastern Mediterranean. Finds in that region show an early modern human presence. Other finds support the Southern Dispersal model, with a crossing from East Africa to the southern Arabian Peninsula through the Straits of Bab-el-Mandeb. It is tempting to think of one momentous event in which people stepped off Africa and into the Middle East, never to look back. In reality, there were likely multiple waves of movement producing gene flow back and forth across these regions as the overall range pushed east. The expanding modern human population could have thrived by using resources along the southern coast of the Arabian Peninsula to South Asia, with side routes moving north along rivers. The maximum range of the species then grew across Asia.
Modern Homo sapiens in the Middle East
Geographically, the Middle East is the ideal place for the African modern Homo sapiens population to inhabit upon expanding out of their home continent. In the Eastern Mediterranean coast of the Levant, there is a wealth of skeletal and material culture linked to modern Homo sapiens. Recent discoveries from Saudi Arabia further add to our view of human life just beyond Africa.
The Caves of Mount Carmel in present-day Israel have preserved skeletal remains and artifacts of modern Homo sapiens, the first-known group living outside Africa. The skeletal presence at Misliya Cave is represented by just part of the left upper jaw of one individual, but it is notable for being dated to a very early time, between 194,000 and 177,000 years ago (Hershkovitz et al. 2018). Later, from 120,000 to 90,000 years ago, fossils of multiple individuals across life stages were found in the caves of Es-Skhul and Qafzeh (Shea and Bar-Yosef 2005). The skeletons had many modern Homo sapiens traits, such as globular crania and more gracile postcranial bones when compared to Neanderthals. Still, there were some archaic traits. For example, the adult male Skhul V also possessed what researchers Daniel Lieberman, Osbjorn Pearson, and Kenneth Mowbray (2000) called marked or clear occipital bunning. Also, compared to later modern humans, the Mount Carmel people were more robust. Skhul V had a particularly impressive brow ridge that was short in height but sharply jutted forward above the eyes (Figure 12.9). The high level of preservation is due to the intentional burial of some of these people. Besides skeletal material, there are signs of artistic or symbolic behavior. For example, the adult male Skhul V had a boar’s jaw on his chest. Similarly, Qafzeh 11, a juvenile with healed cranial trauma, had an impressive deer antler rack placed over his torso (Figure 12.10; Coqueugniot et al. 2014). Perforated seashells colored with ochre, mineral-based pigment, were also found in Qafzeh (Bar-Yosef Mayer, Vandermeersch, and Bar-Yosef 2009).


One remaining question is, what happened to the modern humans of the Levant after 90,000 years ago? Another site attributed to our species did not appear in the region until 47,000 years ago. Competition with Neanderthals may have accounted for the disappearance of modern human occupation since the Neanderthal presence in the Levant lasted longer than the dates of the early modern Homo sapiens. John Shea and Ofer Bar-Yosef (2005) hypothesized that the Mount Carmel modern humans were an initial expansion from Africa that failed. Perhaps they could not succeed due to competition with the Neanderthals who had been there longer and had both cultural and biological adaptations to that environment.
Modern Homo sapiens of China
A long history of paleoanthropology in China has found ample evidence of modern human presence. Four notable sites are the caves at Fuyan, Liujiang, Tianyuan, and Zhoukoudian. In the distant past, these caves would have been at least seasonal shelters that unintentionally preserved evidence of human presence for modern researchers to discover.
At Fuyan Cave in Southern China, paleoanthropologists found 47 adult teeth associated with cave formations dated to between 120,000 and 80,000 years ago (Liu et al. 2015). It is currently the oldest-known modern human site in China, though other researchers question the validity of the date range (Michel et al. 2016). The teeth have the small size and gracile features of modern Homo sapiens dentition.
The fossil Liujiang (or Liukiang) hominin (67,000 years ago) has derived traits that classified it as a modern Homo sapiens, though primitive archaic traits were also present. In the skull, which was found nearly complete, the Liujiang hominin had a taller forehead than archaic Homo sapiens but also had an enlarged occipital region (Figure 12.11; Brown 1999; Wu et al. 2008). Other parts of the skeleton also had a mix of modern and archaic traits: for example, the femur fragments suggested a slender length but with thick bone walls (Woo 1959).

Another Chinese site to describe here is the one that has been studied the longest. In the Zhoukoudian Cave system (Figure 12.12), where Homo erectus and archaic Homo sapiens have also been found, there were three crania of modern Homo sapiens. These crania, which date to between 34,000 and 10,000 years ago, were all more globular than those of archaic humans but still lower and longer than those of later modern humans (Brown 1999; Harvati 2009). When compared to one another, the crania showed significant differences from one another. Comparison of cranial measurements to other populations past and present found no connection with modern East Asians, again showing that human variation was very different from what we see today.

Summary of Modern H. sapiens in the Middle East and Asia
As in Africa, the finds of the Middle East have shown that humans were biologically diverse and had complex relationships with their environment. Work in the Levant showed an initial expansion north from the Sinai Peninsula that did not last. Away from the Levant, expansion continued. Local resources were used to make lithics and decorative items.
The early Asian presence of modern Homo sapiens was complex and varied as befitting the massive continent. What the evidence shows is that people adapted to a wide array of environments that were far removed from Africa. From the Levant to China, humans with modern anatomy used caves that preserved signs of their presence. Faunal and floral remains found in these shelters speak to the flexibility of the human omnivorous diet as local wildlife and foliage became nourishment. Decorative items, often found as burial goods in planned graves, show a flourishing cultural life.
Eventually, modern humans at the southeastern fringe of the geographical range of the species found their way southeast until some became the first humans in Australia.
Crossing to Australia
Expansion of the first modern human Asians, still following the coast, eventually entered an area that researchers call Sunda before continuing on to modern Australia. Sunda was a landmass made up of the modern-day Malay Peninsula, Sumatra, Java, and Borneo. Lowered sea levels connected these places with land bridges, making them easier to traverse. Proceeding past Sunda meant navigating Wallacea, the archipelago that includes the Indonesian islands east of Borneo. In the distant past, there were many megafauna, large animals that migrating humans would have used for food and materials (such as utilizing animals’ hides and bones). Further southeast was another landmass called Sahul, which included New Guinea and Australia as one contiguous continent. Based on fossil evidence, this land had never seen hominins or any other primates before modern Homo sapiens arrived. Sites along this path offer clues about how our species handled the new environment to live successfully as foragers.

The skeletal remains at Lake Mungo, land traditionally owned by Mutthi Mutthi, Ngiampaa, and Paakantji peoples, are the oldest known in the continent. The now-dry lake was one of a series located along the southern coast of Australia in New South Wales, far from where the first people entered from the north (Barbetti and Allen 1972; Bowler et al. 1970). Two individuals dating to around 40,000 years ago show signs of artistic and symbolic behavior, including intentional burial. The bones of Lake Mungo 1 (LM1), an adult female, were crushed repeatedly, colored with red ochre, and cremated (Bowler et al. 1970). Lake Mungo 3 (LM3), a tall, older male with a gracile cranium but robust postcranial bones, had his fingers interlocked over his pelvic region (Brown 2000).
Kow Swamp, within traditional Yorta Yorta land also in southern Australia, contained human crania that looked distinctly different from the ones at Lake Mungo (Durband 2014; Thorne and Macumber 1972). The crania, dated between 9,000 and 20,000 years ago, had extremely robust brow ridges and thick bone walls, but these were paired with globular features on the braincase (Figure 12.13).
While no fossil humans have been found at the Madjedbebe rock shelter in the North Territory of Australia, more than 10,000 artifacts found there show both behavioral modernity and variability (Clarkson et al. 2017). They include a diverse array of stone tools and different shades of ochre for rock art, including mica-based reflective pigment (similar to glitter). These impressive artifacts are as far back as 56,000 years old, providing the date for the earliest-known presence of humans in Australia.
Summary of Modern H. sapiens in Australia
The overall view of the first modern humans in Australia from a biological perspective shows a high amount of skeletal diversity. This is similar to the trends seen earlier in Africa, the Middle East, and East Asia. The earliest-known arrivals brought with them a multifaceted suite of cultural practices as seen in their material culture.
From the Levant to Europe
The first modern human expansion into Europe occurred after other members of our species settled East Asia and Australia. As the evidence from the Levant suggests, modern human movement to Europe may have been hampered by the presence of Neanderthals. Another obstacle was that the colder climate was incompatible with the biology of African modern Homo sapiens, which was adapted for exposure to high temperature and ultraviolet radiation. Still, by 40,000 years ago, modern Homo sapiens had a detectable presence. This time was also the start of the Later Stone Age or Upper Paleolithic, when there was an expansion in cultural complexity. There is a wealth of evidence from this region due to a Western bias in research, the proximity of these findings to Western scientific institutions, and the desire of Western scientists to explore their own past. This section will cover key evidence of early modern human life in Europe, and the typologies used to view cultural changes in this region.

In Romania, the site of Peștera cu Oase (Cave of Bones) had the oldest-known remains of modern Homo sapiens in Europe, dated to around 40,000 years ago (Trinkaus et al. 2003a). Among the bones and teeth of many animals were the fragmented cranium of one person and the mandible of another (the two bones did not fit each other). Both bones have modern human traits similar to the fossils from the Middle East, but they also had Neanderthal traits. Oase 1, the mandible, had a mental eminence but also extremely large molars (Trinkaus et al. 2003b). This mandible has yielded DNA that surprisingly is equally similar to DNA from present-day Europeans and Asians (Fu et al. 2015). This means that Oase 1 was not the direct ancestor of modern Europeans. The Oase 2 cranium has the derived traits of reduced brow ridges along with archaic wide zygomatic cheekbones and an occipital bun (Figure 12.14; Rougier et al. 2007).
Dating to around 26,000 years ago, Předmostí near Přerov in the Czech Republic was a site where people buried over 30 individuals along with many artifacts. Eighteen individuals were found in one mass burial area, a few covered by the scapulae of woolly mammoths (Germonpré, Lázničková-Galetová, and Sablin 2012). The Předmostí crania were more globular than those of archaic humans but tended to be longer and lower than in later modern humans (Figure 12.15; Velemínská et al. 2008). The height of the face was in line with modern residents of Central Europe. There was also skeletal evidence of dog domestication, such as the presence of dog skulls with shorter snouts than in wild wolves (Germonpré, Lázničková-Galetová, and Sablin et al. 2012). In total, Předmostí could have been a settlement dependent on mammoths for subsistence and the artificial selection of early domesticated dogs.

The sequence of modern Homo sapiens technological change in the Later Stone Age has been thoroughly dated and labeled by researchers working in Europe. Among them, the Gravettian tradition of 33,000 years to 21,000 years ago is associated with most of the known curvy female figurines, often assumed to be “Venus” figures. Hunting technology also advanced in this time with the first known boomerang, atlatl (spear thrower), and archery. The Magdalenian tradition spread from 17,000 to 12,000 years ago. This culture further expanded on fine bone tool work, including barbed spearheads and fishhooks (Figure 12.16).

Among the many European sites dating to the Later Stone Age, the famous cave art sites deserve mention. Chauvet-Pont-d’Arc Cave in southern France dates to separate Aurignacian occupations 31,000 years ago and 26,000 years ago. Over a hundred art pieces representing 13 animal species are preserved, from commonly depicted deer and horses to rarer rhinos and owls. Another French cave with art is Lascaux, which is several thousand years younger at 17,000 years ago in the Magdalenian period. At this site, there are over 6,000 painted figures on the walls and ceiling (Figure 12.17). Scaffolding and lighting must have been used to make the paintings on the walls and ceiling deep in the cave. Overall, visiting Lascaux as a contemporary must have been an awesome experience: trekking deeper in the cave lit only by torches giving glimpses of animals all around as mysterious sounds echoed through the galleries.

Summary of Modern H. sapiens in Europe
Study of Europe in the Upper Paleolithic gives a more detailed view of the general pattern of biological and cultural change linked with the arrival of modern Homo sapiens. The modern humans experienced a rapidly changing culture that went through waves of complexity and refinement. Skeletally, the increasing globularity of the cranium and the gracility of the rest of the skeleton continued, though with unique regional traits, too. The cave art sites showed a deeper exploration of creativity though the exact meaning is unclear. With survival dependent on the surrounding ecology, painting the figures may have connected people to important and impressive wildlife at both a physical and spiritual level. Both reverence for animals and the use of caves for an enhanced sensory experience are common to cultures past and present.
Peopling of the Americas
By 25,000 years ago, our species was the only member of Homo left on Earth. Gone were the Neanderthals, Denisovans, Homo naledi, and Homo floresiensis. The range of modern Homo sapiens kept expanding eastward into—using the name given to this area by Europeans much later—the Western Hemisphere. This section will address what we know about the peopling of the Americas, from the first entry to these continents to the rapid spread of Indigenous Americans across its varied environments.
While evidence points to an ancient land bridge called Beringia that allowed people to cross from what is now northeastern Siberia into modern-day Alaska, what people did to cross this land bridge is still being investigated. For most of the 20th century, the accepted theory was the Ice-Free Corridor model. It stated that northeast Asians (East Asians and Siberians) first expanded across Beringia inland through a passage between glaciers that opened into the western Great Plains of the United States, just east of the Rocky Mountains, around 13,000 years ago (Swisher et al. 2013). While life up north in the cold environment would have been harsh, migrating birds and an emerging forest might have provided sustenance as generations expanded through this land (Potter et al. 2018).
However, in recent decades, researchers have accumulated evidence against the Ice-Free Corridor model. Archaeologist K. R. Fladmark (1979) brought the alternate Coastal Route model into the archaeological spotlight; researcher Jon M. Erlandson has been at the forefront of compiling support for this theory (Erlandson et al. 2015). The new focus is the southern edge of the land bridge instead of its center: About 16,000 years ago, members of our species expanded along the coastline from northeast Asia, east through Beringia, and south down the Pacific Coast of North America while the inland was still sealed off by ice. The coast would have been free of ice at least part of the year, and many resources would have been found there, such as fish (e.g., salmon), mammals (e.g., whales, seals, and otters), and plants (e.g., seaweed).
South through the Americas
When the first modern Homo sapiens reached the Western Hemisphere, the spread through the Americas was rapid. Multiple migration waves crossed from North to South America (Posth et al. 2018). Our species took advantage of the lack of hominin competition and the bountiful resources both along the coasts and inland. The Americas had their own wide array of megafauna, which included woolly mammoths (Figure 12.18), mastodons, camels, horses, ground sloths, giant tortoises, and—a favorite of researchers—a two-meter-tall beaver. The reason we cannot see these amazing animals today may be that resources gained from these fauna were crucial to the survival for people over 12,000 years ago (Araujo et al. 2017). Several sites are notable for what they add to our understanding of the distant past in the Americas, including interactions with megafauna and other elements of the environment.

A 2019 discovery may allow researchers to improve theories about the peopling of the Americas. In White Sands National Park, New Mexico, 60 human footprints have been astonishingly dated to around 22,000 years ago (Bennett et al. 2021). This date and location do not match either the Ice-Free Corridor or Coastal Route models. Researchers are now working to verify the find and adjust previous models to account for the new evidence. This groundbreaking find is sparking new theories; it is another example of the fast pace of research performed on our past.
Monte Verde is a landmark site that shows that the human population had expanded down the whole vertical stretch of the Americas to Chile by 14,600 years ago, only a few thousand years after humans first entered the Western Hemisphere from Alaska. The site has been excavated by archaeologist Tom D. Dillehay and his team (2015). The remains of nine distinct edible species of seaweed at the site shows familiarity with coastal resources and relates to the Coastal Route model by showing a connection between the inland people and the sea.

Named after the town in New Mexico, the Clovis stone-tool style is the first example of a widespread culture across much of North America, between 13,400 and 12,700 years ago (Miller, Holliday, and Bright 2013). Clovis points were fluted with two small projections, one on each end of the base, facing away from the head (Figure 12.19). The stone points found at this site match those found as far as the Canadian border and northern Mexico, and from the west coast to the east coast of the United States. Fourteen Clovis sites also contained the remains of mammoths or mastodons, suggesting that hunting megafauna with these points was an important part of life for the Clovis people. After the spread of the Clovis style, it diversified into several regional styles, keeping some of the Clovis form but also developing their own unique touches.
(maybe inlcude a special topic/dig deeper from Dr.Steeves talking about Clovis culture and effects on Indigenous histories)
Summary of Modern H. sapiens in the Americas
Research in Native American origins found some surprising details, refining older models. Genetically, the migration can be considered one long period of movement with splits into regional populations. This finding matches the sudden appearance and diversification of the homegrown Clovis culture. A few thousand years after arrival into the hemisphere, people had already covered the Americas from north to south.
The peopling of the Americas also had a lot of elements in common with the prior spread of humans across Africa, Europe, Asia, and Australia. In all of these expansions, these pioneers explored new lands that tested their ability to adapt, both culturally and biologically. Besides stone-tool technology, the use of ochre as decoration was seen from South Africa to South America. The coasts and rivers were likely avenues in the movement of people, artifacts, and ideas, outlining the land masses while providing access to varied environments. The presence of megafauna aided human success, but this resource was eventually depleted in many parts of the world.
The Big Picture: The Assimilation Hypothesis
How do researchers make sense of all of these modern Homo sapiens discoveries that cover over 300,000 years of time and stretch across every continent except Antarctica? How was modern Homo sapiens related to archaic Homo sapiens?
The Assimilation hypothesis proposes that modern Homo sapiens evolved in Africa first and expanded out but also interbred with the archaic Homo sapiens they encountered outside Africa (Figure 12.20). This hypothesis is powerful since it explains why Africa has the oldest modern human fossils, why early modern humans found in Europe and Asia bear a resemblance to the regional archaics, and why traces of archaic DNA can be found in our genomes today (Dannemann and Racimo 2018; Reich et al. 2010; Reich et al. 2011; Slatkin and Racimo 2016; Smith et al. 2017; Wall and Yoshihara Caldeira Brandt 2016).

While researchers have produced a model that satisfies the data, there are still a lot of questions for paleoanthropologists to answer regarding our origins. What were the patterns of migration in each part of the world? Why did the archaic humans go extinct? In what ways did archaic and modern humans interact? The definitive explanation of how our species started and what our ancestors did is still out there to be found. You are now in a great place to welcome the next discovery about our distant past—maybe you’ll even contribute to our understanding as well.
The Chain Reaction of Agriculture
While it may be hard to imagine today, for most of our species’ existence we were nomadic: moving through the landscape without a singular home. Instead of a refrigerator or pantry stocked with food, we procured nutrition and other resources as needed based on what was available in the environment. Instead of collecting and displaying shelves of stuff, we kept our possessions small for mobility. This section gives an overview of how the foraging lifestyle enabled the expansion of our species and how the invention of a new way of life caused a chain reaction of cultural change.
The Foraging Tradition
There are a variety of possible subsistence strategies, or methods of finding sustenance and resources. To understand our species is to understand the subsistence strategy of foraging, or the search for resources in the environment. While most (but not all) humans today live in cultures that practice agriculture (whereby we greatly shape the environment to mass produce what we need), we have spent far more time as nomadic foragers than as settled agriculturalists. As such, our traits have evolved to be primarily geared toward foraging. For instance, our efficient bipedalism allows persistence-hunting across long distances as well as movement from resource to resource.
How does human foraging, also known as hunting and gathering, work? Anthropologists have used all four fields to answer this question (see Ember n.d.). Typically, people formed bands, or kin-based groups of around 50 people or less (rarely over 100). A band’s organization would be egalitarian, with a flexible hierarchy based on an individual’s age, level of experience, and relationship with others. Everyone would have a general knowledge of the skills assigned to their gender roles, rather than specializing in different occupations. A band would be able to move from place to place in the environment, using knowledge of the area to forage (Figure 12.21). In varied environments—from savannas to tropical forests, deserts, coasts, and the Arctic circle—people found sustenance needed for survival. Our species’s omnivorousness and cultural abilities led us to excel in the generalist-specialist niche.

Humans made extensive use of the foraging subsistence strategy, but this lifestyle did have limitations. The ease of foraging depended on the richness of the environment. Due to the lack of storage, resources had to be dependably found when needed. While a bountiful environment would require just a few hours of foraging a day and could lead to a focus on one location, the level and duration of labor increased greatly in poor or unreliable environments. Labor was also needed to process the acquired resources, which contributed to the foragers’ daily schedule (Crittenden and Schnorr 2017).
The adaptations to foraging found in modern Homo sapiens may explain why our species became so successful both within Africa and in the rapid expansion around the world. Overcoming the limitations, each generation at the edge of our species’s range would have found it beneficial to expand a little further, keeping contact with other bands but moving into unexplored territory where resources were more plentiful. The cumulative effect would have been the spread of modern Homo sapiens across continents and hemispheres.
Why Agriculture?
After hundreds of thousands of years of foraging, some groups of people around 12,000 years ago started to practice agriculture. This transition, called the Neolithic Revolution, occurred at the start of the Holocene epoch. While the reasons for this global change are still being investigated, two likely co-occurring causes are a growing human population and natural global climate change.
Overcrowding could have affected the success of foraging in the environment, leading to the development of a more productive subsistence strategy (Cohen 1977). Foraging works best with low population densities since each band needs a lot of space to support itself. If too many people occupy the same environment, they deplete the area faster. The high population could exceed the carrying capacity, or number of people a location can reliably support. Reaching carrying capacity on a global level due to growing population and limited areas of expansion would have been an increasingly pressing issue after the expansion through the major continents by 14,600 years ago.
A changing global climate immediately preceded the transition to agriculture, so researchers have also explored a connection between the two events. Since the Last Glacial Maximum of 23,000 years ago, the Earth slowly warmed. Then, from 13,000 to 11,700 years ago, the temperature in most of the Northern Hemisphere dropped suddenly in a phenomenon called the Younger Dryas. Glaciers returned in Europe, Asia, and North America. In Mesopotamia, which includes the Levant, the climate changed from warm and humid to cool and dry. The change would have occurred over decades, disrupting the usual nomadic patterns and subsistence of foragers around the world. The disruption to foragers due to the temperature shift could have been a factor in spurring a transition to agriculture. Researchers Gregory K. Dow and colleagues (2009) believe that foraging bands would have clustered in the new resource-rich places where people started to direct their labor to farming the limited area. After the Younger Dryas ended, people expanded out of the clusters with their agricultural knowledge (Figure 12.22).

The double threat of the limitation of human continental expansion and the sudden global climate change may have placed bands in peril as more populations outpaced their environment’s carrying capacity. Not only had a growing population led to increased competition with other bands, but environments worldwide shifted to create more uncertainty. As people in different areas around the world faced this unpredictable situation, they became the independent inventors of agriculture.
Agriculture around the World
Due to global changes to the human experience starting from 12,000 years ago, cultures with no knowledge of each other turned toward intensely farming their local resources (see Figure 12.22). The first farmers engaged in artificial selection of their domesticates to enhance useful traits over generations. The switch to agriculture took time and effort with no guarantee of success and constant challenges (e.g. fires, droughts, diseases, and pests). The regions with the most widespread impact in the face of these obstacles became the primary centers of agriculture (Figure 12.23; Fuller 2010):
- Mesopotamia: The Fertile Crescent from the Tigris and Euphrates rivers through the Levant was where bands started to domesticate plants and animals around 12,000 years ago. The connection between the development of agriculture and the Younger Dryas was especially strong here. Farmed crops included wheat, barley, peas, and lentils. This was also where cattle, pigs, sheep, and goats were domesticated.
- South and East Asia: Multiple regions across this land had varieties of rice, millet, and soybeans by 10,000 years ago. Pigs were farmed with no connection to Mesopotamia. Chickens were also originally from this region, bred for fighting first and food second.
- New Guinea: Agriculture started here 10,000 years ago. Bananas, sugarcane, and taro were native to this island. Sweet potatoes were brought back from voyages to South America around the year C.E. 1000. No known animal farming occurred here.
- Mesoamerica: Agriculture from Central Mexico to northern South America also occurred from 10,000 years ago; it was also only plant based. Maize was a crop bred from teosinte grass, which has become one of the global staples. Beans, squash, and avocados were also grown in this region.
- The Andes: Starting around 8,000 years ago, local domesticated plants started with squash but later included potatoes, tomatoes, beans, and quinoa. Maize was brought down from Mesoamerica. The main farm animals were llamas, alpacas, and guinea pigs.
- Sub-Saharan Africa: This region went through a change 5,000 years ago called the Bantu expansion. The Bantu agriculturalists were established in West Central Africa and then expanded south and east. Native varieties of rice, yams, millet, and sorghum were grown across this area. Cattle were also domesticated here.
- Eastern North America: This region was the last major independent agriculture center, from 4,000 years ago. Squash and sunflower are the produce from this region that are most known today, though sumpweed and pitseed goosefoot were also farmed. Hunting was still the main source of animal products.

By 5,000 years ago, our species was well within the Neolithic Revolution. Agriculturalists spread to neighboring parts of the world with their domesticates, further expanding the use of this subsistence strategy. From this point, the human species changed from being primarily foragers to primarily agriculturalists with skilled control of their environments. The planet changed from mostly unaffected by human presence to being greatly transformed by humans. The revolution took millennia, but it was a true revolution as our species’ lifestyle was dramatically reshaped.
Cultural Effects of Agriculture
The worldwide adoption of agriculture altered the course of human culture and history forever. The core change in human culture due to agriculture is the move toward not moving: rather than live a nomadic lifestyle, farmers had to remain in one area to tend to their crops and livestock. The term for living bound to a certain location is sedentarism. This led to new aspects of life that were uncommon among foragers: the construction of permanent shelters and agricultural infrastructure, such as fields and irrigation, plus the development of storage technology, such as pottery, to preserve extra resources in case of future instability.

The high productivity of successful agriculture sparked further changes (Smith 2009). Since successful agriculture produced a much-greater amount of food and other resources per unit of land compared to foraging, the population growth rate skyrocketed. The surplus of a bountiful harvest also provided insurance for harder times, reducing the risk of famine. Changes happened to society as well. With a few farming households producing enough food to feed many others, other people could focus on other tasks. So began specialization into different occupations such as craftspeople, traders, religious figures, and artists, spurring innovation in these areas as people could now devote time and effort toward specific skills. These interdependent people would settle an area together for convenience. The growth of these settlements led to urbanization, the founding of cities that became the foci of human interaction (Figure 12.24).
The formation of cities led to new issues that sparked the growth of further specializations, called institutions. These are cultural constructs that exist beyond the individual and have wide control over a population. Leadership of these cities became hierarchical with different levels of rank and control. The stratification of society increased social inequality between those with more or less power over others. Under leadership, people built impressive monumental architecture, such as pyramids and palaces, that embodied the wealth and power of these early cities. Alliances could unite cities, forming the earliest states. In several regions of the world, state organization expanded into empires, wide-ranging political entities that covered a variety of cultures.
(Inlcude Special Topic about the Haudesaunee/Iroquois confederacy)
Urbanization brought new challenges as well. The concentration of sedentary peoples was ideal for infectious diseases to thrive since they could jump from person to person and even from livestock to person (Armelagos, Brown, and Turner 2005). While successful agriculture provided a large surplus of food to thwart famine, the food produced offered less diverse food sources than foragers’ diets (Cohen and Armelagos 1984; Cohen and Crane-Kramer 2007). This shift in nutrition caused other diseases to flourish among those who adopted farming, such as dental cavities and malocclusion (the misalignment of teeth caused by soft, agricultural diets). The need to extract “wisdom teeth” or third molars seen in agricultural cultures today stems from this misalignment between the environment our ancestors adapted to and our lifestyles today.
As the new disease trends show, the adoption of agriculture and the ensuing cultural changes were not entirely positive. It is also important to note that this is not an absolutely linear progression of human culture from simple to complex. In many cases, empires have collapsed and, in some cases, cities dispersed to low-density bands that rejected institutions. However, a global trend has emerged since the adoption of agriculture, wherein population and social inequality have increased, leading to the massive and influential nation-states of today.
The rise of states in Europe has a direct impact on many of this book’s topics. Science started as a European cultural practice by the upper class that became a standardized way to study the world. Education became an institution to provide a standardized path toward producing and gaining knowledge. The scientific study of human diversity, embroiled in the race concept that still haunts us today, was connected to the European slave trade and colonialism.
Also starting in Europe, the Industrial Revolution of the 19th century turned cities into centers of mass manufacturing and spurred the rapid development of inventions (Figure 12.25). In the technologically interconnected world of today, human society has reached a new level of complexity with globalization. In this system, goods are mass-produced and consumed in different parts of the world, weakening the reliance on local farms and factories. The imbalanced relationship between consumers and producers of goods further increases economic inequality.

As states based on agriculture and industry keep exerting influence on humanity today, there are people, like the Hadzabe of Tanzania, who continue to live a lifestyle centered on foraging. Due to the overwhelming force that agricultural societies exert, foragers today have been marginalized to live in the least habitable parts of the world—the areas that are not conducive to farming, such as tropical rainforests, deserts, and the Arctic (Headland et al. 1989). Foragers can no longer live in the abundant environments that humans would have enjoyed before the Neolithic Revolution. Interactions with agriculturalists are typically imbalanced, with trade and other exchanges heavily favoring the larger group. One of anthropology’s important roles today is to intelligently and humanely manage equitable interactions between people of different backgrounds and levels of influence.
Special Topic: Indigenous Land Management
Insight into the lives of past modern humans has evolved as researchers revise previous theories and establish new connections with Indigenous knowledge holders.
The outdated view of foraging held that people lived off of the land without leaving an impact on the environment. Accompanying this idea was anthropologist Marshall Sahlins’s (1968) proposal that foragers were the “original affluent society” since they were meeting basic needs and achieving satisfaction with less work hours than agriculturalists and city-dwellers. This view countered an earlier idea that foragers were always on the brink of starvation. Sahlins’s theory took hold in the public eye as an attractive counterpoint to our busy contemporary lives in which we strive to meet our endless wants.
A fruitful type of study involving researchers collaborating with Indigenous experts has found that foragers did not just live off the land with minimal effort nor were they barely surviving in unchanging environments. Instead, they shaped the landscape to their needs using labor and strategies that were more subtle than what European colonizers and subsequent researchers were used to seeing. Research from two regions shows the latest developments in understanding Indigenous land management.
In British Columbia, Canada, the bridging of scientific and Indigenous perspectives has shown that the forests of the region are not untouched wilderness but, rather, have been crafted by Indigenous peoples thousands of years ago. Forest gardens adjacent to archaeological sites show higher plant diversity than unmanaged places even after 150 years (Armstrong et al. 2021). On the coast, 3,500-year-old archaeological sites are evidence of constructed clam gardens, according to Indigenous experts (Lepofsky et al. 2015). Another project, in consultation with Elders of the T’exelc (William Lakes First Nation) in British Columbia, introduced researchers to explanations of how forests were managed before the practice was disrupted by European colonialism (Copes-Gerbitz et al. 2021). Careful management of controlled fires reduced the density of the forest to favor plants such as raspberries and allow easier movement through the landscape.
Similarly, the study of landscapes in Australia, in consultation with Aboriginal Australians today, shows that areas previously considered wilderness by scientists were actually the result of controlling fauna and fires. The presence of grasslands with adjacent forests were purposely constructed to attract kangaroos for hunting (Gammage 2008). People also managed other animal and insect life, from emus to caterpillars. In Tasmania, a shift from productive grassland to wildfire-prone rainforest occurred after Aboriginal Australian land management was replaced by British colonial rule (Fletcher, Hall, and Alexander 2021). The site of Budj Bim of the Gunditjmara people has archaeological features of aquaculture, or the farming of fish, that date back 6,600 years (McNiven et al. 2012; McNiven et al. 2015). These examples show that Indigenous knowledge of how to manipulate the environment may be invaluable at the state level, such as by creating an Aboriginal ranger program to guide modern land management.
Conclusion
Modern Homo sapiens is the species that took the hominin lifestyle the furthest to become the only living member of that lineage. The largest factor that allowed us to persist while other hominins went extinct was likely our advanced ability to culturally adapt to a wide variety of environments. Our species, with its skeletal and behavioral traits, was well-suited to be generalist-specialists who successfully foraged across most of the world’s environments. The biological basis of this adaptation was our reorganized brain that facilitated innovation in cultural adaptations and intelligence for leveraging our social ties and finding ways to acquire resources from the environment. As the brain’s ability increased, it shaped the skull by reducing the evolutionary pressure to have large teeth and robust cranial bones to produce the modern Homo sapiens face.
Our ability to be generalist-specialists is seen in the geographical range that modern Homo sapiens covered in 300,000 years. In Africa, our species formed from multiregional gene flow that loosely connected archaic humans across the continent. People then expanded out to the rest of the continental Eurasia and even further to the Americas.
For most of our species’s existence, foraging was the general subsistence strategy within which people specialized to culturally adapt to their local environment. With omnivorousness and mobility, people found ways to extract and process resources, shaping the environment in return. When resource uncertainty hit the species, people around the world focused on agriculture to have a firmer control of sustenance. The new strategy shifted human history toward exponential growth and innovation, leading to our high dependence on cultural adaptations today.
While a cohesive image of our species has formed in recent years, there is still much to learn about our past. The work of many driven researchers shows that there are amazing new discoveries made all the time that refine our knowledge of human evolution. Technological innovations such as DNA analysis enable scientists to approach lingering questions from new angles. The answers we get allow us to ask even more insightful questions that will lead us to the next revelation. Like the pink limestone strata at Jebel Irhoud, previous effort has taken us so far and you are now ready to see what the next layer of discovery holds.
Special Topic: The Future of Humanity
A common question stemming from understanding human evolution is: What will the genetic and biological traits of our species be hundreds of thousands of years in the future? When faced with this question, people tend to think of directional selection. Maybe our braincases will be even larger, resembling the large-headed and small-bodied aliens of science fiction (Figure 12.26). Or, our hands could be specialized for interacting with our touch-based technology with less risk of repetitive injury. These ideas do not stand up to scrutiny. Since natural selection is based on adaptations that increase reproductive success, any directional change must be due to a higher rate of producing successful offspring compared to other alleles. Larger brains and more agile fingers would be convenient to possess, but they do not translate into an increase in the underlying allele frequencies.

Scientists are hesitant to professionally speculate on the unknowable, and we will never know what is in store for our species one thousand or one million years from now, but there are two trends in human evolution that may carry on into the future: increased genetic variation and a reduction in regional differences.
Rather than a directional change, genetic variation in our species could expand. Our technology can protect us from extreme environments and pathogens, even if our biological traits are not tuned to handle these stressors. The rapid pace of technological advancement means that biological adaptations will become less and less relevant to reproductive success, so nonbeneficial genetic traits will be more likely to remain in the gene pool. Biological anthropologist Jay T. Stock (2008) views environmental stress as needing to defeat two layers of protection before affecting our genetics. The first layer is our cultural adaptations. Our technology and knowledge can reduce pressure on one’s genotype to be “just right” to pass to the next generation. The second defense is our flexible physiology, such as our acclimatory responses. Only stressors not handled by these powerful responses would then cause natural selection on our alleles. These shields are already substantial, and cultural adaptations will only keep increasing in strength.
The increasing ability to travel far from one’s home region means that there will be a mixing of genetic variation on a global level in the future of our species. In recent centuries, gene flow of people around the world has increased, creating admixture in populations that had been separated for tens of thousands of years. For skin color, this means that populations all around the world could exhibit the whole range of skin colors, rather than the current pattern of decreasing melanin pigment farther from the equator. The same trend of intermixing would apply to all other traits, such as blood types. While our genetics will become more varied, the variation will be more intermixed instead of regionally isolated.
Our distant descendants will not likely be dextrous ultraintellectuals; more likely, they will be a highly variable and mobile species supported by novel cultural adaptations that make up for any inherited biological limitations. Technology may even enable the editing of DNA directly, changing these trends. With the uncertainty of our future, these are just the best-educated guesses for now. Our future is open and will be shaped little by little by the environment, our actions, and the actions of our descendants.
Hominin Species Summary
Hominin |
Modern Homo sapiens |
Dates |
315,000 years ago to present |
Region(s) |
Starting in Africa, then expanding around the world |
Famous discoveries |
Cro-Magnon individuals, discovered 1868 in Dordogne, France. Otzi the Ice Man, discovered 1991 in the Alps between Austria and Italy. Kennewick man, discovered 1996 in Washington state. |
Brain size |
1400 cc average |
Dentition |
Extremely small with short cusps. |
Cranial features |
An extremely globular brain case and gracile features throughout the cranium. The mandibular symphysis forms a chin at the anterior-most point. |
Postcranial features |
Gracile skeleton adapted for efficient bipedal locomotion at the expense of the muscular strength of most other large primates. |
Culture |
Extremely extensive and varied culture with many spoken and written languages. Art is ubiquitous. Technology is broad in complexity and impact on the environment. |
Other |
The only living hominin. Chimpanzees and bonobos are the closest living relatives. |
Review Questions
- What are the skeletal and behavioral traits that define modern Homo sapiens? What are the evolutionary explanations for its presence?
- What are some creative ways that researchers have learned about the past by studying fossils and artifacts?
- How do the discoveries mentioned in “First Africa, Then the World” fit the Assimilation model?
- What is foraging? What adaptations do we have for this subsistence strategy? Could you train to be a skilled forager?
- What are aspects of your life that come from dependence on agriculture and its cultural effects? Where did the ingredients of your favorite foods originate from?
Key Terms
African multiregionalism: The idea that modern Homo sapiens evolved as a complex web of small regional populations with sporadic gene flow among them.
Agriculture: The mass production of resources through farming and domestication.
Aquaculture: The farming of fish using techniques such as trapping, channels, and artificial ponds.
Assimilation hypothesis: Current theory of modern human origins stating that the species evolved first in Africa and interbred with archaic humans of Europe and Asia.
Atlatl: A handheld spear thrower that increased the force of thrown projectiles.
Band: A small group of people living together as foragers.
Beringia: Ancient landmass that connected Siberia and Alaska. The ancestors of Indigenous Americans would have crossed this area to reach the Americas.
Carrying capacity: The amount of organisms that an environment can reliably support.
Coastal Route model: Theory that the first Paleoindians crossed to the Americas by following the southern coast of Beringia.
Early Modern Homo sapiens, Early Anatomically Modern Human: Terms used to refer to transitional fossils between archaic and modern Homo sapiens that have a mosaic of traits. Humans like ourselves, who mostly lack archaic traits, are referred to as Late Modern Homo sapiens and simply Anatomically Modern Humans.
Egalitarian: Human organization without strict ranks. Foraging societies tend to be more egalitarian than those based on other subsistence strategies.
Foraging: Lifestyle consisting of frequent movement through the landscape and acquiring resources with minimal storage capacity.
Generalist-specialist niche: The ability to survive in a variety of environments by developing local expertise. Evolution toward this niche may have been what allowed modern Homo sapiens to expand past the geographical range of other human species.
Globalization: A recent increase in the interconnectedness and interdependence of people that is facilitated with long-distance networks.
Globular: Having a rounded appearance. Increased globularity of the braincase is a trait of modern Homo sapiens.
Gracile: Having a smooth and slender quality; the opposite of robust.
Holocene: The epoch of the Cenozoic Era starting around 12,000 years ago and lasting arguably through the present.
Ice-Free Corridor model: Theory that the first Native Americans crossed to the Americas through a passage between glaciers.
Institutions: Long-lasting and influential cultural constructs. Examples include government, organized religion, academia, and the economy.
Last Glacial Maximum: The time 23,000 years ago when the most recent ice age was the most intense.
Later Stone Age: Time period following the Middle Stone Age with a diversification in tool types, starting around 50,000 years ago.
Levant: The eastern coast of the Mediterranean. The site of early modern human expansion from Africa and later one of the centers of agriculture.
Megafauna: Large ancient animals that may have been hunted to extinction by people around the world.
Mental eminence: The chin on the mandible of modern H. sapiens. One of the defining traits of our species.
Microlith: Small stone tool found in the Later Stone Age; also called a bladelet.
Middle Stone Age: Time period known for Mousterian lithics that connects African archaic to modern Homo sapiens.
Monumental architecture: Large and labor-intensive constructions that signify the power of the elite in a sedentary society. A common type is the pyramid, a raised crafted structure topped with a point or platform.
Mosaic: Composed from a mix or composite of traits.
Neolithic Revolution: Time of rapid change to human cultures due to the invention of agriculture, starting around 12,000 years ago.
Ochre: Iron-based mineral pigment that can be a variety of yellows, reds, and browns. Used by modern human cultures worldwide since at least 80,000 years ago.
Sahul: Ancient landmass connecting New Guinea and Australia.
Sedentarism: Lifestyle based on having a stable home area; the opposite of nomadism.
Southern Dispersal model: Theory that modern H. sapiens expanded from East Africa by crossing the Red Sea and following the coast east across Asia.
Subsistence strategy: The method an organism uses to find nourishment and other resources.
Sunda: Ancient Asian landmass that incorporated modern Southeast Asia.
Supraorbital torus: The bony brow ridge across the top of the eye orbits on many hominin crania.
Upper Paleolithic: Time period considered synonymous with the Later Stone Age.
Urbanization: The increase of population density as people settled together in cities.
Wallacea: Archipelago southeast of Sunda with different biodiversity than Asia.
Younger Dryas: The rapid change in global climate—notably a cooling of the Northern Hemisphere—13,000 years ago.
About the Author
Keith Chan, Ph.D.
Grossmont-Cuyamaca Community College District and MiraCosta College, drkeithcchan@gmail.com, Dr. Keith Chan is an instructor of anthropology at Grossmont-Cuyamaca Community College District and MiraCosta College in San Diego County. He reached this step of his anthropological path after many memorable experiences across the country and the hemisphere. He earned a bachelor’s degree in anthropology from the University of California, Berkeley, in 2001. As a graduate student at the University of Missouri, he traveled to Perú with teams of students to study skeletons in the archaeological record to understand the lives of ancient Andeans. He completed his dissertation and earned a Ph.D. in 2011. Inspired by many educators in his journey, Dr. Chan turned his career toward teaching anthropology and helping students understand and appreciate humanity.
For Further Exploration
Websites
First-person virtual tour of Lascaux cave with annotated cave art: Ministère de la Culture and Musée d’Archéologie Nationale. “Visit the cave” Lascaux website.
Online anthropology magazine articles related to paleoanthropology and human evolution: SAPIENS. “Evolution.” SAPIENS website.
Various presentations of information about hominin evolution: Smithsonian Institution. “What does it mean to be human?” Smithsonian National Museum of Natural History website.
Magazine-style articles on archaeology and paleoanthropology: ThoughtCo. “Archaeology.” ThoughtCo. Website.
Database of comparisons across hominins and primates: University of California, San Diego. “MOCA Domains.” Center for Academic Research & Training in Anthropogeny website.
Books
Engaging book that covers human-made changes to the environment with industrialization and globalization: Kolbert, Elizabeth. 2014. The Sixth Extinction: An Unnatural History. New York: Bloomsbury.
Overview of what human life was like among the environmental shifts of the Ice Age: Woodward, Jamie. 2014. The Ice Age: A Very Short Introduction. Oxford: OUP Press.
Articles
Recent review paper about the current state of paleoanthropology research: Stringer, C. 2016. “The Origin and Evolution of Homo sapiens.” Philosophical Transactions of the Royal Society B 371 (1698).
Overview of the history of American paleoanthropology and the many debates that have occurred over the years: Trinkaus, E. 2018. “One Hundred Years of Paleoanthropology: An American Perspective.” American Journal of Physical Anthropology 165 (4): 638–651.
Amazing magazine article that synthesizes hominin evolution and why it is important to study this subject: Wheelwright, Jeff. 2015. “Days of Dysevolution.” Discover 36 (4): 33–39.
Fascinating research on Ötzi, a mummy from 5,000 years ago: Wierer, Ursula, Simona Arrighi, Stefano Bertola, Günther Kaufmann, Benno Baumgarten, Annaluisa Pedrotti, Patrizia Pernter, and Jacques Pelegrin. 2018. “The Iceman’s Lithic Toolkit: Raw Material, Technology, Typology and Use.” PLOS One 13 (6): e0198292. https://doi.org/10.1371/journal.pone.0198292.
Documentaries
PBS NOVA series covering the expansion of modern Homo sapiens and interbreeding with archaic humans: Brown, Nicholas, dir. 2015. First Peoples. Edmonton: Wall to Wall Television. Amazon Prime Video.
PBS NOVA special featuring the footprints found in White Sands National Park: Falk, Bella, dir. 2016. Ice Age Footprints. Boston: Windfall Films. https://www.pbs.org/wgbh/nova/video/ice-age-footprints/.
PBS NOVA special about how modern humans evolved adaptations to different environments. Shows how present-day people live around the world: Thompson, Niobe, dir. 2016. Great Human Odyssey. Edmonton: Clearwater Documentary. https://www.pbs.org/wgbh/nova/evolution/great-human-odyssey.html.
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Acknowledgments
I could not have undertaken this project without the help of many who got me to where I am today. I extend sincere thank yous to the many colleagues and former students who have inspired me to keep learning and talking about anthropology. Thank you also to all who are involved in this textbook project. The anonymous reviewers truly sparked improvements to the chapter. Lastly, the staff of Starbucks #5772 also contributed immensely to this text.
Slender, less rugged, or pronounced features.
Jonathan Marks, Ph.D., University of North Carolina at Charlotte
Adam P. Johnson, M.A., University of North Carolina at Charlotte/University of Texas at San Antonio
This chapter is an adaptation of "Chapter 2: Evolution” by Jonathan Marks. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Explain the relationship among genes, bodies, and organismal change.
- Discuss the shortcomings of simplistic understandings of genetics.
- Describe what is meant by the "biopolitics of heredity."
- Discuss issues caused by misuse of ideas about adaptations and natural selection.
- Examine and correct myths about evolution.
The Human Genome Project, an international initiative launched in 1990, sought to identify the entire genetic makeup of our species. For many scientists, it meant trying to understand the genetic underpinnings of what made humans uniquely human. James Watson, a codiscoverer of the helical shape of DNA, wrote that “when finally interpreted, the genetic messages encoded within our DNA molecules will provide the ultimate answers to the chemical underpinnings of human existence” (Watson 1990, 248). The underlying message is that what makes humans unique can be found in our genes. The Human Genome Project hoped to find the core of who we are and where we come from.
Despite its lofty goal, the Human Genome Project—even after publishing the entire human genome in January 2022—could not fully account for the many factors that contribute to what it is to be human. Richard Lewontin, Steven Rose, and Leon Kamin (2017) argue that genetic determinism of the sort assumed by the Human Genome Project neglects other essential dimensions that contribute to the development and evolution of human bodies, not to mention the role that culture plays. They use an apt metaphor of a cake to illustrate the incompleteness of reductive models. Consider the flavor of a cake and think of the ingredients listed in the recipe. The recipe includes ingredients such as flour, sugar, shortening, vanilla extract, eggs, and milk. Does raw flour taste like cake? Does sugar, vanilla extract, or any of the other ingredients taste like cake? They do not, and knowing the individual flavors of each ingredient does not tell us much about what cake tastes like. Even mixing all of the ingredients in the correct proportions does not get us cake. Instead, external factors such as baking at the right temperature, for the right amount of time, and even the particularities of our evolved sense of taste and smell are all necessary components of experiencing the cake.
Lewontin, Rose, and Kamin (2017) argue that the same is true for humans and other organisms.
Knowing everything about cake ingredients does not allow us to fully know cake. Equally so, knowing everything about the genes found in our DNA does not allow us to fully know humans. Different, interacting levels are implicated in the development and evolution of all organisms, including humans. Genes, the structure of chromosomes, developmental processes, epigenetic tags, environmental factors, and still-other components all play key roles such that genetically reductive models of human development and evolution are woefully inadequate.
The complex interactions across many levels—genetic, developmental, and environmental—explain why we still do not know how our one-dimensional DNA nucleotide sequence results in a four-dimensional organism. This was the unfulfilled promise of the inception of the Human Genome Project in the 1980s and 1990s: the project produced the complete DNA sequence of a human cell in the hopes that it would reveal how human bodies are built and how to cure them when they are built poorly. Yet, that information has remained elusive. Presumably, the knowledge of how organisms are produced from DNA sequences will one day permit us to reconcile the discrepancies between patterns in anatomical evolution and molecular evolution.
In this chapter, we will consider multilevel evolution and explore evolution as a complex interaction between genetic and epigenetic factors as well as the environments in which organisms live. Next, we will examine the biopolitical nature of human evolution. We will then investigate problems that arise from attributing all traits to an adaptive function. Finally, we will address common misconceptions about evolution. The goal of this chapter is to provide you with the necessary toolkit for understanding the molecular, anatomical, and political dimensions of evolution.
Evolution Happens at Multiple Levels
Following Richard Dawkins’s publication of The Selfish Gene in 1976, the scientific imagination was captured by the potential of genomics to reveal how genes are copied by Darwinian selection. Dawkins argues that the genes in individuals that contribute to greater reproductive success are the units of selection. His conception of evolution at the molecular level undercuts the complex interactions between organisms and their environments, which are not expressed genomically but are nevertheless key drivers in evolution.
By the 1980s, the acknowledgment among most biologists that even though genes construct bodies, genes and bodies evolve at different rates and with distinct patterns. This realization led to a renewed focus on how bodies change. The Evolutionary Synthesis of the 1930s–1970s had reduced organisms to their genotypes and species to their gene pools, which provided valuable insights about the processes of biological change, but it was only a first approximation. Animals are in fact reactive and adaptable beings, not passive and inert genotypes. Species are clusters of socially interacting and reproductively compatible organisms.

Once we accept that evolutionary change is fundamentally genetic change, we can ask: How do bodies function and evolve? How do groups of animals come to see one another as potential mates or competitors for mates, as opposed to just other creatures in the environment? Are there evolutionary processes that are not explicable by population genetics? These questions—which lead us beyond reductive assumptions—were raised in the 1980s by Stephen Jay Gould, the leading evolutionary biologist of the late 20th century (see: Gould 2003; 1996).
Gould spearheaded a movement to identify and examine higher-order processes and features of evolution that were not adequately explained by population genetics. For example, extinction, which was such a problem for biologists of the 1600s, could now be seen as playing a more complex role in the history of life than population genetics had been able to model. Gould recognized that there are two kinds of extinctions, each with different consequences: background extinctions and mass extinctions. Background extinctions are those that reflect the balance of nature, because in a competitive Darwinian world, some things go extinct and other things take their place. Ecologically, your species may be adapted to its niche, but if another species comes along that’s better adapted to the same niche, eventually your species will go extinct. It sucks, but it is the way of all life: you come into existence, you endure, and you pass out of existence. But mass extinctions are quite different. They reflect not so much the balance of nature as the wholesale disruption of nature: many species from many different lineages dying off at roughly the same time—presumably as the result of some kind of rare ecological disaster. The situation may not be survival of the fittest as much as survival of the luckiest. The result, then, would be an ecological scramble among the survivors. Having made it through the worst, the survivors could now simply divide up the new ecosystem amongst themselves, since their competitors were gone. Something like this may well have happened about 65 million years ago, when a huge asteroid hit the Yucatan Peninsula, which mammals survived but dinosaurs did not (Figure 17.1). Something like this may be happening now, due to human expansion and environmental degradation. Note, though, that there is only a limited descriptive role here for population genetics: the phenomena we are describing are about organisms and species in ecosystems.
Another question involved the disconnect between properties of species and the properties of gene pools. For example, there are upwards of 15 species of gibbons but only two species of chimpanzees. Why? There are upwards of 20 species of guenons but fewer than ten of baboons. Why? Are there genes for that? It seems unlikely. Gould suggested that species, as units of nature, might have properties that are not reducible to the genes in their cells. For example, rates of speciation and extinction might be properties of their ecologies and histories rather than their genes. Thus, relationships between environmental contexts and variability within a species result in degrees of resistance to extinction and affect the frequency and rates at which clades diversify (Lloyd and Gould 1993). Consistent biases of speciation rates might well produce patterns of macroevolutionary diversity that are difficult to explain genetically and better understood ecologically. Gould called such biases in speciation rates species selection—a higher-order process that invokes competition between species, in addition to the classic Darwinian competition between individuals.
One of Gould’s most important studies involved the very nature of species. In the classical view, a species is continually adapting to its environment until it changes so much that it is a different species than it was at the beginning of this sentence (Eldredge and Gould 1972). That implies that the species is a fundamentally unstable entity through time, continuously changing to fit in. But suppose, argued Gould along with paleontologist Niles Eldredge, a species is more stable through time and only really adapts during periods of ecological instability and change. Then we might expect to find in the fossil record long equilibrium periods—a few million years or so—in which species don’t seem to change much, punctuated by relatively brief periods in which they change a bit and then stabilize again as new species. They called this idea punctuated equilibria. The idea helps to explain certain features of the fossil record, notably the existence of small anatomical “gaps” between closely related fossil forms (Figure 17.2). Its significance lies in the fact that although it incorporates genetics, punctuated equilibria is not really a theory of genetics but one of types bodies in deep time.
Punctuated equilibria is seen across taxa, with long periods in the fossil record representing little phenotypic change. These periods of stability are disrupted by shorter periods of rapid adaptation, the process through which populations of organisms become suited to living in their environments. Phenotypic changes are often coupled with drastic climatic or ecological changes that affect the milieu in which organisms live. For example, throughout much of hominin evolutionary history, brain size was closely associated with body size and thus remained mostly stable. However, changes occurred in average hominin brain size at around 100 thousand years ago, 1 million years ago, and 1.8 million years ago. Several hypotheses have been put forth to explain these changes, including unpredictability in climate and environment (Potts 1998), social development (Barton 1996), and the evolution of language (Deacon 1998). Evidence from the fossil record, paleoclimate models, and comparative anatomy suggests that the changes observed in hominin lineage result from biocultural processes—that is, the coalescence of environmental and cultural factors that selected for larger brains (Marks 2015; Shultz, Nelson, and Dunbar 2012).

In response to the call for a theory of the evolution of form, the field of evo-devo—the intersection of evolutionary and developmental biology—arose. The central focus here is on how changes in form and shape arise. An embryo matures by the stimulation of certain cells to divide, forming growth fields. The interactions and relationships among these growth fields generate the structures of the body. The hox genes that regulate these growth fields turn out to be highly conserved across the animal kingdom. This is because they repeatedly turn on and off the most basic genes guiding the animal’s development, and thus any changes to them would be catastrophic. Indeed, these genes were first identified by manipulating them in fruit flies, such that one could produce a bizarre mutant fruit fly that grew a pair of legs where its antennae were supposed to be (Kaufman, Seeger, and Olsen 1990).
Certain genetic changes can alter the fates of cells and the body parts, while other genetic changes can simply affect the rates at which neighboring groups of cells grow and divide, thus producing physical bumps or dents in the developing body. The result of altering the relationships among these fields of cellular proliferation in the growing embryo is allometry, or the differential growth of body parts. As an animal gets larger—either over the course of its life or over the course of macroevolution—it often has to change shape in order to live at a different size. Many important physiological functions depend on properties of geometric area: the strength of a bone, for example, is proportional to its cross-sectional area. But area is a two-dimensional quality, while growing takes place in three dimensions—as an increase in mass or volume. As an animal expands, its bones necessarily weaken, because volume expands faster than area does. Consequently a bigger animal has more stress on its bones than a smaller animal does and must evolve bones even thicker than they would be by simply scaling the animal up proportionally. In other words, if you expand a mouse to the size of an elephant, it will nevertheless still have much thinner bones than the elephant does. But those giant mouse bones will unfortunately not be adequate to the task. Thus, a giant mouse would have to change aspects of its form to maintain function at a larger size (see Figure 17.3).

Physiologically, we would like to know how the body “knows” when to turn on and off the genes that regulate growth to produce a normal animal. Evolutionarily, we would like to know how the body “learns” to alter the genetic on/off switch (or the genetic “slow down/speed up” switch) to produce an animal that looks different. Moreover, since organisms differ from one another, we would like to know how the developing body distinguishes a range of normal variation from abnormal variation. And, finally, how does abnormal variation eventually become normal in a descendant species?
Taking up these questions, Gould invoked the work of a British geneticist named Conrad H. Waddington, who thought about genetics in less reductive ways than his colleagues. Rather than isolate specific DNA sites to analyze their function, Waddington instead studied the inheritance of an organism’s reactivity—its ability to adapt to the circumstances of its life. In a famous experiment, he grew fruit fly eggs in an atmosphere containing ether. Most died, but a few survived somehow by developing a weird physical feature: a second thorax with a second pair of wings. Waddington bred these flies and soon developed a stable line of flies who would reliably develop a second thorax when grown in ether. Then he began to lower the concentration of ether, while continuing to selectively breed the flies that developed the strange appearance. Eventually he had a line of flies that would stably develop the “bithorax” phenotype–the suite of traits of an organism–even when there was no ether; it had become the “new normal.” The flies had genetically assimilated the bithorax condition.
Waddington was thus able to mimic the inheritance of acquired characteristics: what had been a trait stimulated by ether a few generations ago was now a normal part of the development of the descendants. Waddington recognized that while he had performed a selection experiment on genetic variants, he had not selected for particular traits. Rather, he helped produce the physiological tendency to develop particular traits when appropriately stimulated. He called that tendency plasticity and its converse, the tendency to stay the same even under weird environmental circumstances, canalization. Waddington had initially selected for plasticity, the tendency to develop the bithorax phenotype under weird conditions, and then, later, for canalization, the developmental normalization of that weird physical trait. Although Waddington had high stature in the community of geneticists, evolutionary biologists of the 1950s and 1960s regarded him with suspicion because he was not working within the standard mindset of reductionism, which saw evolution as the spread of genetic variants that coded for favorable traits. Both Waddington and Gould resisted contemporary intellectual paradigms that favored reductive accounts of evolutionary processes. They conceived of evolution as an emergent process in which many external factors (e.g. climate, environment, predation) and internal factors (e.g., genotypes, plasticity, canalization) coalesce to produce the evolutionary trends that we observe in the fossil record and our genome.
While Gould and Waddington both looked beyond the genome to understand evolution, the Human Genome Project—an international project with the goal of identifying each base pair in the human genome in the 1990s—generated a great deal of public interest in analyzing the human DNA sequence from the standpoint of medical genetics. Some of the rhetoric aimed to sell the public on investing a lot of money and resources in sequencing the human genome in order to show the genetic basis of heritable traits, cure genetic diseases, and learn what it means ultimately to be biologically human. However, the Human Genome Project was not actually able to answer those questions through the use of genetics alone, and thus a broader, more holistic account was required.
This holistic account came from decades of research in human biology and anthropology, which understood the human body as highly adaptable, dynamic, and emergent. For example, in the early 20th century, anthropologist Franz Boas measured the skulls of immigrants to the U.S., revealing that environmental, not merely genetic, factors affected skull shape. The growing human body adjusts itself to the conditions of life, such as diet, sunshine, high altitude, hard labor, population density, how babies are carried—any and all of which can have subtle but consistent effects upon its development. There can thus be no normal human form, only a context-specific range of human forms.
However, what the human biologists called human adaptability, evolutionary biologists called developmental plasticity, and evidence quickly began to mount for its cause being epigenetic modifications to DNA. Epigenetic modifications are changes to how genes are used by the body (as opposed to changes in the DNA sequences; see Chapter 3). Scientific interest shifted from the focus of the Human Genome Project to the ways that bodies are made by evolutionary-developmental processes, including epigenetics. What is meant by “epigenetic modification”? Evolution is about how descendants diverge from their ancestors. Inheritance from parent to offspring is still critical to this process, which occurs through genetic recombination: the pairing of homologous chromosomes and sharing of genetic material during meiosis (see Chapter 3). However, in the 21st century, the link between evolution and inheritance has broadened with a clearer understanding of how environmental and developmental factors shape bodies and the expression of genes, including epigenetic inheritance patterns. While offspring inherit their genes through random assortment during meiosis, environmental factors also shape how genes are used. When these epigenetic modifications occur in germ cells, they can be passed onto offspring. In these cases, there is no change in the DNA sequence but rather in how genes are used by the body due to DNA methylation and the structure of chromosomes due to histone acetylation (see Chapter 3).
In addition, we now recognize that evolution is affected by two other forms of intergenerational transmission and inheritance (in addition to genetics and epigenetics). These forms include behavioral variation and culture. That is, behavioral information can be transmitted horizontally (intragenerationally), permitting more rapid ways for organisms to adjust to the environment. And, then there is the fourth mode of transmission: the cultural or symbolic mode. Humans are the only species that horizontally transmits an arbitrary set of rules to govern communication, social interaction, and thought. This shared information is symbolic and has resulted in what we recognize as “culture”: locally emergent worlds of names, words, pictures, classifications, revered pasts, possible futures, spirits, dead ancestors, unborn descendants, in-laws, politeness, taboo, justice, beauty, and story, all accompanied by practices and a material world of tools.
Consequently our contemporary ideas about evolution see the evolutionary processes as hierarchically organized and not restricted to the differential transmission of DNA sequences into the next generation. While that is indeed a significant part of evolution, the organism and species are nevertheless crucial to understanding how those DNA sequences get transmitted. Further, the transmission of epigenetic, behavioral, and symbolic information play a complex role in perpetuating our genes, bodies, and species. In the case of human evolution, one can readily see that symbolic information and cultural adaptation are far more central to our lives and our survival today than DNA and genetic adaptation. It is thus misleading to think of humans passively occupying an environmental niche. Rather, humans are actively engaged in constructing our own niches, as well as adapting to them and using them to adapt. The complex interplay between a species and its active engagement in creating its own ecology is known as niche construction. If we understand natural selection–the process by which populations adapt to their specific environments–as the effects that environmental context has on the reproductive success of organisms, then niche construction is the process through which organisms shape their own selective pressures.
The Biopolitics of Heredity
“Science isn’t political” is a sentiment that you have likely heard before. Science is supposed to be about facts and objectivity. It exists, or at least ought to, outside of petty human concerns. However, the sorts of questions we ask as scientists, the problems we choose to study, the categories and concepts we use, who gets to do science, and whose work gets cited are all shaped by culture. Doing science is a political act. This fact is markedly true for human evolution. While it is easier to create intellectual distance between us and fruit flies and viruses, there is no distance when we are studying ourselves. The hardest lesson to learn about human evolution is that it is intensely political. Indeed, to see it from the opposite side, as it were, the history of creationism—the belief that the universe was divinely created around 6,000 years ago—is essentially a history of legal decisions. For instance, in Tennessee v. John T. Scopes (1925), a schoolteacher was prosecuted for violating a law in Tennessee that prohibited the teaching of human evolution in public schools, where teachers were required by law to teach creationism.
More recently, legal decisions aimed at legislating science education have shaped how students are exposed to evolutionary theory. For instance, McLean v. Arkansas (1982) dispatched “scientific creationism” by arguing that the imposition of balanced teaching of evolution and creationism in science classes violates the Establishment Clause, separating church and state. Additionally, Kitzmiller v. Dover (Pennsylvania) Area School District (2005) dispatched the teaching of “intelligent design” in public school classrooms as it was deemed to not be science. In some cases, people see unbiblical things in evolution, although most Christian theologians are easily able to reconcile science to the Bible. In other cases, people see immoral things in evolution, although there is morality and immorality everywhere. And some people see evolution as an aspect of alt-religion, usurping the authority of science in schools to teach the rejection of the Christian faith, which would be unconstitutional due to the protected separation of church and state.
Clearly, the position that politics has nothing to do with science is untenable. But is the politics in evolution an aberration or is it somehow embedded in science? In the early 20th century, scientists commonly promoted the view that science and politics were separate: science was seen as a pure activity, only rarely corrupted by politics. And yet as early as World War I, the politics of nationalism made a hero of the German chemist Fritz Haber for inventing poison gas. And during World War II, both German doctors and American physicists, recruited to the war effort, helped to end many civilian lives. Therefore, we can think of the apolitical scientist as a self-serving myth that functions to absolve scientists of responsibility for their politics. The history of science shows how every generation of scientists has used evolutionary theory to rationalize political and moral positions. In the very first generation of evolutionary science, Darwin’s Origin of Species (1859) is today far more readable than his Descent of Man (1871). The reason is that Darwin consciously purged The Origin of Species of any discussion of people. And when he finally got around to talking about people, in The Descent of Man, he simply imbued them with the quaint Victorian prejudices of his age, and the result makes you cringe every few pages. There is plenty of politics in there—sexism, racism, and colonialism—because you cannot talk about people apolitically.
One immediate faddish deduction from Darwinism, popularized by Herbert Spencer (1864) as “survival of the fittest,” held that unfettered competition led to advancement in nature and to human history. Since the poor were purported losers in that struggle, anything that made their lives easier would go against the natural order. This position later came to be known ironically as “Social Darwinism.” Spencer was challenged by fellow Darwinian Thomas Huxley (1863), who agreed that struggle was the law of the jungle but observed that we don’t live in jungles anymore. The obligation to make lives better for others is a moral, not a natural, fact. We simultaneously inhabit a natural universe of descent from apes and a moral universe of injustice and inequality, and science is not well served by ignoring the latter.
Concurrently, the German biologist Ernst Haeckel’s 1868 popularization of Darwinism was translated into English a few years later as The History of Creation. As we saw earlier, Haeckel was determined to convince his readers that they were descended from apes, even in the absence of fossil evidence attesting to it. When he made non-Europeans into the missing links that connected his readers to the apes, and depicted them as ugly caricatures, he knew precisely what he was doing. Indeed, even when the degrading racial drawings were deleted from the English translation of his book, the text nevertheless made his arguments quite clear. And a generation later, when the Americans had not yet entered the Great War in 1916, a biologist named Vernon Kellogg visited the German High Command as a neutral observer and found that the officers knew a lot about evolutionary biology, which they had gotten from Haeckel and which rationalized their military aggressions. Kellogg went home and wrote a bestseller about it, called Headquarters Nights (1917). World War I would have been fought with or without evolutionary theory, but as a source of scientific authority, evolution—even if a perversion of the Darwinian theory—had very quickly attained global geopolitical relevance.
Oftentimes, politics in evolutionary science is subtle, due to the pervasive belief in the advancement of science. We recognize the biases of our academic ancestors and modify our scientific stories accordingly. But we can never be free of our own cultural biases, which are invisible to us, as much as our predecessors’ biases were invisible to them. In some cases, the most important cultural issues resurface in different guises each generation, like scientific racism. Scientific racism is the recruitment of science for the evil political ends of racism, and it has proved remarkably impervious to evolution. Before Darwin, there was creationist scientific racism, and after Darwin, there was evolutionist scientific racism. And there is still scientific racism today, self-justified by recourse to evolution, which means that scientists have to be politically astute and sensitive to the uses of their work to counter these social tendencies.
Consider this: Are you just your ancestry, or can you transcend it? If that sounds like a weird question, it was actually quite important to a turn-of-the-20th-century European society in which an old hereditary aristocracy was under increasing threat from a rising middle class. And that is why the very first English textbook of Mendelian genetics concluded with the thought that “permanent progress is a question of breeding rather than of pedagogics; a matter of gametes, not of training … the creature is not made but born” (Punnett 1905, 60). Translation: Not only do we now know a bit about how heredity works, but it’s also the most important thing about you. Trust me, I’m a scientist.
Yet evolution is about how descendants come to differ from ancestors. Do we really know that your heredity, your DNA, your ancestry, is the most important thing about you? That you were born, not made? After all, we do know that you could be born into slavery or as a peasant, and come from a long line of enslaved people or peasants, and yet not have slavery or peasantry be the most important thing about you. Whatever your ancestors were may unfortunately constrain what you can become, but as a moral precept, it should not. But just as science is not purely “facts and objectivity,” ancestry is not a strictly biological concept. Human ancestry is biopolitics, not biology.
Evolution is fundamentally a theory about ancestry, and yet ancestors are, in the broad anthropological sense, sacred: ancestors are often more meaningful symbolically than biologically. Just a few years after The Origin of Species (Darwin 1859), the British politician and writer Benjamin Disraeli declared himself to be on the side of the angels, not the apes, and to “repudiate with indignation and abhorrence those new-fangled theories” (Monypenny, Flavelle, and Buckle 1920, 105). He turned his back on an ape ancestry and looked to the angel; yet, he did so as a prominent Jew-turned-Anglican, who had personally transcended his humble roots and risen to the pinnacle of the Empire. Ancestry was certainly important, and Disraeli was famously proud of his, but it was also certainly not the most important thing, not the primary determinant of his place in the world. Indeed, quite the opposite: Disraeli’s life was built on the transcendence of many centuries of Jewish poverty and oppression in Europe. Humble ancestry was there to be superseded and nobility was there to be earned; Disraeli would later become the Earl of Beaconsfield. Clearly, “are you just your ancestry” is not a value-neutral question, and “the creature is not made, but born” is not a value-neutral answer.
Ancestry being the most important thing about a person became a popular idea twice in 20th century science. First, at the beginning of the century, when the eugenics movement in America called attention to “feeble-minded stocks,” which usually referred to the poor or to immigrants (see Figure 17.4; and see Chapter 2). This movement culminated in Congress restricting the immigration of “feeble-minded races” (said to include Jews and Italians) in 1924, and the Supreme Court declaring it acceptable for states to sterilize their “feeble-minded” citizens involuntarily in 1927. After the Nazis picked up and embellished these ideas during World War II, Americans moved swiftly away from them in some contexts (e.g., for most people of European descent) while still strictly adhering in other contexts (e.g., Japanese internment camps and immigration restrictions).

Ancestry again became paramount in the drumming up of public support for the Human Genome Project in the 1990s. Public support for sequencing the human genome was encouraged by a popular science campaign that featured books titled The Book of Man (Bodmer and McKie 1997), The Human Blueprint (Shapiro 1991), and The Code of Codes (Kevles and Hood 1993). These books generally promised cures for genetic diseases and a deeper understanding of the human condition. We can certainly identify progress in molecular genetics over the last couple of decades since the human genome was sequenced, but that progress has notably not been accompanied by cures for genetic diseases, nor by deeper understandings of the human condition.
Even at the most detailed and refined levels of genetic analysis, we still don’t have much of an understanding of the actual basis by which things seem to “run in families.” While the genetic basis of simple, if tragic, genetic diseases have become well-known—such as sickle-cell anemia, cystic fibrosis, and Tay-Sachs’ Disease—we still haven’t found the ostensible genetic basis for traits that are thought to have a strong genetic component. For example, a recent genetic summary found over 12,000 genetic sites that contributed to height yet still explained only about 40-50 percent of the variation in height among European ancestry but no more than 10-20 percent of variation of other ancestries, which we know strongly runs in families (Yengo et al. 2022).
Partly in reaction to the reductionistic hype of the Human Genome Project, the study of epigenetics has become the subject of great interest. One famous natural experiment involves a Nazi-imposed famine in Holland over the winter of 1944–1945. Children born during and shortly after the famine experienced a higher incidence of certain health problems as adults, many decades later. Apparently, certain genes had been down-regulated early in development and remained that way throughout the course of life. Indeed, this modified regulation of the genes in response to the severe environmental conditions may have been passed on to their children.
Obviously one’s particular genetic constitution may play an important role in one’s life trajectory. But overvaluing that role may have important social and political consequences. In the first place, genotypes are rendered meaningful in a cultural universe. Thus, if you live in a strongly patriarchal society and are born without a Y chromosome (since human males are chromosomally XY and females XX), your genotype will indeed have a strong effect upon your life course. So even though the variation is natural, the consequences are political. The mediating factors are the cultural ideas about how people of different sexes ought to be treated, and the role of the state in permitting certain people to develop and thrive. More broadly, there are implications for public education if variation in intelligence is genetic. There are implications for the legal system if criminality is genetic. There are implications for the justice system if sexual preference, or sexual identity, is genetic. There are implications for the development of sports talent if that is genetic. And yet, even for the human traits that are more straightforward to measure and known to be strongly heritable, the DNA base sequence variation seems to explain little.
Genetic determinism or hereditarianism is the idea that “the creature is made, not born”—or, in a more recent formulation by James Watson, that “our fate is in our genes.” One of the major implications drawn from genetic determinism is that the feature in question must inevitably express itself; therefore, we can’t do anything about it. Therefore, we might as well not fund the social programs designed to ameliorate economic inequality and improve people’s lives, because their courses are fated genetically. And therefore, they don’t deserve better lives.
All of the “therefores” in the preceding paragraph are open to debate. What is important is that the argument relies on a very narrow understanding of the role of genetics in human life, and it misdirects the causes of inequality from cultural to natural processes. By contrast, instead of focusing on genes and imagining them to place an invisible limit upon social progress, we can study the ways in which your DNA sequence does not limit your capability for self-improvement or fix your place in a social hierarchy. In general, two such avenues exist. First, we can examine the ways in which the human body responds and reacts to environmental variation: human adaptability and plasticity. This line of research began with the anthropometric studies of immigrants by Franz Boas in the early 20th century and has now expanded to incorporate the epigenetic inheritance of modified human DNA. And second, we can consider how human lives are shaped by social histories—especially the structural inequalities within the societies in which they grow up.
Although it arises and is refuted every generation, the radical hereditarian position (genetic determinism) perennially claims to speak for both science and evolution. It does not. It is the voice of a radical fringe—perhaps naive, perhaps evil. It is not the authentic voice of science or of evolution. Indeed, keeping Charles Darwin’s name unsullied by protecting it from association with bad science often seems like a full-time job. Culture and epigenetics are very much a part of the human condition, and their roles are significant parts of the complete story of human evolution.
(Sterilization of Indigenous women in Canada) (https://www.thecanadianencyclopedia.ca/en/article/sterilization-of-indigenous-women-in-canada)
Adaptationism and the Panglossian Paradigm
The story of human evolution, and the evolution of all life for that matter, is never settled because evolution is ongoing. Additionally, because the conditions that shape evolutionary trajectories are not predetermined, evolution itself is emergent. Even during periods of ecological stability, when fewer macroevolutionary changes occur, populations of organisms continue to experience change. When ecological stability is disrupted, populations must adapt to the changes. Darwin explained in naturalistic terms how animals adapt to their environments: traits that contribute to an organism's ability to survive and reproduce in specific environments will become more common. The most “fit”—those organisms best suited to the current environmental conditions in which they live—have survived over eons of the history of life on earth to cocreate ecosystems full of animals and plants. Our own bodies are full of evident adaptations: eyes for seeing, ears for hearing, feet for walking on, and so forth.
But what about hands? Feet are adapted to be primarily weight-bearing structures (rather than grasping structures, as in the apes) and that is what we primarily use them for. But we use our hands in many ways: for fine-scale manipulation, greeting, pointing, stimulating a sexual partner, writing, throwing, and cooking, among other uses. So which of these uses express what hands are “for,” when all of them express what hands do?
Gould and Lewontin (1979) illustrate the problem with assuming that the function of a trait defines its evolutionary cause. Consider the case of Dr. Pangloss—the protagonistic of Voltaire’s Candide—who believed that we lived in the best of all possible worlds. Gould and Lewontin use his pronouncement that “noses were made for spectacles and so we have spectacles” to demonstrate the problem with assuming any trait has evolved for a specific purpose. Identifying a function of a trait does not necessitate that the function is the ultimate cause of the trait. Individual traits are not under selection pressures in isolation; in fact, an entire organism must be able to survive and reproduce in their environment. When natural selection results in adaptations, changes that occur in some traits can have cascading effects throughout the phenotype and features that are not under selection pressure can also change.

There is an important lesson in recognizing that what things do in the present is not a good guide to understanding why they came to exist. Gunpowder was invented for entertainment—only later was it adopted for killing people. The Internet was invented to decentralize computers in case of a nuclear attack—and only later adopted for social media. Apes have short thumbs and use their hands in locomotion; our ancestors stopped using their hands in locomotion by about six million years ago and had fairly modern-looking hands by about two million years ago. We can speculate that a combination of selection for abstract thought and dexterity led to evolution of the human hand, with its capability for toolmaking that exceeds what apes can do (see Figure 17.5). But let’s face it—how many tools have you made today?
Consequently, we are obliged to see the human foot as having a purpose to which it is adapted and the human hand as having multiple purposes, most of which are different from what it originally evolved for. Paleontologists Gould and Elisabeth Vrba suggested that an original use be regarded as an adaptation and any additional uses be called “exaptations.” Thus, we would consider the human hand to be an adaptation for toolmaking and an exaptation for writing. So how do we know whether any particular feature is an adaptation, like the walking foot, rather than an exaptation, like the writing hand? Or more broadly, how can we reason rigorously from what a feature does to what it evolved for?
The answer to the question “what did this feature evolve for?” creates an origin myth. This origin myth contains three assumptions: (1) features can be isolated as evolutionary units; (2) there is a specific reason for the existence of any particular feature; and (3) there is a clear and simplistic explanation for why the feature evolved.

The first assumption was appreciated a century ago as the “unit-character problem.” Are the units by which the body grows and evolves the same as units we name? This is clearly not the case: we have genes and we have noses, and we have genes that affect noses, but we don’t have “nose genes.” What is the relationship between the evolving elements that we see, identify, and name, and the elements that biologically exist and evolve? It is hard to know, but we can use the history of science as a guide to see how that fallacy has been used by earlier generations. Back in the 19th century, the early anatomists argued that since the brain contained the mind, they could map different mental states (acquisitiveness, punctuality, sensitivity) onto parts of the brain. Someone who was very introspective, say, would have an enlarged introspection part of the brain, a cranial bulge to represent the hyperactivity of this mental state. The anatomical science was known as phrenology, and it was predicated on the false assumption that units of thought or personality or behavior could be mapped to distinct parts of the brain and physically observed (see Figure17.6). This is the fallacy of reification, imagining that something named is something real.
Long alt text: Side view of human head. At the top are the words “Know Thyself.” On the upper head are small illustrations and word qualities such as “friendship,” “self-esteem,” and “secretiveness.” On the lower part of the man’s man’s face are the words The Phrenological Journal and Science of Health, A First Class Monthly. The caption at the bottom reads: “Specially devoted to the ‘.’ Contains PHRENOLOGY and PHYSIOGNOMY, with all the SIGNS OF CHARACTER, and how to read them; ETHNOLOGY, or the Natural History of Man in all his relations.” (All emphases in original.)

The second assumption, that everything has a reason, has long been recognized as a core belief of religion. Our desire to impose order and simplicity on the workings of the universe, however, does not constrain it to obey simple and orderly causes. Magic, witchcraft, spirits, and divine agency are all powerful explanations for why things happen. Consequently, it is probably not a good idea to lump natural selection in with those. Sometimes things do happen for a reason, of course, but other times things happen as byproducts of other things, or for very complicated and entangled reasons, or for no reason at all. What phenomena have reasons and thereby merit explanation? Chimpanzees have very large testicles, and we think we know why: their promiscuous sexual behavior triggers intense competition for high sperm count. But chimpanzees also have very large ears, but much less scientific attention has been paid to this trait (see Figure 17.7). Why not? Why should there be a reason for chimp testicles but not for chimp ears? What determines the kinds of features that we try to explain, as opposed to the ones that we do not? Again, the assumption that any specific feature has a reason is metaphysical; that is to say, it may be true in any particular case, but to assume it in all cases is gratuitous.
And third, the possibility of knowing what the reason for any particular feature is, assuming that it has one, is a challenge for evolutionary epistemology (the theory of how we know things). Consider the big adaptations of our lineage: bipedalism and language. Nobody doubts that they are good, and they evolved by natural selection, and we know how they work. But why did they evolve? If talking and walking are simply better than not talking and not walking, then why did they evolve in just a single branch of the ape lineage in the primate family tree? We don’t know what bipedalism evolved for, although there are plenty of speculations: walking long distances, running long distances, cooling the head, seeing over tall grass, carrying babies, carrying food, wading, threatening, counting calories, sexual display, and so on. Neither do we know what language evolved for, although there are speculations: coordinating hunting, gossiping, manipulating others. But it is also possible that bipedality is simply the way that a small arboreal ape travels on the ground, if it isn’t in the treetops. Or that language is simply the way that a primate with small canine teeth and certain mental propensities comes to communicate. If that were true, then there might be no reason for bipedality or language: having the unique suite of preconditions and a fortuitous set of circumstances simply set them in motion, and natural selection elaborated and explored their potentials. It is possible that walking and talking simply solved problems that no other lineage had ever solved; but even if so, the fact remains that the rest of the species in the history of life have done pretty well without having solved them.
It is certainly very optimistic to think that all three assumptions (that organisms can be meaningfully atomized, that everything has a reason, and that we can know the reason) would be simultaneously in effect. Indeed, just as there are many ways of adapting (genetically, epigenetically, behaviorally, culturally), there are also many ways of being nonadaptive, which would imply that there is no reason at all for the feature in question.
First, there is the element of randomness of population histories. There are more cases of sickle-cell anemia among sub-Saharan Africans than other peoples, and there is a reason for it: carriers of sickle-cell anemia have a resistance to malaria, which is more frequent in parts of Africa (as discussed in Chapters 4 and 14). But there are more cases of a blood disease called variegated porphyria, a rare genetic metabolic disorder, in the Afrikaners of South Africa (descendants of mostly Dutch settlers in the 17th century) than in other peoples, and there is no reason for it. Yet we know the cause: One of the founding Dutch colonial settlers had the allele–a variant of a gene–and everyone in South Africa with it today is her descendant. But that is not a reason—that is simply an accident of history.
Second, there is the potential mismatch between the past and the present. The value of a particular feature in the past may be changed as the environmental circumstances change. Our species is diurnal, and our ancestors were diurnal. But beginning around a few hundred thousand years ago, our ancestors could build fires, which extended the light period, which was subsequently further amplified by lamps and candles. And over the course of the 20th century, electrical power has made it possible for people to stay up very late when it is dark—working, partying, worrying—to a greater extent than any other closely related species. In other words, we evolved to be diurnal, yet we are now far more nocturnal than any of our recent ancestors or close relatives. Are we adapting to nocturnality? If so, why? Does it even make any sense to speak of the human occupation of a nocturnal ape niche, despite the fact that we empirically seem to be doing just that? And if so, does it make sense to ask what the reason for it is?
Third, there is a genetic phenomenon known as a selective sweep, or the hitchhiker effect. Imagine three genes—A, B, and C—located very closely together on a chromosome. They each have several variants, or alleles, in the population. Now, for whatever reason, it becomes beneficial to have one of the B alleles, say B4; this B4 allele is now under strong positive selection. Obviously, we will expect future generations to be characterized by mostly B4. But what was B4 attached to? Because whatever A and C alleles were adjacent to it will also be quickly spread, simply by virtue of the selection for B4. Even if the A and C alleles are not very good, they will spread because of the good B4 allele between them. Eventually the linkage groups will break up because of genetic crossing-over in future generations. But in the meantime, some random version of genes A and C are proliferating in the species simply because they are joined to superior allele B4. And clearly, the A and C alleles are there because of selection—but not because of selection for them!
Fourth, some features are simply consequences of other properties rather than adaptations to external conditions. We already noted the phenomenon of allometric growth, in which some physical features have to outgrow others to maintain function at an increased size. Can we ask the reason for the massive brow ridges of Homo erectus, or are brow ridges simply what you get when you have a conjunction of thick skull bones, a large face, and a sloping forehead—and, thus, again would have a cause but no reason?
Fifth, some features may be underutilized and on the way out. What is the reason for our two outer toes? They aren’t propulsive, they don’t do anything, and sometimes they’re just in the way. Obviously they are there because we are descended from ancestors with five digits on their hands and feet. Is it possible that a million years from now, we will just have our three largest toes, just as the ancestors of the horse lost their digits in favor of a single hoof per limb? Or will our outer toes find another use, such as stabilizing the landings in our personal jet-packs? For the time being, we can just recognize vestigiality as another nonadaptive explanation for the presence of a given feature.
Finally, Darwin himself recognized that many obvious features do not help an animal survive. Some things may instead help an animal breed. The peacock’s tail feathers do not help it eat, but they do help it mate. There is competition, but only against half of the species. Darwin called this sexual selection. Its result is not a fit to the environment but, rather, a fit to the opposite sex. In some species, that is literally the case, as the male and female genitalia have specific ways of anatomically fitting together. The specific form is less important than the specific match, so inquiring about the reason for a particular form of the reproductive anatomy may be misleading. The specific form may be effectively random, as long as it fits the opposite sex and is different from the anatomies of other species. Nor is sexual selection the only form of selection that can affect the body differently from natural selection. Competition might also take place between biological units other than organisms—perhaps genes, perhaps cells, or populations, or species. The spread of cultural things, such as head-binding or cheap refined fructose or forced labor, can have significant effects upon bodies, which are also not adaptations produced by natural selection. They are often adaptive physiological responses to stresses but not the products of natural selection.
With so many paths available by which a physical feature might have organically arisen without having been the object of natural selection, it is unwise to assume that any individual trait is an adaptation. And that generalization applies to the best-known, best-studied, and most materially based evolutionary adaptations of our lineage. But our cultural behaviors are also highly adaptive, so what about our most familiar social behaviors? Patriarchy, hierarchy, warfare—are these adaptations? Do they have reasons? Are they good for something?
This is where some sloppy thinking has been troublesome. What would it mean to say that patriarchy evolved by natural selection in the human species? If, on the one hand, it means that the human mind evolved by natural selection to be able to create and survive in many different kinds of social and political regimes, of which patriarchy is one, then biological anthropologists will readily agree. If, on the other hand, it means that patriarchy evolved by natural selection, that implies that patriarchy is genetically determined (since natural selection is a genetic process) and out-reproduced the alleles for other, more egalitarian, social forms. This in turn would imply that patriarchy is an adaptation and therefore of some beneficial value in the past and has become an ingrained part of human nature today. This would be bad news, say, if you harbored ambitions of dismantling it. Dismantling patriarchy in that case would be to go against nature, a futile gesture. In other words, this latter interpretation would be a naturalistic manifesto for a conservative political platform: don’t try to dismantle the patriarchy, because it is within us, the product of evolution—suck it up and live with it.
Here, evolution is being used as a political instrument for transforming the human genome into an imaginary glass ceiling against equality. There is thus a convergence between the pseudo-biology of crude adaptationism (the idea that everything is the product of natural selection) and the pseudo-biology of hereditarianism. Naturalizing inequality is not the business of evolutionary theory, and it represents a difficult moral position for a scientist to adopt, as well as a poor scientific position.
Dig Deeper: Evolution of Humans and Its Effects (to be reviewed)
As humans have caused the emergence of the Anthropocene, it is important to inform scholars about the effect of our social and cultural evolution on the rest of the world. Richard Robbins’ Global Problems and Culture of Capitalism explains how the modern culture of consumption has been extremely successful at accommodating populations of people far larger than previously possible. Robbins claims that the globalization attributed to capitalism has allowed the world to make full use of its environmental resources, providing necessities and innovative technologies to humans all over the world (Robbins & Dowty, 2019). In other words, capitalism is an anthropocentric cultural system that highly benefits humans and facilitates our survival with little regard to the development and survival of other forms of life. It would be of high relevance to introduce the idea that our cultural evolution and capacity to modify the environment to meet our needs have established new environmental conditions in which the human species' survival and reproduction rate expand at the detriment of ecosystems and endangerment of other primates and non-human species.
According to a 2019 UN report, following the 16th century, the world has entered a period of extreme environmental destruction that is generating ecological modifications and has led to the extinction of at least 680 vertebrate species and over 9 percent of the domesticated mammals used for food and agriculture (United Nations, 2019). Human lifestyles are causing changes that—if not taken into consideration—could lead to our extinction as a species. The recognition that our evolutionary behavioural development is causing environmental destruction may be the first step for our species to take accountability for the damage that it is causing to others and prevent further damage.
Concluding Thoughts
Now that you have finished reading this chapter, you are equipped to understand the historical and political dimensions of evolution. Evolution is an ongoing process of change and diversification. Evolutionary theory is a tool that we use to understand this process. The development of evolutionary theory is shaped both by scientific innovation and political engagement. Since Darwin first articulated natural selection as an observable mechanism by which species adapt to their environments, our understanding of evolution has grown. Initially, scientists focused on the adaptive aspects of evolution. However, with the emergence of genetics, our understanding of heredity and the level at which evolution acts has changed. Genetics led to a focus on the molecular dimensions of evolution. For some, this focus resulted in reductive accounts of evolution. Further developments in our understanding of evolution shifted our view to epigenetic processes and how organisms shape their own evolutionary pressures (e.g., niche construction).
Evolutionary theory will continue to develop in the future as we invent new technologies, describe new dimensions of biology, and experience cultural changes. Current innovations in evolutionary theory are asking us to consider evolutionary forces beyond natural selection and genetics to include the ways organisms shape their environments (niche construction), inheritances beyond genetics (inclusive inheritance), constraints on evolutionary change (developmental bias), and the ability of bodies to change in response to external factors (plasticity). The future of evolutionary theory looks bright as we continue to explore these and other dimensions. Biological anthropology is well-positioned to be a lively part of this conversation, as it extends standard evolutionary theory by considering the role of culture, social learning, and human intentionality in shaping the evolutionary trajectories of humans (Zeder 2018). Remember, at root, human evolutionary theory consists of two propositions: (1) the human species is descended from other similar species and (2) natural selection has been the primary agent of biological adaptation. Pretty much everything else is subject to some degree of contestation.
Review Questions
- How is the study of your ancestors biopolitical, not just biological? Does that make it less scientific or differently scientific?
- What was gained by reducing organisms to genotypes and species to gene pools? What is gained by reintroducing bodies and species into evolutionary studies?
- How do genetic or molecular studies complement anatomical studies of evolution?
- How are you reducible to your ancestry? If you could meet your ancestors from the year 1700 (and you would have well over a thousand of them!), would their lives be meaningfully similar to yours? Would you even be able to communicate with them?
- The molecular biologist François Jacob argued that evolution is more like a tinkerer than an engineer. In what ways do we seem like precisely engineered machinery, and in what ways do we seem like jerry-rigged or improvised contraptions?
- How might biological anthropology contribute to future developments in evolutionary theory?
Key Terms
Adaptation: A fit between the organism and environment.
Adaptationism: The idea that everything is the product of natural selection.
Allele: A genetic variant.
Allometry: The differential growth of body parts.
Canalization: The tendency of a growing organism to be buffered toward normal development.
Epigenetics: The study of how genetically identical cells and organisms (with the same DNA base sequence) can nevertheless differ in stably inherited ways.
Eugenics: An idea that was popular in the 1920s that society should be improved by breeding “better” kinds of people.
Evo-devo: The study of the origin of form; a contraction of “evolutionary developmental biology.”
Exaptation: An additional beneficial use for a biological feature.
Extinction: The loss of a species from the face of the earth.
Gene: A stretch of DNA with an identifiable function (sometimes broadened to include any DNA with recognizable structural features as well).
Gene pool: Hypothetical summation of the entire genetic composition of population or species.
Genotype: Genetic constitution of an individual organism.
Hereditarianism: The idea that genes or ancestry is the most crucial or salient element in a human life. Generally associated with an argument for natural inequality on pseudo-genetic grounds.
Hox genes: A group of related genes that control for the body plan of an embryo along the head-tail axis.
Inheritance of acquired characteristics: The idea that you pass on the features that developed during your lifetime, not just your genes; also known as Lamarckian inheritance.
Natural selection: A consistent bias in survival and fertility, leading to the overrepresentation of certain features in future generations and an improved fit between an average member of the population and the environment.
Niche construction: The active engagement by which species transform their surroundings in favorable ways, rather than just passively inhabiting them.
Phenotype: Observable manifestation of a genetic constitution, expressed in a particular set of circumstances. The suite of traits of an organism.
Phrenology: The 19th-century anatomical study of bumps on the head as an indication of personality and mental abilities.
Plasticity: The tendency of a growing organism to react developmentally to its particular conditions of life.
Punctuated equilibria: The idea that species are stable through time and are formed very rapidly relative to their duration. (The opposite theory, that species are unstable and constantly changing through time, is called phyletic gradualism.)
Scientific racism: The use of pseudoscientific evidence to support or legitimize racial hierarchy and inequality.
Sexual selection: Natural selection arising through preference by one sex for certain characteristics in individuals of the other sex.
Species selection: A postulated evolutionary process in which selection acts on an entire species population, rather than individuals.
About the Authors
Jonathan Marks, Ph.D.
University of North Carolina at Charlotte, jmarks@uncc.edu
Jonathan Marks is Professor of Anthropology at the University of North Carolina at Charlotte. He has published many books and articles on broad aspects of biological anthropology. In 2006 he was elected a Fellow of the American Association for the Advancement of Science. In 2012 he was awarded the First Citizen’s Bank Scholar’s Medal from UNC Charlotte. In recent years he has been a Visiting Research Fellow at the ESRC Genomics Forum in Edinburgh, a Visiting Research Fellow at the Max Planck Institute for the History of Science in Berlin, and a Templeton Fellow at the Institute for Advanced Study at Notre Dame. His work has received the W. W. Howells Book Prize and the General Anthropology Division Prize for Exemplary Cross-Field Scholarship from the American Anthropological Association as well as the J. I. Staley Prize from the School for Advanced Research. Two of his books are titled What It Means to Be 98% Chimpanzee and Why I Am Not a Scientist, but actually he is about 98 percent scientist and not a chimpanzee.
Adam P. Johnson, M.A.
University of North Carolina at Charlotte/University of Texas at San Antonio, ajohn344@uncc.edu
Adam Johnson is a doctoral candidate at the University of Texas at San Antonio and part-time lecturer at the University of North Carolina at Charlotte. He earned his M.A. in anthropology at UNC-Charlotte in 2017 and will complete his Ph.D. in anthropology at UTSA by 2024. His interests include human-animal relations, science studies, primate behavior, ecology, and the history of anthropology. His recent research project analyzes the social, historical, political, and evolutionary dimensions that shape human-javelina encounters. His goal is to understand how humans and animals find ways to get along in a precarious world.
For Further Exploration
Ackermann, Rebecca Rogers, Alex Mackay, and Michael L. Arnold. 2016. “The Hybrid Origin of ‘Modern’ Humans.” Evolutionary Biology 43 (1): 1–11.
Bateson, Patrick, and Peter Gluckman. 2011. Plasticity, Robustness, Development and Evolution. New York: Cambridge University Press.
Cosans, Christopher E. 2009. Owen's Ape and Darwin's Bulldog: Beyond Darwinism and Creationism. Bloomington, IN: Indiana University Press.
Desmond, Adrian, and James Moore. 2009. Darwin's Sacred Cause: How a Hatred of Slavery Shaped Darwin's Views on Human Evolution. New York: Houghton Mifflin Harcourt.
Dobzhansky, Theodosius, Francisco J. Ayala, G. Ledyard Stebbins, and James W. Valentine. 1977. Evolution. San Francisco: W.H. Freeman and Company.
Fuentes, Agustín. 2017. The Creative Spark: How Imagination Made Humans Exceptional. New York: Dutton.
Gould, Stephen J. 2003. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press.
Haraway, Donna J. 1989. Primate Visions: Gender, Race, and Nature in the World of Modern Science. New York: Routledge.
Huxley, Thomas. 1863. Evidence as to Man's Place in Nature. London: Williams & Norgate.
Jablonka, Eva, and Marion J. Lamb. 2005. Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Cambridge, MA: The MIT Press.
Kuklick, Henrika, ed. 2008. A New History of Anthropology. New York: Blackwell.
Laland, Kevin N., Tobias Uller, Marcus W. Feldman, Kim Sterelny, Gerd B. Muller, Armin Moczek, Eva Jablonka, and John Odling-Smee. 2015. “The Extended Evolutionary Synthesis: Its Structure, Assumptions and Predictions.” Proceedings of the Royal Society, Series B 282 (1813): 20151019.
Lamarck, Jean Baptiste. 1809. Philosophie Zoologique. Paris: Dentu.
Landau, Misia. 1991. Narratives of Human Evolution. New Haven: Yale University Press.
Lee, Sang-Hee. 2017. Close Encounters with Humankind: A Paleoanthropologist Investigates Our Evolving Species. New York: W. W. Norton.
Livingstone, David N. 2008. Adam's Ancestors: Race, Religion, and the Politics of Human Origins. Baltimore: Johns Hopkins University Press.
Marks, Jonathan. 2015. Tales of the Ex-Apes: How We Think about Human Evolution. Berkeley, CA: University of California Press.
Pigliucci, Massimo. 2009. “The Year in Evolutionary Biology 2009: An Extended Synthesis for Evolutionary Biology.” Annals of the New York Academy of Sciences 1168: 218–228.
Simpson, George Gaylord. 1949. The Meaning of Evolution: A Study of the History of Life and of Its Significance for Man. New Haven: Yale University Press.
Sommer, Marianne. 2016. History Within: The Science, Culture, and Politics of Bones, Organisms, and Molecules. Chicago: University of Chicago Press.
Stoczkowski, Wiktor. 2002. Explaining Human Origins: Myth, Imagination and Conjecture. New York: Cambridge University Press.
Tattersall, Ian, and Rob DeSalle. 2019. The Accidental Homo sapiens: Genetics, Behavior, and Free Will. New York: Pegasus.
References
Barton, Robert A. 1996. "Neocortex Size and Behavioural Ecology in Primates." Proceedings of the Royal Society of London. Series B: Biological Sciences 263 (1367): 173–177.
Bodmer, Walter, and Robin McKie. 1997. The Book of Man: The Hman Genome Project and the Quest to Discover our Genetic Heritage. Oxford University Press.
Darwin, Charles. 1859. On the Origin of Species by Means of Natural Selection, or, the Preservation of Favoured Races in the Struggle for Life. London: J. Murray.
Darwin, Charles. 1871. The Descent of Man, and Selection in Relation to Sex. London: J. Murray.
Dawkins, Richard. 1976. The Selfish Gene. Oxford University Press.
Deacon, T. W. 1998. The Symbolic Species: The Co-evolution of Language and the Brain. W. W. Norton & Company.
Eldredge, N., and S. J. Gould. 1972. "Punctuated Equilibria: An Alternative to Phyletic Gradualism." In Models in Paleobiology, edited by T. J. Schopf, 82–115. San Francisco: W. H. Freeman.
Gould, Stephen J. 2003. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press.
Gould, Stephen J. 1996. Mismeasure of Man. New York: WW Norton & Company.
Gould, Stephen Jay, and Richard C. Lewontin. 1979. "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme." Proceedings of the Royal Society of London. Series B: Biological Sciences 205 (1151): 581–598.
Haeckel, Ernst. 1868. Natürliche Schöpfungsgeschichte. Berlin: Reimer.
Huxley, Thomas Henry. 1863. Evidence as to Man’s Place in Nature. London: Williams and Norgate.
Kaufman, Thomas C., Mark A. Seeger, and Gary Olsen. 1990. "Molecular and Genetic Organization of the Antennapedia Gene Complex of Drosophila melanogaster." Advances in Genetics 27: 309–362.
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Marks, Jonathan. 2015. “The Biological Myth of Human Evolution.” In Biologising the Social Sciences: Challenging Darwinian and Neuroscience Explanations, edited by David Canter and David A. Turner, 59–78. London: Routledge.
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Shultz, Susanne, Emma Nelson, and Robin Dunbar. 2012. "Hominin Cognitive Evolution: Identifying Patterns and Processes in the Fossil and Archaeological Record." Philosophical Transactions of the Royal Society B: Biological Sciences 367 (1599): 2130–2140.
Spencer, Herbert. 1864. Principles of Biology. London: Williams and Norgate.
Watson, James D. 1990. "The Human Genome Project: Past, Present, and Future." Science 248 (4951): 44–49.
Yengo, L., Vedantam, S., Marouli, E., Sidorenko, J., Bartell, E., Sakaue, S., Graff, M., Eliasen, A.U., Jiang, Y., Raghavan, S. and Miao, J., 2022. A saturated map of common genetic variants associated with human height. Nature, 610 (7933): 704-712.
Zeder, Melinda A. 2018. "Why Evolutionary Biology Needs Anthropology: Evaluating Core Assumptions of the Extended Evolutionary Synthesis." Evolutionary Anthropology: Issues, News, and Reviews 27 (6): 267–284.
Jonathan Marks, Ph.D., University of North Carolina at Charlotte
Adam P. Johnson, M.A., University of North Carolina at Charlotte/University of Texas at San Antonio
This chapter is an adaptation of "Chapter 2: Evolution” by Jonathan Marks. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Explain the relationship among genes, bodies, and organismal change.
- Discuss the shortcomings of simplistic understandings of genetics.
- Describe what is meant by the "biopolitics of heredity."
- Discuss issues caused by misuse of ideas about adaptations and natural selection.
- Examine and correct myths about evolution.
The Human Genome Project, an international initiative launched in 1990, sought to identify the entire genetic makeup of our species. For many scientists, it meant trying to understand the genetic underpinnings of what made humans uniquely human. James Watson, a codiscoverer of the helical shape of DNA, wrote that “when finally interpreted, the genetic messages encoded within our DNA molecules will provide the ultimate answers to the chemical underpinnings of human existence” (Watson 1990, 248). The underlying message is that what makes humans unique can be found in our genes. The Human Genome Project hoped to find the core of who we are and where we come from.
Despite its lofty goal, the Human Genome Project—even after publishing the entire human genome in January 2022—could not fully account for the many factors that contribute to what it is to be human. Richard Lewontin, Steven Rose, and Leon Kamin (2017) argue that genetic determinism of the sort assumed by the Human Genome Project neglects other essential dimensions that contribute to the development and evolution of human bodies, not to mention the role that culture plays. They use an apt metaphor of a cake to illustrate the incompleteness of reductive models. Consider the flavor of a cake and think of the ingredients listed in the recipe. The recipe includes ingredients such as flour, sugar, shortening, vanilla extract, eggs, and milk. Does raw flour taste like cake? Does sugar, vanilla extract, or any of the other ingredients taste like cake? They do not, and knowing the individual flavors of each ingredient does not tell us much about what cake tastes like. Even mixing all of the ingredients in the correct proportions does not get us cake. Instead, external factors such as baking at the right temperature, for the right amount of time, and even the particularities of our evolved sense of taste and smell are all necessary components of experiencing the cake.
Lewontin, Rose, and Kamin (2017) argue that the same is true for humans and other organisms.
Knowing everything about cake ingredients does not allow us to fully know cake. Equally so, knowing everything about the genes found in our DNA does not allow us to fully know humans. Different, interacting levels are implicated in the development and evolution of all organisms, including humans. Genes, the structure of chromosomes, developmental processes, epigenetic tags, environmental factors, and still-other components all play key roles such that genetically reductive models of human development and evolution are woefully inadequate.
The complex interactions across many levels—genetic, developmental, and environmental—explain why we still do not know how our one-dimensional DNA nucleotide sequence results in a four-dimensional organism. This was the unfulfilled promise of the inception of the Human Genome Project in the 1980s and 1990s: the project produced the complete DNA sequence of a human cell in the hopes that it would reveal how human bodies are built and how to cure them when they are built poorly. Yet, that information has remained elusive. Presumably, the knowledge of how organisms are produced from DNA sequences will one day permit us to reconcile the discrepancies between patterns in anatomical evolution and molecular evolution.
In this chapter, we will consider multilevel evolution and explore evolution as a complex interaction between genetic and epigenetic factors as well as the environments in which organisms live. Next, we will examine the biopolitical nature of human evolution. We will then investigate problems that arise from attributing all traits to an adaptive function. Finally, we will address common misconceptions about evolution. The goal of this chapter is to provide you with the necessary toolkit for understanding the molecular, anatomical, and political dimensions of evolution.
Evolution Happens at Multiple Levels
Following Richard Dawkins’s publication of The Selfish Gene in 1976, the scientific imagination was captured by the potential of genomics to reveal how genes are copied by Darwinian selection. Dawkins argues that the genes in individuals that contribute to greater reproductive success are the units of selection. His conception of evolution at the molecular level undercuts the complex interactions between organisms and their environments, which are not expressed genomically but are nevertheless key drivers in evolution.
By the 1980s, the acknowledgment among most biologists that even though genes construct bodies, genes and bodies evolve at different rates and with distinct patterns. This realization led to a renewed focus on how bodies change. The Evolutionary Synthesis of the 1930s–1970s had reduced organisms to their genotypes and species to their gene pools, which provided valuable insights about the processes of biological change, but it was only a first approximation. Animals are in fact reactive and adaptable beings, not passive and inert genotypes. Species are clusters of socially interacting and reproductively compatible organisms.

Once we accept that evolutionary change is fundamentally genetic change, we can ask: How do bodies function and evolve? How do groups of animals come to see one another as potential mates or competitors for mates, as opposed to just other creatures in the environment? Are there evolutionary processes that are not explicable by population genetics? These questions—which lead us beyond reductive assumptions—were raised in the 1980s by Stephen Jay Gould, the leading evolutionary biologist of the late 20th century (see: Gould 2003; 1996).
Gould spearheaded a movement to identify and examine higher-order processes and features of evolution that were not adequately explained by population genetics. For example, extinction, which was such a problem for biologists of the 1600s, could now be seen as playing a more complex role in the history of life than population genetics had been able to model. Gould recognized that there are two kinds of extinctions, each with different consequences: background extinctions and mass extinctions. Background extinctions are those that reflect the balance of nature, because in a competitive Darwinian world, some things go extinct and other things take their place. Ecologically, your species may be adapted to its niche, but if another species comes along that’s better adapted to the same niche, eventually your species will go extinct. It sucks, but it is the way of all life: you come into existence, you endure, and you pass out of existence. But mass extinctions are quite different. They reflect not so much the balance of nature as the wholesale disruption of nature: many species from many different lineages dying off at roughly the same time—presumably as the result of some kind of rare ecological disaster. The situation may not be survival of the fittest as much as survival of the luckiest. The result, then, would be an ecological scramble among the survivors. Having made it through the worst, the survivors could now simply divide up the new ecosystem amongst themselves, since their competitors were gone. Something like this may well have happened about 65 million years ago, when a huge asteroid hit the Yucatan Peninsula, which mammals survived but dinosaurs did not (Figure 17.1). Something like this may be happening now, due to human expansion and environmental degradation. Note, though, that there is only a limited descriptive role here for population genetics: the phenomena we are describing are about organisms and species in ecosystems.
Another question involved the disconnect between properties of species and the properties of gene pools. For example, there are upwards of 15 species of gibbons but only two species of chimpanzees. Why? There are upwards of 20 species of guenons but fewer than ten of baboons. Why? Are there genes for that? It seems unlikely. Gould suggested that species, as units of nature, might have properties that are not reducible to the genes in their cells. For example, rates of speciation and extinction might be properties of their ecologies and histories rather than their genes. Thus, relationships between environmental contexts and variability within a species result in degrees of resistance to extinction and affect the frequency and rates at which clades diversify (Lloyd and Gould 1993). Consistent biases of speciation rates might well produce patterns of macroevolutionary diversity that are difficult to explain genetically and better understood ecologically. Gould called such biases in speciation rates species selection—a higher-order process that invokes competition between species, in addition to the classic Darwinian competition between individuals.
One of Gould’s most important studies involved the very nature of species. In the classical view, a species is continually adapting to its environment until it changes so much that it is a different species than it was at the beginning of this sentence (Eldredge and Gould 1972). That implies that the species is a fundamentally unstable entity through time, continuously changing to fit in. But suppose, argued Gould along with paleontologist Niles Eldredge, a species is more stable through time and only really adapts during periods of ecological instability and change. Then we might expect to find in the fossil record long equilibrium periods—a few million years or so—in which species don’t seem to change much, punctuated by relatively brief periods in which they change a bit and then stabilize again as new species. They called this idea punctuated equilibria. The idea helps to explain certain features of the fossil record, notably the existence of small anatomical “gaps” between closely related fossil forms (Figure 17.2). Its significance lies in the fact that although it incorporates genetics, punctuated equilibria is not really a theory of genetics but one of types bodies in deep time.
Punctuated equilibria is seen across taxa, with long periods in the fossil record representing little phenotypic change. These periods of stability are disrupted by shorter periods of rapid adaptation, the process through which populations of organisms become suited to living in their environments. Phenotypic changes are often coupled with drastic climatic or ecological changes that affect the milieu in which organisms live. For example, throughout much of hominin evolutionary history, brain size was closely associated with body size and thus remained mostly stable. However, changes occurred in average hominin brain size at around 100 thousand years ago, 1 million years ago, and 1.8 million years ago. Several hypotheses have been put forth to explain these changes, including unpredictability in climate and environment (Potts 1998), social development (Barton 1996), and the evolution of language (Deacon 1998). Evidence from the fossil record, paleoclimate models, and comparative anatomy suggests that the changes observed in hominin lineage result from biocultural processes—that is, the coalescence of environmental and cultural factors that selected for larger brains (Marks 2015; Shultz, Nelson, and Dunbar 2012).

In response to the call for a theory of the evolution of form, the field of evo-devo—the intersection of evolutionary and developmental biology—arose. The central focus here is on how changes in form and shape arise. An embryo matures by the stimulation of certain cells to divide, forming growth fields. The interactions and relationships among these growth fields generate the structures of the body. The hox genes that regulate these growth fields turn out to be highly conserved across the animal kingdom. This is because they repeatedly turn on and off the most basic genes guiding the animal’s development, and thus any changes to them would be catastrophic. Indeed, these genes were first identified by manipulating them in fruit flies, such that one could produce a bizarre mutant fruit fly that grew a pair of legs where its antennae were supposed to be (Kaufman, Seeger, and Olsen 1990).
Certain genetic changes can alter the fates of cells and the body parts, while other genetic changes can simply affect the rates at which neighboring groups of cells grow and divide, thus producing physical bumps or dents in the developing body. The result of altering the relationships among these fields of cellular proliferation in the growing embryo is allometry, or the differential growth of body parts. As an animal gets larger—either over the course of its life or over the course of macroevolution—it often has to change shape in order to live at a different size. Many important physiological functions depend on properties of geometric area: the strength of a bone, for example, is proportional to its cross-sectional area. But area is a two-dimensional quality, while growing takes place in three dimensions—as an increase in mass or volume. As an animal expands, its bones necessarily weaken, because volume expands faster than area does. Consequently a bigger animal has more stress on its bones than a smaller animal does and must evolve bones even thicker than they would be by simply scaling the animal up proportionally. In other words, if you expand a mouse to the size of an elephant, it will nevertheless still have much thinner bones than the elephant does. But those giant mouse bones will unfortunately not be adequate to the task. Thus, a giant mouse would have to change aspects of its form to maintain function at a larger size (see Figure 17.3).

Physiologically, we would like to know how the body “knows” when to turn on and off the genes that regulate growth to produce a normal animal. Evolutionarily, we would like to know how the body “learns” to alter the genetic on/off switch (or the genetic “slow down/speed up” switch) to produce an animal that looks different. Moreover, since organisms differ from one another, we would like to know how the developing body distinguishes a range of normal variation from abnormal variation. And, finally, how does abnormal variation eventually become normal in a descendant species?
Taking up these questions, Gould invoked the work of a British geneticist named Conrad H. Waddington, who thought about genetics in less reductive ways than his colleagues. Rather than isolate specific DNA sites to analyze their function, Waddington instead studied the inheritance of an organism’s reactivity—its ability to adapt to the circumstances of its life. In a famous experiment, he grew fruit fly eggs in an atmosphere containing ether. Most died, but a few survived somehow by developing a weird physical feature: a second thorax with a second pair of wings. Waddington bred these flies and soon developed a stable line of flies who would reliably develop a second thorax when grown in ether. Then he began to lower the concentration of ether, while continuing to selectively breed the flies that developed the strange appearance. Eventually he had a line of flies that would stably develop the “bithorax” phenotype–the suite of traits of an organism–even when there was no ether; it had become the “new normal.” The flies had genetically assimilated the bithorax condition.
Waddington was thus able to mimic the inheritance of acquired characteristics: what had been a trait stimulated by ether a few generations ago was now a normal part of the development of the descendants. Waddington recognized that while he had performed a selection experiment on genetic variants, he had not selected for particular traits. Rather, he helped produce the physiological tendency to develop particular traits when appropriately stimulated. He called that tendency plasticity and its converse, the tendency to stay the same even under weird environmental circumstances, canalization. Waddington had initially selected for plasticity, the tendency to develop the bithorax phenotype under weird conditions, and then, later, for canalization, the developmental normalization of that weird physical trait. Although Waddington had high stature in the community of geneticists, evolutionary biologists of the 1950s and 1960s regarded him with suspicion because he was not working within the standard mindset of reductionism, which saw evolution as the spread of genetic variants that coded for favorable traits. Both Waddington and Gould resisted contemporary intellectual paradigms that favored reductive accounts of evolutionary processes. They conceived of evolution as an emergent process in which many external factors (e.g. climate, environment, predation) and internal factors (e.g., genotypes, plasticity, canalization) coalesce to produce the evolutionary trends that we observe in the fossil record and our genome.
While Gould and Waddington both looked beyond the genome to understand evolution, the Human Genome Project—an international project with the goal of identifying each base pair in the human genome in the 1990s—generated a great deal of public interest in analyzing the human DNA sequence from the standpoint of medical genetics. Some of the rhetoric aimed to sell the public on investing a lot of money and resources in sequencing the human genome in order to show the genetic basis of heritable traits, cure genetic diseases, and learn what it means ultimately to be biologically human. However, the Human Genome Project was not actually able to answer those questions through the use of genetics alone, and thus a broader, more holistic account was required.
This holistic account came from decades of research in human biology and anthropology, which understood the human body as highly adaptable, dynamic, and emergent. For example, in the early 20th century, anthropologist Franz Boas measured the skulls of immigrants to the U.S., revealing that environmental, not merely genetic, factors affected skull shape. The growing human body adjusts itself to the conditions of life, such as diet, sunshine, high altitude, hard labor, population density, how babies are carried—any and all of which can have subtle but consistent effects upon its development. There can thus be no normal human form, only a context-specific range of human forms.
However, what the human biologists called human adaptability, evolutionary biologists called developmental plasticity, and evidence quickly began to mount for its cause being epigenetic modifications to DNA. Epigenetic modifications are changes to how genes are used by the body (as opposed to changes in the DNA sequences; see Chapter 3). Scientific interest shifted from the focus of the Human Genome Project to the ways that bodies are made by evolutionary-developmental processes, including epigenetics. What is meant by “epigenetic modification”? Evolution is about how descendants diverge from their ancestors. Inheritance from parent to offspring is still critical to this process, which occurs through genetic recombination: the pairing of homologous chromosomes and sharing of genetic material during meiosis (see Chapter 3). However, in the 21st century, the link between evolution and inheritance has broadened with a clearer understanding of how environmental and developmental factors shape bodies and the expression of genes, including epigenetic inheritance patterns. While offspring inherit their genes through random assortment during meiosis, environmental factors also shape how genes are used. When these epigenetic modifications occur in germ cells, they can be passed onto offspring. In these cases, there is no change in the DNA sequence but rather in how genes are used by the body due to DNA methylation and the structure of chromosomes due to histone acetylation (see Chapter 3).
In addition, we now recognize that evolution is affected by two other forms of intergenerational transmission and inheritance (in addition to genetics and epigenetics). These forms include behavioral variation and culture. That is, behavioral information can be transmitted horizontally (intragenerationally), permitting more rapid ways for organisms to adjust to the environment. And, then there is the fourth mode of transmission: the cultural or symbolic mode. Humans are the only species that horizontally transmits an arbitrary set of rules to govern communication, social interaction, and thought. This shared information is symbolic and has resulted in what we recognize as “culture”: locally emergent worlds of names, words, pictures, classifications, revered pasts, possible futures, spirits, dead ancestors, unborn descendants, in-laws, politeness, taboo, justice, beauty, and story, all accompanied by practices and a material world of tools.
Consequently our contemporary ideas about evolution see the evolutionary processes as hierarchically organized and not restricted to the differential transmission of DNA sequences into the next generation. While that is indeed a significant part of evolution, the organism and species are nevertheless crucial to understanding how those DNA sequences get transmitted. Further, the transmission of epigenetic, behavioral, and symbolic information play a complex role in perpetuating our genes, bodies, and species. In the case of human evolution, one can readily see that symbolic information and cultural adaptation are far more central to our lives and our survival today than DNA and genetic adaptation. It is thus misleading to think of humans passively occupying an environmental niche. Rather, humans are actively engaged in constructing our own niches, as well as adapting to them and using them to adapt. The complex interplay between a species and its active engagement in creating its own ecology is known as niche construction. If we understand natural selection–the process by which populations adapt to their specific environments–as the effects that environmental context has on the reproductive success of organisms, then niche construction is the process through which organisms shape their own selective pressures.
The Biopolitics of Heredity
“Science isn’t political” is a sentiment that you have likely heard before. Science is supposed to be about facts and objectivity. It exists, or at least ought to, outside of petty human concerns. However, the sorts of questions we ask as scientists, the problems we choose to study, the categories and concepts we use, who gets to do science, and whose work gets cited are all shaped by culture. Doing science is a political act. This fact is markedly true for human evolution. While it is easier to create intellectual distance between us and fruit flies and viruses, there is no distance when we are studying ourselves. The hardest lesson to learn about human evolution is that it is intensely political. Indeed, to see it from the opposite side, as it were, the history of creationism—the belief that the universe was divinely created around 6,000 years ago—is essentially a history of legal decisions. For instance, in Tennessee v. John T. Scopes (1925), a schoolteacher was prosecuted for violating a law in Tennessee that prohibited the teaching of human evolution in public schools, where teachers were required by law to teach creationism.
More recently, legal decisions aimed at legislating science education have shaped how students are exposed to evolutionary theory. For instance, McLean v. Arkansas (1982) dispatched “scientific creationism” by arguing that the imposition of balanced teaching of evolution and creationism in science classes violates the Establishment Clause, separating church and state. Additionally, Kitzmiller v. Dover (Pennsylvania) Area School District (2005) dispatched the teaching of “intelligent design” in public school classrooms as it was deemed to not be science. In some cases, people see unbiblical things in evolution, although most Christian theologians are easily able to reconcile science to the Bible. In other cases, people see immoral things in evolution, although there is morality and immorality everywhere. And some people see evolution as an aspect of alt-religion, usurping the authority of science in schools to teach the rejection of the Christian faith, which would be unconstitutional due to the protected separation of church and state.
Clearly, the position that politics has nothing to do with science is untenable. But is the politics in evolution an aberration or is it somehow embedded in science? In the early 20th century, scientists commonly promoted the view that science and politics were separate: science was seen as a pure activity, only rarely corrupted by politics. And yet as early as World War I, the politics of nationalism made a hero of the German chemist Fritz Haber for inventing poison gas. And during World War II, both German doctors and American physicists, recruited to the war effort, helped to end many civilian lives. Therefore, we can think of the apolitical scientist as a self-serving myth that functions to absolve scientists of responsibility for their politics. The history of science shows how every generation of scientists has used evolutionary theory to rationalize political and moral positions. In the very first generation of evolutionary science, Darwin’s Origin of Species (1859) is today far more readable than his Descent of Man (1871). The reason is that Darwin consciously purged The Origin of Species of any discussion of people. And when he finally got around to talking about people, in The Descent of Man, he simply imbued them with the quaint Victorian prejudices of his age, and the result makes you cringe every few pages. There is plenty of politics in there—sexism, racism, and colonialism—because you cannot talk about people apolitically.
One immediate faddish deduction from Darwinism, popularized by Herbert Spencer (1864) as “survival of the fittest,” held that unfettered competition led to advancement in nature and to human history. Since the poor were purported losers in that struggle, anything that made their lives easier would go against the natural order. This position later came to be known ironically as “Social Darwinism.” Spencer was challenged by fellow Darwinian Thomas Huxley (1863), who agreed that struggle was the law of the jungle but observed that we don’t live in jungles anymore. The obligation to make lives better for others is a moral, not a natural, fact. We simultaneously inhabit a natural universe of descent from apes and a moral universe of injustice and inequality, and science is not well served by ignoring the latter.
Concurrently, the German biologist Ernst Haeckel’s 1868 popularization of Darwinism was translated into English a few years later as The History of Creation. As we saw earlier, Haeckel was determined to convince his readers that they were descended from apes, even in the absence of fossil evidence attesting to it. When he made non-Europeans into the missing links that connected his readers to the apes, and depicted them as ugly caricatures, he knew precisely what he was doing. Indeed, even when the degrading racial drawings were deleted from the English translation of his book, the text nevertheless made his arguments quite clear. And a generation later, when the Americans had not yet entered the Great War in 1916, a biologist named Vernon Kellogg visited the German High Command as a neutral observer and found that the officers knew a lot about evolutionary biology, which they had gotten from Haeckel and which rationalized their military aggressions. Kellogg went home and wrote a bestseller about it, called Headquarters Nights (1917). World War I would have been fought with or without evolutionary theory, but as a source of scientific authority, evolution—even if a perversion of the Darwinian theory—had very quickly attained global geopolitical relevance.
Oftentimes, politics in evolutionary science is subtle, due to the pervasive belief in the advancement of science. We recognize the biases of our academic ancestors and modify our scientific stories accordingly. But we can never be free of our own cultural biases, which are invisible to us, as much as our predecessors’ biases were invisible to them. In some cases, the most important cultural issues resurface in different guises each generation, like scientific racism. Scientific racism is the recruitment of science for the evil political ends of racism, and it has proved remarkably impervious to evolution. Before Darwin, there was creationist scientific racism, and after Darwin, there was evolutionist scientific racism. And there is still scientific racism today, self-justified by recourse to evolution, which means that scientists have to be politically astute and sensitive to the uses of their work to counter these social tendencies.
Consider this: Are you just your ancestry, or can you transcend it? If that sounds like a weird question, it was actually quite important to a turn-of-the-20th-century European society in which an old hereditary aristocracy was under increasing threat from a rising middle class. And that is why the very first English textbook of Mendelian genetics concluded with the thought that “permanent progress is a question of breeding rather than of pedagogics; a matter of gametes, not of training … the creature is not made but born” (Punnett 1905, 60). Translation: Not only do we now know a bit about how heredity works, but it’s also the most important thing about you. Trust me, I’m a scientist.
Yet evolution is about how descendants come to differ from ancestors. Do we really know that your heredity, your DNA, your ancestry, is the most important thing about you? That you were born, not made? After all, we do know that you could be born into slavery or as a peasant, and come from a long line of enslaved people or peasants, and yet not have slavery or peasantry be the most important thing about you. Whatever your ancestors were may unfortunately constrain what you can become, but as a moral precept, it should not. But just as science is not purely “facts and objectivity,” ancestry is not a strictly biological concept. Human ancestry is biopolitics, not biology.
Evolution is fundamentally a theory about ancestry, and yet ancestors are, in the broad anthropological sense, sacred: ancestors are often more meaningful symbolically than biologically. Just a few years after The Origin of Species (Darwin 1859), the British politician and writer Benjamin Disraeli declared himself to be on the side of the angels, not the apes, and to “repudiate with indignation and abhorrence those new-fangled theories” (Monypenny, Flavelle, and Buckle 1920, 105). He turned his back on an ape ancestry and looked to the angel; yet, he did so as a prominent Jew-turned-Anglican, who had personally transcended his humble roots and risen to the pinnacle of the Empire. Ancestry was certainly important, and Disraeli was famously proud of his, but it was also certainly not the most important thing, not the primary determinant of his place in the world. Indeed, quite the opposite: Disraeli’s life was built on the transcendence of many centuries of Jewish poverty and oppression in Europe. Humble ancestry was there to be superseded and nobility was there to be earned; Disraeli would later become the Earl of Beaconsfield. Clearly, “are you just your ancestry” is not a value-neutral question, and “the creature is not made, but born” is not a value-neutral answer.
Ancestry being the most important thing about a person became a popular idea twice in 20th century science. First, at the beginning of the century, when the eugenics movement in America called attention to “feeble-minded stocks,” which usually referred to the poor or to immigrants (see Figure 17.4; and see Chapter 2). This movement culminated in Congress restricting the immigration of “feeble-minded races” (said to include Jews and Italians) in 1924, and the Supreme Court declaring it acceptable for states to sterilize their “feeble-minded” citizens involuntarily in 1927. After the Nazis picked up and embellished these ideas during World War II, Americans moved swiftly away from them in some contexts (e.g., for most people of European descent) while still strictly adhering in other contexts (e.g., Japanese internment camps and immigration restrictions).

Ancestry again became paramount in the drumming up of public support for the Human Genome Project in the 1990s. Public support for sequencing the human genome was encouraged by a popular science campaign that featured books titled The Book of Man (Bodmer and McKie 1997), The Human Blueprint (Shapiro 1991), and The Code of Codes (Kevles and Hood 1993). These books generally promised cures for genetic diseases and a deeper understanding of the human condition. We can certainly identify progress in molecular genetics over the last couple of decades since the human genome was sequenced, but that progress has notably not been accompanied by cures for genetic diseases, nor by deeper understandings of the human condition.
Even at the most detailed and refined levels of genetic analysis, we still don’t have much of an understanding of the actual basis by which things seem to “run in families.” While the genetic basis of simple, if tragic, genetic diseases have become well-known—such as sickle-cell anemia, cystic fibrosis, and Tay-Sachs’ Disease—we still haven’t found the ostensible genetic basis for traits that are thought to have a strong genetic component. For example, a recent genetic summary found over 12,000 genetic sites that contributed to height yet still explained only about 40-50 percent of the variation in height among European ancestry but no more than 10-20 percent of variation of other ancestries, which we know strongly runs in families (Yengo et al. 2022).
Partly in reaction to the reductionistic hype of the Human Genome Project, the study of epigenetics has become the subject of great interest. One famous natural experiment involves a Nazi-imposed famine in Holland over the winter of 1944–1945. Children born during and shortly after the famine experienced a higher incidence of certain health problems as adults, many decades later. Apparently, certain genes had been down-regulated early in development and remained that way throughout the course of life. Indeed, this modified regulation of the genes in response to the severe environmental conditions may have been passed on to their children.
Obviously one’s particular genetic constitution may play an important role in one’s life trajectory. But overvaluing that role may have important social and political consequences. In the first place, genotypes are rendered meaningful in a cultural universe. Thus, if you live in a strongly patriarchal society and are born without a Y chromosome (since human males are chromosomally XY and females XX), your genotype will indeed have a strong effect upon your life course. So even though the variation is natural, the consequences are political. The mediating factors are the cultural ideas about how people of different sexes ought to be treated, and the role of the state in permitting certain people to develop and thrive. More broadly, there are implications for public education if variation in intelligence is genetic. There are implications for the legal system if criminality is genetic. There are implications for the justice system if sexual preference, or sexual identity, is genetic. There are implications for the development of sports talent if that is genetic. And yet, even for the human traits that are more straightforward to measure and known to be strongly heritable, the DNA base sequence variation seems to explain little.
Genetic determinism or hereditarianism is the idea that “the creature is made, not born”—or, in a more recent formulation by James Watson, that “our fate is in our genes.” One of the major implications drawn from genetic determinism is that the feature in question must inevitably express itself; therefore, we can’t do anything about it. Therefore, we might as well not fund the social programs designed to ameliorate economic inequality and improve people’s lives, because their courses are fated genetically. And therefore, they don’t deserve better lives.
All of the “therefores” in the preceding paragraph are open to debate. What is important is that the argument relies on a very narrow understanding of the role of genetics in human life, and it misdirects the causes of inequality from cultural to natural processes. By contrast, instead of focusing on genes and imagining them to place an invisible limit upon social progress, we can study the ways in which your DNA sequence does not limit your capability for self-improvement or fix your place in a social hierarchy. In general, two such avenues exist. First, we can examine the ways in which the human body responds and reacts to environmental variation: human adaptability and plasticity. This line of research began with the anthropometric studies of immigrants by Franz Boas in the early 20th century and has now expanded to incorporate the epigenetic inheritance of modified human DNA. And second, we can consider how human lives are shaped by social histories—especially the structural inequalities within the societies in which they grow up.
Although it arises and is refuted every generation, the radical hereditarian position (genetic determinism) perennially claims to speak for both science and evolution. It does not. It is the voice of a radical fringe—perhaps naive, perhaps evil. It is not the authentic voice of science or of evolution. Indeed, keeping Charles Darwin’s name unsullied by protecting it from association with bad science often seems like a full-time job. Culture and epigenetics are very much a part of the human condition, and their roles are significant parts of the complete story of human evolution.
(Sterilization of Indigenous women in Canada) (https://www.thecanadianencyclopedia.ca/en/article/sterilization-of-indigenous-women-in-canada)
Adaptationism and the Panglossian Paradigm
The story of human evolution, and the evolution of all life for that matter, is never settled because evolution is ongoing. Additionally, because the conditions that shape evolutionary trajectories are not predetermined, evolution itself is emergent. Even during periods of ecological stability, when fewer macroevolutionary changes occur, populations of organisms continue to experience change. When ecological stability is disrupted, populations must adapt to the changes. Darwin explained in naturalistic terms how animals adapt to their environments: traits that contribute to an organism's ability to survive and reproduce in specific environments will become more common. The most “fit”—those organisms best suited to the current environmental conditions in which they live—have survived over eons of the history of life on earth to cocreate ecosystems full of animals and plants. Our own bodies are full of evident adaptations: eyes for seeing, ears for hearing, feet for walking on, and so forth.
But what about hands? Feet are adapted to be primarily weight-bearing structures (rather than grasping structures, as in the apes) and that is what we primarily use them for. But we use our hands in many ways: for fine-scale manipulation, greeting, pointing, stimulating a sexual partner, writing, throwing, and cooking, among other uses. So which of these uses express what hands are “for,” when all of them express what hands do?
Gould and Lewontin (1979) illustrate the problem with assuming that the function of a trait defines its evolutionary cause. Consider the case of Dr. Pangloss—the protagonistic of Voltaire’s Candide—who believed that we lived in the best of all possible worlds. Gould and Lewontin use his pronouncement that “noses were made for spectacles and so we have spectacles” to demonstrate the problem with assuming any trait has evolved for a specific purpose. Identifying a function of a trait does not necessitate that the function is the ultimate cause of the trait. Individual traits are not under selection pressures in isolation; in fact, an entire organism must be able to survive and reproduce in their environment. When natural selection results in adaptations, changes that occur in some traits can have cascading effects throughout the phenotype and features that are not under selection pressure can also change.

There is an important lesson in recognizing that what things do in the present is not a good guide to understanding why they came to exist. Gunpowder was invented for entertainment—only later was it adopted for killing people. The Internet was invented to decentralize computers in case of a nuclear attack—and only later adopted for social media. Apes have short thumbs and use their hands in locomotion; our ancestors stopped using their hands in locomotion by about six million years ago and had fairly modern-looking hands by about two million years ago. We can speculate that a combination of selection for abstract thought and dexterity led to evolution of the human hand, with its capability for toolmaking that exceeds what apes can do (see Figure 17.5). But let’s face it—how many tools have you made today?
Consequently, we are obliged to see the human foot as having a purpose to which it is adapted and the human hand as having multiple purposes, most of which are different from what it originally evolved for. Paleontologists Gould and Elisabeth Vrba suggested that an original use be regarded as an adaptation and any additional uses be called “exaptations.” Thus, we would consider the human hand to be an adaptation for toolmaking and an exaptation for writing. So how do we know whether any particular feature is an adaptation, like the walking foot, rather than an exaptation, like the writing hand? Or more broadly, how can we reason rigorously from what a feature does to what it evolved for?
The answer to the question “what did this feature evolve for?” creates an origin myth. This origin myth contains three assumptions: (1) features can be isolated as evolutionary units; (2) there is a specific reason for the existence of any particular feature; and (3) there is a clear and simplistic explanation for why the feature evolved.

The first assumption was appreciated a century ago as the “unit-character problem.” Are the units by which the body grows and evolves the same as units we name? This is clearly not the case: we have genes and we have noses, and we have genes that affect noses, but we don’t have “nose genes.” What is the relationship between the evolving elements that we see, identify, and name, and the elements that biologically exist and evolve? It is hard to know, but we can use the history of science as a guide to see how that fallacy has been used by earlier generations. Back in the 19th century, the early anatomists argued that since the brain contained the mind, they could map different mental states (acquisitiveness, punctuality, sensitivity) onto parts of the brain. Someone who was very introspective, say, would have an enlarged introspection part of the brain, a cranial bulge to represent the hyperactivity of this mental state. The anatomical science was known as phrenology, and it was predicated on the false assumption that units of thought or personality or behavior could be mapped to distinct parts of the brain and physically observed (see Figure17.6). This is the fallacy of reification, imagining that something named is something real.
Long alt text: Side view of human head. At the top are the words “Know Thyself.” On the upper head are small illustrations and word qualities such as “friendship,” “self-esteem,” and “secretiveness.” On the lower part of the man’s man’s face are the words The Phrenological Journal and Science of Health, A First Class Monthly. The caption at the bottom reads: “Specially devoted to the ‘.’ Contains PHRENOLOGY and PHYSIOGNOMY, with all the SIGNS OF CHARACTER, and how to read them; ETHNOLOGY, or the Natural History of Man in all his relations.” (All emphases in original.)

The second assumption, that everything has a reason, has long been recognized as a core belief of religion. Our desire to impose order and simplicity on the workings of the universe, however, does not constrain it to obey simple and orderly causes. Magic, witchcraft, spirits, and divine agency are all powerful explanations for why things happen. Consequently, it is probably not a good idea to lump natural selection in with those. Sometimes things do happen for a reason, of course, but other times things happen as byproducts of other things, or for very complicated and entangled reasons, or for no reason at all. What phenomena have reasons and thereby merit explanation? Chimpanzees have very large testicles, and we think we know why: their promiscuous sexual behavior triggers intense competition for high sperm count. But chimpanzees also have very large ears, but much less scientific attention has been paid to this trait (see Figure 17.7). Why not? Why should there be a reason for chimp testicles but not for chimp ears? What determines the kinds of features that we try to explain, as opposed to the ones that we do not? Again, the assumption that any specific feature has a reason is metaphysical; that is to say, it may be true in any particular case, but to assume it in all cases is gratuitous.
And third, the possibility of knowing what the reason for any particular feature is, assuming that it has one, is a challenge for evolutionary epistemology (the theory of how we know things). Consider the big adaptations of our lineage: bipedalism and language. Nobody doubts that they are good, and they evolved by natural selection, and we know how they work. But why did they evolve? If talking and walking are simply better than not talking and not walking, then why did they evolve in just a single branch of the ape lineage in the primate family tree? We don’t know what bipedalism evolved for, although there are plenty of speculations: walking long distances, running long distances, cooling the head, seeing over tall grass, carrying babies, carrying food, wading, threatening, counting calories, sexual display, and so on. Neither do we know what language evolved for, although there are speculations: coordinating hunting, gossiping, manipulating others. But it is also possible that bipedality is simply the way that a small arboreal ape travels on the ground, if it isn’t in the treetops. Or that language is simply the way that a primate with small canine teeth and certain mental propensities comes to communicate. If that were true, then there might be no reason for bipedality or language: having the unique suite of preconditions and a fortuitous set of circumstances simply set them in motion, and natural selection elaborated and explored their potentials. It is possible that walking and talking simply solved problems that no other lineage had ever solved; but even if so, the fact remains that the rest of the species in the history of life have done pretty well without having solved them.
It is certainly very optimistic to think that all three assumptions (that organisms can be meaningfully atomized, that everything has a reason, and that we can know the reason) would be simultaneously in effect. Indeed, just as there are many ways of adapting (genetically, epigenetically, behaviorally, culturally), there are also many ways of being nonadaptive, which would imply that there is no reason at all for the feature in question.
First, there is the element of randomness of population histories. There are more cases of sickle-cell anemia among sub-Saharan Africans than other peoples, and there is a reason for it: carriers of sickle-cell anemia have a resistance to malaria, which is more frequent in parts of Africa (as discussed in Chapters 4 and 14). But there are more cases of a blood disease called variegated porphyria, a rare genetic metabolic disorder, in the Afrikaners of South Africa (descendants of mostly Dutch settlers in the 17th century) than in other peoples, and there is no reason for it. Yet we know the cause: One of the founding Dutch colonial settlers had the allele–a variant of a gene–and everyone in South Africa with it today is her descendant. But that is not a reason—that is simply an accident of history.
Second, there is the potential mismatch between the past and the present. The value of a particular feature in the past may be changed as the environmental circumstances change. Our species is diurnal, and our ancestors were diurnal. But beginning around a few hundred thousand years ago, our ancestors could build fires, which extended the light period, which was subsequently further amplified by lamps and candles. And over the course of the 20th century, electrical power has made it possible for people to stay up very late when it is dark—working, partying, worrying—to a greater extent than any other closely related species. In other words, we evolved to be diurnal, yet we are now far more nocturnal than any of our recent ancestors or close relatives. Are we adapting to nocturnality? If so, why? Does it even make any sense to speak of the human occupation of a nocturnal ape niche, despite the fact that we empirically seem to be doing just that? And if so, does it make sense to ask what the reason for it is?
Third, there is a genetic phenomenon known as a selective sweep, or the hitchhiker effect. Imagine three genes—A, B, and C—located very closely together on a chromosome. They each have several variants, or alleles, in the population. Now, for whatever reason, it becomes beneficial to have one of the B alleles, say B4; this B4 allele is now under strong positive selection. Obviously, we will expect future generations to be characterized by mostly B4. But what was B4 attached to? Because whatever A and C alleles were adjacent to it will also be quickly spread, simply by virtue of the selection for B4. Even if the A and C alleles are not very good, they will spread because of the good B4 allele between them. Eventually the linkage groups will break up because of genetic crossing-over in future generations. But in the meantime, some random version of genes A and C are proliferating in the species simply because they are joined to superior allele B4. And clearly, the A and C alleles are there because of selection—but not because of selection for them!
Fourth, some features are simply consequences of other properties rather than adaptations to external conditions. We already noted the phenomenon of allometric growth, in which some physical features have to outgrow others to maintain function at an increased size. Can we ask the reason for the massive brow ridges of Homo erectus, or are brow ridges simply what you get when you have a conjunction of thick skull bones, a large face, and a sloping forehead—and, thus, again would have a cause but no reason?
Fifth, some features may be underutilized and on the way out. What is the reason for our two outer toes? They aren’t propulsive, they don’t do anything, and sometimes they’re just in the way. Obviously they are there because we are descended from ancestors with five digits on their hands and feet. Is it possible that a million years from now, we will just have our three largest toes, just as the ancestors of the horse lost their digits in favor of a single hoof per limb? Or will our outer toes find another use, such as stabilizing the landings in our personal jet-packs? For the time being, we can just recognize vestigiality as another nonadaptive explanation for the presence of a given feature.
Finally, Darwin himself recognized that many obvious features do not help an animal survive. Some things may instead help an animal breed. The peacock’s tail feathers do not help it eat, but they do help it mate. There is competition, but only against half of the species. Darwin called this sexual selection. Its result is not a fit to the environment but, rather, a fit to the opposite sex. In some species, that is literally the case, as the male and female genitalia have specific ways of anatomically fitting together. The specific form is less important than the specific match, so inquiring about the reason for a particular form of the reproductive anatomy may be misleading. The specific form may be effectively random, as long as it fits the opposite sex and is different from the anatomies of other species. Nor is sexual selection the only form of selection that can affect the body differently from natural selection. Competition might also take place between biological units other than organisms—perhaps genes, perhaps cells, or populations, or species. The spread of cultural things, such as head-binding or cheap refined fructose or forced labor, can have significant effects upon bodies, which are also not adaptations produced by natural selection. They are often adaptive physiological responses to stresses but not the products of natural selection.
With so many paths available by which a physical feature might have organically arisen without having been the object of natural selection, it is unwise to assume that any individual trait is an adaptation. And that generalization applies to the best-known, best-studied, and most materially based evolutionary adaptations of our lineage. But our cultural behaviors are also highly adaptive, so what about our most familiar social behaviors? Patriarchy, hierarchy, warfare—are these adaptations? Do they have reasons? Are they good for something?
This is where some sloppy thinking has been troublesome. What would it mean to say that patriarchy evolved by natural selection in the human species? If, on the one hand, it means that the human mind evolved by natural selection to be able to create and survive in many different kinds of social and political regimes, of which patriarchy is one, then biological anthropologists will readily agree. If, on the other hand, it means that patriarchy evolved by natural selection, that implies that patriarchy is genetically determined (since natural selection is a genetic process) and out-reproduced the alleles for other, more egalitarian, social forms. This in turn would imply that patriarchy is an adaptation and therefore of some beneficial value in the past and has become an ingrained part of human nature today. This would be bad news, say, if you harbored ambitions of dismantling it. Dismantling patriarchy in that case would be to go against nature, a futile gesture. In other words, this latter interpretation would be a naturalistic manifesto for a conservative political platform: don’t try to dismantle the patriarchy, because it is within us, the product of evolution—suck it up and live with it.
Here, evolution is being used as a political instrument for transforming the human genome into an imaginary glass ceiling against equality. There is thus a convergence between the pseudo-biology of crude adaptationism (the idea that everything is the product of natural selection) and the pseudo-biology of hereditarianism. Naturalizing inequality is not the business of evolutionary theory, and it represents a difficult moral position for a scientist to adopt, as well as a poor scientific position.
Dig Deeper: Evolution of the Anthropocene (to be reviewed)
As humans have caused the emergence of the Anthropocene, it is important to inform scholars about the effect of our social and cultural evolution on the rest of the world. Richard Robbins’ Global Problems and Culture of Capitalism explains how the modern culture of consumption has been extremely successful at accommodating populations of people far larger than previously possible. Robbins claims that the globalization attributed to capitalism has allowed the world to make full use of its environmental resources, providing necessities and innovative technologies to humans all over the world (Robbins & Dowty, 2019). In other words, capitalism is an anthropocentric cultural system that highly benefits humans and facilitates our survival with little regard to the development and survival of other forms of life. It would be of high relevance to introduce the idea that our cultural evolution and capacity to modify the environment to meet our needs have established new environmental conditions in which the human species' survival and reproduction rate expand at the detriment of ecosystems and endangerment of other primates and non-human species.
According to a 2019 UN report, following the 16th century, the world has entered a period of extreme environmental destruction that is generating ecological modifications and has led to the extinction of at least 680 vertebrate species and over 9 percent of the domesticated mammals used for food and agriculture (United Nations, 2019). Human lifestyles are causing changes that—if not taken into consideration—could lead to our extinction as a species. The recognition that our evolutionary behavioural development is causing environmental destruction may be the first step for our species to take accountability for the damage that it is causing to others and prevent further damage.
Concluding Thoughts
Now that you have finished reading this chapter, you are equipped to understand the historical and political dimensions of evolution. Evolution is an ongoing process of change and diversification. Evolutionary theory is a tool that we use to understand this process. The development of evolutionary theory is shaped both by scientific innovation and political engagement. Since Darwin first articulated natural selection as an observable mechanism by which species adapt to their environments, our understanding of evolution has grown. Initially, scientists focused on the adaptive aspects of evolution. However, with the emergence of genetics, our understanding of heredity and the level at which evolution acts has changed. Genetics led to a focus on the molecular dimensions of evolution. For some, this focus resulted in reductive accounts of evolution. Further developments in our understanding of evolution shifted our view to epigenetic processes and how organisms shape their own evolutionary pressures (e.g., niche construction).
Evolutionary theory will continue to develop in the future as we invent new technologies, describe new dimensions of biology, and experience cultural changes. Current innovations in evolutionary theory are asking us to consider evolutionary forces beyond natural selection and genetics to include the ways organisms shape their environments (niche construction), inheritances beyond genetics (inclusive inheritance), constraints on evolutionary change (developmental bias), and the ability of bodies to change in response to external factors (plasticity). The future of evolutionary theory looks bright as we continue to explore these and other dimensions. Biological anthropology is well-positioned to be a lively part of this conversation, as it extends standard evolutionary theory by considering the role of culture, social learning, and human intentionality in shaping the evolutionary trajectories of humans (Zeder 2018). Remember, at root, human evolutionary theory consists of two propositions: (1) the human species is descended from other similar species and (2) natural selection has been the primary agent of biological adaptation. Pretty much everything else is subject to some degree of contestation.
Review Questions
- How is the study of your ancestors biopolitical, not just biological? Does that make it less scientific or differently scientific?
- What was gained by reducing organisms to genotypes and species to gene pools? What is gained by reintroducing bodies and species into evolutionary studies?
- How do genetic or molecular studies complement anatomical studies of evolution?
- How are you reducible to your ancestry? If you could meet your ancestors from the year 1700 (and you would have well over a thousand of them!), would their lives be meaningfully similar to yours? Would you even be able to communicate with them?
- The molecular biologist François Jacob argued that evolution is more like a tinkerer than an engineer. In what ways do we seem like precisely engineered machinery, and in what ways do we seem like jerry-rigged or improvised contraptions?
- How might biological anthropology contribute to future developments in evolutionary theory?
Key Terms
Adaptation: A fit between the organism and environment.
Adaptationism: The idea that everything is the product of natural selection.
Allele: A genetic variant.
Allometry: The differential growth of body parts.
Canalization: The tendency of a growing organism to be buffered toward normal development.
Epigenetics: The study of how genetically identical cells and organisms (with the same DNA base sequence) can nevertheless differ in stably inherited ways.
Eugenics: An idea that was popular in the 1920s that society should be improved by breeding “better” kinds of people.
Evo-devo: The study of the origin of form; a contraction of “evolutionary developmental biology.”
Exaptation: An additional beneficial use for a biological feature.
Extinction: The loss of a species from the face of the earth.
Gene: A stretch of DNA with an identifiable function (sometimes broadened to include any DNA with recognizable structural features as well).
Gene pool: Hypothetical summation of the entire genetic composition of population or species.
Genotype: Genetic constitution of an individual organism.
Hereditarianism: The idea that genes or ancestry is the most crucial or salient element in a human life. Generally associated with an argument for natural inequality on pseudo-genetic grounds.
Hox genes: A group of related genes that control for the body plan of an embryo along the head-tail axis.
Inheritance of acquired characteristics: The idea that you pass on the features that developed during your lifetime, not just your genes; also known as Lamarckian inheritance.
Natural selection: A consistent bias in survival and fertility, leading to the overrepresentation of certain features in future generations and an improved fit between an average member of the population and the environment.
Niche construction: The active engagement by which species transform their surroundings in favorable ways, rather than just passively inhabiting them.
Phenotype: Observable manifestation of a genetic constitution, expressed in a particular set of circumstances. The suite of traits of an organism.
Phrenology: The 19th-century anatomical study of bumps on the head as an indication of personality and mental abilities.
Plasticity: The tendency of a growing organism to react developmentally to its particular conditions of life.
Punctuated equilibria: The idea that species are stable through time and are formed very rapidly relative to their duration. (The opposite theory, that species are unstable and constantly changing through time, is called phyletic gradualism.)
Scientific racism: The use of pseudoscientific evidence to support or legitimize racial hierarchy and inequality.
Sexual selection: Natural selection arising through preference by one sex for certain characteristics in individuals of the other sex.
Species selection: A postulated evolutionary process in which selection acts on an entire species population, rather than individuals.
About the Authors
Jonathan Marks, Ph.D.
University of North Carolina at Charlotte, jmarks@uncc.edu
Jonathan Marks is Professor of Anthropology at the University of North Carolina at Charlotte. He has published many books and articles on broad aspects of biological anthropology. In 2006 he was elected a Fellow of the American Association for the Advancement of Science. In 2012 he was awarded the First Citizen’s Bank Scholar’s Medal from UNC Charlotte. In recent years he has been a Visiting Research Fellow at the ESRC Genomics Forum in Edinburgh, a Visiting Research Fellow at the Max Planck Institute for the History of Science in Berlin, and a Templeton Fellow at the Institute for Advanced Study at Notre Dame. His work has received the W. W. Howells Book Prize and the General Anthropology Division Prize for Exemplary Cross-Field Scholarship from the American Anthropological Association as well as the J. I. Staley Prize from the School for Advanced Research. Two of his books are titled What It Means to Be 98% Chimpanzee and Why I Am Not a Scientist, but actually he is about 98 percent scientist and not a chimpanzee.
Adam P. Johnson, M.A.
University of North Carolina at Charlotte/University of Texas at San Antonio, ajohn344@uncc.edu
Adam Johnson is a doctoral candidate at the University of Texas at San Antonio and part-time lecturer at the University of North Carolina at Charlotte. He earned his M.A. in anthropology at UNC-Charlotte in 2017 and will complete his Ph.D. in anthropology at UTSA by 2024. His interests include human-animal relations, science studies, primate behavior, ecology, and the history of anthropology. His recent research project analyzes the social, historical, political, and evolutionary dimensions that shape human-javelina encounters. His goal is to understand how humans and animals find ways to get along in a precarious world.
For Further Exploration
Ackermann, Rebecca Rogers, Alex Mackay, and Michael L. Arnold. 2016. “The Hybrid Origin of ‘Modern’ Humans.” Evolutionary Biology 43 (1): 1–11.
Bateson, Patrick, and Peter Gluckman. 2011. Plasticity, Robustness, Development and Evolution. New York: Cambridge University Press.
Cosans, Christopher E. 2009. Owen's Ape and Darwin's Bulldog: Beyond Darwinism and Creationism. Bloomington, IN: Indiana University Press.
Desmond, Adrian, and James Moore. 2009. Darwin's Sacred Cause: How a Hatred of Slavery Shaped Darwin's Views on Human Evolution. New York: Houghton Mifflin Harcourt.
Dobzhansky, Theodosius, Francisco J. Ayala, G. Ledyard Stebbins, and James W. Valentine. 1977. Evolution. San Francisco: W.H. Freeman and Company.
Fuentes, Agustín. 2017. The Creative Spark: How Imagination Made Humans Exceptional. New York: Dutton.
Gould, Stephen J. 2003. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press.
Haraway, Donna J. 1989. Primate Visions: Gender, Race, and Nature in the World of Modern Science. New York: Routledge.
Huxley, Thomas. 1863. Evidence as to Man's Place in Nature. London: Williams & Norgate.
Jablonka, Eva, and Marion J. Lamb. 2005. Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Cambridge, MA: The MIT Press.
Kuklick, Henrika, ed. 2008. A New History of Anthropology. New York: Blackwell.
Laland, Kevin N., Tobias Uller, Marcus W. Feldman, Kim Sterelny, Gerd B. Muller, Armin Moczek, Eva Jablonka, and John Odling-Smee. 2015. “The Extended Evolutionary Synthesis: Its Structure, Assumptions and Predictions.” Proceedings of the Royal Society, Series B 282 (1813): 20151019.
Lamarck, Jean Baptiste. 1809. Philosophie Zoologique. Paris: Dentu.
Landau, Misia. 1991. Narratives of Human Evolution. New Haven: Yale University Press.
Lee, Sang-Hee. 2017. Close Encounters with Humankind: A Paleoanthropologist Investigates Our Evolving Species. New York: W. W. Norton.
Livingstone, David N. 2008. Adam's Ancestors: Race, Religion, and the Politics of Human Origins. Baltimore: Johns Hopkins University Press.
Marks, Jonathan. 2015. Tales of the Ex-Apes: How We Think about Human Evolution. Berkeley, CA: University of California Press.
Pigliucci, Massimo. 2009. “The Year in Evolutionary Biology 2009: An Extended Synthesis for Evolutionary Biology.” Annals of the New York Academy of Sciences 1168: 218–228.
Simpson, George Gaylord. 1949. The Meaning of Evolution: A Study of the History of Life and of Its Significance for Man. New Haven: Yale University Press.
Sommer, Marianne. 2016. History Within: The Science, Culture, and Politics of Bones, Organisms, and Molecules. Chicago: University of Chicago Press.
Stoczkowski, Wiktor. 2002. Explaining Human Origins: Myth, Imagination and Conjecture. New York: Cambridge University Press.
Tattersall, Ian, and Rob DeSalle. 2019. The Accidental Homo sapiens: Genetics, Behavior, and Free Will. New York: Pegasus.
References
Barton, Robert A. 1996. "Neocortex Size and Behavioural Ecology in Primates." Proceedings of the Royal Society of London. Series B: Biological Sciences 263 (1367): 173–177.
Bodmer, Walter, and Robin McKie. 1997. The Book of Man: The Hman Genome Project and the Quest to Discover our Genetic Heritage. Oxford University Press.
Darwin, Charles. 1859. On the Origin of Species by Means of Natural Selection, or, the Preservation of Favoured Races in the Struggle for Life. London: J. Murray.
Darwin, Charles. 1871. The Descent of Man, and Selection in Relation to Sex. London: J. Murray.
Dawkins, Richard. 1976. The Selfish Gene. Oxford University Press.
Deacon, T. W. 1998. The Symbolic Species: The Co-evolution of Language and the Brain. W. W. Norton & Company.
Eldredge, N., and S. J. Gould. 1972. "Punctuated Equilibria: An Alternative to Phyletic Gradualism." In Models in Paleobiology, edited by T. J. Schopf, 82–115. San Francisco: W. H. Freeman.
Gould, Stephen J. 2003. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press.
Gould, Stephen J. 1996. Mismeasure of Man. New York: WW Norton & Company.
Gould, Stephen Jay, and Richard C. Lewontin. 1979. "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme." Proceedings of the Royal Society of London. Series B: Biological Sciences 205 (1151): 581–598.
Haeckel, Ernst. 1868. Natürliche Schöpfungsgeschichte. Berlin: Reimer.
Huxley, Thomas Henry. 1863. Evidence as to Man’s Place in Nature. London: Williams and Norgate.
Kaufman, Thomas C., Mark A. Seeger, and Gary Olsen. 1990. "Molecular and Genetic Organization of the Antennapedia Gene Complex of Drosophila melanogaster." Advances in Genetics 27: 309–362.
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Marks, Jonathan. 2015. “The Biological Myth of Human Evolution.” In Biologising the Social Sciences: Challenging Darwinian and Neuroscience Explanations, edited by David Canter and David A. Turner, 59–78. London: Routledge.
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Shultz, Susanne, Emma Nelson, and Robin Dunbar. 2012. "Hominin Cognitive Evolution: Identifying Patterns and Processes in the Fossil and Archaeological Record." Philosophical Transactions of the Royal Society B: Biological Sciences 367 (1599): 2130–2140.
Spencer, Herbert. 1864. Principles of Biology. London: Williams and Norgate.
Watson, James D. 1990. "The Human Genome Project: Past, Present, and Future." Science 248 (4951): 44–49.
Yengo, L., Vedantam, S., Marouli, E., Sidorenko, J., Bartell, E., Sakaue, S., Graff, M., Eliasen, A.U., Jiang, Y., Raghavan, S. and Miao, J., 2022. A saturated map of common genetic variants associated with human height. Nature, 610 (7933): 704-712.
Zeder, Melinda A. 2018. "Why Evolutionary Biology Needs Anthropology: Evaluating Core Assumptions of the Extended Evolutionary Synthesis." Evolutionary Anthropology: Issues, News, and Reviews 27 (6): 267–284.
Jonathan Marks, Ph.D., University of North Carolina at Charlotte
Adam P. Johnson, M.A., University of North Carolina at Charlotte/University of Texas at San Antonio
This chapter is an adaptation of "Chapter 2: Evolution” by Jonathan Marks. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Explain the relationship among genes, bodies, and organismal change.
- Discuss the shortcomings of simplistic understandings of genetics.
- Describe what is meant by the "biopolitics of heredity."
- Discuss issues caused by misuse of ideas about adaptations and natural selection.
- Examine and correct myths about evolution.
The Human Genome Project, an international initiative launched in 1990, sought to identify the entire genetic makeup of our species. For many scientists, it meant trying to understand the genetic underpinnings of what made humans uniquely human. James Watson, a codiscoverer of the helical shape of DNA, wrote that “when finally interpreted, the genetic messages encoded within our DNA molecules will provide the ultimate answers to the chemical underpinnings of human existence” (Watson 1990, 248). The underlying message is that what makes humans unique can be found in our genes. The Human Genome Project hoped to find the core of who we are and where we come from.
Despite its lofty goal, the Human Genome Project—even after publishing the entire human genome in January 2022—could not fully account for the many factors that contribute to what it is to be human. Richard Lewontin, Steven Rose, and Leon Kamin (2017) argue that genetic determinism of the sort assumed by the Human Genome Project neglects other essential dimensions that contribute to the development and evolution of human bodies, not to mention the role that culture plays. They use an apt metaphor of a cake to illustrate the incompleteness of reductive models. Consider the flavor of a cake and think of the ingredients listed in the recipe. The recipe includes ingredients such as flour, sugar, shortening, vanilla extract, eggs, and milk. Does raw flour taste like cake? Does sugar, vanilla extract, or any of the other ingredients taste like cake? They do not, and knowing the individual flavors of each ingredient does not tell us much about what cake tastes like. Even mixing all of the ingredients in the correct proportions does not get us cake. Instead, external factors such as baking at the right temperature, for the right amount of time, and even the particularities of our evolved sense of taste and smell are all necessary components of experiencing the cake.
Lewontin, Rose, and Kamin (2017) argue that the same is true for humans and other organisms.
Knowing everything about cake ingredients does not allow us to fully know cake. Equally so, knowing everything about the genes found in our DNA does not allow us to fully know humans. Different, interacting levels are implicated in the development and evolution of all organisms, including humans. Genes, the structure of chromosomes, developmental processes, epigenetic tags, environmental factors, and still-other components all play key roles such that genetically reductive models of human development and evolution are woefully inadequate.
The complex interactions across many levels—genetic, developmental, and environmental—explain why we still do not know how our one-dimensional DNA nucleotide sequence results in a four-dimensional organism. This was the unfulfilled promise of the inception of the Human Genome Project in the 1980s and 1990s: the project produced the complete DNA sequence of a human cell in the hopes that it would reveal how human bodies are built and how to cure them when they are built poorly. Yet, that information has remained elusive. Presumably, the knowledge of how organisms are produced from DNA sequences will one day permit us to reconcile the discrepancies between patterns in anatomical evolution and molecular evolution.
In this chapter, we will consider multilevel evolution and explore evolution as a complex interaction between genetic and epigenetic factors as well as the environments in which organisms live. Next, we will examine the biopolitical nature of human evolution. We will then investigate problems that arise from attributing all traits to an adaptive function. Finally, we will address common misconceptions about evolution. The goal of this chapter is to provide you with the necessary toolkit for understanding the molecular, anatomical, and political dimensions of evolution.
Evolution Happens at Multiple Levels
Following Richard Dawkins’s publication of The Selfish Gene in 1976, the scientific imagination was captured by the potential of genomics to reveal how genes are copied by Darwinian selection. Dawkins argues that the genes in individuals that contribute to greater reproductive success are the units of selection. His conception of evolution at the molecular level undercuts the complex interactions between organisms and their environments, which are not expressed genomically but are nevertheless key drivers in evolution.
By the 1980s, the acknowledgment among most biologists that even though genes construct bodies, genes and bodies evolve at different rates and with distinct patterns. This realization led to a renewed focus on how bodies change. The Evolutionary Synthesis of the 1930s–1970s had reduced organisms to their genotypes and species to their gene pools, which provided valuable insights about the processes of biological change, but it was only a first approximation. Animals are in fact reactive and adaptable beings, not passive and inert genotypes. Species are clusters of socially interacting and reproductively compatible organisms.

Once we accept that evolutionary change is fundamentally genetic change, we can ask: How do bodies function and evolve? How do groups of animals come to see one another as potential mates or competitors for mates, as opposed to just other creatures in the environment? Are there evolutionary processes that are not explicable by population genetics? These questions—which lead us beyond reductive assumptions—were raised in the 1980s by Stephen Jay Gould, the leading evolutionary biologist of the late 20th century (see: Gould 2003; 1996).
Gould spearheaded a movement to identify and examine higher-order processes and features of evolution that were not adequately explained by population genetics. For example, extinction, which was such a problem for biologists of the 1600s, could now be seen as playing a more complex role in the history of life than population genetics had been able to model. Gould recognized that there are two kinds of extinctions, each with different consequences: background extinctions and mass extinctions. Background extinctions are those that reflect the balance of nature, because in a competitive Darwinian world, some things go extinct and other things take their place. Ecologically, your species may be adapted to its niche, but if another species comes along that’s better adapted to the same niche, eventually your species will go extinct. It sucks, but it is the way of all life: you come into existence, you endure, and you pass out of existence. But mass extinctions are quite different. They reflect not so much the balance of nature as the wholesale disruption of nature: many species from many different lineages dying off at roughly the same time—presumably as the result of some kind of rare ecological disaster. The situation may not be survival of the fittest as much as survival of the luckiest. The result, then, would be an ecological scramble among the survivors. Having made it through the worst, the survivors could now simply divide up the new ecosystem amongst themselves, since their competitors were gone. Something like this may well have happened about 65 million years ago, when a huge asteroid hit the Yucatan Peninsula, which mammals survived but dinosaurs did not (Figure 17.1). Something like this may be happening now, due to human expansion and environmental degradation. Note, though, that there is only a limited descriptive role here for population genetics: the phenomena we are describing are about organisms and species in ecosystems.
Another question involved the disconnect between properties of species and the properties of gene pools. For example, there are upwards of 15 species of gibbons but only two species of chimpanzees. Why? There are upwards of 20 species of guenons but fewer than ten of baboons. Why? Are there genes for that? It seems unlikely. Gould suggested that species, as units of nature, might have properties that are not reducible to the genes in their cells. For example, rates of speciation and extinction might be properties of their ecologies and histories rather than their genes. Thus, relationships between environmental contexts and variability within a species result in degrees of resistance to extinction and affect the frequency and rates at which clades diversify (Lloyd and Gould 1993). Consistent biases of speciation rates might well produce patterns of macroevolutionary diversity that are difficult to explain genetically and better understood ecologically. Gould called such biases in speciation rates species selection—a higher-order process that invokes competition between species, in addition to the classic Darwinian competition between individuals.
One of Gould’s most important studies involved the very nature of species. In the classical view, a species is continually adapting to its environment until it changes so much that it is a different species than it was at the beginning of this sentence (Eldredge and Gould 1972). That implies that the species is a fundamentally unstable entity through time, continuously changing to fit in. But suppose, argued Gould along with paleontologist Niles Eldredge, a species is more stable through time and only really adapts during periods of ecological instability and change. Then we might expect to find in the fossil record long equilibrium periods—a few million years or so—in which species don’t seem to change much, punctuated by relatively brief periods in which they change a bit and then stabilize again as new species. They called this idea punctuated equilibria. The idea helps to explain certain features of the fossil record, notably the existence of small anatomical “gaps” between closely related fossil forms (Figure 17.2). Its significance lies in the fact that although it incorporates genetics, punctuated equilibria is not really a theory of genetics but one of types bodies in deep time.
Punctuated equilibria is seen across taxa, with long periods in the fossil record representing little phenotypic change. These periods of stability are disrupted by shorter periods of rapid adaptation, the process through which populations of organisms become suited to living in their environments. Phenotypic changes are often coupled with drastic climatic or ecological changes that affect the milieu in which organisms live. For example, throughout much of hominin evolutionary history, brain size was closely associated with body size and thus remained mostly stable. However, changes occurred in average hominin brain size at around 100 thousand years ago, 1 million years ago, and 1.8 million years ago. Several hypotheses have been put forth to explain these changes, including unpredictability in climate and environment (Potts 1998), social development (Barton 1996), and the evolution of language (Deacon 1998). Evidence from the fossil record, paleoclimate models, and comparative anatomy suggests that the changes observed in hominin lineage result from biocultural processes—that is, the coalescence of environmental and cultural factors that selected for larger brains (Marks 2015; Shultz, Nelson, and Dunbar 2012).

In response to the call for a theory of the evolution of form, the field of evo-devo—the intersection of evolutionary and developmental biology—arose. The central focus here is on how changes in form and shape arise. An embryo matures by the stimulation of certain cells to divide, forming growth fields. The interactions and relationships among these growth fields generate the structures of the body. The hox genes that regulate these growth fields turn out to be highly conserved across the animal kingdom. This is because they repeatedly turn on and off the most basic genes guiding the animal’s development, and thus any changes to them would be catastrophic. Indeed, these genes were first identified by manipulating them in fruit flies, such that one could produce a bizarre mutant fruit fly that grew a pair of legs where its antennae were supposed to be (Kaufman, Seeger, and Olsen 1990).
Certain genetic changes can alter the fates of cells and the body parts, while other genetic changes can simply affect the rates at which neighboring groups of cells grow and divide, thus producing physical bumps or dents in the developing body. The result of altering the relationships among these fields of cellular proliferation in the growing embryo is allometry, or the differential growth of body parts. As an animal gets larger—either over the course of its life or over the course of macroevolution—it often has to change shape in order to live at a different size. Many important physiological functions depend on properties of geometric area: the strength of a bone, for example, is proportional to its cross-sectional area. But area is a two-dimensional quality, while growing takes place in three dimensions—as an increase in mass or volume. As an animal expands, its bones necessarily weaken, because volume expands faster than area does. Consequently a bigger animal has more stress on its bones than a smaller animal does and must evolve bones even thicker than they would be by simply scaling the animal up proportionally. In other words, if you expand a mouse to the size of an elephant, it will nevertheless still have much thinner bones than the elephant does. But those giant mouse bones will unfortunately not be adequate to the task. Thus, a giant mouse would have to change aspects of its form to maintain function at a larger size (see Figure 17.3).

Physiologically, we would like to know how the body “knows” when to turn on and off the genes that regulate growth to produce a normal animal. Evolutionarily, we would like to know how the body “learns” to alter the genetic on/off switch (or the genetic “slow down/speed up” switch) to produce an animal that looks different. Moreover, since organisms differ from one another, we would like to know how the developing body distinguishes a range of normal variation from abnormal variation. And, finally, how does abnormal variation eventually become normal in a descendant species?
Taking up these questions, Gould invoked the work of a British geneticist named Conrad H. Waddington, who thought about genetics in less reductive ways than his colleagues. Rather than isolate specific DNA sites to analyze their function, Waddington instead studied the inheritance of an organism’s reactivity—its ability to adapt to the circumstances of its life. In a famous experiment, he grew fruit fly eggs in an atmosphere containing ether. Most died, but a few survived somehow by developing a weird physical feature: a second thorax with a second pair of wings. Waddington bred these flies and soon developed a stable line of flies who would reliably develop a second thorax when grown in ether. Then he began to lower the concentration of ether, while continuing to selectively breed the flies that developed the strange appearance. Eventually he had a line of flies that would stably develop the “bithorax” phenotype–the suite of traits of an organism–even when there was no ether; it had become the “new normal.” The flies had genetically assimilated the bithorax condition.
Waddington was thus able to mimic the inheritance of acquired characteristics: what had been a trait stimulated by ether a few generations ago was now a normal part of the development of the descendants. Waddington recognized that while he had performed a selection experiment on genetic variants, he had not selected for particular traits. Rather, he helped produce the physiological tendency to develop particular traits when appropriately stimulated. He called that tendency plasticity and its converse, the tendency to stay the same even under weird environmental circumstances, canalization. Waddington had initially selected for plasticity, the tendency to develop the bithorax phenotype under weird conditions, and then, later, for canalization, the developmental normalization of that weird physical trait. Although Waddington had high stature in the community of geneticists, evolutionary biologists of the 1950s and 1960s regarded him with suspicion because he was not working within the standard mindset of reductionism, which saw evolution as the spread of genetic variants that coded for favorable traits. Both Waddington and Gould resisted contemporary intellectual paradigms that favored reductive accounts of evolutionary processes. They conceived of evolution as an emergent process in which many external factors (e.g. climate, environment, predation) and internal factors (e.g., genotypes, plasticity, canalization) coalesce to produce the evolutionary trends that we observe in the fossil record and our genome.
While Gould and Waddington both looked beyond the genome to understand evolution, the Human Genome Project—an international project with the goal of identifying each base pair in the human genome in the 1990s—generated a great deal of public interest in analyzing the human DNA sequence from the standpoint of medical genetics. Some of the rhetoric aimed to sell the public on investing a lot of money and resources in sequencing the human genome in order to show the genetic basis of heritable traits, cure genetic diseases, and learn what it means ultimately to be biologically human. However, the Human Genome Project was not actually able to answer those questions through the use of genetics alone, and thus a broader, more holistic account was required.
This holistic account came from decades of research in human biology and anthropology, which understood the human body as highly adaptable, dynamic, and emergent. For example, in the early 20th century, anthropologist Franz Boas measured the skulls of immigrants to the U.S., revealing that environmental, not merely genetic, factors affected skull shape. The growing human body adjusts itself to the conditions of life, such as diet, sunshine, high altitude, hard labor, population density, how babies are carried—any and all of which can have subtle but consistent effects upon its development. There can thus be no normal human form, only a context-specific range of human forms.
However, what the human biologists called human adaptability, evolutionary biologists called developmental plasticity, and evidence quickly began to mount for its cause being epigenetic modifications to DNA. Epigenetic modifications are changes to how genes are used by the body (as opposed to changes in the DNA sequences; see Chapter 3). Scientific interest shifted from the focus of the Human Genome Project to the ways that bodies are made by evolutionary-developmental processes, including epigenetics. What is meant by “epigenetic modification”? Evolution is about how descendants diverge from their ancestors. Inheritance from parent to offspring is still critical to this process, which occurs through genetic recombination: the pairing of homologous chromosomes and sharing of genetic material during meiosis (see Chapter 3). However, in the 21st century, the link between evolution and inheritance has broadened with a clearer understanding of how environmental and developmental factors shape bodies and the expression of genes, including epigenetic inheritance patterns. While offspring inherit their genes through random assortment during meiosis, environmental factors also shape how genes are used. When these epigenetic modifications occur in germ cells, they can be passed onto offspring. In these cases, there is no change in the DNA sequence but rather in how genes are used by the body due to DNA methylation and the structure of chromosomes due to histone acetylation (see Chapter 3).
In addition, we now recognize that evolution is affected by two other forms of intergenerational transmission and inheritance (in addition to genetics and epigenetics). These forms include behavioral variation and culture. That is, behavioral information can be transmitted horizontally (intragenerationally), permitting more rapid ways for organisms to adjust to the environment. And, then there is the fourth mode of transmission: the cultural or symbolic mode. Humans are the only species that horizontally transmits an arbitrary set of rules to govern communication, social interaction, and thought. This shared information is symbolic and has resulted in what we recognize as “culture”: locally emergent worlds of names, words, pictures, classifications, revered pasts, possible futures, spirits, dead ancestors, unborn descendants, in-laws, politeness, taboo, justice, beauty, and story, all accompanied by practices and a material world of tools.
Consequently our contemporary ideas about evolution see the evolutionary processes as hierarchically organized and not restricted to the differential transmission of DNA sequences into the next generation. While that is indeed a significant part of evolution, the organism and species are nevertheless crucial to understanding how those DNA sequences get transmitted. Further, the transmission of epigenetic, behavioral, and symbolic information play a complex role in perpetuating our genes, bodies, and species. In the case of human evolution, one can readily see that symbolic information and cultural adaptation are far more central to our lives and our survival today than DNA and genetic adaptation. It is thus misleading to think of humans passively occupying an environmental niche. Rather, humans are actively engaged in constructing our own niches, as well as adapting to them and using them to adapt. The complex interplay between a species and its active engagement in creating its own ecology is known as niche construction. If we understand natural selection–the process by which populations adapt to their specific environments–as the effects that environmental context has on the reproductive success of organisms, then niche construction is the process through which organisms shape their own selective pressures.
The Biopolitics of Heredity
“Science isn’t political” is a sentiment that you have likely heard before. Science is supposed to be about facts and objectivity. It exists, or at least ought to, outside of petty human concerns. However, the sorts of questions we ask as scientists, the problems we choose to study, the categories and concepts we use, who gets to do science, and whose work gets cited are all shaped by culture. Doing science is a political act. This fact is markedly true for human evolution. While it is easier to create intellectual distance between us and fruit flies and viruses, there is no distance when we are studying ourselves. The hardest lesson to learn about human evolution is that it is intensely political. Indeed, to see it from the opposite side, as it were, the history of creationism—the belief that the universe was divinely created around 6,000 years ago—is essentially a history of legal decisions. For instance, in Tennessee v. John T. Scopes (1925), a schoolteacher was prosecuted for violating a law in Tennessee that prohibited the teaching of human evolution in public schools, where teachers were required by law to teach creationism.
More recently, legal decisions aimed at legislating science education have shaped how students are exposed to evolutionary theory. For instance, McLean v. Arkansas (1982) dispatched “scientific creationism” by arguing that the imposition of balanced teaching of evolution and creationism in science classes violates the Establishment Clause, separating church and state. Additionally, Kitzmiller v. Dover (Pennsylvania) Area School District (2005) dispatched the teaching of “intelligent design” in public school classrooms as it was deemed to not be science. In some cases, people see unbiblical things in evolution, although most Christian theologians are easily able to reconcile science to the Bible. In other cases, people see immoral things in evolution, although there is morality and immorality everywhere. And some people see evolution as an aspect of alt-religion, usurping the authority of science in schools to teach the rejection of the Christian faith, which would be unconstitutional due to the protected separation of church and state.
Clearly, the position that politics has nothing to do with science is untenable. But is the politics in evolution an aberration or is it somehow embedded in science? In the early 20th century, scientists commonly promoted the view that science and politics were separate: science was seen as a pure activity, only rarely corrupted by politics. And yet as early as World War I, the politics of nationalism made a hero of the German chemist Fritz Haber for inventing poison gas. And during World War II, both German doctors and American physicists, recruited to the war effort, helped to end many civilian lives. Therefore, we can think of the apolitical scientist as a self-serving myth that functions to absolve scientists of responsibility for their politics. The history of science shows how every generation of scientists has used evolutionary theory to rationalize political and moral positions. In the very first generation of evolutionary science, Darwin’s Origin of Species (1859) is today far more readable than his Descent of Man (1871). The reason is that Darwin consciously purged The Origin of Species of any discussion of people. And when he finally got around to talking about people, in The Descent of Man, he simply imbued them with the quaint Victorian prejudices of his age, and the result makes you cringe every few pages. There is plenty of politics in there—sexism, racism, and colonialism—because you cannot talk about people apolitically.
One immediate faddish deduction from Darwinism, popularized by Herbert Spencer (1864) as “survival of the fittest,” held that unfettered competition led to advancement in nature and to human history. Since the poor were purported losers in that struggle, anything that made their lives easier would go against the natural order. This position later came to be known ironically as “Social Darwinism.” Spencer was challenged by fellow Darwinian Thomas Huxley (1863), who agreed that struggle was the law of the jungle but observed that we don’t live in jungles anymore. The obligation to make lives better for others is a moral, not a natural, fact. We simultaneously inhabit a natural universe of descent from apes and a moral universe of injustice and inequality, and science is not well served by ignoring the latter.
Concurrently, the German biologist Ernst Haeckel’s 1868 popularization of Darwinism was translated into English a few years later as The History of Creation. As we saw earlier, Haeckel was determined to convince his readers that they were descended from apes, even in the absence of fossil evidence attesting to it. When he made non-Europeans into the missing links that connected his readers to the apes, and depicted them as ugly caricatures, he knew precisely what he was doing. Indeed, even when the degrading racial drawings were deleted from the English translation of his book, the text nevertheless made his arguments quite clear. And a generation later, when the Americans had not yet entered the Great War in 1916, a biologist named Vernon Kellogg visited the German High Command as a neutral observer and found that the officers knew a lot about evolutionary biology, which they had gotten from Haeckel and which rationalized their military aggressions. Kellogg went home and wrote a bestseller about it, called Headquarters Nights (1917). World War I would have been fought with or without evolutionary theory, but as a source of scientific authority, evolution—even if a perversion of the Darwinian theory—had very quickly attained global geopolitical relevance.
Oftentimes, politics in evolutionary science is subtle, due to the pervasive belief in the advancement of science. We recognize the biases of our academic ancestors and modify our scientific stories accordingly. But we can never be free of our own cultural biases, which are invisible to us, as much as our predecessors’ biases were invisible to them. In some cases, the most important cultural issues resurface in different guises each generation, like scientific racism. Scientific racism is the recruitment of science for the evil political ends of racism, and it has proved remarkably impervious to evolution. Before Darwin, there was creationist scientific racism, and after Darwin, there was evolutionist scientific racism. And there is still scientific racism today, self-justified by recourse to evolution, which means that scientists have to be politically astute and sensitive to the uses of their work to counter these social tendencies.
Consider this: Are you just your ancestry, or can you transcend it? If that sounds like a weird question, it was actually quite important to a turn-of-the-20th-century European society in which an old hereditary aristocracy was under increasing threat from a rising middle class. And that is why the very first English textbook of Mendelian genetics concluded with the thought that “permanent progress is a question of breeding rather than of pedagogics; a matter of gametes, not of training … the creature is not made but born” (Punnett 1905, 60). Translation: Not only do we now know a bit about how heredity works, but it’s also the most important thing about you. Trust me, I’m a scientist.
Yet evolution is about how descendants come to differ from ancestors. Do we really know that your heredity, your DNA, your ancestry, is the most important thing about you? That you were born, not made? After all, we do know that you could be born into slavery or as a peasant, and come from a long line of enslaved people or peasants, and yet not have slavery or peasantry be the most important thing about you. Whatever your ancestors were may unfortunately constrain what you can become, but as a moral precept, it should not. But just as science is not purely “facts and objectivity,” ancestry is not a strictly biological concept. Human ancestry is biopolitics, not biology.
Evolution is fundamentally a theory about ancestry, and yet ancestors are, in the broad anthropological sense, sacred: ancestors are often more meaningful symbolically than biologically. Just a few years after The Origin of Species (Darwin 1859), the British politician and writer Benjamin Disraeli declared himself to be on the side of the angels, not the apes, and to “repudiate with indignation and abhorrence those new-fangled theories” (Monypenny, Flavelle, and Buckle 1920, 105). He turned his back on an ape ancestry and looked to the angel; yet, he did so as a prominent Jew-turned-Anglican, who had personally transcended his humble roots and risen to the pinnacle of the Empire. Ancestry was certainly important, and Disraeli was famously proud of his, but it was also certainly not the most important thing, not the primary determinant of his place in the world. Indeed, quite the opposite: Disraeli’s life was built on the transcendence of many centuries of Jewish poverty and oppression in Europe. Humble ancestry was there to be superseded and nobility was there to be earned; Disraeli would later become the Earl of Beaconsfield. Clearly, “are you just your ancestry” is not a value-neutral question, and “the creature is not made, but born” is not a value-neutral answer.
Ancestry being the most important thing about a person became a popular idea twice in 20th century science. First, at the beginning of the century, when the eugenics movement in America called attention to “feeble-minded stocks,” which usually referred to the poor or to immigrants (see Figure 17.4; and see Chapter 2). This movement culminated in Congress restricting the immigration of “feeble-minded races” (said to include Jews and Italians) in 1924, and the Supreme Court declaring it acceptable for states to sterilize their “feeble-minded” citizens involuntarily in 1927. After the Nazis picked up and embellished these ideas during World War II, Americans moved swiftly away from them in some contexts (e.g., for most people of European descent) while still strictly adhering in other contexts (e.g., Japanese internment camps and immigration restrictions).

Ancestry again became paramount in the drumming up of public support for the Human Genome Project in the 1990s. Public support for sequencing the human genome was encouraged by a popular science campaign that featured books titled The Book of Man (Bodmer and McKie 1997), The Human Blueprint (Shapiro 1991), and The Code of Codes (Kevles and Hood 1993). These books generally promised cures for genetic diseases and a deeper understanding of the human condition. We can certainly identify progress in molecular genetics over the last couple of decades since the human genome was sequenced, but that progress has notably not been accompanied by cures for genetic diseases, nor by deeper understandings of the human condition.
Even at the most detailed and refined levels of genetic analysis, we still don’t have much of an understanding of the actual basis by which things seem to “run in families.” While the genetic basis of simple, if tragic, genetic diseases have become well-known—such as sickle-cell anemia, cystic fibrosis, and Tay-Sachs’ Disease—we still haven’t found the ostensible genetic basis for traits that are thought to have a strong genetic component. For example, a recent genetic summary found over 12,000 genetic sites that contributed to height yet still explained only about 40-50 percent of the variation in height among European ancestry but no more than 10-20 percent of variation of other ancestries, which we know strongly runs in families (Yengo et al. 2022).
Partly in reaction to the reductionistic hype of the Human Genome Project, the study of epigenetics has become the subject of great interest. One famous natural experiment involves a Nazi-imposed famine in Holland over the winter of 1944–1945. Children born during and shortly after the famine experienced a higher incidence of certain health problems as adults, many decades later. Apparently, certain genes had been down-regulated early in development and remained that way throughout the course of life. Indeed, this modified regulation of the genes in response to the severe environmental conditions may have been passed on to their children.
Obviously one’s particular genetic constitution may play an important role in one’s life trajectory. But overvaluing that role may have important social and political consequences. In the first place, genotypes are rendered meaningful in a cultural universe. Thus, if you live in a strongly patriarchal society and are born without a Y chromosome (since human males are chromosomally XY and females XX), your genotype will indeed have a strong effect upon your life course. So even though the variation is natural, the consequences are political. The mediating factors are the cultural ideas about how people of different sexes ought to be treated, and the role of the state in permitting certain people to develop and thrive. More broadly, there are implications for public education if variation in intelligence is genetic. There are implications for the legal system if criminality is genetic. There are implications for the justice system if sexual preference, or sexual identity, is genetic. There are implications for the development of sports talent if that is genetic. And yet, even for the human traits that are more straightforward to measure and known to be strongly heritable, the DNA base sequence variation seems to explain little.
Genetic determinism or hereditarianism is the idea that “the creature is made, not born”—or, in a more recent formulation by James Watson, that “our fate is in our genes.” One of the major implications drawn from genetic determinism is that the feature in question must inevitably express itself; therefore, we can’t do anything about it. Therefore, we might as well not fund the social programs designed to ameliorate economic inequality and improve people’s lives, because their courses are fated genetically. And therefore, they don’t deserve better lives.
All of the “therefores” in the preceding paragraph are open to debate. What is important is that the argument relies on a very narrow understanding of the role of genetics in human life, and it misdirects the causes of inequality from cultural to natural processes. By contrast, instead of focusing on genes and imagining them to place an invisible limit upon social progress, we can study the ways in which your DNA sequence does not limit your capability for self-improvement or fix your place in a social hierarchy. In general, two such avenues exist. First, we can examine the ways in which the human body responds and reacts to environmental variation: human adaptability and plasticity. This line of research began with the anthropometric studies of immigrants by Franz Boas in the early 20th century and has now expanded to incorporate the epigenetic inheritance of modified human DNA. And second, we can consider how human lives are shaped by social histories—especially the structural inequalities within the societies in which they grow up.
Although it arises and is refuted every generation, the radical hereditarian position (genetic determinism) perennially claims to speak for both science and evolution. It does not. It is the voice of a radical fringe—perhaps naive, perhaps evil. It is not the authentic voice of science or of evolution. Indeed, keeping Charles Darwin’s name unsullied by protecting it from association with bad science often seems like a full-time job. Culture and epigenetics are very much a part of the human condition, and their roles are significant parts of the complete story of human evolution.
(Sterilization of Indigenous women in Canada) (https://www.thecanadianencyclopedia.ca/en/article/sterilization-of-indigenous-women-in-canada)
Adaptationism and the Panglossian Paradigm
The story of human evolution, and the evolution of all life for that matter, is never settled because evolution is ongoing. Additionally, because the conditions that shape evolutionary trajectories are not predetermined, evolution itself is emergent. Even during periods of ecological stability, when fewer macroevolutionary changes occur, populations of organisms continue to experience change. When ecological stability is disrupted, populations must adapt to the changes. Darwin explained in naturalistic terms how animals adapt to their environments: traits that contribute to an organism's ability to survive and reproduce in specific environments will become more common. The most “fit”—those organisms best suited to the current environmental conditions in which they live—have survived over eons of the history of life on earth to cocreate ecosystems full of animals and plants. Our own bodies are full of evident adaptations: eyes for seeing, ears for hearing, feet for walking on, and so forth.
But what about hands? Feet are adapted to be primarily weight-bearing structures (rather than grasping structures, as in the apes) and that is what we primarily use them for. But we use our hands in many ways: for fine-scale manipulation, greeting, pointing, stimulating a sexual partner, writing, throwing, and cooking, among other uses. So which of these uses express what hands are “for,” when all of them express what hands do?
Gould and Lewontin (1979) illustrate the problem with assuming that the function of a trait defines its evolutionary cause. Consider the case of Dr. Pangloss—the protagonistic of Voltaire’s Candide—who believed that we lived in the best of all possible worlds. Gould and Lewontin use his pronouncement that “noses were made for spectacles and so we have spectacles” to demonstrate the problem with assuming any trait has evolved for a specific purpose. Identifying a function of a trait does not necessitate that the function is the ultimate cause of the trait. Individual traits are not under selection pressures in isolation; in fact, an entire organism must be able to survive and reproduce in their environment. When natural selection results in adaptations, changes that occur in some traits can have cascading effects throughout the phenotype and features that are not under selection pressure can also change.

There is an important lesson in recognizing that what things do in the present is not a good guide to understanding why they came to exist. Gunpowder was invented for entertainment—only later was it adopted for killing people. The Internet was invented to decentralize computers in case of a nuclear attack—and only later adopted for social media. Apes have short thumbs and use their hands in locomotion; our ancestors stopped using their hands in locomotion by about six million years ago and had fairly modern-looking hands by about two million years ago. We can speculate that a combination of selection for abstract thought and dexterity led to evolution of the human hand, with its capability for toolmaking that exceeds what apes can do (see Figure 17.5). But let’s face it—how many tools have you made today?
Consequently, we are obliged to see the human foot as having a purpose to which it is adapted and the human hand as having multiple purposes, most of which are different from what it originally evolved for. Paleontologists Gould and Elisabeth Vrba suggested that an original use be regarded as an adaptation and any additional uses be called “exaptations.” Thus, we would consider the human hand to be an adaptation for toolmaking and an exaptation for writing. So how do we know whether any particular feature is an adaptation, like the walking foot, rather than an exaptation, like the writing hand? Or more broadly, how can we reason rigorously from what a feature does to what it evolved for?
The answer to the question “what did this feature evolve for?” creates an origin myth. This origin myth contains three assumptions: (1) features can be isolated as evolutionary units; (2) there is a specific reason for the existence of any particular feature; and (3) there is a clear and simplistic explanation for why the feature evolved.

The first assumption was appreciated a century ago as the “unit-character problem.” Are the units by which the body grows and evolves the same as units we name? This is clearly not the case: we have genes and we have noses, and we have genes that affect noses, but we don’t have “nose genes.” What is the relationship between the evolving elements that we see, identify, and name, and the elements that biologically exist and evolve? It is hard to know, but we can use the history of science as a guide to see how that fallacy has been used by earlier generations. Back in the 19th century, the early anatomists argued that since the brain contained the mind, they could map different mental states (acquisitiveness, punctuality, sensitivity) onto parts of the brain. Someone who was very introspective, say, would have an enlarged introspection part of the brain, a cranial bulge to represent the hyperactivity of this mental state. The anatomical science was known as phrenology, and it was predicated on the false assumption that units of thought or personality or behavior could be mapped to distinct parts of the brain and physically observed (see Figure17.6). This is the fallacy of reification, imagining that something named is something real.
Long alt text: Side view of human head. At the top are the words “Know Thyself.” On the upper head are small illustrations and word qualities such as “friendship,” “self-esteem,” and “secretiveness.” On the lower part of the man’s man’s face are the words The Phrenological Journal and Science of Health, A First Class Monthly. The caption at the bottom reads: “Specially devoted to the ‘.’ Contains PHRENOLOGY and PHYSIOGNOMY, with all the SIGNS OF CHARACTER, and how to read them; ETHNOLOGY, or the Natural History of Man in all his relations.” (All emphases in original.)

The second assumption, that everything has a reason, has long been recognized as a core belief of religion. Our desire to impose order and simplicity on the workings of the universe, however, does not constrain it to obey simple and orderly causes. Magic, witchcraft, spirits, and divine agency are all powerful explanations for why things happen. Consequently, it is probably not a good idea to lump natural selection in with those. Sometimes things do happen for a reason, of course, but other times things happen as byproducts of other things, or for very complicated and entangled reasons, or for no reason at all. What phenomena have reasons and thereby merit explanation? Chimpanzees have very large testicles, and we think we know why: their promiscuous sexual behavior triggers intense competition for high sperm count. But chimpanzees also have very large ears, but much less scientific attention has been paid to this trait (see Figure 17.7). Why not? Why should there be a reason for chimp testicles but not for chimp ears? What determines the kinds of features that we try to explain, as opposed to the ones that we do not? Again, the assumption that any specific feature has a reason is metaphysical; that is to say, it may be true in any particular case, but to assume it in all cases is gratuitous.
And third, the possibility of knowing what the reason for any particular feature is, assuming that it has one, is a challenge for evolutionary epistemology (the theory of how we know things). Consider the big adaptations of our lineage: bipedalism and language. Nobody doubts that they are good, and they evolved by natural selection, and we know how they work. But why did they evolve? If talking and walking are simply better than not talking and not walking, then why did they evolve in just a single branch of the ape lineage in the primate family tree? We don’t know what bipedalism evolved for, although there are plenty of speculations: walking long distances, running long distances, cooling the head, seeing over tall grass, carrying babies, carrying food, wading, threatening, counting calories, sexual display, and so on. Neither do we know what language evolved for, although there are speculations: coordinating hunting, gossiping, manipulating others. But it is also possible that bipedality is simply the way that a small arboreal ape travels on the ground, if it isn’t in the treetops. Or that language is simply the way that a primate with small canine teeth and certain mental propensities comes to communicate. If that were true, then there might be no reason for bipedality or language: having the unique suite of preconditions and a fortuitous set of circumstances simply set them in motion, and natural selection elaborated and explored their potentials. It is possible that walking and talking simply solved problems that no other lineage had ever solved; but even if so, the fact remains that the rest of the species in the history of life have done pretty well without having solved them.
It is certainly very optimistic to think that all three assumptions (that organisms can be meaningfully atomized, that everything has a reason, and that we can know the reason) would be simultaneously in effect. Indeed, just as there are many ways of adapting (genetically, epigenetically, behaviorally, culturally), there are also many ways of being nonadaptive, which would imply that there is no reason at all for the feature in question.
First, there is the element of randomness of population histories. There are more cases of sickle-cell anemia among sub-Saharan Africans than other peoples, and there is a reason for it: carriers of sickle-cell anemia have a resistance to malaria, which is more frequent in parts of Africa (as discussed in Chapters 4 and 14). But there are more cases of a blood disease called variegated porphyria, a rare genetic metabolic disorder, in the Afrikaners of South Africa (descendants of mostly Dutch settlers in the 17th century) than in other peoples, and there is no reason for it. Yet we know the cause: One of the founding Dutch colonial settlers had the allele–a variant of a gene–and everyone in South Africa with it today is her descendant. But that is not a reason—that is simply an accident of history.
Second, there is the potential mismatch between the past and the present. The value of a particular feature in the past may be changed as the environmental circumstances change. Our species is diurnal, and our ancestors were diurnal. But beginning around a few hundred thousand years ago, our ancestors could build fires, which extended the light period, which was subsequently further amplified by lamps and candles. And over the course of the 20th century, electrical power has made it possible for people to stay up very late when it is dark—working, partying, worrying—to a greater extent than any other closely related species. In other words, we evolved to be diurnal, yet we are now far more nocturnal than any of our recent ancestors or close relatives. Are we adapting to nocturnality? If so, why? Does it even make any sense to speak of the human occupation of a nocturnal ape niche, despite the fact that we empirically seem to be doing just that? And if so, does it make sense to ask what the reason for it is?
Third, there is a genetic phenomenon known as a selective sweep, or the hitchhiker effect. Imagine three genes—A, B, and C—located very closely together on a chromosome. They each have several variants, or alleles, in the population. Now, for whatever reason, it becomes beneficial to have one of the B alleles, say B4; this B4 allele is now under strong positive selection. Obviously, we will expect future generations to be characterized by mostly B4. But what was B4 attached to? Because whatever A and C alleles were adjacent to it will also be quickly spread, simply by virtue of the selection for B4. Even if the A and C alleles are not very good, they will spread because of the good B4 allele between them. Eventually the linkage groups will break up because of genetic crossing-over in future generations. But in the meantime, some random version of genes A and C are proliferating in the species simply because they are joined to superior allele B4. And clearly, the A and C alleles are there because of selection—but not because of selection for them!
Fourth, some features are simply consequences of other properties rather than adaptations to external conditions. We already noted the phenomenon of allometric growth, in which some physical features have to outgrow others to maintain function at an increased size. Can we ask the reason for the massive brow ridges of Homo erectus, or are brow ridges simply what you get when you have a conjunction of thick skull bones, a large face, and a sloping forehead—and, thus, again would have a cause but no reason?
Fifth, some features may be underutilized and on the way out. What is the reason for our two outer toes? They aren’t propulsive, they don’t do anything, and sometimes they’re just in the way. Obviously they are there because we are descended from ancestors with five digits on their hands and feet. Is it possible that a million years from now, we will just have our three largest toes, just as the ancestors of the horse lost their digits in favor of a single hoof per limb? Or will our outer toes find another use, such as stabilizing the landings in our personal jet-packs? For the time being, we can just recognize vestigiality as another nonadaptive explanation for the presence of a given feature.
Finally, Darwin himself recognized that many obvious features do not help an animal survive. Some things may instead help an animal breed. The peacock’s tail feathers do not help it eat, but they do help it mate. There is competition, but only against half of the species. Darwin called this sexual selection. Its result is not a fit to the environment but, rather, a fit to the opposite sex. In some species, that is literally the case, as the male and female genitalia have specific ways of anatomically fitting together. The specific form is less important than the specific match, so inquiring about the reason for a particular form of the reproductive anatomy may be misleading. The specific form may be effectively random, as long as it fits the opposite sex and is different from the anatomies of other species. Nor is sexual selection the only form of selection that can affect the body differently from natural selection. Competition might also take place between biological units other than organisms—perhaps genes, perhaps cells, or populations, or species. The spread of cultural things, such as head-binding or cheap refined fructose or forced labor, can have significant effects upon bodies, which are also not adaptations produced by natural selection. They are often adaptive physiological responses to stresses but not the products of natural selection.
With so many paths available by which a physical feature might have organically arisen without having been the object of natural selection, it is unwise to assume that any individual trait is an adaptation. And that generalization applies to the best-known, best-studied, and most materially based evolutionary adaptations of our lineage. But our cultural behaviors are also highly adaptive, so what about our most familiar social behaviors? Patriarchy, hierarchy, warfare—are these adaptations? Do they have reasons? Are they good for something?
This is where some sloppy thinking has been troublesome. What would it mean to say that patriarchy evolved by natural selection in the human species? If, on the one hand, it means that the human mind evolved by natural selection to be able to create and survive in many different kinds of social and political regimes, of which patriarchy is one, then biological anthropologists will readily agree. If, on the other hand, it means that patriarchy evolved by natural selection, that implies that patriarchy is genetically determined (since natural selection is a genetic process) and out-reproduced the alleles for other, more egalitarian, social forms. This in turn would imply that patriarchy is an adaptation and therefore of some beneficial value in the past and has become an ingrained part of human nature today. This would be bad news, say, if you harbored ambitions of dismantling it. Dismantling patriarchy in that case would be to go against nature, a futile gesture. In other words, this latter interpretation would be a naturalistic manifesto for a conservative political platform: don’t try to dismantle the patriarchy, because it is within us, the product of evolution—suck it up and live with it.
Here, evolution is being used as a political instrument for transforming the human genome into an imaginary glass ceiling against equality. There is thus a convergence between the pseudo-biology of crude adaptationism (the idea that everything is the product of natural selection) and the pseudo-biology of hereditarianism. Naturalizing inequality is not the business of evolutionary theory, and it represents a difficult moral position for a scientist to adopt, as well as a poor scientific position.
Evolution of the Anthropocene (to be reviewed)
As humans have caused the emergence of the Anthropocene, it is important to inform scholars about the effect of our social and cultural evolution on the rest of the world. Richard Robbins’ Global Problems and Culture of Capitalism explains how the modern culture of consumption has been extremely successful at accommodating populations of people far larger than previously possible. Robbins claims that the globalization attributed to capitalism has allowed the world to make full use of its environmental resources, providing necessities and innovative technologies to humans all over the world (Robbins & Dowty, 2019). In other words, capitalism is an anthropocentric cultural system that highly benefits humans and facilitates our survival with little regard to the development and survival of other forms of life. It would be of high relevance to introduce the idea that our cultural evolution and capacity to modify the environment to meet our needs have established new environmental conditions in which the human species' survival and reproduction rate expand at the detriment of ecosystems and endangerment of other primates and non-human species.
According to a 2019 UN report, following the 16th century, the world has entered a period of extreme environmental destruction that is generating ecological modifications and has led to the extinction of at least 680 vertebrate species and over 9 percent of the domesticated mammals used for food and agriculture (United Nations, 2019). Human lifestyles are causing changes that—if not taken into consideration—could lead to our extinction as a species. The recognition that our evolutionary behavioural development is causing environmental destruction may be the first step for our species to take accountability for the damage that it is causing to others and prevent further damage.
Concluding Thoughts
Now that you have finished reading this chapter, you are equipped to understand the historical and political dimensions of evolution. Evolution is an ongoing process of change and diversification. Evolutionary theory is a tool that we use to understand this process. The development of evolutionary theory is shaped both by scientific innovation and political engagement. Since Darwin first articulated natural selection as an observable mechanism by which species adapt to their environments, our understanding of evolution has grown. Initially, scientists focused on the adaptive aspects of evolution. However, with the emergence of genetics, our understanding of heredity and the level at which evolution acts has changed. Genetics led to a focus on the molecular dimensions of evolution. For some, this focus resulted in reductive accounts of evolution. Further developments in our understanding of evolution shifted our view to epigenetic processes and how organisms shape their own evolutionary pressures (e.g., niche construction).
Evolutionary theory will continue to develop in the future as we invent new technologies, describe new dimensions of biology, and experience cultural changes. Current innovations in evolutionary theory are asking us to consider evolutionary forces beyond natural selection and genetics to include the ways organisms shape their environments (niche construction), inheritances beyond genetics (inclusive inheritance), constraints on evolutionary change (developmental bias), and the ability of bodies to change in response to external factors (plasticity). The future of evolutionary theory looks bright as we continue to explore these and other dimensions. Biological anthropology is well-positioned to be a lively part of this conversation, as it extends standard evolutionary theory by considering the role of culture, social learning, and human intentionality in shaping the evolutionary trajectories of humans (Zeder 2018). Remember, at root, human evolutionary theory consists of two propositions: (1) the human species is descended from other similar species and (2) natural selection has been the primary agent of biological adaptation. Pretty much everything else is subject to some degree of contestation.
Review Questions
- How is the study of your ancestors biopolitical, not just biological? Does that make it less scientific or differently scientific?
- What was gained by reducing organisms to genotypes and species to gene pools? What is gained by reintroducing bodies and species into evolutionary studies?
- How do genetic or molecular studies complement anatomical studies of evolution?
- How are you reducible to your ancestry? If you could meet your ancestors from the year 1700 (and you would have well over a thousand of them!), would their lives be meaningfully similar to yours? Would you even be able to communicate with them?
- The molecular biologist François Jacob argued that evolution is more like a tinkerer than an engineer. In what ways do we seem like precisely engineered machinery, and in what ways do we seem like jerry-rigged or improvised contraptions?
- How might biological anthropology contribute to future developments in evolutionary theory?
Key Terms
Adaptation: A fit between the organism and environment.
Adaptationism: The idea that everything is the product of natural selection.
Allele: A genetic variant.
Allometry: The differential growth of body parts.
Canalization: The tendency of a growing organism to be buffered toward normal development.
Epigenetics: The study of how genetically identical cells and organisms (with the same DNA base sequence) can nevertheless differ in stably inherited ways.
Eugenics: An idea that was popular in the 1920s that society should be improved by breeding “better” kinds of people.
Evo-devo: The study of the origin of form; a contraction of “evolutionary developmental biology.”
Exaptation: An additional beneficial use for a biological feature.
Extinction: The loss of a species from the face of the earth.
Gene: A stretch of DNA with an identifiable function (sometimes broadened to include any DNA with recognizable structural features as well).
Gene pool: Hypothetical summation of the entire genetic composition of population or species.
Genotype: Genetic constitution of an individual organism.
Hereditarianism: The idea that genes or ancestry is the most crucial or salient element in a human life. Generally associated with an argument for natural inequality on pseudo-genetic grounds.
Hox genes: A group of related genes that control for the body plan of an embryo along the head-tail axis.
Inheritance of acquired characteristics: The idea that you pass on the features that developed during your lifetime, not just your genes; also known as Lamarckian inheritance.
Natural selection: A consistent bias in survival and fertility, leading to the overrepresentation of certain features in future generations and an improved fit between an average member of the population and the environment.
Niche construction: The active engagement by which species transform their surroundings in favorable ways, rather than just passively inhabiting them.
Phenotype: Observable manifestation of a genetic constitution, expressed in a particular set of circumstances. The suite of traits of an organism.
Phrenology: The 19th-century anatomical study of bumps on the head as an indication of personality and mental abilities.
Plasticity: The tendency of a growing organism to react developmentally to its particular conditions of life.
Punctuated equilibria: The idea that species are stable through time and are formed very rapidly relative to their duration. (The opposite theory, that species are unstable and constantly changing through time, is called phyletic gradualism.)
Scientific racism: The use of pseudoscientific evidence to support or legitimize racial hierarchy and inequality.
Sexual selection: Natural selection arising through preference by one sex for certain characteristics in individuals of the other sex.
Species selection: A postulated evolutionary process in which selection acts on an entire species population, rather than individuals.
About the Authors
Jonathan Marks, Ph.D.
University of North Carolina at Charlotte, jmarks@uncc.edu
Jonathan Marks is Professor of Anthropology at the University of North Carolina at Charlotte. He has published many books and articles on broad aspects of biological anthropology. In 2006 he was elected a Fellow of the American Association for the Advancement of Science. In 2012 he was awarded the First Citizen’s Bank Scholar’s Medal from UNC Charlotte. In recent years he has been a Visiting Research Fellow at the ESRC Genomics Forum in Edinburgh, a Visiting Research Fellow at the Max Planck Institute for the History of Science in Berlin, and a Templeton Fellow at the Institute for Advanced Study at Notre Dame. His work has received the W. W. Howells Book Prize and the General Anthropology Division Prize for Exemplary Cross-Field Scholarship from the American Anthropological Association as well as the J. I. Staley Prize from the School for Advanced Research. Two of his books are titled What It Means to Be 98% Chimpanzee and Why I Am Not a Scientist, but actually he is about 98 percent scientist and not a chimpanzee.
Adam P. Johnson, M.A.
University of North Carolina at Charlotte/University of Texas at San Antonio, ajohn344@uncc.edu
Adam Johnson is a doctoral candidate at the University of Texas at San Antonio and part-time lecturer at the University of North Carolina at Charlotte. He earned his M.A. in anthropology at UNC-Charlotte in 2017 and will complete his Ph.D. in anthropology at UTSA by 2024. His interests include human-animal relations, science studies, primate behavior, ecology, and the history of anthropology. His recent research project analyzes the social, historical, political, and evolutionary dimensions that shape human-javelina encounters. His goal is to understand how humans and animals find ways to get along in a precarious world.
For Further Exploration
Ackermann, Rebecca Rogers, Alex Mackay, and Michael L. Arnold. 2016. “The Hybrid Origin of ‘Modern’ Humans.” Evolutionary Biology 43 (1): 1–11.
Bateson, Patrick, and Peter Gluckman. 2011. Plasticity, Robustness, Development and Evolution. New York: Cambridge University Press.
Cosans, Christopher E. 2009. Owen's Ape and Darwin's Bulldog: Beyond Darwinism and Creationism. Bloomington, IN: Indiana University Press.
Desmond, Adrian, and James Moore. 2009. Darwin's Sacred Cause: How a Hatred of Slavery Shaped Darwin's Views on Human Evolution. New York: Houghton Mifflin Harcourt.
Dobzhansky, Theodosius, Francisco J. Ayala, G. Ledyard Stebbins, and James W. Valentine. 1977. Evolution. San Francisco: W.H. Freeman and Company.
Fuentes, Agustín. 2017. The Creative Spark: How Imagination Made Humans Exceptional. New York: Dutton.
Gould, Stephen J. 2003. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press.
Haraway, Donna J. 1989. Primate Visions: Gender, Race, and Nature in the World of Modern Science. New York: Routledge.
Huxley, Thomas. 1863. Evidence as to Man's Place in Nature. London: Williams & Norgate.
Jablonka, Eva, and Marion J. Lamb. 2005. Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Cambridge, MA: The MIT Press.
Kuklick, Henrika, ed. 2008. A New History of Anthropology. New York: Blackwell.
Laland, Kevin N., Tobias Uller, Marcus W. Feldman, Kim Sterelny, Gerd B. Muller, Armin Moczek, Eva Jablonka, and John Odling-Smee. 2015. “The Extended Evolutionary Synthesis: Its Structure, Assumptions and Predictions.” Proceedings of the Royal Society, Series B 282 (1813): 20151019.
Lamarck, Jean Baptiste. 1809. Philosophie Zoologique. Paris: Dentu.
Landau, Misia. 1991. Narratives of Human Evolution. New Haven: Yale University Press.
Lee, Sang-Hee. 2017. Close Encounters with Humankind: A Paleoanthropologist Investigates Our Evolving Species. New York: W. W. Norton.
Livingstone, David N. 2008. Adam's Ancestors: Race, Religion, and the Politics of Human Origins. Baltimore: Johns Hopkins University Press.
Marks, Jonathan. 2015. Tales of the Ex-Apes: How We Think about Human Evolution. Berkeley, CA: University of California Press.
Pigliucci, Massimo. 2009. “The Year in Evolutionary Biology 2009: An Extended Synthesis for Evolutionary Biology.” Annals of the New York Academy of Sciences 1168: 218–228.
Simpson, George Gaylord. 1949. The Meaning of Evolution: A Study of the History of Life and of Its Significance for Man. New Haven: Yale University Press.
Sommer, Marianne. 2016. History Within: The Science, Culture, and Politics of Bones, Organisms, and Molecules. Chicago: University of Chicago Press.
Stoczkowski, Wiktor. 2002. Explaining Human Origins: Myth, Imagination and Conjecture. New York: Cambridge University Press.
Tattersall, Ian, and Rob DeSalle. 2019. The Accidental Homo sapiens: Genetics, Behavior, and Free Will. New York: Pegasus.
References
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Yengo, L., Vedantam, S., Marouli, E., Sidorenko, J., Bartell, E., Sakaue, S., Graff, M., Eliasen, A.U., Jiang, Y., Raghavan, S. and Miao, J., 2022. A saturated map of common genetic variants associated with human height. Nature, 610 (7933): 704-712.
Zeder, Melinda A. 2018. "Why Evolutionary Biology Needs Anthropology: Evaluating Core Assumptions of the Extended Evolutionary Synthesis." Evolutionary Anthropology: Issues, News, and Reviews 27 (6): 267–284.
Kerryn Warren, Ph.D., Grad Coach International
Lindsay Hunter, M.A., University of Iowa
Navashni Naidoo, M.Sc., University of Cape Town
Silindokuhle Mavuso, M.Sc., University of Witwatersrand
This chapter is a revision from "Chapter 9: Early Hominins" by Kerryn Warren, K. Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, and Nomawethu Hlazo. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Understand what is meant by “derived” and “ancestral” traits and why this is relevant for understanding early hominin evolution.
- Understand changing paleoclimates and paleoenvironments as potential factors influencing early hominin adaptations.
- Describe the anatomical changes associated with bipedalism and dentition in early hominins, as well as their implications..
- Describe early hominin genera and species, including their currently understood dates and geographic expanses.
- Describe the earliest stone tool techno-complexes and their impact on the transition from early hominins to our genus.
Defining Hominins
It is through our study of our hominin ancestors and relatives that we are exposed to a world of “might have beens”: of other paths not taken by our species, other ways of being human. But to better understand these different evolutionary trajectories, we must first define the terms we are using. If an imaginary line were drawn between ourselves and our closest relatives, the great apes, bipedalism (or habitually walking upright on two feet) is where that line would be. Hominin, then, means everyone on “our” side of the line: humans and all of our extinct bipedal ancestors and relatives since our divergence from the last common ancestor (LCA) we share with chimpanzees.
Historic interpretations of our evolution, prior to our finding of early hominin fossils, varied. Debates in the mid-1800s regarding hominin origins focused on two key issues:
- Where did we evolve?
- Which traits evolved first?
Charles Darwin hypothesized that we evolved in Africa, as he was convinced that we shared greater commonality with chimpanzees and gorillas on the continent (Darwin 1871). Others, such as Ernst Haeckel and Eugène Dubois, insisted that we were closer in affinity to orangutans and that we evolved in Eurasia where, until the discovery of the Taung Child in South Africa in 1924, all humanlike fossils (of Neanderthals and Homo erectus) had been found (Shipman 2002).
Within this conversation, naturalists and early paleoanthropologists (people who study human evolution) speculated about which human traits came first. These included the evolution of a big brain (encephalization), the evolution of the way in which we move about on two legs (bipedalism), and the evolution of our flat faces and small teeth (indications of dietary change). Original hypotheses suggested that, in order to be motivated to change diet and move about in a bipedal fashion, the large brain needed to have evolved first, as is seen in the fossil species mentioned above.
However, we now know that bipedal locomotion is one of the first things that evolved in our lineage, with early relatives having more apelike dentition and small brain sizes. While brain size expansion is seen primarily in our genus, Homo, earlier hominin brain sizes were highly variable between and within taxa, from 300 cc (cranial capacity, cm3), estimated in Ardipithecus, to 550 cc, estimated in Paranthropus boisei. The lower estimates are well within the range of variation of nonhuman extant great apes. In addition, body size variability also plays a role in the interpretation of whether brain size could be considered large or small for a particular species or specimen. In this chapter, we will tease out the details of early hominin evolution in terms of morphology (i.e. the study of the form, size, or shape of things; in this case, skeletal parts).
We also know that early human evolution occurred in a very complicated fashion. There were multiple species (multiple genera) that featured diversity in their diets and locomotion. Specimens have been found all along the East African Rift System (EARS); that is, in Ethiopia, Kenya, Tanzania, and Malawi; see Figure 9.1), in limestone caves in South Africa, and in Chad. Dates of these early relatives range from around 7 million years ago (mya) to around 1 mya, overlapping temporally with members of our genus, Homo.

Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another, and they consider which of these species were able to make and use tools. As a result, every site discovery in the patchy hominin fossil record tells us more about our evolution. In addition, recent scientific techniques (not available even ten years ago) provide new insights into the diets, environments, and lifestyles of these ancient relatives.
In the past, taxonomy was primarily based on morphology. Today it is tied to known relationships based on molecular phylogeny (e.g., based on DNA) or a combination of the two. This is complicated when applied to living taxa, but becomes much more difficult when we try to categorize ancestor-descendant relationships for long-extinct species whose molecular information is no longer preserved. We therefore find ourselves falling back on morphological comparisons, often of teeth and partially fossilized skeletal material.
It is here that we turn to the related concepts of cladistics and phylogenetics. Cladistics groups organisms according to their last common ancestors based on shared derived traits. In the case of early hominins, these are often morphological traits that differ from those seen in earlier populations. These new or modified traits provide evidence of evolutionary relationships, and organisms with the same derived traits are grouped in the same clade (Figure 9.2). For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade of birds. In this chapter, we will examine the grouping of the Robust Australopithecines, whose cranial and dental features differ from those of earlier hominins, and therefore are considered derived.

Dig Deeper: Problems Defining Hominin Species
It is worth noting that species designations for early hominin specimens are often highly contested. This is due to the fragmentary nature of the fossil record, the large timescale (millions of years) with which paleoanthropologists need to work, and the difficulty in evaluating whether morphological differences and similarities are due to meaningful phylogenetic or biological differences or subtle differences/variation in niche occupation or time. In other words, do morphological differences really indicate different species? How would classifying species in the paleoanthropological record compare with classifying living species today, for whom we can sequence genomes and observe lifestyles?
There are also broader philosophical differences among researchers when it comes to paleo-species designations. Some scientists, known as “lumpers,” argue that large variability is expected among multiple populations in a given species over time. These researchers will therefore prefer to “lump” specimens of subtle differences into single taxa. Others, known as “splitters,” argue that species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences. In general, splitters would consider geographic differences among populations as meaning that a species is polytypic (i.e., capable of interacting and breeding biologically but having morphological population differences). This is worth keeping in mind when learning about why species designations may be contested.

This further plays a role in evaluating ancestry. Debates over which species “gave rise” to which continue to this day. It is common to try to create “lineages” of species to determine when one species evolved into another over time. We refer to these as chronospecies (Figure 9.3). Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record. More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
Finally, it is worth considering the process of fossil discovery and publication. Some fossils are easily diagnostic to a species level and allow for easy and accurate interpretation. Some, however, are more controversial. This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species (e.g., a fossil of a patella or knee bone). Researchers often need to make several important claims when announcing or publishing a find: a secure date (if possible), clear association with other finds, and an adequate comparison among multiple species (both extant and fossil). Therefore, it is not uncommon that an important find was made years before it is scientifically published.
Paleoenvironment and Hominin Evolution
There is no doubt that one of the major selective pressures in hominin evolution is the environment. Large-scale changes in global and regional climate, as well as alterations to the environment, are (thought to be) all linked to (all) hominin diversification, dispersal, and extinction (Maslin et al. 2014). Environmental reconstructions often use modern analogues. Let us take, for instance, the hippopotamus. It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive. Such instances have occurred multiple times in the past, and the bones of some fauna (i.e., animals, like the hippopotamus) that are sensitive to these changes give us insights into these events.
Yet reconstructing a paleoenvironment relies on a range of techniques, which vary depending on whether research interests focus on local changes or more global environmental changes/reconstructions. For local environments (such as a single site or region), comparing the faunal assemblages (collections of fossils of animals found at a site) with animals found in certain modern environments allows us to determine if past environments mirror current ones in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes. Other techniques are also useful in this regard. Chemical analyses, for instance, can reveal the diets of individual fauna, providing clues as to the relative wetness or dryness of their environment (e.g., nitrogen isotopes; Kingston and Harrison 2007).
Global climatic changes in the distant past, which fluctuated between being colder and drier and warmer and wetter on average, would have global implications for environmental change (Figure 9.4). These can be studied by comparing marine core and terrestrial soil data across multiple sites. These techniques are based on chemical analysis, such as examination of the nitrogen and oxygen isotopes in shells and sediments. Similarly, analyzing pollen grains shows which kinds of flora survived in an environment at a specific time period. There are multiple lines of evidence that allow us to visualize global climate trends over millions of years (although it should be noted that the direction and extent of these changes could differ by geographic region).

Both local and global climatic/environmental changes have been used to understand factors affecting our evolution (DeHeinzelin et al. 1999; Kingston 2007). Environmental change acts as an important factor regarding the onset of several important hominin traits seen in early hominins and discussed in this chapter. Namely, the environment has been interpreted as the following:
- the driving force behind the evolution of bipedalism,
- the reason for change and variation in early hominin diets, and
- the diversification of multiple early hominin species.
There are numerous hypotheses regarding how climate has driven and continues to drive human evolution. Here, we will focus on just three popular hypotheses.
Savannah Hypothesis (or Aridity Hypothesis)
The hypothesis: This popular theory suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion (Figure 9.5). It was first proposed by Darwin (1871) and supported by anthropologists like Raymond Dart (1925). However, this idea was supported by little fossil or paleoenvironmental evidence and was later refined as the Aridity Hypothesis. This hypothesis states that the long-term aridification and, thereby, expansion of savannah biomes were drivers in diversification in early hominin evolution (deMenocal 2004; deMenocal and Bloemendal 1995). It advocates for periods of accelerated aridification leading to early hominin speciation events.

The evidence: While early bipedal hominins are often associated with wetter, more closed environments (i.e., not the Savannah Hypothesis), both marine and terrestrial records seem to support general cooling, drying conditions, with isotopic records indicating an increase in grasslands (i.e., colder and wetter climatic conditions) between 8 mya and 6 mya across the African continent (Cerling et al. 2011). This can be contrasted with later climatic changes derived from aeolian dust records (sediments transported to the site of interest by wind), which demonstrate increases in seasonal rainfall between 3 mya and 2.6 mya, 1.8 mya and 1.6 mya, and 1.2 mya and 0.8 mya (deMenocal 2004; deMenocal and Bloemendal 1995).
Interpretation(s): Despite a relatively scarce early hominin record, it is clear that two important factors occur around the time period in which we see increasing aridity. The first factor is the diversification of taxa, where high morphological variation between specimens has led to the naming of multiple hominin genera and species. The second factor is the observation that the earliest hominin fossils appear to have traits associated with bipedalism and are dated to around the drying period (as based on isotopic records). Some have argued that it is more accurately a combination of bipedalism and arboreal locomotion, which will be discussed later. However, the local environments in which these early specimens are found (as based on the faunal assemblages) do not appear to have been dry.
Turnover Pulse Hypothesis
The hypothesis: In 1985, paleontologist Elisabeth Vbra noticed that in periods of extreme and rapid climate change, ungulates (hoofed mammals of various kinds) that had generalized diets fared better than those with specialized diets (Vrba 1988, 1998). Specialist eaters (those who rely primarily on specific food types) faced extinction at greater rates than their generalist (those who can eat more varied and variable diets) counterparts because they were unable to adapt to new environments (Vrba 2000). Thus, periods with extreme climate change would be associated with high faunal turnover: that is, the extinction of many species and the speciation, diversification, and migration of many others to occupy various niches.
The evidence: The onset of the Quaternary Ice Age, between 2.5 mya and 3 mya, brought extreme global, cyclical interglacial and glacial periods (warmer, wetter periods with less ice at the poles, and colder, drier periods with more ice near the poles). Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites (Behrensmeyer et al. 1997; Bobe and Behrensmeyer 2004). Similarly, work in the Cape Floristic Belt of South Africa shows that extreme changes in climate play a role in extinction and migration in ungulates. While this theory was originally developed for ungulates, its proponents have argued that it can be applied to hominins as well. However, the link between climate and speciation is only vaguely understood (Faith and Behrensmeyer 2013).
Interpretation(s): While the evidence of rapid faunal turnover among ungulates during this time period appears clear, there is still some debate around its usefulness as applied to the paleoanthropological record. Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct.
Variability Selection Hypothesis
The hypothesis: This hypothesis was first articulated by paleoanthropologist Richard Potts (1998). It links the high amount of climatic variability over the last 7 million years to both behavioral and morphological changes. Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context (Potts 1998, 2013). The Variability Selection Hypothesis states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations (Potts 2013).
The evidence: The evidence for this theory is similar to that for the Turnover Pulse Hypothesis: large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
Interpretation(s): In this way, the Variability Selection Hypothesis allows for a more flexible interpretation of the evolution of bipedalism in hominins and a more fluid interpretation of the Turnover Pulse Hypothesis, where species turnover is meant to be more rapid. In some ways, this hypothesis accommodates both environmental data and our interpretations of an evolution toward greater variability among species and the survivability of generalists.
Paleoenvironment Summary
Some hypotheses presented in this section pay specific attention to habitat (Savannah Hypothesis) while others point to large-scale climatic forces (Variability Selection Hypothesis). Some may be interpreted to describe the evolution of traits such as bipedalism (Savannah Hypothesis), and others generally explain the diversification of early hominins (Turnover Pulse and Variability Selection Hypotheses). While there is no consensus as to how the environment drove our evolution, it is clear that the environment shaped both habitat and resource availability in ways that would have influenced our early ancestors physically and behaviorally.
Derived Adaptations: Bipedalism
The unique form of locomotion exhibited by modern humans, called obligate bipedalism, is important in distinguishing our species from the extant (living) great apes. The ability to walk habitually upright is thus considered one of the defining attributes of the hominin lineage. We also differ from other animals that walk bipedally (such as kangaroos) in that we do not have a tail to balance us as we move.
The origin of bipedalism in hominins has been debated in paleoanthropology, but at present there are two main ideas: (theories)
- early hominins initially lived in trees, but increasingly started living on the ground, so we were a product of an arboreal last common ancestor (LCA) or,
- our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
Most research supports the first theory of an arboreal LCA based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking. This would mean that both humans and chimpanzees can be considered “derived” in terms of locomotion since chimpanzees would have independently evolved knuckle-walking.
There are many current ideas regarding selective pressures that would lead to early hominins adapting upright posture and locomotion. Many of these selective pressures, as we have seen in the previous section, coincide with a shift in environmental conditions, supported by paleoenvironmental data. In general, however, it appears that, like extant great apes, early hominins thrived in forested regions with dense tree coverage, which would indicate an arboreal lifestyle. As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse such that bipedalism would become more important.
There are several proposed selective pressures for bipedalism:
- Energy conservation: Modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land. While chimpanzees, for instance, are faster than humans terrestrially, they expend large amounts of energy being so. Adaptations to bipedalism include “stacking” the majority of the weight of the body over a small area around the center of gravity (i.e., the head is above the chest, which is above the pelvis, which is over the knees, which are above the feet). This reduces the amount of muscle needed to be engaged during locomotion to “pull us up” and allows us to travel longer distances expending far less energy.
- Thermoregulation: Less surface area (i.e., only the head and shoulders) is exposed to direct sunlight during the hottest parts of the day (i.e., midday). This means that the body has less need to employ additional “cooling” mechanisms such as sweating, which additionally means less water loss.
- Bipedalism (Freeing of Hands): This method of locomotion freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use of tools.
These selective pressures are not mutually exclusive. Bipedality could have evolved from a combination of these selective pressures, in ways that increased the chances of early hominin survival.
Skeletal Adaptations for Bipedalism

Humans have highly specialized adaptations to facilitate obligate bipedalism (Figure 9.6). Many of these adaptations occur within the soft tissue of the body (e.g., muscles and tendons). However, when analyzing the paleoanthropological record for evidence of the emergence of bipedalism, all that remains is the fossilized bone. Interpretations of locomotion are therefore often based on comparative analyses between fossil remains and the skeletons of extant primates with known locomotor behaviors. These adaptations occur throughout the skeleton and are summarized in Figure 9.7.
The majority of these adaptations occur in the postcranium (the skeleton from below the head) and are outlined in Figure 9.7. In general, these adaptations allow for greater stability and strength in the lower limb, by allowing for more shock absorption, for a larger surface area for muscle attachment, and for the “stacking” of the skeleton directly over the center of gravity to reduce energy needed to be kept upright. These adaptations often mean less flexibility in areas such as the knee and foot.
However, these adaptations come at a cost. Evolving from a nonobligate bipedal ancestor means that the adaptations we have are evolutionary compromises. For instance, the valgus knee (angle at the knee) is an essential adaptation to balance the body weight above the ankle during bipedal locomotion. However, the strain and shock absorption at an angled knee eventually takes its toll. For example, runners often experience joint pain. Similarly, the long neck of the femur absorbs stress and accommodates for a larger pelvis, but it is a weak point, resulting in hip replacements being commonplace among the elderly, especially in cases where the bone additionally weakens through osteoporosis. Finally, the S-shaped curve in our spine allows us to stand upright, relative to the more curved C-shaped spine of an LCA. Yet the weaknesses in the curves can lead to pinching of nerves and back pain. Since many of these problems primarily are only seen in old age, they can potentially be seen as an evolutionary compromise.
Despite relatively few postcranial fragments, the fossil record in early hominins indicates a complex pattern of emergence of bipedalism. Key features, such as a more anteriorly placed foramen magnum, are argued to be seen even in the earliest discovered hominins, indicating an upright posture (Dart 1925). Some early species appear to have a mix of ancestral (arboreal) and derived (bipedal) traits, which indicates a mixed locomotion and a more mosaic evolution of the trait. Some early hominins appear to, for instance, have bowl-shaped pelvises (hip bones) and angled femurs suitable for bipedalism but also have retained an opposable hallux (big toe) or curved fingers and longer arms (for arboreal locomotion). These mixed morphologies may indicate that earlier hominins were not fully obligate bipeds and thus thrived in mosaic environments.
Yet the associations between postcranial and the more diagnostic cranial fossils and bones are not always clear, muddying our understanding of the specific species to which fossils belong (Grine et al. 2022).
Region | Feature | Obligate Biped (H. sapiens) | Nonobligate Biped |
Cranium | Position of the foramen magnum | Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground). | Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground. |
Post
cranium |
Body proportions | Shorter upper limb (not used for locomotion). | Longer upper limbs (used for locomotion). |
Post
cranium |
Spinal curvature | S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis). | C-curve. |
Post
cranium |
Vertebrae | Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission). | Gracile lumbar vertebrae compared to those of modern humans. |
Post
cranium |
Pelvis | Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces. | Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface. |
Post
cranium |
Lower limb | In general, longer, more robust lower limbs and more stable, larger joints.
|
In general, smaller, more gracile limbs with more flexible joints.
|
Post
cranium |
Foot | Rigid, robust foot, without a midtarsal break.
Nonopposable and large, robust big toe (for push off while walking) and large heel for shock absorbance. |
Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping. |
It is also worth noting that, while not directly related to bipedalism per se, other postcranial adaptations are evident in the hominin fossil record from some of the earlier hominins. For instance, the hand and finger morphologies of many of the earliest hominins indicate adaptations consistent with arboreality. These include longer hands, more curved metacarpals and phalanges (long bones in the hand and fingers, respectively), and a shorter, relatively weaker thumb. This allows for gripping onto curved surfaces during locomotion. The earliest hominins appear to have mixed morphologies for both bipedalism and arborealism. However, among Australopiths (members of the genus, Australopithecus), there are indications for greater reliance on bipedalism as the primary form of locomotion. Similarly, adaptations consistent with tool manufacture (shorter fingers and a longer, more robust thumb, in contrast to the features associated with arborealism) have been argued to appear before the genus Homo.
(Special Topic with student projects: fear of snakes, cultural or biological? Biology, culture, and the fear of snakes, Snake Detection Theory)
It is suggested that primates have three major predators: raptors, felines, and snakes; however, many studies show that of these carnivores, snakes were one of the first that mammals had to contend with alongside dinosaurs, as felines and raptors evolved at a much slower pace than their reptilian competition. Herpetologists trace the evolution of constricting snakes to about 100 million years ago, and by the time mammals arrived around 75 million years ago, constrictors were already well established as a formidable threat (Greene, 2017). Both co-existed for millennia and each sustained selective pressures requiring them to evolve specific traits to survive. When venomous snakes eventually emerged 55 to 65 million years ago, they posed yet an additional threat to proto-primates as they required less distance for the predator to kill (2017). Alongside camouflage and silent movement techniques, it was the development of the snake’s hollow fangs through which to deliver venom that was most transformative to primate evolution. As such, primates evolved their pre-conscious attention, and visual acuity to cope with this new threat; therefore, while snakes were adapting morphologically to feed themselves, they were unwittingly teaching proto-primates valuable lessons in predator detection and reacting appropriately in order to survive. In a 2009 Harvard University study, Lynne A. Isbell hypothesizes that envenoming snakes are linked to being directly responsible for the origins of the evolving complex brains and superior visual capacity in the lineage of anthropoids leading to humans (Isbell, 2009). Forward-facing eyes for binocular vision, depth perception, enhanced visual acuity, stereoscopic and trichromatic colour vision, all traits necessary for snake detection; and the quick motor responses from the primate’s fight, flight, or freeze defence mechanism to circumvent a snake’s squeeze or bite. Numerous laboratory studies show that humans and primates both sense and visually detect snakes more rapidly than other threatening stimuli (Van Le Et al., 2013). These experiments show that snakes elicited the strongest, fastest responses (Van Le Et al., 2013). This is known as ‘Snake Detection Theory’ and is the evolution of the primate’s complex brain, visual acuity, and rapid motor responses towards snakes in its environment that are the adaptations needed to live successfully as arboreal beings. It is not fortuitous then, that primates that never coexisted with venomous snakes, such as lemurs in Madagascar, have less visual acuity, better olfaction and smaller brains. Within Isbell’s work, a collaborative study by a group of neuroscientists tested this hypothesis and found that, indeed, there is higher neural firing and activity in multiple areas of the primate brain, notably in the pulvinar, a region responsible for visual attention and oculomotor behaviour (Isbell, L., 2009). Today, the fear of snakes is widespread in humans, often shown through avoidance and disgust. A study in The Journal of Ethnobiology and Ethnomedicine notes that snakes are over-hunted and excluded from conservation efforts worldwide (Ceríaco, 2012). While cultural factors shape our sentiments, instinct also plays a role—such as the developed avoidance behaviors toward threats like snakes. This blend of instinct and cultural influence is not only seen in behavior but also deeply embedded in the stories we tell. Many cultures depict mythological snakes as harbingers of death or chaos. In the Bible, Satan becomes a snake to tempt Eve. Norse mythology features Jörmungandr, the world serpent who signals the apocalypse. Egyptian myth tells of Apophis, who battles the sun god Ra nightly. Mesoamerican lore includes Quetzalcoatl, a feathered serpent linked to water and death. Though sources vary, these myths consistently portray snakes as threats. As such, the widespread fear of snakes may reflect both evolutionary and cultural influences. Understood as an adaptive response inherited from primate ancestors—who developed avoidance behaviors toward potentially dangerous stimuli—and reinforced through myths and religious narratives, the enduring presence of snakes as potent figures of fear across human societies and primate groups highlights the complex intertwining of instinct and cultural meaning in shaping human behavior.
Early Hominins: Sahelanthropus and Orrorin
We see evidence for bipedalism in some of the earliest fossil hominins, dated from within our estimates of our divergence from chimpanzees. These hominins, however, also indicate evidence for arboreal locomotion.
The earliest dated hominin find (between 6 mya and 7 mya, based on radiometric dating of volcanic tufts) has been argued to come from Chad and is named Sahelanthropus tchadensis (Figure 9.8; Brunet et al. 1995). The initial discovery was made in 2001 by Ahounta Djimdoumalbaye and announced in Nature in 2002 by a team led by French paleontologist Michel Brunet. The find has a small cranial capacity (360 cc) and smaller canines than those in extant great apes, though they are larger and pointier than those in humans. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. A short cranial base and a foramen magnum that is more humanlike in positioning have been argued to indicate upright walking.

Initially, the inclusion of Sahelanthropus in the hominin family was debated by researchers, since the evidence for bipedalism is based on cranial evidence alone, which is not as convincing as postcranial evidence. Yet, a femur (thigh bone) and ulnae (upper arm bones) thought to belong to Sahelanthropus was discovered in 2001 (although not published until 2022). These bones may support the idea that the hominin was in fact a terrestrial biped with arboreal capabilities and behaviors (Daver et al. 2022).
Orrorin tugenensis (Orrorin meaning “original man”), dated to between 6 mya and 5.7 mya, was discovered near Tugen Hills in Kenya in 2000. Smaller cheek teeth (molars and premolars) than those in even more recent hominins, thick enamel, and reduced, but apelike, canines characterize this species. This is the first species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains. One of the most important elements discovered was a proximal femur, BAR 1002'00. The femur is the thigh bone, and the proximal part is that which articulates with the pelvis; this is very important for studying posture and locomotion. This femur indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins. Some have argued that features of the finger bones suggest potential tool-making capabilities, although many researchers argue that these features are also consistent with climbing.
Early Hominins: The Genus Ardipithecus
Another genus, Ardipithecus, is argued to be represented by at least two species: Ardipithecus (Ar.) ramidus and Ar. kadabba.
Ardipithecus ramidus (“ramid” means root in the Afar language) is currently the best-known of the earliest hominins (Figure 9.9). Unlike Sahelanthropus and Orrorin, this species has a large sample size of over 110 specimens from Aramis alone. Dated to 4.4 mya, Ar. ramidus was found in Ethiopia (in the Middle Awash region and in Gona). This species was announced in 1994 by American palaeoanthropologist Tim White, based on a partial female skeleton nicknamed “Ardi” (ARA-VP-6/500; White et al. 1994). Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, she had an opposable big toe (hallux), similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. A small brain (300 cc to 350 cc), midfacial projection, and slight prognathism show retained ancestral cranial features, but the cheek bones are less flared and robust than in later hominins.

Ardipithecus kadabba (the species name means “oldest ancestor” in the Afar language) is known from localities on the western margin of the Middle Awash region, the same locality where Ar. ramidus has been found. Specimens include mandibular fragments and isolated teeth as well as a few postcranial elements from the Asa Koma (5.5 mya to 5.77 mya) and Kuseralee Members (5.2 mya), well-dated and understood (but temporally separate) volcanic layers in East Africa. This species was discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie. Originally these specimens were referred to as a subspecies of Ar. ramidus. In 2002, six teeth were discovered at Asa Koma and the dental-wear patterns confirmed that this was a distinct species, named Ar. kadabba, in 2004. One of the postcranial remains recovered included a 5.2 million-year-old toe bone that demonstrated features that are associated with toeing off (pushing off the ground with the big toe leaving last) during walking, a characteristic unique to bipedal walkers. However, the toe bone was found in the Kuseralee Member, and therefore some doubt has been cast by researchers about its association with the teeth from the Asa Koma Member.
Bipedal Trends in Early Hominins: Summary
Trends toward bipedalism are seen in our earliest hominin finds. However, many specimens also indicate retained capabilities for climbing. Trends include a larger, more robust hallux; a more compact foot, with an arch; a robust, long femur, angled at the knee; a robust tibia; a bowl-shaped pelvis; and a more anterior foramen magnum. While the level of bipedality in Salehanthropus tchadenisis is debated since there are few fossils and no postcranial evidence, Orrorin tugenensis and Ardipithecus kadabba show clear indications of some of these bipedal trends. However, some retained ancestral traits, such as an opposable hallux in Ardipithecus, indicate some retention in climbing ability.
Derived Adaptations: Early Hominin Dention
The Importance of Teeth
Teeth are abundant in the fossil record, primarily because they are already highly mineralized as they are forming, far more so than even bone. Because of this, teeth preserve readily. And, because they preserve readily, they are well-studied and better understood than many skeletal elements. In the sparse hominin (and primate) fossil record, teeth are, in some cases, all we have.
Teeth also reveal a lot about the individual from whom they came. We can tell what they evolved to eat, to which other species they may be closely related, and even, to some extent, the level of sexual dimorphism, or general variability, within a given species. This is powerful information that can be contained in a single tooth. With a little more observation, the wearing patterns on a tooth can tell us about the diet of the individual in the weeks leading up to its death. Furthermore, the way in which a tooth is formed, and the timing of formation, can reveal information about changes in diet (or even mobility) over infancy and childhood, using isotopic analyses. When it comes to our earliest hominin relatives, this information is vital for understanding how they lived.
The purpose of comparing different hominin species is to better understand the functional morphology as it applies to dentition. In this, we mean that the morphology of the teeth or masticatory system (which includes jaws) can reveal something about the way in which they were used and, therefore, the kinds of foods these hominins ate. When comparing the features of hominin groups, it is worth considering modern analogues (i.e., animals with which to compare) to make more appropriate assumptions about diet. In this way, hominin dentition is often compared with that of chimpanzees and gorillas (our close ape relatives), as well as with that of modern humans.
The most divergent group, however, is humans. Humans around the world have incredibly varied diets. Among hunter-gatherers, it can vary from a honey- and plant-rich diet, as seen in the Hadza in Tanzania, to a diet almost entirely reliant on animal fat and protein, as seen in Inuits in polar regions of the world. We are therefore considered generalists, more general than the largely frugivorous (fruit-eating) chimpanzee or the folivorous (foliage-eating) gorilla, as discussed in Chapter 5.
One way in which all humans are similar is our reliance on the processing of our food. We cut up and tear meat with tools using our hands, instead of using our front teeth (incisors and canines). We smash and grind up hard seeds, instead of crushing them with our hind teeth (molars). This means that, unlike our ape relatives, we can rely more on developing tools to navigate our complex and varied diets. (We could say) Our brain, therefore, is our primary masticatory organ. Evolutionarily, our teeth have reduced in size and our faces are flatter, or more orthognathic, partially in response to our increased reliance on our hands and brain to process food. Similarly, a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat. These trends begin early on in our evolution. The link has been made between some of the earliest evidence for stone tool manufacture, the earliest members of our genus, and the features that we associate with these specimens.
General Dental Trends in Early Hominins
Several trends are visible in the dentition of early hominins. However, all tend to have the same dental formula. The dental formula tells us how many of each tooth type are present in each quadrant of the mouth. Going from the front of the mouth, this includes the square, flat incisors; the pointy canines; the small, flatter premolars; and the larger hind molars. In many primates, from Old World monkeys to great apes, the typical dental formula is 2:1:2:3. This means that if we divide the mouth into quadrants, each has two incisors, one canine, two premolars, and three molars. The eight teeth per quadrant total 32 teeth in all (although some humans have fewer teeth due to the absence of their wisdom teeth, or third molars).

The morphology of the individual teeth is where we see the most change. Among primates, large incisors are associated with food procurement or preparation (such as biting small fruits), while small incisors indicate a diet that may contain small seeds or leaves (where the preparation is primarily in the back of the mouth). Most hominins have relatively large, flat, vertically aligned incisors that occlude (touch) relatively well, forming a “bite.” This differs from, for instance, the orangutan, whose teeth stick out (i.e., are procumbent).
While the teeth are often aligned with diet, the canines may be misleading in that regard. We tend to associate pointy, large canines with the ripping required for meat, and the reduction (or, in some animals, the absence) of canines as indicative of herbivorous diets. In humans, our canines are often a similar size to our incisors and therefore considered incisiform (Figure 9.10). However, our closest relatives all have very long, pointy canines, particularly on their upper dentition. This is true even for the gorilla, which lives almost exclusively on plants. The canines in these instances reveal more about social structure and sexual dimorphism than diet, as large canines often signal dominance.
Early on in human evolution, we see a reduction in canine size. Sahelanthropus tchadensis and Orrorin tugenensis both have smaller canines than those in extant great apes, yet the canines are still larger and pointier than those in humans or more recent hominins. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. In Ardipithecus ramidus, there is no obvious difference between male and female canine size, yet they are still slightly larger and pointier than in modern humans. This implies a less sexually dimorphic social structure in the earlier hominins relative to modern-day chimpanzees and gorillas.
Along with a reduction in canine size is the reduction or elimination of a canine diastema: a gap between the teeth on the mandible that allows room for elongated teeth on the maxilla to “fit” in the mouth. Absence of a diastema is an excellent indication of a reduction in canine size. In animals with large canines (such as baboons), there is also often a honing P3, where the first premolar (also known as P3 for evolutionary reasons) is triangular in shape, “sharpened” by the extended canine from the upper dentition. This is also seen in some early hominins: Ardipithecus, for example, has small canines that are almost the same height as its incisors, although still larger than those in recent hominins.
The hind dentition, such as the bicuspid (two cusped) premolars or the much larger molars, are also highly indicative of a generalist diet in hominins. Among the earliest hominins, the molars are larger than we see in our genus, increasing in size to the back of the mouth and angled in such a way from the much smaller anterior dentition as to give these hominins a parabolic (V-shaped) dental arch. This differs from our living relatives and some early hominins, such as Sahelanthropus, whose molars and premolars are relatively parallel between the left and right sides of the mouth, creating a U-shape.
Among more recent early hominins, the molars are larger than those in the earliest hominins and far larger than those in our own genus, Homo. Large, short molars with thick enamel allowed our early cousins to grind fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing. In our genus, the hind dentition is far smaller than in these early hominins. Our teeth also have medium-size cusps, which allow for both efficient grinding and tearing/shearing meats.
Understanding the dental morphology has allowed researchers to extrapolate very specific behaviors of early hominins. It is worth noting that while teeth preserve well and are abundant, a slew of other morphological traits additionally provide evidence for many of these hypotheses. Yet there are some traits that are ambiguous. For instance, while there are definitely high levels of sexual dimorphism in Au. afarensis, discussed in the next section, the canine teeth are reduced in size, implying that while canines may be useful indicators for sexual dimorphism, it is also worth considering other evidence.
In summary, trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the ancestral dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
Special Topic: Contested Species
Many named species are highly debated and argued to have specimens associated with a more variable Au. afarensis or Au. anamensis species. Sometimes these specimens are dated to times when, or found in places in which, there are “gaps” in the palaeoanthropological record. These are argued to represent chronospecies or variants of Au. afarensis. However, it is possible that, with more discoveries, the distinct species types will hold.
Australopithecus bahrelghazali is dated to within the time period of Au. afarensis (3.6 mya; Brunet et al. 1995) and was the first Australopithecine to be discovered in Chad in central Africa. Researchers argue that the holotype, whom discoverers have named “Abel,” falls under the range of variation of Au. afarensis and therefore that A. bahrelghazali does not fall into a new species (Lebatard et al. 2008). If “Abel” is a member of Au. afarensis, the geographic range of the species would be greatly extended.
On a different note, Australopithecus deyiremada (meaning “close relative” in the Ethiopian language of Afar) is dated to 3.5 mya to 3.3 mya and is based on fossil mandible bones discovered in 2011 in Woranso-Mille (in the Afar region of Ethiopia) by Yohannes Haile-Selassie, an Ethiopian paleoanthropologist (Haile-Selassie et al. 2019). The discovery indicated, in contrast to Au. afarensis, smaller teeth with thicker enamel (potentially suggesting a harder diet) as well as a larger mandible and more projecting cheekbones. This find may be evidence that more than one closely related hominin species occupied the same region at the same temporal period (Haile-Selassie et al. 2015; Spoor 2015) or that other Au. afarensis specimens have been incorrectly designated. However, others have argued that this species has been prematurely identified and that more evidence is needed before splitting the taxa, since the variation appears subtle and may be due to slightly different niche occupations between populations over time.
Australopithecus garhi is another species found in the Middle Awash region of Ethiopia. It is currently dated to 2.5 mya (younger than Au. afarensis). Researchers have suggested it fills in a much-needed temporal “gap” between hominin finds in the region, with some anatomical differences, such as a relatively large cranial capacity (450 cc) and larger hind dentition than seen in other gracile Australopithecines. Similarly, the species has been argued to have longer hind limbs than Au. afarensis, although it was still able to move arboreally (Asfaw et al. 1999). However, this species is not well documented or understood and is based on only several fossil specimens. More astonishingly, crude stone tools resembling Oldowan (which will be described later) have been found in association with Au. garhi. While lacking some of the features of the Oldowan, this is one of the earliest technologies found in direct association with a hominin.
Kenyanthopus platyops (the name “platyops” refers to its flatter-faced appearance) is a highly contested genus/species designation of a specimen (KNM-WT 40000) from Lake Turkana in Kenya, discovered by Maeve Leakey in 1999 (Figure 9.11). Dated to between 3.5 mya and 3.2 mya, some have suggested this specimen is an Australopithecus, perhaps even Au. afarensis (with a brain size which is difficult to determine, yet appears small), while still others have placed this specimen in Homo (small dentition and flat-orthognathic face). While taxonomic placing of this species is quite divided, the discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis (Leakey et al. 2001). Some researchers have additionally associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this specimen.

The Genus Australopithecus
The Australopithecines are a diverse group of hominins, comprising various species. Australopithecus is the given group or genus name. It stems from the Latin word Australo, meaning “southern,” and the Greek word pithecus, meaning “ape.” Within this section, we will outline these differing species’ geological and temporal distributions across Africa, unique derived and/or shared traits, and importance in the fossil record.

Between 3 mya and 1 mya, there seems to be differences in dietary strategy between different species of hominins designated as Australopithecines. A pattern of larger posterior dentition (even relative to the incisors and canines in the front of the mouth), thick enamel, and cranial evidence for extremely large chewing muscles is far more pronounced in a group known as the robust australopithecines. This pattern is extremely relative to their earlier contemporaries or predecessors, the gracile australopithecines, and is certainly larger than those seen in early Homo, which emerged during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins (Figure 9.12).
Because of these differences, this section has been divided into “gracile” and “robust” Australopithecines, highlighting the morphological differences between the two groups (which many researchers have designated as separate genera: Australopithecus and Paranthropus, respectively) and then focusing on the individual species. It is worth noting, however, that not all researchers accept these clades as biologically or genetically distinct, with some researchers insisting that the relative gracile and robust features found in these species are due to parallel evolutionary events toward similar dietary niches.
Despite this genus’ ancestral traits and small cranial capacity, all members show evidence of bipedal locomotion. It is generally accepted that Australopithecus species display varying degrees of arborealism along with bipedality.
Gracile Australopithecines
This section describes individual species from across Africa. These species are called “gracile australopithecines” because of their smaller and less robust features compared to the divergent “robust” group. Numerous Australopithecine species have been named, but some are only based on a handful of fossil finds, whose designations are controversial.
East African Australopithecines
East African Australopithecines are found throughout the EARS, and they include the earliest species associated with this genus. Numerous fossil-yielding sites, such as Olduvai, Turkana, and Laetoli, have excellent, datable stratigraphy, owing to the layers of volcanic tufts that have accumulated over millions of years. These tufts may be dated using absolute dating techniques, such as Potassium-Argon dating (described in Chapter 7). This means that it is possible to know a relatively refined date for any fossil if the context (i.e., exact location) of that find is known. Similarly, comparisons between the faunal assemblages of these stratigraphic layers have allowed researchers to chronologically identify environmental changes.

The earliest known Australopithecine is dated to 4.2 mya to 3.8 mya. Australopithecus anamensis (after “Anam,” meaning “lake” from the Turkana region in Kenya; Leakey et al. 1995; Patterson and Howells 1967) is currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia; Figure 9.13). Recently, a 2019 find from Ethiopia, named MRD, after Miro Dora where it was found, was discovered by an Ethiopian herder named Ali Bereino. It is one of the most complete cranial finds of this species (Ward et al. 1999). A small brain size (370 cc), relatively large canines, projecting cheekbones, and earholes show more ancestral features as compared to those of more recent Australopithecines. The most important element discovered with this species is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking. Similarly, the earliest found hominin femur belongs to this species. Ancestral traits in the upper limb (such as the humerus) indicate some retained arboreal locomotion.
Some researchers suggest that Au. anamensis is an intermediate form of the chronospecies that becomes Au. afarensis, evolving from Ar. ramidus. However, this is debated, with other researchers suggesting morphological similarities and affinities with more recent species instead. Almost 100 specimens, representing over 20 individuals, have been found to date (Leakey et al. 1995; McHenry 2009; Ward et al. 1999).
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. Au. afarensis (which means “from the Afar region”) is dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia (Figure 9.14). The most famous individual from this species is a partial female skeleton discovered in Hadar (Ethiopia), later nicknamed “Lucy,” after the Beatles’ song “Lucy in the Sky with Diamonds,” which was played in celebration of the find (Johanson et al. 1978; Kimbel and Delezene 2009). This skeleton was found in 1974 by Donald Johanson and dates to approximately 3.2 mya. In addition, in 2002 a juvenile of the species was found by Zeresenay Alemseged and given the name “Selam” (meaning “peace,” DIK 1-1), though it is popularly known as “Lucy’s Child” or as the “Dikika Child” (Alemseged et al. 2006). Similarly, the “Laetoli Footprints” (discussed in Chapter 7; Hay and Leakey 1982; Leakey and Hay 1979) have drawn much attention.


The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans (indicative of a generalist diet); in addition, Au. afarensis has a prognathic face (the face below the eyes juts anteriorly) and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus. Despite a reduction in canine size in this species, large overall size variation indicates high levels of sexual dimorphism.
Skeletal evidence indicates that this species was bipedal, as its pelvis and lower limb demonstrate a humanlike femoral neck, valgus knee, and bowl-shaped hip (Figure 9.15). More evidence of bipedalism is found in the footprints of this species. Au. afarensis is associated with the Laetoli Footprints, a 24-meter trackway of hominin fossil footprints preserved in volcanic ash discovered by Mary Leakey in Tanzania and dated to 3.5 mya to 3 mya. This set of prints is thought to have been produced by three bipedal individuals as there are no knuckle imprints, no opposable big toes, and a clear arch is present. The infants of this species are thought to have been more arboreal than the adults, as discovered through analyses of the foot bones of the Dikika Child dated to 3.32 mya (Alemseged et al. 2006).
Although not found in direct association with stone tools, potential evidence for cut marks on bones, found at Dikika, and dated to 3.39 mya indicates a possible temporal/ geographic overlap between meat eating, tool use, and this species. However, this evidence is fiercely debated. Others have associated the cut marks with the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species.
South African Australopithecines
Since the discovery of the Taung Child, there have been numerous Australopithecine discoveries from the region known as “The Cradle of Humankind,” which was recently given UNESCO World Heritage Site status as “The Fossil Hominid Sites of South Africa.” The limestone caves found in the Cradle allow for the excellent preservation of fossils. Past animals navigating the landscape and falling into cave openings, or caves used as dens by carnivores, led to the accumulation of deposits over millions of years. Many of the hominin fossils, encased in breccia (hard, calcareous sedimentary rock), are recently exposed from limestone quarries mined in the previous century. This means that extracting fossils requires excellent and detailed exposed work, often by a team of skilled technicians.
While these sites have historically been difficult to date, with mixed assemblages accumulated over large time periods, advances in techniques such as uranium-series dating have allowed for greater accuracy. Historically, the excellent faunal record from East Africa has been used to compare sites based on relative dating, whereby environmental and faunal changes and extinction events allow us to know which hominin finds are relatively younger or older than others.
The discovery of the Taung Child in 1924 (discussed in the Special Topic box “The Taung Child” below) shifted the focus of palaeoanthropological research from Europe to Africa, although acceptance of this shift was slow (Broom 1947; Dart 1925). The species to which it is assigned, Australopithecus africanus (name meaning “Southern Ape of Africa”), is currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa (Figure 9.16). A relatively large brain (400 cc to 500 cc), small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits. Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism. However, the sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some ancestral features. Although not in direct association with stone tools, a 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities.

Another famous Au. africanus skull (the skull of “Mrs. Ples”) was previously attributed to Plesianthropus transvaalensis, meaning “near human from the Transvaal,” the old name for Gauteng Province, South Africa (Broom 1947, 1950). The name was shortened by contemporary journalists to “Ples” (Figure 9.17). Due to the prevailing mores of the time, the assumed female found herself married, at least in name, and has become widely known as “Mrs. Ples.” It was later reassigned to Au. africanus and is now argued by some to be a young male rather than an adult female cranium (Thackeray 2000, Thackeray et al. 2002).

In 2008, nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger, noted a clavicle bone in some leftover mining breccia in the Malapa Fossil Site (South Africa). After rigorous studies, the species, Australopithecus sediba (meaning “fountain” or “wellspring” in the South African language of Sesotho), was named in 2010 (Figure 9.18; Berger et al. 2010). The first type specimen belongs to a juvenile male, Karabo (MH1), but the species is known from at least six partial skeletons, from infants through adults. These specimens are currently dated to 1.97 mya (Dirks et al. 2010). The discoverers have argued that Au. sediba shows mosaic features between Au. africanus and the genus, Homo, which potentially indicates a transitional species, although this is heavily debated. These features include a small brain size (Australopithecus-like; 420 cc to 450 cc) but gracile mandible and small teeth (Homo-like). Similarly, the postcranial skeletons are also said to have mosaic features: scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. Some researchers have argued that Au. sediba shows a modern hand morphology (shorter fingers and a longer thumb), indicating that adaptations to tool manufacture and use may be present in this species.

Another famous Australopithecine find from South Africa is that of the nearly complete skeleton now known as “Little Foot” (Clarke 1998, 2013). Little Foot (StW 573) is potentially the earliest dated South African hominin fossil, dating to 3.7 mya, based on radiostopic techniques, although some argue that it is younger than 3 mya (Pickering and Kramers 2010). The name is jokingly in contrast to the cryptid species “bigfoot” and is named because the initial discovery of four ankle bones indicated bipedality. Little Foot was discovered by Ron Clarke in 1994, when he came across the ankle bones while sorting through monkey fossils in the University of Witwatersrand collections (Clarke and Tobias 1995). He asked Stephen Motsumi and Nkwane Molefe to identify the known records of the fossils, which allowed them to find the rest of the specimen within just days of searching the Sterkfontein Caves’ Silberberg Grotto.
The discoverers of Little Foot insist that other fossil finds, previously identified as Au. Africanus, be placed in this new species based on shared ancestral traits with older East African Australopithecines (Clarke and Kuman 2019). These include features such as a relatively large brain size (408 cc), robust zygomatic arch, and a flatter midface. Furthermore, the discoverers have argued that the heavy anterior dental wear patterns, relatively large anterior dentition, and smaller hind dentition of this specimen more closely resemble that of Au. anamensis or Au. afarensis. It has thus been placed in the species Australopithecus prometheus. This species name refers to a previously defunct taxon named by Raymond Dart. The species designation was, through analyzing Little Foot, revived by Ron Clarke, who insists that many other fossil hominin specimens have prematurely been placed into Au. africanus. Others say that it is more likely that Au. africanus is a more variable species and not representative of two distinct species.
Paranthropus “Robust” Australopithecines
In the robust australopithecines, the specialized nature of the teeth and masticatory system, such as flaring zygomatic arches (cheekbones), accommodate very large temporalis (chewing) muscles. These features also include a large, broad, dish-shaped face and and a large mandible with extremely large posterior dentition (referred to as megadonts) and hyper-thick enamel (Kimbel 2015; Lee-Thorp 2011; Wood 2010). Research has revolved around the shared adaptations of these “robust” australopithecines, linking their morphologies to a diet of hard and/or tough foods (Brain 1967; Rak 1988). Some argued that the diet of the robust australopithecines was so specific that any change in environment would have accelerated their extinction. The generalist nature of the teeth of the gracile australopithecines, and of early Homo, would have made them more capable of adapting to environmental change. However, some have suggested that the features of the robust australopithecines might have developed as an effective response to what are known as fallback foods in hard times rather than indicating a lack of adaptability.
There are currently three widely accepted robust australopithecus or, Paranthropus, species: P. aethiopicus, which has more ancestral traits, and P. boisei and P. robustus, which are more derived in their features (Strait et al. 1997; Wood and Schroer 2017). These three species have been grouped together by a majority of scholars as a single genus as they share more derived features (are more closely related to each other; or, in other words, are monophyletic) than the other australopithecines (Grine 1988; Hlazo 2015; Strait et al. 1997; Wood 2010 ). While researchers have mostly agreed to use the umbrella term Paranthropus, there are those who disagree (Constantino and Wood 2004, 2007; Wood 2010).
As a collective, this genus spans 2.7 mya to 1.0 mya, although the dates of the individual species differ. The earliest of the Paranthropus species, Paranthropus aethiopicus, is dated to between 2.7 mya and 2.3 mya and currently found in Tanzania, Kenya, and Ethiopia in the EARS system (Figure 9.19; Constantino and Wood 2007; Hlazo 2015; Kimbel 2015; Walker et al. 1986; White 1988). It is well known because of one specimen known as the “Black Skull” (KNM–WT 17000), so called because of the mineral manganese that stained it black during fossilization (Kimbel 2015). As with all robust Australopithecines, P. aethiopicus has the shared derived traits of large, flat premolars and molars; large, flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle); a sagittal crest (ridge on the top of the skull) for increased muscle attachment of the chewing muscles to the skull; and a robust mandible and supraorbital torus (brow ridge). However, only a few teeth have been found. A proximal tibia indicates bipedality and similar body size to Au. afarensis. In recent years, researchers have discovered and assigned a proximal tibia and juvenile cranium (L.338y-6) to the species (Wood and Boyle 2016).

First attributed as Zinjanthropus boisei (with the first discovery going by the nickname “Zinj” or sometimes “Nutcracker Man”), Paranthropus boisei was discovered in 1959 by Mary Leakey (see Figure 9.20 and 9.21; Hay 1990; Leakey 1959). This “robust” australopith species is distributed across countries in East Africa at sites such as Kenya (Koobi Fora, West Turkana, and Chesowanja), Malawi (Malema-Chiwondo), Tanzania (Olduvai Gorge and Peninj), and Ethiopia (Omo River Basin and Konso). The hypodigm, sample of fossils whose features define the group, has been found by researchers to date to roughly 2.4 mya to 1.4 mya. Due to the nature of its exaggerated, larger, and more robust features, P. boisei has been termed hyper-robust—that is, even more heavily built than other robust species, with very large, flat posterior dentition (Kimbel 2015). Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). Another famous specimen from this species is the Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu.


Paranthropus robustus was the first taxon to be discovered within the genus in Kromdraai B by a schoolboy named Gert Terblanche; subsequent fossil discoveries were made by researcher Robert Broom in 1938 (Figure 9.22; Broom 1938a, 1938b, 1950), with the holotype specimen TM 1517 (Broom 1938a, 1938b, 1950; Hlazo 2018). Paranthropus robustus dates approximately from 2.0 mya to 1 mya and is the only taxon from the genus to be discovered in South Africa. Several of these fossils are fragmentary in nature, distorted, and not well preserved because they have been recovered from quarry breccia using explosives. P. robustus features are neither as “hyper-robust” as P. boisei nor as ancestral as P. aethiopicus; instead, they have been described as being less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring; Rak 1983; Walker and Leakey 1988). Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick-enameled dentition.

Comparisons between Gracile and Robust Australopiths
Comparisons between gracile and robust australopithecines may indicate different phylogenetic groupings or parallel evolution in several species. In general, the robust australopithecines have large temporalis (chewing) muscles, as indicated by flaring zygomatic arches, sagittal crests, and robust mandibles (jawbones). Their hind dentition is large (megadont), with low cusps and thick enamel. Within the gracile australopithecines, researchers have debated the relatedness of the species, or even whether these species should be lumped together to represent more variable or polytypic species. Often researchers will attempt to draw chronospecific trajectories, with one taxon said to evolve into another over time.
Special Topic: The Taung Child

The well-known fossil of a juvenile Australopithecine, the “Taung Child,” was the first early hominin evidence ever discovered and was the first to demonstrate our common human heritage in Africa (Figure 9.23; Dart 1925). The tiny facial skeleton and natural endocast were discovered in 1924 by a local quarryman in the North West Province in South Africa and were painstakingly removed from the surrounding cement-like breccia by Raymond Dart using his wife’s knitting needles. When first shared with the scientific community in 1925, it was discounted as being nothing more than a young monkey of some kind. Prevailing biases of the time made it too difficult to contemplate that this small-brained hominin could have anything to do with our own history. The fact that it was discovered in Africa simply served to strengthen this bias.
Early Tool Use and Technology
Early Stone Age Technology (ESA)
The Early Stone Age (ESA) marks the beginning of recognizable technology made by our human ancestors. Stone-tool (or lithic) technology is defined by the fracturing of rocks and the manufacture of tools through a process called knapping. The Stone Age lasted for more than 3 million years and is broken up into chronological periods called the Early (ESA), Middle (MSA), and Later Stone Ages (LSA). Each period is further broken up into a different techno-complex, a term encompassing multiple assemblages (collections of artifacts) that share similar traits in terms of artifact production and morphology. The ESA spanned the largest technological time period of human innovation from over 3 million years ago to around 300,000 years ago and is associated almost entirely with hominin species prior to modern Homo sapiens. As the ESA advanced, stone tool makers (known as knappers) began to change the ways they detached flakes and eventually were able to shape artifacts into functional tools. These advances in technology go together with the developments in human evolution and cognition, dispersal of populations across the African continent and the world, and climatic changes.
In order to understand the ESA, it is important to consider that not all assemblages are exactly the same within each techno-complex: one can have multiple phases and traditions at different sites (Lombard et al. 2012). However, there is an overarching commonality between them. Within stone tool assemblages, both flakes or cores (the rocks from which flakes are removed) are used as tools. Large Cutting Tools (LCTs) are tools that are shaped to have functional edges. It is important to note that the information presented here is a small fraction of what is known about the ESA, and there are ongoing debates and discoveries within archaeology.
Currently, the oldest-known stone tools, which form the techno-complex the Lomekwian, date to 3.3 mya (Harmand et al. 2015; Toth 1985). They were found at a site called Lomekwi 3 in Kenya. This techno-complex is the most recently defined and pushed back the oldest-known date for lithic technology. There is only one known site thus far and, due to the age of the site, it is associated with species prior to Homo, such as Kenyanthropus platyops. Flakes were produced through indirect percussion, whereby the knappers held a rock and hit it against another rock resting on the ground. The pieces are very chunky and do not display the same fracture patterns seen in later techno-complexes. Lomekwian knappers likely aimed to get a sharp-edged piece on a flake, which would have been functional, although the specific function is currently unknown.
Stone tool use, however, is not only understood through the direct discovery of the tools. Cut marks on fossilized animal bones may illuminate the functionality of stone tools. In one controversial study in 2010, researchers argued that cut marks on a pair of animal bones from Dikika (Ethiopia), dated to 3.4 mya, were from stone tools. The discoverers suggested that they be more securely associated, temporally, with Au. afarensis. However, others have noted that these marks are consistent with teeth marks from crocodiles and other carnivores.

The Oldowan techno-complex is far more established in the scientific literature (Leakey 1971). It is called the Oldowan because it was originally discovered in Olduvai Gorge, Tanzania, but the oldest assemblage is from Gona in Ethiopia, dated to 2.6 mya (Semaw 2000). The techno-complex is defined as a core and flake industry. Like the Lomekwian, there was an aim to get sharp-edged flakes, but this was achieved through a different production method. Knappers were able to actively hold or manipulate the core being knapped, which they could directly hit using a hammerstone. This technique is known as free-hand percussion, and it demonstrates an understanding of fracture mechanics. It has long been argued that the Oldowan hominins were skillful in tool manufacture.
Because Oldowan knapping requires skill, earlier researchers have attributed these tools to members of our genus, Homo. However, some have argued that these tools are in more direct association with hominins in the genera described in this chapter (Figure 9.24).
Invisible Tool Manufacture and Use
The vast majority of our understanding of these early hominins comes from fossils and reconstructed paleoenvironments. It is only from 3 mya when we can start “looking into their minds” and lifestyles by analyzing their manufacture and use of stone tools. However, the vast majority of tool use in primates (and, one can argue, in humans) is not with durable materials like stone. All of our extant great ape relatives have been observed using sticks, leaves, and other materials for some secondary purpose (to wade across rivers, to “fish” for termites, or to absorb water for drinking). It is possible that the majority of early hominin tool use and manufacture may be invisible to us because of this preservation bias.
Chapter Summary
The fossil record of our earliest hominin relatives has allowed paleoanthropologists to unpack some of the mysteries of our evolution. We now know that traits associated with bipedalism evolved before other “human-like” traits, even though the first hominins were still very capable of arboreal locomotion. We also know that, for much of this time, hominin taxa were diverse in the way they looked and what they ate, and they were widely distributed across the African continent. And we know that the environments in which these hominins lived underwent many changes over this time during several warming and cooling phases.
Yet this knowledge has opened up many new mysteries. We still need to better differentiate some taxa. In addition, there are ongoing debates about why certain traits evolved and what they meant for the extinction of some of our relatives (like the robust australopiths). The capabilities of these early hominins with respect to tool use and manufacture is also still uncertain.
Hominin Species Summaries
Hominin |
Sahelanthropus tchadensis |
Dates |
7 mya to 6 mya |
Region(s) |
Chad |
Famous discoveries |
The initial discovery, made in 2001. |
Brain size |
360 cc average |
Dentition |
Smaller than in extant great apes; larger and pointier than in humans. Canines worn at the tips. |
Cranial features |
A short cranial base and a foramen magnum (hole in which the spinal cord enters the cranium) that is more humanlike in positioning; has been argued to indicate upright walking. |
Postcranial features |
Currently little published postcranial material. |
Culture |
N/A |
Other |
The extent to which this hominin was bipedal is currently heavily debated. If so, it would indicate an arboreal bipedal ancestor of hominins, not a knuckle-walker like chimpanzees. |
Hominin |
Orrorin tugenensis |
Dates |
6 mya to 5.7 mya |
Region(s) |
Tugen Hills (Kenya) |
Famous discoveries |
Original discovery in 2000. |
Brain size |
N/A |
Dentition |
Smaller cheek teeth (molars and premolars) than even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines. |
Cranial features |
Not many found |
Postcranial features |
Fragmentary leg, arm, and finger bones have been found. Indicates bipedal locomotion. |
Culture |
Potential toolmaking capability based on hand morphology, but nothing found directly. |
Other |
This is the earliest species that clearly indicates adaptations for bipedal locomotion. |
Hominin |
Ardipithecus kadabba |
Dates |
5.2 mya to 5.8 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
Discovered by Yohannes Haile-Selassie in 1997. |
Brain size |
N/A |
Dentition |
Larger hind dentition than in modern chimpanzees. Thick enamel and larger canines than in later hominins. |
Cranial features |
N/A |
Postcranial features |
A large hallux (big toe) bone indicates a bipedal “push off.” |
Culture |
N/A |
Other |
Faunal evidence indicates a mixed grassland/woodland environment. |
Hominin |
Ardipithecus ramidus |
Dates |
4.4 mya |
Region(s) |
Middle Awash region and Gona (Ethiopia) |
Famous discoveries |
A partial female skeleton nicknamed “Ardi” (ARA-VP-6/500) (found in 1994). |
Brain size |
300 cc to 350 cc |
Dentition |
Little differences between the canines of males and females (small sexual dimorphism). |
Cranial features |
Midfacial projection, slightly prognathic. Cheekbones less flared and robust than in later hominins. |
Postcranial features |
Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, an opposable big toe similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. |
Culture |
None directly associated |
Other |
Over 110 specimens from Aramis |
Hominin |
Australopithecus anamensis |
Dates |
4.2 mya to 3.8 mya |
Region(s) |
Turkana region (Kenya); Middle Awash (Ethiopia) |
Famous discoveries |
A 2019 find from Ethiopia, named MRD. |
Brain size |
370 cc |
Dentition |
Relatively large canines compared with more recent Australopithecines. |
Cranial features |
Projecting cheekbones and ancestral earholes. |
Postcranial features |
Lower limb bones (tibia and femur) indicate bipedality; arboreal features in upper limb bones (humerus) found. |
Culture |
N/A |
Other |
Almost 100 specimens, representing over 20 individuals, have been found to date. |
Hominin |
Australopithecus afarensis |
Dates |
3.9 mya to 2.9 mya |
Region(s) |
Afar Region, Omo, Maka, Fejej, and Belohdelie (Ethiopia); Laetoli (Tanzania); Koobi Fora (Kenya) |
Famous discoveries |
Lucy (discovery: 1974), Selam (Dikika Child, discovery: 2000), Laetoli Footprints (discovery: 1976). |
Brain size |
380 cc to 430 cc |
Dentition |
Reduced canines and molars relative to great apes but larger than in modern humans. |
Cranial features |
Prognathic face, facial features indicate relatively strong chewing musculature (compared with Homo) but less extreme than in Paranthropus. |
Postcranial features |
Clear evidence for bipedalism from lower limb postcranial bones. Laetoli Footprints indicate humanlike walking. Dikika Child bones indicate retained ancestral arboreal traits in the postcrania. |
Culture |
None directly, but close in age and proximity to controversial cut marks at Dikika and early tools in Lomekwi. |
Other |
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. |
Hominin |
Australopithecus bahrelghazali |
Dates |
3.6 mya |
Region(s) |
Chad |
Famous discoveries |
“Abel,” the holotype (discovery: 1995). |
Brain size |
N/A |
Dentition |
N/A |
Cranial features |
N/A |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Arguably within range of variation of Au. afarensis. |
Hominin |
Australopithecus prometheus |
Dates |
3.7 mya (debated) |
Region(s) |
Sterkfontein (South Africa) |
Famous discoveries |
“Little Foot” (StW 573) (discovery: 1994) |
Brain size |
408 cc (Little Foot estimate) |
Dentition |
Heavy anterior dental wear patterns, relatively large anterior dentition and smaller hind dentition, similar to Au. afarensis. |
Cranial features |
Relatively larger brain size, robust zygomatic arch, and a flatter midface. |
Postcranial features |
The initial discovery of four ankle bones indicated bipedality. |
Culture |
N/A |
Other |
Highly debated new species designation. |
Hominin |
Australopithecus deyiremada |
Dates |
3.5 mya to 3.3 mya |
Region(s) |
Woranso-Mille (Afar region, Ethiopia) |
Famous discoveries |
First fossil mandible bones were discovered in 2011 in the Afar region of Ethiopia by Yohannes Haile-Selassie. |
Brain size |
N/A |
Dentition |
Smaller teeth with thicker enamel than seen in Au. afarensis, with a potentially hardier diet. |
Cranial features |
Larger mandible and more projecting cheekbones than in Au. afarensis. |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Contested species designation; arguably a member of Au. afarensis. |
Hominin |
Kenyanthopus platyops |
Dates |
3.5 mya to 3.2 mya |
Region(s) |
Lake Turkana (Kenya) |
Famous discoveries |
KNM–WT 40000 (discovered 1999) |
Brain size |
Difficult to determine but appears within the range of Australopithecus afarensis. |
Dentition |
Small molars/dentition (Homo-like characteristic) |
Cranial features |
Flatter (i.e., orthognathic) face |
Postcranial features |
N/A |
Culture |
Some have associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species/specimen. |
Other |
Taxonomic placing of this species is quite divided. The discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis. |
Hominin |
Australopithecus africanus |
Dates |
3.3 mya to 2.1 mya |
Region(s) |
Sterkfontein, Taung, Makapansgat, Gladysvale (South Africa) |
Famous discoveries |
Taung Child (discovery in 1994), “Mrs. Ples” (discover in 1947), Little Foot (arguable; discovery in 1994). |
Brain size |
400 cc to 500 cc |
Dentition |
Smaller teeth (derived) relative to Au. afarensis. Small canines with no diastema. |
Cranial features |
A rounder skull compared with Au. afarensis in East Africa. A sloping face (ancestral). |
Postcranial features |
Similar postcranial evidence for bipedal locomotion (derived pelvis) with retained arboreal locomotion, e.g., curved phalanges (fingers), as seen in Au. afarensis. |
Culture |
None with direct evidence. |
Other |
A 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities. |
Hominin |
Australopithecus garhi |
Dates |
2.5 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
N/A |
Brain size |
450 cc |
Dentition |
Larger hind dentition than seen in other gracile Australopithecines. |
Cranial features |
N/A |
Postcranial features |
A femur of a fragmentary partial skeleton, argued to belong to Au. garhi, indicates this species may be longer-limbed than Au. afarensis, although still able to move arboreally. |
Culture |
Crude stone tools resembling Oldowan (described later) have been found in association with Au. garhi. |
Other |
This species is not well documented or understood and is based on only a few fossil specimens. |
Hominin |
Paranthropus aethiopicus |
Dates |
2.7 mya to 2.3 mya |
Region(s) |
West Turkana (Kenya); Laetoli (Tanzania); Omo River Basin (Ethiopia) |
Famous discoveries |
The “Black Skull” (KNM–WT 17000) (discovery 1985). |
Brain Size |
410 cc |
Dentition |
P. aethiopicus has the shared derived traits of large flat premolars and molars, although few teeth have been found. |
Cranial features |
Large flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle), a sagittal crest for increased muscle attachment of the chewing muscles to the skull, and a robust mandible and supraorbital torus (brow ridge). |
Postcranial features |
A proximal tibia indicates bipedality and similar size to Au. afarensis. |
Culture |
N/A |
Other |
The “Black Skull” is so called because of the mineral manganese that stained it black during fossilization. |
Hominin |
Paranthropus boisei |
Dates |
2.4 mya to 1.4 mya |
Region(s) |
Koobi Fora, West Turkana, and Chesowanja (Kenya); Malema-Chiwondo (Malawi), Olduvai Gorge and Peninj (Tanzania); and Omo River basin and Konso (Ethiopia) |
Famous discoveries |
“Zinj,” or sometimes “Nutcracker Man” (OH5), in 1959 by Mary Leakey. The Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu. |
Brain size |
500 cc to 550 cc |
Dentition |
Very large, flat posterior dentition (largest of all hominins currently known). Much smaller anterior dentition. Very thick dental enamel. |
Cranial features |
Indications of very large chewing muscles (e.g., flaring zygomatic arches and a large sagittal crest). |
Postcranial features |
Evidence for high variability and sexual dimorphism, with estimates of males at 1.37 meters tall and females at 1.24 meters. |
Culture |
Richard Leakey and Bernard Wood have both suggested that P. boisei could have made and used stone tools. Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. |
Other |
Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). This differs from what is seen in P. robustus. |
Hominin |
Australopithecus sediba |
Dates |
1.97 mya |
Region(s) |
Malapa Fossil Site (South Africa) |
Famous discoveries |
Karabo (MH1) (discovery in 2008) |
Brain size |
420 cc to 450 cc |
Dentition |
Small dentition with Australopithecine cusp-spacing. |
Cranial features |
Small brain size (Australopithecus-like) but gracile mandible (Homo-like). |
Postcranial features |
Scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (tree climbing, particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. |
Culture |
None of direct association, but some have argued that a modern hand morphology (shorter fingers and a longer thumb) means that adaptations to tool manufacture and use may be present in this species. |
Other |
It was first discovered through a clavicle bone in 2008 by nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger. |
Hominin |
Paranthropus robustus |
Dates |
2.3 mya to 1 mya |
Region(s) |
Kromdraai B, Swartkrans, Gondolin, Drimolen, and Coopers Cave (South Africa) |
Famous discoveries |
SK48 (original skull) |
Brain size |
410 cc to 530 cc |
Dentition |
Large posterior teeth with thick enamel, consistent with other Robust Australopithecines. Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick enameled dentition. |
Cranial features |
P. robustus features are neither as “hyper-robust” as P. boisei or as ancestral in features as P. aethiopicus. They have been described as less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring). |
Postcranial features |
Reconstructions indicate sexual dimorphism. |
Culture |
N/A |
Other |
Several of these fossils are fragmentary in nature, distorted, and not well preserved, because they have been recovered from quarry breccia using explosives. |
Review Questions
- What is the difference between a “derived” versus an “ancestral” trait? Give an example of both, seen in Au. afarensis.
- Which of the paleoenvironment hypotheses have been used to describe early hominin diversity, and which have been used to describe bipedalism?
- Which anatomical features for bipedalism do we see in early hominins?
- Describe the dentition of gracile and robust australopithecines. What might these tell us about their diets?
- List the hominin species argued to be associated with stone tool technologies. Are you convinced of these associations? Why/why not?
Key Terms
Arboreal: Related to trees or woodland.
Aridification: Becoming increasingly arid or dry, as related to the climate or environment.
Aridity Hypothesis: The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution.
Assemblage: A collection demonstrating a pattern. Often pertaining to a site or region.
Bipedalism: The locomotor ability to walk on two legs.
Breccia: Hard, calcareous sedimentary rock.
Canines: The pointy teeth just next to the incisors, in the front of the mouth.
Cheek teeth: Or hind dentition (molars and premolars).
Chronospecies: Species that are said to evolve into another species, in a linear fashion, over time.
Clade: A group of species or taxa with a shared common ancestor.
Cladistics: The field of grouping organisms into those with shared ancestry.
Context: As pertaining to palaeoanthropology, this term refers to the place where an artifact or fossil is found.
Cores: The remains of a rock that has been flaked or knapped.
Cusps: The ridges or “bumps” on the teeth.
Dental formula: A technique to describe the number of incisors, canines, premolars, and molars in each quadrant of the mouth.
Derived traits: Newly evolved traits that differ from those seen in the ancestor.
Diastema: A tooth gap between the incisors and canines.
Early Stone Age (ESA): The earliest-described archaeological period in which we start seeing stone-tool technology.
East African Rift System (EARS): This term is often used to refer to the Rift Valley, expanding from Malawi to Ethiopia. This active geological structure is responsible for much of the visibility of the paleoanthropological record in East Africa.
Enamel: The highly mineralized outer layer of the tooth.
Encephalization: Expansion of the brain.
Extant: Currently living—i.e., not extinct.
Fallback foods: Foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
Fauna: The animals of a particular region, habitat, or geological period.
Faunal assemblages: Collections of fossils of the animals found at a site.
Faunal turnover: The rate at which species go extinct and are replaced with new species.
Flake: The piece knocked off of a stone core during the manufacture of a tool, which may be used as a stone tool.
Flora: The plants of a particular region, habitat, or geological period.
Folivorous: Foliage-eating.
Foramen magnum: The large hole (foramen) at the base of the cranium, through which the spinal cord enters the skull.
Fossil: The remains or impression of an organism from the past.
Frugivorous: Fruit-eating.
Generalist: A species that can thrive in a wide variety of habitats and can have a varied diet.
Glacial: Colder, drier periods during an ice age when there is more ice trapped at the poles.
Gracile: Slender, less rugged, or pronounced features.
Hallux: The big toe.
Holotype: A single specimen from which a species or taxon is described or named.
Hominin: A primate category that includes humans and our fossil relatives since our divergence from extant great apes.
Honing P3: The mandibular premolar alongside the canine (in primates, the P3), which is angled to give space for (and sharpen) the upper canines.
Hyper-robust: Even more robust than considered normal in the Paranthropus genus.
Hypodigm: A sample (here, fossil) from which researchers extrapolate features of a population.
Incisiform: An adjective referring to a canine that appears more incisor-like in morphology.
Incisors: The teeth in the front of the mouth, used to bite off food.
Interglacial: A period of milder climate in between two glacial periods.
Isotopes: Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses.
Knappers: The people who fractured rocks in order to manufacture tools.
Knapping: The fracturing of rocks for the manufacture of tools.
Large Cutting Tool (LCT): A tool that is shaped to have functional edges.
Last Common Ancestor (LCA): The hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence.
Lithic: Relating to stone (here to stone tools).
Lumbar lordosis: The inward curving of the lower (lumbar) parts of the spine. The lower curve in the human S-shaped spine.
Lumpers: Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
Megadont: An organism with extremely large dentition compared with body size.
Metacarpals: The long bones of the hand that connect to the phalanges (finger bones).
Molars: The largest, most posterior of the hind dentition.
Monophyletic: A taxon or group of taxa descended from a common ancestor that is not shared with another taxon or group.
Morphology: The study of the form or size and shape of things; in this case, skeletal parts.
Mosaic evolution: The concept that evolutionary change does not occur homogeneously throughout the body in organisms.
Obligate bipedalism: Where the primary form of locomotion for an organism is bipedal.
Occlude: When the teeth from the maxilla come into contact with the teeth in the mandible.
Oldowan: Lower Paleolithic, the earliest stone tool culture.
Orthognathic: The face below the eyes is relatively flat and does not jut out anteriorly.
Paleoanthropologists: Researchers that study human evolution.
Paleoenvironment: An environment from a period in the Earth’s geological past.
Parabolic: Like a parabola (parabola-shaped).
Phalanges: Long bones in the hand and fingers.
Phylogenetics: The study of phylogeny.
Phylogeny: The study of the evolutionary relationships between groups of organisms.
Pliocene: A geological epoch between the Miocene and Pleistocene.
Polytypic: In reference to taxonomy, having two or more group variants capable of interacting and breeding biologically but having morphological population differences.
Postcranium: The skeleton below the cranium (head).
Premolars: The smallest of the hind teeth, behind the canines.
Procumbent: In reference to incisors, tilting forward.
Prognathic: In reference to the face, the area below the eyes juts anteriorly.
Quaternary Ice Age: The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles.
Relative dating: Dating techniques that refer to a temporal sequence (i.e., older or younger than others in the reference) and do not estimate actual or absolute dates.
Robust: Rugged or exaggerated features.
Site: A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
Specialist: A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
Splitters: Researchers who prefer to split a highly variable taxon into multiple groups or species.
Taxa: Plural of taxon, a taxonomic group such as species, genus, or family.
Taxonomy: The science of grouping and classifying organisms.
Techno-complex: A term encompassing multiple assemblages that share similar traits in terms of artifact production and morphology.
Thermoregulation: Maintaining body temperature through physiologically cooling or warming the body.
Ungulates: Hoofed mammals—e.g., cows and kudu.
Volcanic tufts: Rock made from ash from volcanic eruptions in the past.
Valgus knee: The angle of the knee between the femur and tibia, which allows for weight distribution to be angled closer to the point above the center of gravity (i.e., between the feet) in bipeds.
About the Authors
Kerryn Warren, Ph.D.
Grad Coach International, kerryn.warren@gmail.com
Kerryn Warren is a dissertation coach at Grad Coach International and is passionate about stimulating research thinking in students of all levels. She has lectured on multiple topics, including archaeology and human evolution, with her research and science communication interests including hybridization in the hominin fossil record (stemming from research from her Ph.D.) and understanding how evolution is taught in South African schools. She also worked as one of the “Underground Astronauts,” selected to excavate Homo naledi remains from the Rising Star Cave System in the Cradle of Humankind.
K. Lindsay Hunter, M.A., Ph.D. candidate
CARTA, k.lindsay.hunter@gmail.com
Lindsay Hunter is a trained palaeoanthropologist who uses her more than 15 years of experience to make sense of the distant past of our species to build a better future. She received her master’s degree in biological anthropology from the University of Iowa and is completing her Ph.D. in archaeology at the University of the Witwatersrand in Johannesburg, South Africa. She has studied fossil and human bone collections across five continents with major grant support from the National Science Foundation (United States) and the Wenner-Gren Foundation for Anthropological Research. As a National Geographic Explorer, Lindsay developed and managed the National Geographic–sponsored Umsuka Public Palaeoanthropology Project in the Cradle of Humankind World Heritage Site (CoH WHS) in South Africa from within Westbury Township, Johannesburg, between 2016–2019. She currently serves as the Community Engagement & Advancement Director for CARTA: The UC San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny in La Jolla, California.
Navashni Naidoo, M.Sc.
University of Cape Town, nnaidoo2@illinois.edu
Navashni Naidoo is a researcher at Nelson Mandela University, lecturing on physical geology. She completed her Master’s in Science in Archaeology in 2017 at the University of Cape Town. Her research interests include developing paleoenvironmental proxies suited to the African continent, behavioral ecology, and engaging with community-driven archaeological projects. She has excavated at Stone Age sites across Southern Africa and East Africa. Navashni is currently pursuing a PhD in the Department of Anthropology at the University of Illinois.
Silindokuhle Mavuso, M.Sc.
University of Witwatersrand, S.muvaso@ru.ac.za
Silindokuhle has always been curious about the world around him and how it has been shaped. He is a lecturer at Rhodes University of Witwatersrand (Wits), and conducts research on palaeoenvironmental reconstruction and change of the northeastern Turkana Basin’s Pleistocene sequence. Silindokuhle began his education with a B.Sc. (Geology, Archaeology, and Environmental and Geographical Sciences) from the University of Cape Town before moving to Wits for a B.Sc. Honors (geology and paleontology) and M.Sc. in geology. He is currently concluding his PhD Studies. During this time, he has gained more training as a Koobi Fora Fieldschool fellow (Kenya) as well as an Erasmus Mundus scholar (France). Silindokuhle is a Plio-Pleistocene geologist with a specific focus on identifying and explaining past environments that are associated with early human life and development through time. He is interested in a wide range of disciplines such as micromorphology, sedimentology, geochemistry, geochronology, and sequence stratigraphy. He has worked with teams from significant eastern and southern African hominid sites including Elandsfontein, Rising Star, Sterkfontein, Gondolin, Laetoli, Olduvai, and Koobi Fora.
For Further Exploration
The Smithsonian Institution website hosts descriptions of fossil species, an interactive timeline, and much more.
The Maropeng Museum website hosts a wealth of information regarding South African Fossil Bearing sites in the Cradle of Humankind.
This quick comparison between Homo naledi and Australopithecus sediba from the Perot Museum.
This explanation of the braided stream by the Perot Museum.
A collation of 3-D files for visualizing (or even 3-D printing) for homes, schools, and universities.
PBS learning materials, including videos and diagrams of the Laetoli footprints, bipedalism, and fossils.
A wealth of information from the Australian Museum website, including species descriptions, family trees, and explanations of bipedalism and diet.
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Acknowledgements
All of the authors in this section are students and early career researchers in paleoanthropology and related fields in South Africa (or at least have worked in South Africa). We wish to thank everyone who supports young and diverse talent in this field and would love to further acknowledge Black, African, and female academics who have helped pave the way for us.
Kerryn Warren, Ph.D., Grad Coach International
Lindsay Hunter, M.A., University of Iowa
Navashni Naidoo, M.Sc., University of Cape Town
Silindokuhle Mavuso, M.Sc., University of Witwatersrand
This chapter is a revision from "Chapter 9: Early Hominins" by Kerryn Warren, K. Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, and Nomawethu Hlazo. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Understand what is meant by “derived” and “ancestral” traits and why this is relevant for understanding early hominin evolution.
- Understand changing paleoclimates and paleoenvironments as potential factors influencing early hominin adaptations.
- Describe the anatomical changes associated with bipedalism and dentition in early hominins, as well as their implications..
- Describe early hominin genera and species, including their currently understood dates and geographic expanses.
- Describe the earliest stone tool techno-complexes and their impact on the transition from early hominins to our genus.
Defining Hominins
It is through our study of our hominin ancestors and relatives that we are exposed to a world of “might have beens”: of other paths not taken by our species, other ways of being human. But to better understand these different evolutionary trajectories, we must first define the terms we are using. If an imaginary line were drawn between ourselves and our closest relatives, the great apes, bipedalism (or habitually walking upright on two feet) is where that line would be. Hominin, then, means everyone on “our” side of the line: humans and all of our extinct bipedal ancestors and relatives since our divergence from the last common ancestor (LCA) we share with chimpanzees.
Historic interpretations of our evolution, prior to our finding of early hominin fossils, varied. Debates in the mid-1800s regarding hominin origins focused on two key issues:
- Where did we evolve?
- Which traits evolved first?
Charles Darwin hypothesized that we evolved in Africa, as he was convinced that we shared greater commonality with chimpanzees and gorillas on the continent (Darwin 1871). Others, such as Ernst Haeckel and Eugène Dubois, insisted that we were closer in affinity to orangutans and that we evolved in Eurasia where, until the discovery of the Taung Child in South Africa in 1924, all humanlike fossils (of Neanderthals and Homo erectus) had been found (Shipman 2002).
Within this conversation, naturalists and early paleoanthropologists (people who study human evolution) speculated about which human traits came first. These included the evolution of a big brain (encephalization), the evolution of the way in which we move about on two legs (bipedalism), and the evolution of our flat faces and small teeth (indications of dietary change). Original hypotheses suggested that, in order to be motivated to change diet and move about in a bipedal fashion, the large brain needed to have evolved first, as is seen in the fossil species mentioned above.
However, we now know that bipedal locomotion is one of the first things that evolved in our lineage, with early relatives having more apelike dentition and small brain sizes. While brain size expansion is seen primarily in our genus, Homo, earlier hominin brain sizes were highly variable between and within taxa, from 300 cc (cranial capacity, cm3), estimated in Ardipithecus, to 550 cc, estimated in Paranthropus boisei. The lower estimates are well within the range of variation of nonhuman extant great apes. In addition, body size variability also plays a role in the interpretation of whether brain size could be considered large or small for a particular species or specimen. In this chapter, we will tease out the details of early hominin evolution in terms of morphology (i.e. the study of the form, size, or shape of things; in this case, skeletal parts).
We also know that early human evolution occurred in a very complicated fashion. There were multiple species (multiple genera) that featured diversity in their diets and locomotion. Specimens have been found all along the East African Rift System (EARS); that is, in Ethiopia, Kenya, Tanzania, and Malawi; see Figure 9.1), in limestone caves in South Africa, and in Chad. Dates of these early relatives range from around 7 million years ago (mya) to around 1 mya, overlapping temporally with members of our genus, Homo.

Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another, and they consider which of these species were able to make and use tools. As a result, every site discovery in the patchy hominin fossil record tells us more about our evolution. In addition, recent scientific techniques (not available even ten years ago) provide new insights into the diets, environments, and lifestyles of these ancient relatives.
In the past, taxonomy was primarily based on morphology. Today it is tied to known relationships based on molecular phylogeny (e.g., based on DNA) or a combination of the two. This is complicated when applied to living taxa, but becomes much more difficult when we try to categorize ancestor-descendant relationships for long-extinct species whose molecular information is no longer preserved. We therefore find ourselves falling back on morphological comparisons, often of teeth and partially fossilized skeletal material.
It is here that we turn to the related concepts of cladistics and phylogenetics. Cladistics groups organisms according to their last common ancestors based on shared derived traits. In the case of early hominins, these are often morphological traits that differ from those seen in earlier populations. These new or modified traits provide evidence of evolutionary relationships, and organisms with the same derived traits are grouped in the same clade (Figure 9.2). For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade of birds. In this chapter, we will examine the grouping of the Robust Australopithecines, whose cranial and dental features differ from those of earlier hominins, and therefore are considered derived.

Dig Deeper: Problems Defining Hominin Species
It is worth noting that species designations for early hominin specimens are often highly contested. This is due to the fragmentary nature of the fossil record, the large timescale (millions of years) with which paleoanthropologists need to work, and the difficulty in evaluating whether morphological differences and similarities are due to meaningful phylogenetic or biological differences or subtle differences/variation in niche occupation or time. In other words, do morphological differences really indicate different species? How would classifying species in the paleoanthropological record compare with classifying living species today, for whom we can sequence genomes and observe lifestyles?
There are also broader philosophical differences among researchers when it comes to paleo-species designations. Some scientists, known as “lumpers,” argue that large variability is expected among multiple populations in a given species over time. These researchers will therefore prefer to “lump” specimens of subtle differences into single taxa. Others, known as “splitters,” argue that species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences. In general, splitters would consider geographic differences among populations as meaning that a species is polytypic (i.e., capable of interacting and breeding biologically but having morphological population differences). This is worth keeping in mind when learning about why species designations may be contested.

This further plays a role in evaluating ancestry. Debates over which species “gave rise” to which continue to this day. It is common to try to create “lineages” of species to determine when one species evolved into another over time. We refer to these as chronospecies (Figure 9.3). Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record. More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
Finally, it is worth considering the process of fossil discovery and publication. Some fossils are easily diagnostic to a species level and allow for easy and accurate interpretation. Some, however, are more controversial. This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species (e.g., a fossil of a patella or knee bone). Researchers often need to make several important claims when announcing or publishing a find: a secure date (if possible), clear association with other finds, and an adequate comparison among multiple species (both extant and fossil). Therefore, it is not uncommon that an important find was made years before it is scientifically published.
Paleoenvironment and Hominin Evolution
There is no doubt that one of the major selective pressures in hominin evolution is the environment. Large-scale changes in global and regional climate, as well as alterations to the environment, are (thought to be) all linked to (all) hominin diversification, dispersal, and extinction (Maslin et al. 2014). Environmental reconstructions often use modern analogues. Let us take, for instance, the hippopotamus. It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive. Such instances have occurred multiple times in the past, and the bones of some fauna (i.e., animals, like the hippopotamus) that are sensitive to these changes give us insights into these events.
Yet reconstructing a paleoenvironment relies on a range of techniques, which vary depending on whether research interests focus on local changes or more global environmental changes/reconstructions. For local environments (such as a single site or region), comparing the faunal assemblages (collections of fossils of animals found at a site) with animals found in certain modern environments allows us to determine if past environments mirror current ones in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes. Other techniques are also useful in this regard. Chemical analyses, for instance, can reveal the diets of individual fauna, providing clues as to the relative wetness or dryness of their environment (e.g., nitrogen isotopes; Kingston and Harrison 2007).
Global climatic changes in the distant past, which fluctuated between being colder and drier and warmer and wetter on average, would have global implications for environmental change (Figure 9.4). These can be studied by comparing marine core and terrestrial soil data across multiple sites. These techniques are based on chemical analysis, such as examination of the nitrogen and oxygen isotopes in shells and sediments. Similarly, analyzing pollen grains shows which kinds of flora survived in an environment at a specific time period. There are multiple lines of evidence that allow us to visualize global climate trends over millions of years (although it should be noted that the direction and extent of these changes could differ by geographic region).

Both local and global climatic/environmental changes have been used to understand factors affecting our evolution (DeHeinzelin et al. 1999; Kingston 2007). Environmental change acts as an important factor regarding the onset of several important hominin traits seen in early hominins and discussed in this chapter. Namely, the environment has been interpreted as the following:
- the driving force behind the evolution of bipedalism,
- the reason for change and variation in early hominin diets, and
- the diversification of multiple early hominin species.
There are numerous hypotheses regarding how climate has driven and continues to drive human evolution. Here, we will focus on just three popular hypotheses.
Savannah Hypothesis (or Aridity Hypothesis)
The hypothesis: This popular theory suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion (Figure 9.5). It was first proposed by Darwin (1871) and supported by anthropologists like Raymond Dart (1925). However, this idea was supported by little fossil or paleoenvironmental evidence and was later refined as the Aridity Hypothesis. This hypothesis states that the long-term aridification and, thereby, expansion of savannah biomes were drivers in diversification in early hominin evolution (deMenocal 2004; deMenocal and Bloemendal 1995). It advocates for periods of accelerated aridification leading to early hominin speciation events.

The evidence: While early bipedal hominins are often associated with wetter, more closed environments (i.e., not the Savannah Hypothesis), both marine and terrestrial records seem to support general cooling, drying conditions, with isotopic records indicating an increase in grasslands (i.e., colder and wetter climatic conditions) between 8 mya and 6 mya across the African continent (Cerling et al. 2011). This can be contrasted with later climatic changes derived from aeolian dust records (sediments transported to the site of interest by wind), which demonstrate increases in seasonal rainfall between 3 mya and 2.6 mya, 1.8 mya and 1.6 mya, and 1.2 mya and 0.8 mya (deMenocal 2004; deMenocal and Bloemendal 1995).
Interpretation(s): Despite a relatively scarce early hominin record, it is clear that two important factors occur around the time period in which we see increasing aridity. The first factor is the diversification of taxa, where high morphological variation between specimens has led to the naming of multiple hominin genera and species. The second factor is the observation that the earliest hominin fossils appear to have traits associated with bipedalism and are dated to around the drying period (as based on isotopic records). Some have argued that it is more accurately a combination of bipedalism and arboreal locomotion, which will be discussed later. However, the local environments in which these early specimens are found (as based on the faunal assemblages) do not appear to have been dry.
Turnover Pulse Hypothesis
The hypothesis: In 1985, paleontologist Elisabeth Vbra noticed that in periods of extreme and rapid climate change, ungulates (hoofed mammals of various kinds) that had generalized diets fared better than those with specialized diets (Vrba 1988, 1998). Specialist eaters (those who rely primarily on specific food types) faced extinction at greater rates than their generalist (those who can eat more varied and variable diets) counterparts because they were unable to adapt to new environments (Vrba 2000). Thus, periods with extreme climate change would be associated with high faunal turnover: that is, the extinction of many species and the speciation, diversification, and migration of many others to occupy various niches.
The evidence: The onset of the Quaternary Ice Age, between 2.5 mya and 3 mya, brought extreme global, cyclical interglacial and glacial periods (warmer, wetter periods with less ice at the poles, and colder, drier periods with more ice near the poles). Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites (Behrensmeyer et al. 1997; Bobe and Behrensmeyer 2004). Similarly, work in the Cape Floristic Belt of South Africa shows that extreme changes in climate play a role in extinction and migration in ungulates. While this theory was originally developed for ungulates, its proponents have argued that it can be applied to hominins as well. However, the link between climate and speciation is only vaguely understood (Faith and Behrensmeyer 2013).
Interpretation(s): While the evidence of rapid faunal turnover among ungulates during this time period appears clear, there is still some debate around its usefulness as applied to the paleoanthropological record. Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct.
Variability Selection Hypothesis
The hypothesis: This hypothesis was first articulated by paleoanthropologist Richard Potts (1998). It links the high amount of climatic variability over the last 7 million years to both behavioral and morphological changes. Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context (Potts 1998, 2013). The Variability Selection Hypothesis states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations (Potts 2013).
The evidence: The evidence for this theory is similar to that for the Turnover Pulse Hypothesis: large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
Interpretation(s): In this way, the Variability Selection Hypothesis allows for a more flexible interpretation of the evolution of bipedalism in hominins and a more fluid interpretation of the Turnover Pulse Hypothesis, where species turnover is meant to be more rapid. In some ways, this hypothesis accommodates both environmental data and our interpretations of an evolution toward greater variability among species and the survivability of generalists.
Paleoenvironment Summary
Some hypotheses presented in this section pay specific attention to habitat (Savannah Hypothesis) while others point to large-scale climatic forces (Variability Selection Hypothesis). Some may be interpreted to describe the evolution of traits such as bipedalism (Savannah Hypothesis), and others generally explain the diversification of early hominins (Turnover Pulse and Variability Selection Hypotheses). While there is no consensus as to how the environment drove our evolution, it is clear that the environment shaped both habitat and resource availability in ways that would have influenced our early ancestors physically and behaviorally.
Derived Adaptations: Bipedalism
The unique form of locomotion exhibited by modern humans, called obligate bipedalism, is important in distinguishing our species from the extant (living) great apes. The ability to walk habitually upright is thus considered one of the defining attributes of the hominin lineage. We also differ from other animals that walk bipedally (such as kangaroos) in that we do not have a tail to balance us as we move.
The origin of bipedalism in hominins has been debated in paleoanthropology, but at present there are two main ideas: (theories)
- early hominins initially lived in trees, but increasingly started living on the ground, so we were a product of an arboreal last common ancestor (LCA) or,
- our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
Most research supports the first theory of an arboreal LCA based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking. This would mean that both humans and chimpanzees can be considered “derived” in terms of locomotion since chimpanzees would have independently evolved knuckle-walking.
There are many current ideas regarding selective pressures that would lead to early hominins adapting upright posture and locomotion. Many of these selective pressures, as we have seen in the previous section, coincide with a shift in environmental conditions, supported by paleoenvironmental data. In general, however, it appears that, like extant great apes, early hominins thrived in forested regions with dense tree coverage, which would indicate an arboreal lifestyle. As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse such that bipedalism would become more important.
There are several proposed selective pressures for bipedalism:
- Energy conservation: Modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land. While chimpanzees, for instance, are faster than humans terrestrially, they expend large amounts of energy being so. Adaptations to bipedalism include “stacking” the majority of the weight of the body over a small area around the center of gravity (i.e., the head is above the chest, which is above the pelvis, which is over the knees, which are above the feet). This reduces the amount of muscle needed to be engaged during locomotion to “pull us up” and allows us to travel longer distances expending far less energy.
- Thermoregulation: Less surface area (i.e., only the head and shoulders) is exposed to direct sunlight during the hottest parts of the day (i.e., midday). This means that the body has less need to employ additional “cooling” mechanisms such as sweating, which additionally means less water loss.
- Bipedalism (Freeing of Hands): This method of locomotion freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use of tools.
These selective pressures are not mutually exclusive. Bipedality could have evolved from a combination of these selective pressures, in ways that increased the chances of early hominin survival.
Skeletal Adaptations for Bipedalism

Humans have highly specialized adaptations to facilitate obligate bipedalism (Figure 9.6). Many of these adaptations occur within the soft tissue of the body (e.g., muscles and tendons). However, when analyzing the paleoanthropological record for evidence of the emergence of bipedalism, all that remains is the fossilized bone. Interpretations of locomotion are therefore often based on comparative analyses between fossil remains and the skeletons of extant primates with known locomotor behaviors. These adaptations occur throughout the skeleton and are summarized in Figure 9.7.
The majority of these adaptations occur in the postcranium (the skeleton from below the head) and are outlined in Figure 9.7. In general, these adaptations allow for greater stability and strength in the lower limb, by allowing for more shock absorption, for a larger surface area for muscle attachment, and for the “stacking” of the skeleton directly over the center of gravity to reduce energy needed to be kept upright. These adaptations often mean less flexibility in areas such as the knee and foot.
However, these adaptations come at a cost. Evolving from a nonobligate bipedal ancestor means that the adaptations we have are evolutionary compromises. For instance, the valgus knee (angle at the knee) is an essential adaptation to balance the body weight above the ankle during bipedal locomotion. However, the strain and shock absorption at an angled knee eventually takes its toll. For example, runners often experience joint pain. Similarly, the long neck of the femur absorbs stress and accommodates for a larger pelvis, but it is a weak point, resulting in hip replacements being commonplace among the elderly, especially in cases where the bone additionally weakens through osteoporosis. Finally, the S-shaped curve in our spine allows us to stand upright, relative to the more curved C-shaped spine of an LCA. Yet the weaknesses in the curves can lead to pinching of nerves and back pain. Since many of these problems primarily are only seen in old age, they can potentially be seen as an evolutionary compromise.
Despite relatively few postcranial fragments, the fossil record in early hominins indicates a complex pattern of emergence of bipedalism. Key features, such as a more anteriorly placed foramen magnum, are argued to be seen even in the earliest discovered hominins, indicating an upright posture (Dart 1925). Some early species appear to have a mix of ancestral (arboreal) and derived (bipedal) traits, which indicates a mixed locomotion and a more mosaic evolution of the trait. Some early hominins appear to, for instance, have bowl-shaped pelvises (hip bones) and angled femurs suitable for bipedalism but also have retained an opposable hallux (big toe) or curved fingers and longer arms (for arboreal locomotion). These mixed morphologies may indicate that earlier hominins were not fully obligate bipeds and thus thrived in mosaic environments.
Yet the associations between postcranial and the more diagnostic cranial fossils and bones are not always clear, muddying our understanding of the specific species to which fossils belong (Grine et al. 2022).
Region | Feature | Obligate Biped (H. sapiens) | Nonobligate Biped |
Cranium | Position of the foramen magnum | Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground). | Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground. |
Post
cranium |
Body proportions | Shorter upper limb (not used for locomotion). | Longer upper limbs (used for locomotion). |
Post
cranium |
Spinal curvature | S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis). | C-curve. |
Post
cranium |
Vertebrae | Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission). | Gracile lumbar vertebrae compared to those of modern humans. |
Post
cranium |
Pelvis | Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces. | Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface. |
Post
cranium |
Lower limb | In general, longer, more robust lower limbs and more stable, larger joints.
|
In general, smaller, more gracile limbs with more flexible joints.
|
Post
cranium |
Foot | Rigid, robust foot, without a midtarsal break.
Nonopposable and large, robust big toe (for push off while walking) and large heel for shock absorbance. |
Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping. |
It is also worth noting that, while not directly related to bipedalism per se, other postcranial adaptations are evident in the hominin fossil record from some of the earlier hominins. For instance, the hand and finger morphologies of many of the earliest hominins indicate adaptations consistent with arboreality. These include longer hands, more curved metacarpals and phalanges (long bones in the hand and fingers, respectively), and a shorter, relatively weaker thumb. This allows for gripping onto curved surfaces during locomotion. The earliest hominins appear to have mixed morphologies for both bipedalism and arborealism. However, among Australopiths (members of the genus, Australopithecus), there are indications for greater reliance on bipedalism as the primary form of locomotion. Similarly, adaptations consistent with tool manufacture (shorter fingers and a longer, more robust thumb, in contrast to the features associated with arborealism) have been argued to appear before the genus Homo.
(Special Topic with student projects: fear of snakes, cultural or biological? Biology, culture, and the fear of snakes, Snake Detection Theory)

It is suggested that primates have three major predators: raptors, felines, and snakes; however, many studies show that of these carnivores, snakes were one of the first that mammals had to contend with alongside dinosaurs, as felines and raptors evolved at a much slower pace than their reptilian competition. Herpetologists trace the evolution of constricting snakes to about 100 million years ago, and by the time mammals arrived around 75 million years ago, constrictors were already well established as a formidable threat (Greene, 2017). Both co-existed for millennia and each sustained selective pressures requiring them to evolve specific traits to survive. When venomous snakes eventually emerged 55 to 65 million years ago, they posed yet an additional threat to proto-primates as they required less distance for the predator to kill (2017). Alongside camouflage and silent movement techniques, it was the development of the snake’s hollow fangs through which to deliver venom that was most transformative to primate evolution. As such, primates evolved their pre-conscious attention, and visual acuity to cope with this new threat; therefore, while snakes were adapting morphologically to feed themselves, they were unwittingly teaching proto-primates valuable lessons in predator detection and reacting appropriately in order to survive.
In a 2009 Harvard University study, Lynne A. Isbell hypothesizes that envenoming snakes are linked to being directly responsible for the origins of the evolving complex brains and superior visual capacity in the lineage of anthropoids leading to humans (Isbell, 2009). Forward-facing eyes for binocular vision, depth perception, enhanced visual acuity, stereoscopic and trichromatic colour vision, all traits necessary for snake detection; and the quick motor responses from the primate’s fight, flight, or freeze defence mechanism to circumvent a snake’s squeeze or bite. Numerous laboratory studies show that humans and primates both sense and visually detect snakes more rapidly than other threatening stimuli (Van Le Et al., 2013). These experiments show that snakes elicited the strongest, fastest responses (Van Le Et al., 2013). This is known as ‘Snake Detection Theory’ and is the evolution of the primate’s complex brain, visual acuity, and rapid motor responses towards snakes in its environment that are the adaptations needed to live successfully as arboreal beings. It is not fortuitous then, that primates that never coexisted with venomous snakes, such as lemurs in Madagascar, have less visual acuity, better olfaction and smaller brains. Within Isbell’s work, a collaborative study by a group of neuroscientists tested this hypothesis and found that, indeed, there is higher neural firing and activity in multiple areas of the primate brain, notably in the pulvinar, a region responsible for visual attention and oculomotor behaviour (Isbell, L., 2009).

Today, the fear of snakes is widespread in humans, often shown through avoidance and disgust. A study in The Journal of Ethnobiology and Ethnomedicine notes that snakes are over-hunted and excluded from conservation efforts worldwide (Ceríaco, 2012). While cultural factors shape our sentiments, instinct also plays a role—such as the developed avoidance behaviors toward threats like snakes. This blend of instinct and cultural influence is not only seen in behavior but also deeply embedded in the stories we tell. Many cultures depict mythological snakes as harbingers of death or chaos. In the Bible, Satan becomes a snake to tempt Eve. Norse mythology features Jörmungandr, the world serpent who signals the apocalypse. Egyptian myth tells of Apophis, who battles the sun god Ra nightly. Though sources vary, these myths consistently portray snakes as threats. As such, the widespread fear of snakes may reflect both evolutionary and cultural influences. Understood as an adaptive response inherited from primate ancestors—who developed avoidance behaviors toward potentially dangerous stimuli—and reinforced through myths and religious narratives, the enduring presence of snakes as potent figures of fear across human societies and primate groups highlights the complex intertwining of instinct and cultural meaning in shaping human behavior.
Early Hominins: Sahelanthropus and Orrorin
We see evidence for bipedalism in some of the earliest fossil hominins, dated from within our estimates of our divergence from chimpanzees. These hominins, however, also indicate evidence for arboreal locomotion.
The earliest dated hominin find (between 6 mya and 7 mya, based on radiometric dating of volcanic tufts) has been argued to come from Chad and is named Sahelanthropus tchadensis (Figure 9.8; Brunet et al. 1995). The initial discovery was made in 2001 by Ahounta Djimdoumalbaye and announced in Nature in 2002 by a team led by French paleontologist Michel Brunet. The find has a small cranial capacity (360 cc) and smaller canines than those in extant great apes, though they are larger and pointier than those in humans. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. A short cranial base and a foramen magnum that is more humanlike in positioning have been argued to indicate upright walking.

Initially, the inclusion of Sahelanthropus in the hominin family was debated by researchers, since the evidence for bipedalism is based on cranial evidence alone, which is not as convincing as postcranial evidence. Yet, a femur (thigh bone) and ulnae (upper arm bones) thought to belong to Sahelanthropus was discovered in 2001 (although not published until 2022). These bones may support the idea that the hominin was in fact a terrestrial biped with arboreal capabilities and behaviors (Daver et al. 2022).
Orrorin tugenensis (Orrorin meaning “original man”), dated to between 6 mya and 5.7 mya, was discovered near Tugen Hills in Kenya in 2000. Smaller cheek teeth (molars and premolars) than those in even more recent hominins, thick enamel, and reduced, but apelike, canines characterize this species. This is the first species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains. One of the most important elements discovered was a proximal femur, BAR 1002'00. The femur is the thigh bone, and the proximal part is that which articulates with the pelvis; this is very important for studying posture and locomotion. This femur indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins. Some have argued that features of the finger bones suggest potential tool-making capabilities, although many researchers argue that these features are also consistent with climbing.
Early Hominins: The Genus Ardipithecus
Another genus, Ardipithecus, is argued to be represented by at least two species: Ardipithecus (Ar.) ramidus and Ar. kadabba.
Ardipithecus ramidus (“ramid” means root in the Afar language) is currently the best-known of the earliest hominins (Figure 9.9). Unlike Sahelanthropus and Orrorin, this species has a large sample size of over 110 specimens from Aramis alone. Dated to 4.4 mya, Ar. ramidus was found in Ethiopia (in the Middle Awash region and in Gona). This species was announced in 1994 by American palaeoanthropologist Tim White, based on a partial female skeleton nicknamed “Ardi” (ARA-VP-6/500; White et al. 1994). Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, she had an opposable big toe (hallux), similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. A small brain (300 cc to 350 cc), midfacial projection, and slight prognathism show retained ancestral cranial features, but the cheek bones are less flared and robust than in later hominins.

Ardipithecus kadabba (the species name means “oldest ancestor” in the Afar language) is known from localities on the western margin of the Middle Awash region, the same locality where Ar. ramidus has been found. Specimens include mandibular fragments and isolated teeth as well as a few postcranial elements from the Asa Koma (5.5 mya to 5.77 mya) and Kuseralee Members (5.2 mya), well-dated and understood (but temporally separate) volcanic layers in East Africa. This species was discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie. Originally these specimens were referred to as a subspecies of Ar. ramidus. In 2002, six teeth were discovered at Asa Koma and the dental-wear patterns confirmed that this was a distinct species, named Ar. kadabba, in 2004. One of the postcranial remains recovered included a 5.2 million-year-old toe bone that demonstrated features that are associated with toeing off (pushing off the ground with the big toe leaving last) during walking, a characteristic unique to bipedal walkers. However, the toe bone was found in the Kuseralee Member, and therefore some doubt has been cast by researchers about its association with the teeth from the Asa Koma Member.
Bipedal Trends in Early Hominins: Summary
Trends toward bipedalism are seen in our earliest hominin finds. However, many specimens also indicate retained capabilities for climbing. Trends include a larger, more robust hallux; a more compact foot, with an arch; a robust, long femur, angled at the knee; a robust tibia; a bowl-shaped pelvis; and a more anterior foramen magnum. While the level of bipedality in Salehanthropus tchadenisis is debated since there are few fossils and no postcranial evidence, Orrorin tugenensis and Ardipithecus kadabba show clear indications of some of these bipedal trends. However, some retained ancestral traits, such as an opposable hallux in Ardipithecus, indicate some retention in climbing ability.
Derived Adaptations: Early Hominin Dention
The Importance of Teeth
Teeth are abundant in the fossil record, primarily because they are already highly mineralized as they are forming, far more so than even bone. Because of this, teeth preserve readily. And, because they preserve readily, they are well-studied and better understood than many skeletal elements. In the sparse hominin (and primate) fossil record, teeth are, in some cases, all we have.
Teeth also reveal a lot about the individual from whom they came. We can tell what they evolved to eat, to which other species they may be closely related, and even, to some extent, the level of sexual dimorphism, or general variability, within a given species. This is powerful information that can be contained in a single tooth. With a little more observation, the wearing patterns on a tooth can tell us about the diet of the individual in the weeks leading up to its death. Furthermore, the way in which a tooth is formed, and the timing of formation, can reveal information about changes in diet (or even mobility) over infancy and childhood, using isotopic analyses. When it comes to our earliest hominin relatives, this information is vital for understanding how they lived.
The purpose of comparing different hominin species is to better understand the functional morphology as it applies to dentition. In this, we mean that the morphology of the teeth or masticatory system (which includes jaws) can reveal something about the way in which they were used and, therefore, the kinds of foods these hominins ate. When comparing the features of hominin groups, it is worth considering modern analogues (i.e., animals with which to compare) to make more appropriate assumptions about diet. In this way, hominin dentition is often compared with that of chimpanzees and gorillas (our close ape relatives), as well as with that of modern humans.
The most divergent group, however, is humans. Humans around the world have incredibly varied diets. Among hunter-gatherers, it can vary from a honey- and plant-rich diet, as seen in the Hadza in Tanzania, to a diet almost entirely reliant on animal fat and protein, as seen in Inuits in polar regions of the world. We are therefore considered generalists, more general than the largely frugivorous (fruit-eating) chimpanzee or the folivorous (foliage-eating) gorilla, as discussed in Chapter 5.
One way in which all humans are similar is our reliance on the processing of our food. We cut up and tear meat with tools using our hands, instead of using our front teeth (incisors and canines). We smash and grind up hard seeds, instead of crushing them with our hind teeth (molars). This means that, unlike our ape relatives, we can rely more on developing tools to navigate our complex and varied diets. (We could say) Our brain, therefore, is our primary masticatory organ. Evolutionarily, our teeth have reduced in size and our faces are flatter, or more orthognathic, partially in response to our increased reliance on our hands and brain to process food. Similarly, a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat. These trends begin early on in our evolution. The link has been made between some of the earliest evidence for stone tool manufacture, the earliest members of our genus, and the features that we associate with these specimens.
General Dental Trends in Early Hominins
Several trends are visible in the dentition of early hominins. However, all tend to have the same dental formula. The dental formula tells us how many of each tooth type are present in each quadrant of the mouth. Going from the front of the mouth, this includes the square, flat incisors; the pointy canines; the small, flatter premolars; and the larger hind molars. In many primates, from Old World monkeys to great apes, the typical dental formula is 2:1:2:3. This means that if we divide the mouth into quadrants, each has two incisors, one canine, two premolars, and three molars. The eight teeth per quadrant total 32 teeth in all (although some humans have fewer teeth due to the absence of their wisdom teeth, or third molars).

The morphology of the individual teeth is where we see the most change. Among primates, large incisors are associated with food procurement or preparation (such as biting small fruits), while small incisors indicate a diet that may contain small seeds or leaves (where the preparation is primarily in the back of the mouth). Most hominins have relatively large, flat, vertically aligned incisors that occlude (touch) relatively well, forming a “bite.” This differs from, for instance, the orangutan, whose teeth stick out (i.e., are procumbent).
While the teeth are often aligned with diet, the canines may be misleading in that regard. We tend to associate pointy, large canines with the ripping required for meat, and the reduction (or, in some animals, the absence) of canines as indicative of herbivorous diets. In humans, our canines are often a similar size to our incisors and therefore considered incisiform (Figure 9.10). However, our closest relatives all have very long, pointy canines, particularly on their upper dentition. This is true even for the gorilla, which lives almost exclusively on plants. The canines in these instances reveal more about social structure and sexual dimorphism than diet, as large canines often signal dominance.
Early on in human evolution, we see a reduction in canine size. Sahelanthropus tchadensis and Orrorin tugenensis both have smaller canines than those in extant great apes, yet the canines are still larger and pointier than those in humans or more recent hominins. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. In Ardipithecus ramidus, there is no obvious difference between male and female canine size, yet they are still slightly larger and pointier than in modern humans. This implies a less sexually dimorphic social structure in the earlier hominins relative to modern-day chimpanzees and gorillas.
Along with a reduction in canine size is the reduction or elimination of a canine diastema: a gap between the teeth on the mandible that allows room for elongated teeth on the maxilla to “fit” in the mouth. Absence of a diastema is an excellent indication of a reduction in canine size. In animals with large canines (such as baboons), there is also often a honing P3, where the first premolar (also known as P3 for evolutionary reasons) is triangular in shape, “sharpened” by the extended canine from the upper dentition. This is also seen in some early hominins: Ardipithecus, for example, has small canines that are almost the same height as its incisors, although still larger than those in recent hominins.
The hind dentition, such as the bicuspid (two cusped) premolars or the much larger molars, are also highly indicative of a generalist diet in hominins. Among the earliest hominins, the molars are larger than we see in our genus, increasing in size to the back of the mouth and angled in such a way from the much smaller anterior dentition as to give these hominins a parabolic (V-shaped) dental arch. This differs from our living relatives and some early hominins, such as Sahelanthropus, whose molars and premolars are relatively parallel between the left and right sides of the mouth, creating a U-shape.
Among more recent early hominins, the molars are larger than those in the earliest hominins and far larger than those in our own genus, Homo. Large, short molars with thick enamel allowed our early cousins to grind fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing. In our genus, the hind dentition is far smaller than in these early hominins. Our teeth also have medium-size cusps, which allow for both efficient grinding and tearing/shearing meats.
Understanding the dental morphology has allowed researchers to extrapolate very specific behaviors of early hominins. It is worth noting that while teeth preserve well and are abundant, a slew of other morphological traits additionally provide evidence for many of these hypotheses. Yet there are some traits that are ambiguous. For instance, while there are definitely high levels of sexual dimorphism in Au. afarensis, discussed in the next section, the canine teeth are reduced in size, implying that while canines may be useful indicators for sexual dimorphism, it is also worth considering other evidence.
In summary, trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the ancestral dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
Special Topic: Contested Species
Many named species are highly debated and argued to have specimens associated with a more variable Au. afarensis or Au. anamensis species. Sometimes these specimens are dated to times when, or found in places in which, there are “gaps” in the palaeoanthropological record. These are argued to represent chronospecies or variants of Au. afarensis. However, it is possible that, with more discoveries, the distinct species types will hold.
Australopithecus bahrelghazali is dated to within the time period of Au. afarensis (3.6 mya; Brunet et al. 1995) and was the first Australopithecine to be discovered in Chad in central Africa. Researchers argue that the holotype, whom discoverers have named “Abel,” falls under the range of variation of Au. afarensis and therefore that A. bahrelghazali does not fall into a new species (Lebatard et al. 2008). If “Abel” is a member of Au. afarensis, the geographic range of the species would be greatly extended.
On a different note, Australopithecus deyiremada (meaning “close relative” in the Ethiopian language of Afar) is dated to 3.5 mya to 3.3 mya and is based on fossil mandible bones discovered in 2011 in Woranso-Mille (in the Afar region of Ethiopia) by Yohannes Haile-Selassie, an Ethiopian paleoanthropologist (Haile-Selassie et al. 2019). The discovery indicated, in contrast to Au. afarensis, smaller teeth with thicker enamel (potentially suggesting a harder diet) as well as a larger mandible and more projecting cheekbones. This find may be evidence that more than one closely related hominin species occupied the same region at the same temporal period (Haile-Selassie et al. 2015; Spoor 2015) or that other Au. afarensis specimens have been incorrectly designated. However, others have argued that this species has been prematurely identified and that more evidence is needed before splitting the taxa, since the variation appears subtle and may be due to slightly different niche occupations between populations over time.
Australopithecus garhi is another species found in the Middle Awash region of Ethiopia. It is currently dated to 2.5 mya (younger than Au. afarensis). Researchers have suggested it fills in a much-needed temporal “gap” between hominin finds in the region, with some anatomical differences, such as a relatively large cranial capacity (450 cc) and larger hind dentition than seen in other gracile Australopithecines. Similarly, the species has been argued to have longer hind limbs than Au. afarensis, although it was still able to move arboreally (Asfaw et al. 1999). However, this species is not well documented or understood and is based on only several fossil specimens. More astonishingly, crude stone tools resembling Oldowan (which will be described later) have been found in association with Au. garhi. While lacking some of the features of the Oldowan, this is one of the earliest technologies found in direct association with a hominin.
Kenyanthopus platyops (the name “platyops” refers to its flatter-faced appearance) is a highly contested genus/species designation of a specimen (KNM-WT 40000) from Lake Turkana in Kenya, discovered by Maeve Leakey in 1999 (Figure 9.11). Dated to between 3.5 mya and 3.2 mya, some have suggested this specimen is an Australopithecus, perhaps even Au. afarensis (with a brain size which is difficult to determine, yet appears small), while still others have placed this specimen in Homo (small dentition and flat-orthognathic face). While taxonomic placing of this species is quite divided, the discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis (Leakey et al. 2001). Some researchers have additionally associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this specimen.

The Genus Australopithecus
The Australopithecines are a diverse group of hominins, comprising various species. Australopithecus is the given group or genus name. It stems from the Latin word Australo, meaning “southern,” and the Greek word pithecus, meaning “ape.” Within this section, we will outline these differing species’ geological and temporal distributions across Africa, unique derived and/or shared traits, and importance in the fossil record.

Between 3 mya and 1 mya, there seems to be differences in dietary strategy between different species of hominins designated as Australopithecines. A pattern of larger posterior dentition (even relative to the incisors and canines in the front of the mouth), thick enamel, and cranial evidence for extremely large chewing muscles is far more pronounced in a group known as the robust australopithecines. This pattern is extremely relative to their earlier contemporaries or predecessors, the gracile australopithecines, and is certainly larger than those seen in early Homo, which emerged during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins (Figure 9.12).
Because of these differences, this section has been divided into “gracile” and “robust” Australopithecines, highlighting the morphological differences between the two groups (which many researchers have designated as separate genera: Australopithecus and Paranthropus, respectively) and then focusing on the individual species. It is worth noting, however, that not all researchers accept these clades as biologically or genetically distinct, with some researchers insisting that the relative gracile and robust features found in these species are due to parallel evolutionary events toward similar dietary niches.
Despite this genus’ ancestral traits and small cranial capacity, all members show evidence of bipedal locomotion. It is generally accepted that Australopithecus species display varying degrees of arborealism along with bipedality.
Gracile Australopithecines
This section describes individual species from across Africa. These species are called “gracile australopithecines” because of their smaller and less robust features compared to the divergent “robust” group. Numerous Australopithecine species have been named, but some are only based on a handful of fossil finds, whose designations are controversial.
East African Australopithecines
East African Australopithecines are found throughout the EARS, and they include the earliest species associated with this genus. Numerous fossil-yielding sites, such as Olduvai, Turkana, and Laetoli, have excellent, datable stratigraphy, owing to the layers of volcanic tufts that have accumulated over millions of years. These tufts may be dated using absolute dating techniques, such as Potassium-Argon dating (described in Chapter 7). This means that it is possible to know a relatively refined date for any fossil if the context (i.e., exact location) of that find is known. Similarly, comparisons between the faunal assemblages of these stratigraphic layers have allowed researchers to chronologically identify environmental changes.

The earliest known Australopithecine is dated to 4.2 mya to 3.8 mya. Australopithecus anamensis (after “Anam,” meaning “lake” from the Turkana region in Kenya; Leakey et al. 1995; Patterson and Howells 1967) is currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia; Figure 9.13). Recently, a 2019 find from Ethiopia, named MRD, after Miro Dora where it was found, was discovered by an Ethiopian herder named Ali Bereino. It is one of the most complete cranial finds of this species (Ward et al. 1999). A small brain size (370 cc), relatively large canines, projecting cheekbones, and earholes show more ancestral features as compared to those of more recent Australopithecines. The most important element discovered with this species is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking. Similarly, the earliest found hominin femur belongs to this species. Ancestral traits in the upper limb (such as the humerus) indicate some retained arboreal locomotion.
Some researchers suggest that Au. anamensis is an intermediate form of the chronospecies that becomes Au. afarensis, evolving from Ar. ramidus. However, this is debated, with other researchers suggesting morphological similarities and affinities with more recent species instead. Almost 100 specimens, representing over 20 individuals, have been found to date (Leakey et al. 1995; McHenry 2009; Ward et al. 1999).
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. Au. afarensis (which means “from the Afar region”) is dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia (Figure 9.14). The most famous individual from this species is a partial female skeleton discovered in Hadar (Ethiopia), later nicknamed “Lucy,” after the Beatles’ song “Lucy in the Sky with Diamonds,” which was played in celebration of the find (Johanson et al. 1978; Kimbel and Delezene 2009). This skeleton was found in 1974 by Donald Johanson and dates to approximately 3.2 mya. In addition, in 2002 a juvenile of the species was found by Zeresenay Alemseged and given the name “Selam” (meaning “peace,” DIK 1-1), though it is popularly known as “Lucy’s Child” or as the “Dikika Child” (Alemseged et al. 2006). Similarly, the “Laetoli Footprints” (discussed in Chapter 7; Hay and Leakey 1982; Leakey and Hay 1979) have drawn much attention.


The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans (indicative of a generalist diet); in addition, Au. afarensis has a prognathic face (the face below the eyes juts anteriorly) and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus. Despite a reduction in canine size in this species, large overall size variation indicates high levels of sexual dimorphism.
Skeletal evidence indicates that this species was bipedal, as its pelvis and lower limb demonstrate a humanlike femoral neck, valgus knee, and bowl-shaped hip (Figure 9.15). More evidence of bipedalism is found in the footprints of this species. Au. afarensis is associated with the Laetoli Footprints, a 24-meter trackway of hominin fossil footprints preserved in volcanic ash discovered by Mary Leakey in Tanzania and dated to 3.5 mya to 3 mya. This set of prints is thought to have been produced by three bipedal individuals as there are no knuckle imprints, no opposable big toes, and a clear arch is present. The infants of this species are thought to have been more arboreal than the adults, as discovered through analyses of the foot bones of the Dikika Child dated to 3.32 mya (Alemseged et al. 2006).
Although not found in direct association with stone tools, potential evidence for cut marks on bones, found at Dikika, and dated to 3.39 mya indicates a possible temporal/ geographic overlap between meat eating, tool use, and this species. However, this evidence is fiercely debated. Others have associated the cut marks with the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species.
South African Australopithecines
Since the discovery of the Taung Child, there have been numerous Australopithecine discoveries from the region known as “The Cradle of Humankind,” which was recently given UNESCO World Heritage Site status as “The Fossil Hominid Sites of South Africa.” The limestone caves found in the Cradle allow for the excellent preservation of fossils. Past animals navigating the landscape and falling into cave openings, or caves used as dens by carnivores, led to the accumulation of deposits over millions of years. Many of the hominin fossils, encased in breccia (hard, calcareous sedimentary rock), are recently exposed from limestone quarries mined in the previous century. This means that extracting fossils requires excellent and detailed exposed work, often by a team of skilled technicians.
While these sites have historically been difficult to date, with mixed assemblages accumulated over large time periods, advances in techniques such as uranium-series dating have allowed for greater accuracy. Historically, the excellent faunal record from East Africa has been used to compare sites based on relative dating, whereby environmental and faunal changes and extinction events allow us to know which hominin finds are relatively younger or older than others.
The discovery of the Taung Child in 1924 (discussed in the Special Topic box “The Taung Child” below) shifted the focus of palaeoanthropological research from Europe to Africa, although acceptance of this shift was slow (Broom 1947; Dart 1925). The species to which it is assigned, Australopithecus africanus (name meaning “Southern Ape of Africa”), is currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa (Figure 9.16). A relatively large brain (400 cc to 500 cc), small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits. Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism. However, the sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some ancestral features. Although not in direct association with stone tools, a 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities.

Another famous Au. africanus skull (the skull of “Mrs. Ples”) was previously attributed to Plesianthropus transvaalensis, meaning “near human from the Transvaal,” the old name for Gauteng Province, South Africa (Broom 1947, 1950). The name was shortened by contemporary journalists to “Ples” (Figure 9.17). Due to the prevailing mores of the time, the assumed female found herself married, at least in name, and has become widely known as “Mrs. Ples.” It was later reassigned to Au. africanus and is now argued by some to be a young male rather than an adult female cranium (Thackeray 2000, Thackeray et al. 2002).

In 2008, nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger, noted a clavicle bone in some leftover mining breccia in the Malapa Fossil Site (South Africa). After rigorous studies, the species, Australopithecus sediba (meaning “fountain” or “wellspring” in the South African language of Sesotho), was named in 2010 (Figure 9.18; Berger et al. 2010). The first type specimen belongs to a juvenile male, Karabo (MH1), but the species is known from at least six partial skeletons, from infants through adults. These specimens are currently dated to 1.97 mya (Dirks et al. 2010). The discoverers have argued that Au. sediba shows mosaic features between Au. africanus and the genus, Homo, which potentially indicates a transitional species, although this is heavily debated. These features include a small brain size (Australopithecus-like; 420 cc to 450 cc) but gracile mandible and small teeth (Homo-like). Similarly, the postcranial skeletons are also said to have mosaic features: scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. Some researchers have argued that Au. sediba shows a modern hand morphology (shorter fingers and a longer thumb), indicating that adaptations to tool manufacture and use may be present in this species.

Another famous Australopithecine find from South Africa is that of the nearly complete skeleton now known as “Little Foot” (Clarke 1998, 2013). Little Foot (StW 573) is potentially the earliest dated South African hominin fossil, dating to 3.7 mya, based on radiostopic techniques, although some argue that it is younger than 3 mya (Pickering and Kramers 2010). The name is jokingly in contrast to the cryptid species “bigfoot” and is named because the initial discovery of four ankle bones indicated bipedality. Little Foot was discovered by Ron Clarke in 1994, when he came across the ankle bones while sorting through monkey fossils in the University of Witwatersrand collections (Clarke and Tobias 1995). He asked Stephen Motsumi and Nkwane Molefe to identify the known records of the fossils, which allowed them to find the rest of the specimen within just days of searching the Sterkfontein Caves’ Silberberg Grotto.
The discoverers of Little Foot insist that other fossil finds, previously identified as Au. Africanus, be placed in this new species based on shared ancestral traits with older East African Australopithecines (Clarke and Kuman 2019). These include features such as a relatively large brain size (408 cc), robust zygomatic arch, and a flatter midface. Furthermore, the discoverers have argued that the heavy anterior dental wear patterns, relatively large anterior dentition, and smaller hind dentition of this specimen more closely resemble that of Au. anamensis or Au. afarensis. It has thus been placed in the species Australopithecus prometheus. This species name refers to a previously defunct taxon named by Raymond Dart. The species designation was, through analyzing Little Foot, revived by Ron Clarke, who insists that many other fossil hominin specimens have prematurely been placed into Au. africanus. Others say that it is more likely that Au. africanus is a more variable species and not representative of two distinct species.
Paranthropus “Robust” Australopithecines
In the robust australopithecines, the specialized nature of the teeth and masticatory system, such as flaring zygomatic arches (cheekbones), accommodate very large temporalis (chewing) muscles. These features also include a large, broad, dish-shaped face and and a large mandible with extremely large posterior dentition (referred to as megadonts) and hyper-thick enamel (Kimbel 2015; Lee-Thorp 2011; Wood 2010). Research has revolved around the shared adaptations of these “robust” australopithecines, linking their morphologies to a diet of hard and/or tough foods (Brain 1967; Rak 1988). Some argued that the diet of the robust australopithecines was so specific that any change in environment would have accelerated their extinction. The generalist nature of the teeth of the gracile australopithecines, and of early Homo, would have made them more capable of adapting to environmental change. However, some have suggested that the features of the robust australopithecines might have developed as an effective response to what are known as fallback foods in hard times rather than indicating a lack of adaptability.
There are currently three widely accepted robust australopithecus or, Paranthropus, species: P. aethiopicus, which has more ancestral traits, and P. boisei and P. robustus, which are more derived in their features (Strait et al. 1997; Wood and Schroer 2017). These three species have been grouped together by a majority of scholars as a single genus as they share more derived features (are more closely related to each other; or, in other words, are monophyletic) than the other australopithecines (Grine 1988; Hlazo 2015; Strait et al. 1997; Wood 2010 ). While researchers have mostly agreed to use the umbrella term Paranthropus, there are those who disagree (Constantino and Wood 2004, 2007; Wood 2010).
As a collective, this genus spans 2.7 mya to 1.0 mya, although the dates of the individual species differ. The earliest of the Paranthropus species, Paranthropus aethiopicus, is dated to between 2.7 mya and 2.3 mya and currently found in Tanzania, Kenya, and Ethiopia in the EARS system (Figure 9.19; Constantino and Wood 2007; Hlazo 2015; Kimbel 2015; Walker et al. 1986; White 1988). It is well known because of one specimen known as the “Black Skull” (KNM–WT 17000), so called because of the mineral manganese that stained it black during fossilization (Kimbel 2015). As with all robust Australopithecines, P. aethiopicus has the shared derived traits of large, flat premolars and molars; large, flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle); a sagittal crest (ridge on the top of the skull) for increased muscle attachment of the chewing muscles to the skull; and a robust mandible and supraorbital torus (brow ridge). However, only a few teeth have been found. A proximal tibia indicates bipedality and similar body size to Au. afarensis. In recent years, researchers have discovered and assigned a proximal tibia and juvenile cranium (L.338y-6) to the species (Wood and Boyle 2016).

First attributed as Zinjanthropus boisei (with the first discovery going by the nickname “Zinj” or sometimes “Nutcracker Man”), Paranthropus boisei was discovered in 1959 by Mary Leakey (see Figure 9.20 and 9.21; Hay 1990; Leakey 1959). This “robust” australopith species is distributed across countries in East Africa at sites such as Kenya (Koobi Fora, West Turkana, and Chesowanja), Malawi (Malema-Chiwondo), Tanzania (Olduvai Gorge and Peninj), and Ethiopia (Omo River Basin and Konso). The hypodigm, sample of fossils whose features define the group, has been found by researchers to date to roughly 2.4 mya to 1.4 mya. Due to the nature of its exaggerated, larger, and more robust features, P. boisei has been termed hyper-robust—that is, even more heavily built than other robust species, with very large, flat posterior dentition (Kimbel 2015). Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). Another famous specimen from this species is the Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu.


Paranthropus robustus was the first taxon to be discovered within the genus in Kromdraai B by a schoolboy named Gert Terblanche; subsequent fossil discoveries were made by researcher Robert Broom in 1938 (Figure 9.22; Broom 1938a, 1938b, 1950), with the holotype specimen TM 1517 (Broom 1938a, 1938b, 1950; Hlazo 2018). Paranthropus robustus dates approximately from 2.0 mya to 1 mya and is the only taxon from the genus to be discovered in South Africa. Several of these fossils are fragmentary in nature, distorted, and not well preserved because they have been recovered from quarry breccia using explosives. P. robustus features are neither as “hyper-robust” as P. boisei nor as ancestral as P. aethiopicus; instead, they have been described as being less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring; Rak 1983; Walker and Leakey 1988). Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick-enameled dentition.

Comparisons between Gracile and Robust Australopiths
Comparisons between gracile and robust australopithecines may indicate different phylogenetic groupings or parallel evolution in several species. In general, the robust australopithecines have large temporalis (chewing) muscles, as indicated by flaring zygomatic arches, sagittal crests, and robust mandibles (jawbones). Their hind dentition is large (megadont), with low cusps and thick enamel. Within the gracile australopithecines, researchers have debated the relatedness of the species, or even whether these species should be lumped together to represent more variable or polytypic species. Often researchers will attempt to draw chronospecific trajectories, with one taxon said to evolve into another over time.
Special Topic: The Taung Child

The well-known fossil of a juvenile Australopithecine, the “Taung Child,” was the first early hominin evidence ever discovered and was the first to demonstrate our common human heritage in Africa (Figure 9.23; Dart 1925). The tiny facial skeleton and natural endocast were discovered in 1924 by a local quarryman in the North West Province in South Africa and were painstakingly removed from the surrounding cement-like breccia by Raymond Dart using his wife’s knitting needles. When first shared with the scientific community in 1925, it was discounted as being nothing more than a young monkey of some kind. Prevailing biases of the time made it too difficult to contemplate that this small-brained hominin could have anything to do with our own history. The fact that it was discovered in Africa simply served to strengthen this bias.
Early Tool Use and Technology
Early Stone Age Technology (ESA)
The Early Stone Age (ESA) marks the beginning of recognizable technology made by our human ancestors. Stone-tool (or lithic) technology is defined by the fracturing of rocks and the manufacture of tools through a process called knapping. The Stone Age lasted for more than 3 million years and is broken up into chronological periods called the Early (ESA), Middle (MSA), and Later Stone Ages (LSA). Each period is further broken up into a different techno-complex, a term encompassing multiple assemblages (collections of artifacts) that share similar traits in terms of artifact production and morphology. The ESA spanned the largest technological time period of human innovation from over 3 million years ago to around 300,000 years ago and is associated almost entirely with hominin species prior to modern Homo sapiens. As the ESA advanced, stone tool makers (known as knappers) began to change the ways they detached flakes and eventually were able to shape artifacts into functional tools. These advances in technology go together with the developments in human evolution and cognition, dispersal of populations across the African continent and the world, and climatic changes.
In order to understand the ESA, it is important to consider that not all assemblages are exactly the same within each techno-complex: one can have multiple phases and traditions at different sites (Lombard et al. 2012). However, there is an overarching commonality between them. Within stone tool assemblages, both flakes or cores (the rocks from which flakes are removed) are used as tools. Large Cutting Tools (LCTs) are tools that are shaped to have functional edges. It is important to note that the information presented here is a small fraction of what is known about the ESA, and there are ongoing debates and discoveries within archaeology.
Currently, the oldest-known stone tools, which form the techno-complex the Lomekwian, date to 3.3 mya (Harmand et al. 2015; Toth 1985). They were found at a site called Lomekwi 3 in Kenya. This techno-complex is the most recently defined and pushed back the oldest-known date for lithic technology. There is only one known site thus far and, due to the age of the site, it is associated with species prior to Homo, such as Kenyanthropus platyops. Flakes were produced through indirect percussion, whereby the knappers held a rock and hit it against another rock resting on the ground. The pieces are very chunky and do not display the same fracture patterns seen in later techno-complexes. Lomekwian knappers likely aimed to get a sharp-edged piece on a flake, which would have been functional, although the specific function is currently unknown.
Stone tool use, however, is not only understood through the direct discovery of the tools. Cut marks on fossilized animal bones may illuminate the functionality of stone tools. In one controversial study in 2010, researchers argued that cut marks on a pair of animal bones from Dikika (Ethiopia), dated to 3.4 mya, were from stone tools. The discoverers suggested that they be more securely associated, temporally, with Au. afarensis. However, others have noted that these marks are consistent with teeth marks from crocodiles and other carnivores.

The Oldowan techno-complex is far more established in the scientific literature (Leakey 1971). It is called the Oldowan because it was originally discovered in Olduvai Gorge, Tanzania, but the oldest assemblage is from Gona in Ethiopia, dated to 2.6 mya (Semaw 2000). The techno-complex is defined as a core and flake industry. Like the Lomekwian, there was an aim to get sharp-edged flakes, but this was achieved through a different production method. Knappers were able to actively hold or manipulate the core being knapped, which they could directly hit using a hammerstone. This technique is known as free-hand percussion, and it demonstrates an understanding of fracture mechanics. It has long been argued that the Oldowan hominins were skillful in tool manufacture.
Because Oldowan knapping requires skill, earlier researchers have attributed these tools to members of our genus, Homo. However, some have argued that these tools are in more direct association with hominins in the genera described in this chapter (Figure 9.24).
Invisible Tool Manufacture and Use
The vast majority of our understanding of these early hominins comes from fossils and reconstructed paleoenvironments. It is only from 3 mya when we can start “looking into their minds” and lifestyles by analyzing their manufacture and use of stone tools. However, the vast majority of tool use in primates (and, one can argue, in humans) is not with durable materials like stone. All of our extant great ape relatives have been observed using sticks, leaves, and other materials for some secondary purpose (to wade across rivers, to “fish” for termites, or to absorb water for drinking). It is possible that the majority of early hominin tool use and manufacture may be invisible to us because of this preservation bias.
Chapter Summary
The fossil record of our earliest hominin relatives has allowed paleoanthropologists to unpack some of the mysteries of our evolution. We now know that traits associated with bipedalism evolved before other “human-like” traits, even though the first hominins were still very capable of arboreal locomotion. We also know that, for much of this time, hominin taxa were diverse in the way they looked and what they ate, and they were widely distributed across the African continent. And we know that the environments in which these hominins lived underwent many changes over this time during several warming and cooling phases.
Yet this knowledge has opened up many new mysteries. We still need to better differentiate some taxa. In addition, there are ongoing debates about why certain traits evolved and what they meant for the extinction of some of our relatives (like the robust australopiths). The capabilities of these early hominins with respect to tool use and manufacture is also still uncertain.
Hominin Species Summaries
Hominin |
Sahelanthropus tchadensis |
Dates |
7 mya to 6 mya |
Region(s) |
Chad |
Famous discoveries |
The initial discovery, made in 2001. |
Brain size |
360 cc average |
Dentition |
Smaller than in extant great apes; larger and pointier than in humans. Canines worn at the tips. |
Cranial features |
A short cranial base and a foramen magnum (hole in which the spinal cord enters the cranium) that is more humanlike in positioning; has been argued to indicate upright walking. |
Postcranial features |
Currently little published postcranial material. |
Culture |
N/A |
Other |
The extent to which this hominin was bipedal is currently heavily debated. If so, it would indicate an arboreal bipedal ancestor of hominins, not a knuckle-walker like chimpanzees. |
Hominin |
Orrorin tugenensis |
Dates |
6 mya to 5.7 mya |
Region(s) |
Tugen Hills (Kenya) |
Famous discoveries |
Original discovery in 2000. |
Brain size |
N/A |
Dentition |
Smaller cheek teeth (molars and premolars) than even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines. |
Cranial features |
Not many found |
Postcranial features |
Fragmentary leg, arm, and finger bones have been found. Indicates bipedal locomotion. |
Culture |
Potential toolmaking capability based on hand morphology, but nothing found directly. |
Other |
This is the earliest species that clearly indicates adaptations for bipedal locomotion. |
Hominin |
Ardipithecus kadabba |
Dates |
5.2 mya to 5.8 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
Discovered by Yohannes Haile-Selassie in 1997. |
Brain size |
N/A |
Dentition |
Larger hind dentition than in modern chimpanzees. Thick enamel and larger canines than in later hominins. |
Cranial features |
N/A |
Postcranial features |
A large hallux (big toe) bone indicates a bipedal “push off.” |
Culture |
N/A |
Other |
Faunal evidence indicates a mixed grassland/woodland environment. |
Hominin |
Ardipithecus ramidus |
Dates |
4.4 mya |
Region(s) |
Middle Awash region and Gona (Ethiopia) |
Famous discoveries |
A partial female skeleton nicknamed “Ardi” (ARA-VP-6/500) (found in 1994). |
Brain size |
300 cc to 350 cc |
Dentition |
Little differences between the canines of males and females (small sexual dimorphism). |
Cranial features |
Midfacial projection, slightly prognathic. Cheekbones less flared and robust than in later hominins. |
Postcranial features |
Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, an opposable big toe similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. |
Culture |
None directly associated |
Other |
Over 110 specimens from Aramis |
Hominin |
Australopithecus anamensis |
Dates |
4.2 mya to 3.8 mya |
Region(s) |
Turkana region (Kenya); Middle Awash (Ethiopia) |
Famous discoveries |
A 2019 find from Ethiopia, named MRD. |
Brain size |
370 cc |
Dentition |
Relatively large canines compared with more recent Australopithecines. |
Cranial features |
Projecting cheekbones and ancestral earholes. |
Postcranial features |
Lower limb bones (tibia and femur) indicate bipedality; arboreal features in upper limb bones (humerus) found. |
Culture |
N/A |
Other |
Almost 100 specimens, representing over 20 individuals, have been found to date. |
Hominin |
Australopithecus afarensis |
Dates |
3.9 mya to 2.9 mya |
Region(s) |
Afar Region, Omo, Maka, Fejej, and Belohdelie (Ethiopia); Laetoli (Tanzania); Koobi Fora (Kenya) |
Famous discoveries |
Lucy (discovery: 1974), Selam (Dikika Child, discovery: 2000), Laetoli Footprints (discovery: 1976). |
Brain size |
380 cc to 430 cc |
Dentition |
Reduced canines and molars relative to great apes but larger than in modern humans. |
Cranial features |
Prognathic face, facial features indicate relatively strong chewing musculature (compared with Homo) but less extreme than in Paranthropus. |
Postcranial features |
Clear evidence for bipedalism from lower limb postcranial bones. Laetoli Footprints indicate humanlike walking. Dikika Child bones indicate retained ancestral arboreal traits in the postcrania. |
Culture |
None directly, but close in age and proximity to controversial cut marks at Dikika and early tools in Lomekwi. |
Other |
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. |
Hominin |
Australopithecus bahrelghazali |
Dates |
3.6 mya |
Region(s) |
Chad |
Famous discoveries |
“Abel,” the holotype (discovery: 1995). |
Brain size |
N/A |
Dentition |
N/A |
Cranial features |
N/A |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Arguably within range of variation of Au. afarensis. |
Hominin |
Australopithecus prometheus |
Dates |
3.7 mya (debated) |
Region(s) |
Sterkfontein (South Africa) |
Famous discoveries |
“Little Foot” (StW 573) (discovery: 1994) |
Brain size |
408 cc (Little Foot estimate) |
Dentition |
Heavy anterior dental wear patterns, relatively large anterior dentition and smaller hind dentition, similar to Au. afarensis. |
Cranial features |
Relatively larger brain size, robust zygomatic arch, and a flatter midface. |
Postcranial features |
The initial discovery of four ankle bones indicated bipedality. |
Culture |
N/A |
Other |
Highly debated new species designation. |
Hominin |
Australopithecus deyiremada |
Dates |
3.5 mya to 3.3 mya |
Region(s) |
Woranso-Mille (Afar region, Ethiopia) |
Famous discoveries |
First fossil mandible bones were discovered in 2011 in the Afar region of Ethiopia by Yohannes Haile-Selassie. |
Brain size |
N/A |
Dentition |
Smaller teeth with thicker enamel than seen in Au. afarensis, with a potentially hardier diet. |
Cranial features |
Larger mandible and more projecting cheekbones than in Au. afarensis. |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Contested species designation; arguably a member of Au. afarensis. |
Hominin |
Kenyanthopus platyops |
Dates |
3.5 mya to 3.2 mya |
Region(s) |
Lake Turkana (Kenya) |
Famous discoveries |
KNM–WT 40000 (discovered 1999) |
Brain size |
Difficult to determine but appears within the range of Australopithecus afarensis. |
Dentition |
Small molars/dentition (Homo-like characteristic) |
Cranial features |
Flatter (i.e., orthognathic) face |
Postcranial features |
N/A |
Culture |
Some have associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species/specimen. |
Other |
Taxonomic placing of this species is quite divided. The discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis. |
Hominin |
Australopithecus africanus |
Dates |
3.3 mya to 2.1 mya |
Region(s) |
Sterkfontein, Taung, Makapansgat, Gladysvale (South Africa) |
Famous discoveries |
Taung Child (discovery in 1994), “Mrs. Ples” (discover in 1947), Little Foot (arguable; discovery in 1994). |
Brain size |
400 cc to 500 cc |
Dentition |
Smaller teeth (derived) relative to Au. afarensis. Small canines with no diastema. |
Cranial features |
A rounder skull compared with Au. afarensis in East Africa. A sloping face (ancestral). |
Postcranial features |
Similar postcranial evidence for bipedal locomotion (derived pelvis) with retained arboreal locomotion, e.g., curved phalanges (fingers), as seen in Au. afarensis. |
Culture |
None with direct evidence. |
Other |
A 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities. |
Hominin |
Australopithecus garhi |
Dates |
2.5 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
N/A |
Brain size |
450 cc |
Dentition |
Larger hind dentition than seen in other gracile Australopithecines. |
Cranial features |
N/A |
Postcranial features |
A femur of a fragmentary partial skeleton, argued to belong to Au. garhi, indicates this species may be longer-limbed than Au. afarensis, although still able to move arboreally. |
Culture |
Crude stone tools resembling Oldowan (described later) have been found in association with Au. garhi. |
Other |
This species is not well documented or understood and is based on only a few fossil specimens. |
Hominin |
Paranthropus aethiopicus |
Dates |
2.7 mya to 2.3 mya |
Region(s) |
West Turkana (Kenya); Laetoli (Tanzania); Omo River Basin (Ethiopia) |
Famous discoveries |
The “Black Skull” (KNM–WT 17000) (discovery 1985). |
Brain Size |
410 cc |
Dentition |
P. aethiopicus has the shared derived traits of large flat premolars and molars, although few teeth have been found. |
Cranial features |
Large flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle), a sagittal crest for increased muscle attachment of the chewing muscles to the skull, and a robust mandible and supraorbital torus (brow ridge). |
Postcranial features |
A proximal tibia indicates bipedality and similar size to Au. afarensis. |
Culture |
N/A |
Other |
The “Black Skull” is so called because of the mineral manganese that stained it black during fossilization. |
Hominin |
Paranthropus boisei |
Dates |
2.4 mya to 1.4 mya |
Region(s) |
Koobi Fora, West Turkana, and Chesowanja (Kenya); Malema-Chiwondo (Malawi), Olduvai Gorge and Peninj (Tanzania); and Omo River basin and Konso (Ethiopia) |
Famous discoveries |
“Zinj,” or sometimes “Nutcracker Man” (OH5), in 1959 by Mary Leakey. The Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu. |
Brain size |
500 cc to 550 cc |
Dentition |
Very large, flat posterior dentition (largest of all hominins currently known). Much smaller anterior dentition. Very thick dental enamel. |
Cranial features |
Indications of very large chewing muscles (e.g., flaring zygomatic arches and a large sagittal crest). |
Postcranial features |
Evidence for high variability and sexual dimorphism, with estimates of males at 1.37 meters tall and females at 1.24 meters. |
Culture |
Richard Leakey and Bernard Wood have both suggested that P. boisei could have made and used stone tools. Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. |
Other |
Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). This differs from what is seen in P. robustus. |
Hominin |
Australopithecus sediba |
Dates |
1.97 mya |
Region(s) |
Malapa Fossil Site (South Africa) |
Famous discoveries |
Karabo (MH1) (discovery in 2008) |
Brain size |
420 cc to 450 cc |
Dentition |
Small dentition with Australopithecine cusp-spacing. |
Cranial features |
Small brain size (Australopithecus-like) but gracile mandible (Homo-like). |
Postcranial features |
Scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (tree climbing, particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. |
Culture |
None of direct association, but some have argued that a modern hand morphology (shorter fingers and a longer thumb) means that adaptations to tool manufacture and use may be present in this species. |
Other |
It was first discovered through a clavicle bone in 2008 by nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger. |
Hominin |
Paranthropus robustus |
Dates |
2.3 mya to 1 mya |
Region(s) |
Kromdraai B, Swartkrans, Gondolin, Drimolen, and Coopers Cave (South Africa) |
Famous discoveries |
SK48 (original skull) |
Brain size |
410 cc to 530 cc |
Dentition |
Large posterior teeth with thick enamel, consistent with other Robust Australopithecines. Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick enameled dentition. |
Cranial features |
P. robustus features are neither as “hyper-robust” as P. boisei or as ancestral in features as P. aethiopicus. They have been described as less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring). |
Postcranial features |
Reconstructions indicate sexual dimorphism. |
Culture |
N/A |
Other |
Several of these fossils are fragmentary in nature, distorted, and not well preserved, because they have been recovered from quarry breccia using explosives. |
Review Questions
- What is the difference between a “derived” versus an “ancestral” trait? Give an example of both, seen in Au. afarensis.
- Which of the paleoenvironment hypotheses have been used to describe early hominin diversity, and which have been used to describe bipedalism?
- Which anatomical features for bipedalism do we see in early hominins?
- Describe the dentition of gracile and robust australopithecines. What might these tell us about their diets?
- List the hominin species argued to be associated with stone tool technologies. Are you convinced of these associations? Why/why not?
Key Terms
Arboreal: Related to trees or woodland.
Aridification: Becoming increasingly arid or dry, as related to the climate or environment.
Aridity Hypothesis: The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution.
Assemblage: A collection demonstrating a pattern. Often pertaining to a site or region.
Bipedalism: The locomotor ability to walk on two legs.
Breccia: Hard, calcareous sedimentary rock.
Canines: The pointy teeth just next to the incisors, in the front of the mouth.
Cheek teeth: Or hind dentition (molars and premolars).
Chronospecies: Species that are said to evolve into another species, in a linear fashion, over time.
Clade: A group of species or taxa with a shared common ancestor.
Cladistics: The field of grouping organisms into those with shared ancestry.
Context: As pertaining to palaeoanthropology, this term refers to the place where an artifact or fossil is found.
Cores: The remains of a rock that has been flaked or knapped.
Cusps: The ridges or “bumps” on the teeth.
Dental formula: A technique to describe the number of incisors, canines, premolars, and molars in each quadrant of the mouth.
Derived traits: Newly evolved traits that differ from those seen in the ancestor.
Diastema: A tooth gap between the incisors and canines.
Early Stone Age (ESA): The earliest-described archaeological period in which we start seeing stone-tool technology.
East African Rift System (EARS): This term is often used to refer to the Rift Valley, expanding from Malawi to Ethiopia. This active geological structure is responsible for much of the visibility of the paleoanthropological record in East Africa.
Enamel: The highly mineralized outer layer of the tooth.
Encephalization: Expansion of the brain.
Extant: Currently living—i.e., not extinct.
Fallback foods: Foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
Fauna: The animals of a particular region, habitat, or geological period.
Faunal assemblages: Collections of fossils of the animals found at a site.
Faunal turnover: The rate at which species go extinct and are replaced with new species.
Flake: The piece knocked off of a stone core during the manufacture of a tool, which may be used as a stone tool.
Flora: The plants of a particular region, habitat, or geological period.
Folivorous: Foliage-eating.
Foramen magnum: The large hole (foramen) at the base of the cranium, through which the spinal cord enters the skull.
Fossil: The remains or impression of an organism from the past.
Frugivorous: Fruit-eating.
Generalist: A species that can thrive in a wide variety of habitats and can have a varied diet.
Glacial: Colder, drier periods during an ice age when there is more ice trapped at the poles.
Gracile: Slender, less rugged, or pronounced features.
Hallux: The big toe.
Holotype: A single specimen from which a species or taxon is described or named.
Hominin: A primate category that includes humans and our fossil relatives since our divergence from extant great apes.
Honing P3: The mandibular premolar alongside the canine (in primates, the P3), which is angled to give space for (and sharpen) the upper canines.
Hyper-robust: Even more robust than considered normal in the Paranthropus genus.
Hypodigm: A sample (here, fossil) from which researchers extrapolate features of a population.
Incisiform: An adjective referring to a canine that appears more incisor-like in morphology.
Incisors: The teeth in the front of the mouth, used to bite off food.
Interglacial: A period of milder climate in between two glacial periods.
Isotopes: Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses.
Knappers: The people who fractured rocks in order to manufacture tools.
Knapping: The fracturing of rocks for the manufacture of tools.
Large Cutting Tool (LCT): A tool that is shaped to have functional edges.
Last Common Ancestor (LCA): The hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence.
Lithic: Relating to stone (here to stone tools).
Lumbar lordosis: The inward curving of the lower (lumbar) parts of the spine. The lower curve in the human S-shaped spine.
Lumpers: Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
Megadont: An organism with extremely large dentition compared with body size.
Metacarpals: The long bones of the hand that connect to the phalanges (finger bones).
Molars: The largest, most posterior of the hind dentition.
Monophyletic: A taxon or group of taxa descended from a common ancestor that is not shared with another taxon or group.
Morphology: The study of the form or size and shape of things; in this case, skeletal parts.
Mosaic evolution: The concept that evolutionary change does not occur homogeneously throughout the body in organisms.
Obligate bipedalism: Where the primary form of locomotion for an organism is bipedal.
Occlude: When the teeth from the maxilla come into contact with the teeth in the mandible.
Oldowan: Lower Paleolithic, the earliest stone tool culture.
Orthognathic: The face below the eyes is relatively flat and does not jut out anteriorly.
Paleoanthropologists: Researchers that study human evolution.
Paleoenvironment: An environment from a period in the Earth’s geological past.
Parabolic: Like a parabola (parabola-shaped).
Phalanges: Long bones in the hand and fingers.
Phylogenetics: The study of phylogeny.
Phylogeny: The study of the evolutionary relationships between groups of organisms.
Pliocene: A geological epoch between the Miocene and Pleistocene.
Polytypic: In reference to taxonomy, having two or more group variants capable of interacting and breeding biologically but having morphological population differences.
Postcranium: The skeleton below the cranium (head).
Premolars: The smallest of the hind teeth, behind the canines.
Procumbent: In reference to incisors, tilting forward.
Prognathic: In reference to the face, the area below the eyes juts anteriorly.
Quaternary Ice Age: The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles.
Relative dating: Dating techniques that refer to a temporal sequence (i.e., older or younger than others in the reference) and do not estimate actual or absolute dates.
Robust: Rugged or exaggerated features.
Site: A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
Specialist: A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
Splitters: Researchers who prefer to split a highly variable taxon into multiple groups or species.
Taxa: Plural of taxon, a taxonomic group such as species, genus, or family.
Taxonomy: The science of grouping and classifying organisms.
Techno-complex: A term encompassing multiple assemblages that share similar traits in terms of artifact production and morphology.
Thermoregulation: Maintaining body temperature through physiologically cooling or warming the body.
Ungulates: Hoofed mammals—e.g., cows and kudu.
Volcanic tufts: Rock made from ash from volcanic eruptions in the past.
Valgus knee: The angle of the knee between the femur and tibia, which allows for weight distribution to be angled closer to the point above the center of gravity (i.e., between the feet) in bipeds.
About the Authors
Kerryn Warren, Ph.D.
Grad Coach International, kerryn.warren@gmail.com
Kerryn Warren is a dissertation coach at Grad Coach International and is passionate about stimulating research thinking in students of all levels. She has lectured on multiple topics, including archaeology and human evolution, with her research and science communication interests including hybridization in the hominin fossil record (stemming from research from her Ph.D.) and understanding how evolution is taught in South African schools. She also worked as one of the “Underground Astronauts,” selected to excavate Homo naledi remains from the Rising Star Cave System in the Cradle of Humankind.
K. Lindsay Hunter, M.A., Ph.D. candidate
CARTA, k.lindsay.hunter@gmail.com
Lindsay Hunter is a trained palaeoanthropologist who uses her more than 15 years of experience to make sense of the distant past of our species to build a better future. She received her master’s degree in biological anthropology from the University of Iowa and is completing her Ph.D. in archaeology at the University of the Witwatersrand in Johannesburg, South Africa. She has studied fossil and human bone collections across five continents with major grant support from the National Science Foundation (United States) and the Wenner-Gren Foundation for Anthropological Research. As a National Geographic Explorer, Lindsay developed and managed the National Geographic–sponsored Umsuka Public Palaeoanthropology Project in the Cradle of Humankind World Heritage Site (CoH WHS) in South Africa from within Westbury Township, Johannesburg, between 2016–2019. She currently serves as the Community Engagement & Advancement Director for CARTA: The UC San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny in La Jolla, California.
Navashni Naidoo, M.Sc.
University of Cape Town, nnaidoo2@illinois.edu
Navashni Naidoo is a researcher at Nelson Mandela University, lecturing on physical geology. She completed her Master’s in Science in Archaeology in 2017 at the University of Cape Town. Her research interests include developing paleoenvironmental proxies suited to the African continent, behavioral ecology, and engaging with community-driven archaeological projects. She has excavated at Stone Age sites across Southern Africa and East Africa. Navashni is currently pursuing a PhD in the Department of Anthropology at the University of Illinois.
Silindokuhle Mavuso, M.Sc.
University of Witwatersrand, S.muvaso@ru.ac.za
Silindokuhle has always been curious about the world around him and how it has been shaped. He is a lecturer at Rhodes University of Witwatersrand (Wits), and conducts research on palaeoenvironmental reconstruction and change of the northeastern Turkana Basin’s Pleistocene sequence. Silindokuhle began his education with a B.Sc. (Geology, Archaeology, and Environmental and Geographical Sciences) from the University of Cape Town before moving to Wits for a B.Sc. Honors (geology and paleontology) and M.Sc. in geology. He is currently concluding his PhD Studies. During this time, he has gained more training as a Koobi Fora Fieldschool fellow (Kenya) as well as an Erasmus Mundus scholar (France). Silindokuhle is a Plio-Pleistocene geologist with a specific focus on identifying and explaining past environments that are associated with early human life and development through time. He is interested in a wide range of disciplines such as micromorphology, sedimentology, geochemistry, geochronology, and sequence stratigraphy. He has worked with teams from significant eastern and southern African hominid sites including Elandsfontein, Rising Star, Sterkfontein, Gondolin, Laetoli, Olduvai, and Koobi Fora.
For Further Exploration
The Smithsonian Institution website hosts descriptions of fossil species, an interactive timeline, and much more.
The Maropeng Museum website hosts a wealth of information regarding South African Fossil Bearing sites in the Cradle of Humankind.
This quick comparison between Homo naledi and Australopithecus sediba from the Perot Museum.
This explanation of the braided stream by the Perot Museum.
A collation of 3-D files for visualizing (or even 3-D printing) for homes, schools, and universities.
PBS learning materials, including videos and diagrams of the Laetoli footprints, bipedalism, and fossils.
A wealth of information from the Australian Museum website, including species descriptions, family trees, and explanations of bipedalism and diet.
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Acknowledgements
All of the authors in this section are students and early career researchers in paleoanthropology and related fields in South Africa (or at least have worked in South Africa). We wish to thank everyone who supports young and diverse talent in this field and would love to further acknowledge Black, African, and female academics who have helped pave the way for us.
Kerryn Warren, Ph.D., Grad Coach International
Lindsay Hunter, M.A., University of Iowa
Navashni Naidoo, M.Sc., University of Cape Town
Silindokuhle Mavuso, M.Sc., University of Witwatersrand
This chapter is a revision from "Chapter 9: Early Hominins" by Kerryn Warren, K. Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, and Nomawethu Hlazo. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Understand what is meant by “derived” and “ancestral” traits and why this is relevant for understanding early hominin evolution.
- Understand changing paleoclimates and paleoenvironments as potential factors influencing early hominin adaptations.
- Describe the anatomical changes associated with bipedalism and dentition in early hominins, as well as their implications..
- Describe early hominin genera and species, including their currently understood dates and geographic expanses.
- Describe the earliest stone tool techno-complexes and their impact on the transition from early hominins to our genus.
Defining Hominins
It is through our study of our hominin ancestors and relatives that we are exposed to a world of “might have beens”: of other paths not taken by our species, other ways of being human. But to better understand these different evolutionary trajectories, we must first define the terms we are using. If an imaginary line were drawn between ourselves and our closest relatives, the great apes, bipedalism (or habitually walking upright on two feet) is where that line would be. Hominin, then, means everyone on “our” side of the line: humans and all of our extinct bipedal ancestors and relatives since our divergence from the last common ancestor (LCA) we share with chimpanzees.
Historic interpretations of our evolution, prior to our finding of early hominin fossils, varied. Debates in the mid-1800s regarding hominin origins focused on two key issues:
- Where did we evolve?
- Which traits evolved first?
Charles Darwin hypothesized that we evolved in Africa, as he was convinced that we shared greater commonality with chimpanzees and gorillas on the continent (Darwin 1871). Others, such as Ernst Haeckel and Eugène Dubois, insisted that we were closer in affinity to orangutans and that we evolved in Eurasia where, until the discovery of the Taung Child in South Africa in 1924, all humanlike fossils (of Neanderthals and Homo erectus) had been found (Shipman 2002).
Within this conversation, naturalists and early paleoanthropologists (people who study human evolution) speculated about which human traits came first. These included the evolution of a big brain (encephalization), the evolution of the way in which we move about on two legs (bipedalism), and the evolution of our flat faces and small teeth (indications of dietary change). Original hypotheses suggested that, in order to be motivated to change diet and move about in a bipedal fashion, the large brain needed to have evolved first, as is seen in the fossil species mentioned above.
However, we now know that bipedal locomotion is one of the first things that evolved in our lineage, with early relatives having more apelike dentition and small brain sizes. While brain size expansion is seen primarily in our genus, Homo, earlier hominin brain sizes were highly variable between and within taxa, from 300 cc (cranial capacity, cm3), estimated in Ardipithecus, to 550 cc, estimated in Paranthropus boisei. The lower estimates are well within the range of variation of nonhuman extant great apes. In addition, body size variability also plays a role in the interpretation of whether brain size could be considered large or small for a particular species or specimen. In this chapter, we will tease out the details of early hominin evolution in terms of morphology (i.e. the study of the form, size, or shape of things; in this case, skeletal parts).
We also know that early human evolution occurred in a very complicated fashion. There were multiple species (multiple genera) that featured diversity in their diets and locomotion. Specimens have been found all along the East African Rift System (EARS); that is, in Ethiopia, Kenya, Tanzania, and Malawi; see Figure 9.1), in limestone caves in South Africa, and in Chad. Dates of these early relatives range from around 7 million years ago (mya) to around 1 mya, overlapping temporally with members of our genus, Homo.

Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another, and they consider which of these species were able to make and use tools. As a result, every site discovery in the patchy hominin fossil record tells us more about our evolution. In addition, recent scientific techniques (not available even ten years ago) provide new insights into the diets, environments, and lifestyles of these ancient relatives.
In the past, taxonomy was primarily based on morphology. Today it is tied to known relationships based on molecular phylogeny (e.g., based on DNA) or a combination of the two. This is complicated when applied to living taxa, but becomes much more difficult when we try to categorize ancestor-descendant relationships for long-extinct species whose molecular information is no longer preserved. We therefore find ourselves falling back on morphological comparisons, often of teeth and partially fossilized skeletal material.
It is here that we turn to the related concepts of cladistics and phylogenetics. Cladistics groups organisms according to their last common ancestors based on shared derived traits. In the case of early hominins, these are often morphological traits that differ from those seen in earlier populations. These new or modified traits provide evidence of evolutionary relationships, and organisms with the same derived traits are grouped in the same clade (Figure 9.2). For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade of birds. In this chapter, we will examine the grouping of the Robust Australopithecines, whose cranial and dental features differ from those of earlier hominins, and therefore are considered derived.

Dig Deeper: Problems Defining Hominin Species
It is worth noting that species designations for early hominin specimens are often highly contested. This is due to the fragmentary nature of the fossil record, the large timescale (millions of years) with which paleoanthropologists need to work, and the difficulty in evaluating whether morphological differences and similarities are due to meaningful phylogenetic or biological differences or subtle differences/variation in niche occupation or time. In other words, do morphological differences really indicate different species? How would classifying species in the paleoanthropological record compare with classifying living species today, for whom we can sequence genomes and observe lifestyles?
There are also broader philosophical differences among researchers when it comes to paleo-species designations. Some scientists, known as “lumpers,” argue that large variability is expected among multiple populations in a given species over time. These researchers will therefore prefer to “lump” specimens of subtle differences into single taxa. Others, known as “splitters,” argue that species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences. In general, splitters would consider geographic differences among populations as meaning that a species is polytypic (i.e., capable of interacting and breeding biologically but having morphological population differences). This is worth keeping in mind when learning about why species designations may be contested.

This further plays a role in evaluating ancestry. Debates over which species “gave rise” to which continue to this day. It is common to try to create “lineages” of species to determine when one species evolved into another over time. We refer to these as chronospecies (Figure 9.3). Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record. More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
Finally, it is worth considering the process of fossil discovery and publication. Some fossils are easily diagnostic to a species level and allow for easy and accurate interpretation. Some, however, are more controversial. This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species (e.g., a fossil of a patella or knee bone). Researchers often need to make several important claims when announcing or publishing a find: a secure date (if possible), clear association with other finds, and an adequate comparison among multiple species (both extant and fossil). Therefore, it is not uncommon that an important find was made years before it is scientifically published.
Paleoenvironment and Hominin Evolution
There is no doubt that one of the major selective pressures in hominin evolution is the environment. Large-scale changes in global and regional climate, as well as alterations to the environment, are (thought to be) all linked to (all) hominin diversification, dispersal, and extinction (Maslin et al. 2014). Environmental reconstructions often use modern analogues. Let us take, for instance, the hippopotamus. It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive. Such instances have occurred multiple times in the past, and the bones of some fauna (i.e., animals, like the hippopotamus) that are sensitive to these changes give us insights into these events.
Yet reconstructing a paleoenvironment relies on a range of techniques, which vary depending on whether research interests focus on local changes or more global environmental changes/reconstructions. For local environments (such as a single site or region), comparing the faunal assemblages (collections of fossils of animals found at a site) with animals found in certain modern environments allows us to determine if past environments mirror current ones in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes. Other techniques are also useful in this regard. Chemical analyses, for instance, can reveal the diets of individual fauna, providing clues as to the relative wetness or dryness of their environment (e.g., nitrogen isotopes; Kingston and Harrison 2007).
Global climatic changes in the distant past, which fluctuated between being colder and drier and warmer and wetter on average, would have global implications for environmental change (Figure 9.4). These can be studied by comparing marine core and terrestrial soil data across multiple sites. These techniques are based on chemical analysis, such as examination of the nitrogen and oxygen isotopes in shells and sediments. Similarly, analyzing pollen grains shows which kinds of flora survived in an environment at a specific time period. There are multiple lines of evidence that allow us to visualize global climate trends over millions of years (although it should be noted that the direction and extent of these changes could differ by geographic region).

Both local and global climatic/environmental changes have been used to understand factors affecting our evolution (DeHeinzelin et al. 1999; Kingston 2007). Environmental change acts as an important factor regarding the onset of several important hominin traits seen in early hominins and discussed in this chapter. Namely, the environment has been interpreted as the following:
- the driving force behind the evolution of bipedalism,
- the reason for change and variation in early hominin diets, and
- the diversification of multiple early hominin species.
There are numerous hypotheses regarding how climate has driven and continues to drive human evolution. Here, we will focus on just three popular hypotheses.
Savannah Hypothesis (or Aridity Hypothesis)
The hypothesis: This popular theory suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion (Figure 9.5). It was first proposed by Darwin (1871) and supported by anthropologists like Raymond Dart (1925). However, this idea was supported by little fossil or paleoenvironmental evidence and was later refined as the Aridity Hypothesis. This hypothesis states that the long-term aridification and, thereby, expansion of savannah biomes were drivers in diversification in early hominin evolution (deMenocal 2004; deMenocal and Bloemendal 1995). It advocates for periods of accelerated aridification leading to early hominin speciation events.

The evidence: While early bipedal hominins are often associated with wetter, more closed environments (i.e., not the Savannah Hypothesis), both marine and terrestrial records seem to support general cooling, drying conditions, with isotopic records indicating an increase in grasslands (i.e., colder and wetter climatic conditions) between 8 mya and 6 mya across the African continent (Cerling et al. 2011). This can be contrasted with later climatic changes derived from aeolian dust records (sediments transported to the site of interest by wind), which demonstrate increases in seasonal rainfall between 3 mya and 2.6 mya, 1.8 mya and 1.6 mya, and 1.2 mya and 0.8 mya (deMenocal 2004; deMenocal and Bloemendal 1995).
Interpretation(s): Despite a relatively scarce early hominin record, it is clear that two important factors occur around the time period in which we see increasing aridity. The first factor is the diversification of taxa, where high morphological variation between specimens has led to the naming of multiple hominin genera and species. The second factor is the observation that the earliest hominin fossils appear to have traits associated with bipedalism and are dated to around the drying period (as based on isotopic records). Some have argued that it is more accurately a combination of bipedalism and arboreal locomotion, which will be discussed later. However, the local environments in which these early specimens are found (as based on the faunal assemblages) do not appear to have been dry.
Turnover Pulse Hypothesis
The hypothesis: In 1985, paleontologist Elisabeth Vbra noticed that in periods of extreme and rapid climate change, ungulates (hoofed mammals of various kinds) that had generalized diets fared better than those with specialized diets (Vrba 1988, 1998). Specialist eaters (those who rely primarily on specific food types) faced extinction at greater rates than their generalist (those who can eat more varied and variable diets) counterparts because they were unable to adapt to new environments (Vrba 2000). Thus, periods with extreme climate change would be associated with high faunal turnover: that is, the extinction of many species and the speciation, diversification, and migration of many others to occupy various niches.
The evidence: The onset of the Quaternary Ice Age, between 2.5 mya and 3 mya, brought extreme global, cyclical interglacial and glacial periods (warmer, wetter periods with less ice at the poles, and colder, drier periods with more ice near the poles). Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites (Behrensmeyer et al. 1997; Bobe and Behrensmeyer 2004). Similarly, work in the Cape Floristic Belt of South Africa shows that extreme changes in climate play a role in extinction and migration in ungulates. While this theory was originally developed for ungulates, its proponents have argued that it can be applied to hominins as well. However, the link between climate and speciation is only vaguely understood (Faith and Behrensmeyer 2013).
Interpretation(s): While the evidence of rapid faunal turnover among ungulates during this time period appears clear, there is still some debate around its usefulness as applied to the paleoanthropological record. Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct.
Variability Selection Hypothesis
The hypothesis: This hypothesis was first articulated by paleoanthropologist Richard Potts (1998). It links the high amount of climatic variability over the last 7 million years to both behavioral and morphological changes. Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context (Potts 1998, 2013). The Variability Selection Hypothesis states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations (Potts 2013).
The evidence: The evidence for this theory is similar to that for the Turnover Pulse Hypothesis: large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
Interpretation(s): In this way, the Variability Selection Hypothesis allows for a more flexible interpretation of the evolution of bipedalism in hominins and a more fluid interpretation of the Turnover Pulse Hypothesis, where species turnover is meant to be more rapid. In some ways, this hypothesis accommodates both environmental data and our interpretations of an evolution toward greater variability among species and the survivability of generalists.
Paleoenvironment Summary
Some hypotheses presented in this section pay specific attention to habitat (Savannah Hypothesis) while others point to large-scale climatic forces (Variability Selection Hypothesis). Some may be interpreted to describe the evolution of traits such as bipedalism (Savannah Hypothesis), and others generally explain the diversification of early hominins (Turnover Pulse and Variability Selection Hypotheses). While there is no consensus as to how the environment drove our evolution, it is clear that the environment shaped both habitat and resource availability in ways that would have influenced our early ancestors physically and behaviorally.
Derived Adaptations: Bipedalism
The unique form of locomotion exhibited by modern humans, called obligate bipedalism, is important in distinguishing our species from the extant (living) great apes. The ability to walk habitually upright is thus considered one of the defining attributes of the hominin lineage. We also differ from other animals that walk bipedally (such as kangaroos) in that we do not have a tail to balance us as we move.
The origin of bipedalism in hominins has been debated in paleoanthropology, but at present there are two main ideas: (theories)
- early hominins initially lived in trees, but increasingly started living on the ground, so we were a product of an arboreal last common ancestor (LCA) or,
- our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
Most research supports the first theory of an arboreal LCA based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking. This would mean that both humans and chimpanzees can be considered “derived” in terms of locomotion since chimpanzees would have independently evolved knuckle-walking.
There are many current ideas regarding selective pressures that would lead to early hominins adapting upright posture and locomotion. Many of these selective pressures, as we have seen in the previous section, coincide with a shift in environmental conditions, supported by paleoenvironmental data. In general, however, it appears that, like extant great apes, early hominins thrived in forested regions with dense tree coverage, which would indicate an arboreal lifestyle. As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse such that bipedalism would become more important.
There are several proposed selective pressures for bipedalism:
- Energy conservation: Modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land. While chimpanzees, for instance, are faster than humans terrestrially, they expend large amounts of energy being so. Adaptations to bipedalism include “stacking” the majority of the weight of the body over a small area around the center of gravity (i.e., the head is above the chest, which is above the pelvis, which is over the knees, which are above the feet). This reduces the amount of muscle needed to be engaged during locomotion to “pull us up” and allows us to travel longer distances expending far less energy.
- Thermoregulation: Less surface area (i.e., only the head and shoulders) is exposed to direct sunlight during the hottest parts of the day (i.e., midday). This means that the body has less need to employ additional “cooling” mechanisms such as sweating, which additionally means less water loss.
- Bipedalism (Freeing of Hands): This method of locomotion freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use of tools.
These selective pressures are not mutually exclusive. Bipedality could have evolved from a combination of these selective pressures, in ways that increased the chances of early hominin survival.
Skeletal Adaptations for Bipedalism

Humans have highly specialized adaptations to facilitate obligate bipedalism (Figure 9.6). Many of these adaptations occur within the soft tissue of the body (e.g., muscles and tendons). However, when analyzing the paleoanthropological record for evidence of the emergence of bipedalism, all that remains is the fossilized bone. Interpretations of locomotion are therefore often based on comparative analyses between fossil remains and the skeletons of extant primates with known locomotor behaviors. These adaptations occur throughout the skeleton and are summarized in Figure 9.7.
The majority of these adaptations occur in the postcranium (the skeleton from below the head) and are outlined in Figure 9.7. In general, these adaptations allow for greater stability and strength in the lower limb, by allowing for more shock absorption, for a larger surface area for muscle attachment, and for the “stacking” of the skeleton directly over the center of gravity to reduce energy needed to be kept upright. These adaptations often mean less flexibility in areas such as the knee and foot.
However, these adaptations come at a cost. Evolving from a nonobligate bipedal ancestor means that the adaptations we have are evolutionary compromises. For instance, the valgus knee (angle at the knee) is an essential adaptation to balance the body weight above the ankle during bipedal locomotion. However, the strain and shock absorption at an angled knee eventually takes its toll. For example, runners often experience joint pain. Similarly, the long neck of the femur absorbs stress and accommodates for a larger pelvis, but it is a weak point, resulting in hip replacements being commonplace among the elderly, especially in cases where the bone additionally weakens through osteoporosis. Finally, the S-shaped curve in our spine allows us to stand upright, relative to the more curved C-shaped spine of an LCA. Yet the weaknesses in the curves can lead to pinching of nerves and back pain. Since many of these problems primarily are only seen in old age, they can potentially be seen as an evolutionary compromise.
Despite relatively few postcranial fragments, the fossil record in early hominins indicates a complex pattern of emergence of bipedalism. Key features, such as a more anteriorly placed foramen magnum, are argued to be seen even in the earliest discovered hominins, indicating an upright posture (Dart 1925). Some early species appear to have a mix of ancestral (arboreal) and derived (bipedal) traits, which indicates a mixed locomotion and a more mosaic evolution of the trait. Some early hominins appear to, for instance, have bowl-shaped pelvises (hip bones) and angled femurs suitable for bipedalism but also have retained an opposable hallux (big toe) or curved fingers and longer arms (for arboreal locomotion). These mixed morphologies may indicate that earlier hominins were not fully obligate bipeds and thus thrived in mosaic environments.
Yet the associations between postcranial and the more diagnostic cranial fossils and bones are not always clear, muddying our understanding of the specific species to which fossils belong (Grine et al. 2022).
Region | Feature | Obligate Biped (H. sapiens) | Nonobligate Biped |
Cranium | Position of the foramen magnum | Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground). | Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground. |
Post
cranium |
Body proportions | Shorter upper limb (not used for locomotion). | Longer upper limbs (used for locomotion). |
Post
cranium |
Spinal curvature | S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis). | C-curve. |
Post
cranium |
Vertebrae | Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission). | Gracile lumbar vertebrae compared to those of modern humans. |
Post
cranium |
Pelvis | Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces. | Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface. |
Post
cranium |
Lower limb | In general, longer, more robust lower limbs and more stable, larger joints.
|
In general, smaller, more gracile limbs with more flexible joints.
|
Post
cranium |
Foot | Rigid, robust foot, without a midtarsal break.
Nonopposable and large, robust big toe (for push off while walking) and large heel for shock absorbance. |
Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping. |
It is also worth noting that, while not directly related to bipedalism per se, other postcranial adaptations are evident in the hominin fossil record from some of the earlier hominins. For instance, the hand and finger morphologies of many of the earliest hominins indicate adaptations consistent with arboreality. These include longer hands, more curved metacarpals and phalanges (long bones in the hand and fingers, respectively), and a shorter, relatively weaker thumb. This allows for gripping onto curved surfaces during locomotion. The earliest hominins appear to have mixed morphologies for both bipedalism and arborealism. However, among Australopiths (members of the genus, Australopithecus), there are indications for greater reliance on bipedalism as the primary form of locomotion. Similarly, adaptations consistent with tool manufacture (shorter fingers and a longer, more robust thumb, in contrast to the features associated with arborealism) have been argued to appear before the genus Homo.
Special Topic: Fear of Snakes — A Cultural or Biological Response?

It is suggested that primates have three major predators: raptors, felines, and snakes; however, many studies show that of these carnivores, snakes were one of the first that mammals had to contend with alongside dinosaurs, as felines and raptors evolved at a much slower pace than their reptilian competition. Herpetologists trace the evolution of constricting snakes to about 100 million years ago, and by the time mammals arrived around 75 million years ago, constrictors were already well established as a formidable threat (Greene, 2017). Both co-existed for millennia and each sustained selective pressures requiring them to evolve specific traits to survive. When venomous snakes eventually emerged 55 to 65 million years ago, they posed yet an additional threat to proto-primates as they required less distance for the predator to kill (2017). Alongside camouflage and silent movement techniques, it was the development of the snake’s hollow fangs through which to deliver venom that was most transformative to primate evolution. As such, primates evolved their pre-conscious attention, and visual acuity to cope with this new threat; therefore, while snakes were adapting morphologically to feed themselves, they were unwittingly teaching proto-primates valuable lessons in predator detection and reacting appropriately in order to survive.
In a 2009 Harvard University study, Lynne A. Isbell hypothesizes that envenoming snakes are linked to being directly responsible for the origins of the evolving complex brains and superior visual capacity in the lineage of anthropoids leading to humans (Isbell, 2009). Forward-facing eyes for binocular vision, depth perception, enhanced visual acuity, stereoscopic and trichromatic colour vision, all traits necessary for snake detection; and the quick motor responses from the primate’s fight, flight, or freeze defence mechanism to circumvent a snake’s squeeze or bite. Numerous laboratory studies show that humans and primates both sense and visually detect snakes more rapidly than other threatening stimuli (Van Le Et al., 2013). These experiments show that snakes elicited the strongest, fastest responses (Van Le Et al., 2013). This is known as ‘Snake Detection Theory’ and is the evolution of the primate’s complex brain, visual acuity, and rapid motor responses towards snakes in its environment that are the adaptations needed to live successfully as arboreal beings. It is not fortuitous then, that primates that never coexisted with venomous snakes, such as lemurs in Madagascar, have less visual acuity, better olfaction and smaller brains. Within Isbell’s work, a collaborative study by a group of neuroscientists tested this hypothesis and found that, indeed, there is higher neural firing and activity in multiple areas of the primate brain, notably in the pulvinar, a region responsible for visual attention and oculomotor behaviour (Isbell, L., 2009).

Today, the fear of snakes is widespread in humans, often shown through avoidance and disgust. A study in The Journal of Ethnobiology and Ethnomedicine notes that snakes are over-hunted and excluded from conservation efforts worldwide (Ceríaco, 2012). While cultural factors shape our sentiments, instinct also plays a role—such as the developed avoidance behaviors toward threats like snakes. This blend of instinct and cultural influence is not only seen in behavior but also deeply embedded in the stories we tell. Many cultures depict mythological snakes as harbingers of death or chaos. In the Bible, Satan becomes a snake to tempt Eve. Norse mythology features Jörmungandr, the world serpent who signals the apocalypse. Egyptian myth tells of Apophis, who battles the sun god Ra nightly. Though sources vary, these myths consistently portray snakes as threats. As such, the widespread fear of snakes may reflect both evolutionary and cultural influences. Understood as an adaptive response inherited from primate ancestors—who developed avoidance behaviors toward potentially dangerous stimuli—and reinforced through myths and religious narratives, the enduring presence of snakes as potent figures of fear across human societies and primate groups highlights the complex intertwining of instinct and cultural meaning in shaping human behavior.
Early Hominins: Sahelanthropus and Orrorin
We see evidence for bipedalism in some of the earliest fossil hominins, dated from within our estimates of our divergence from chimpanzees. These hominins, however, also indicate evidence for arboreal locomotion.
The earliest dated hominin find (between 6 mya and 7 mya, based on radiometric dating of volcanic tufts) has been argued to come from Chad and is named Sahelanthropus tchadensis (Figure 9.8; Brunet et al. 1995). The initial discovery was made in 2001 by Ahounta Djimdoumalbaye and announced in Nature in 2002 by a team led by French paleontologist Michel Brunet. The find has a small cranial capacity (360 cc) and smaller canines than those in extant great apes, though they are larger and pointier than those in humans. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. A short cranial base and a foramen magnum that is more humanlike in positioning have been argued to indicate upright walking.

Initially, the inclusion of Sahelanthropus in the hominin family was debated by researchers, since the evidence for bipedalism is based on cranial evidence alone, which is not as convincing as postcranial evidence. Yet, a femur (thigh bone) and ulnae (upper arm bones) thought to belong to Sahelanthropus was discovered in 2001 (although not published until 2022). These bones may support the idea that the hominin was in fact a terrestrial biped with arboreal capabilities and behaviors (Daver et al. 2022).
Orrorin tugenensis (Orrorin meaning “original man”), dated to between 6 mya and 5.7 mya, was discovered near Tugen Hills in Kenya in 2000. Smaller cheek teeth (molars and premolars) than those in even more recent hominins, thick enamel, and reduced, but apelike, canines characterize this species. This is the first species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains. One of the most important elements discovered was a proximal femur, BAR 1002'00. The femur is the thigh bone, and the proximal part is that which articulates with the pelvis; this is very important for studying posture and locomotion. This femur indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins. Some have argued that features of the finger bones suggest potential tool-making capabilities, although many researchers argue that these features are also consistent with climbing.
Early Hominins: The Genus Ardipithecus
Another genus, Ardipithecus, is argued to be represented by at least two species: Ardipithecus (Ar.) ramidus and Ar. kadabba.
Ardipithecus ramidus (“ramid” means root in the Afar language) is currently the best-known of the earliest hominins (Figure 9.9). Unlike Sahelanthropus and Orrorin, this species has a large sample size of over 110 specimens from Aramis alone. Dated to 4.4 mya, Ar. ramidus was found in Ethiopia (in the Middle Awash region and in Gona). This species was announced in 1994 by American palaeoanthropologist Tim White, based on a partial female skeleton nicknamed “Ardi” (ARA-VP-6/500; White et al. 1994). Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, she had an opposable big toe (hallux), similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. A small brain (300 cc to 350 cc), midfacial projection, and slight prognathism show retained ancestral cranial features, but the cheek bones are less flared and robust than in later hominins.

Ardipithecus kadabba (the species name means “oldest ancestor” in the Afar language) is known from localities on the western margin of the Middle Awash region, the same locality where Ar. ramidus has been found. Specimens include mandibular fragments and isolated teeth as well as a few postcranial elements from the Asa Koma (5.5 mya to 5.77 mya) and Kuseralee Members (5.2 mya), well-dated and understood (but temporally separate) volcanic layers in East Africa. This species was discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie. Originally these specimens were referred to as a subspecies of Ar. ramidus. In 2002, six teeth were discovered at Asa Koma and the dental-wear patterns confirmed that this was a distinct species, named Ar. kadabba, in 2004. One of the postcranial remains recovered included a 5.2 million-year-old toe bone that demonstrated features that are associated with toeing off (pushing off the ground with the big toe leaving last) during walking, a characteristic unique to bipedal walkers. However, the toe bone was found in the Kuseralee Member, and therefore some doubt has been cast by researchers about its association with the teeth from the Asa Koma Member.
Bipedal Trends in Early Hominins: Summary
Trends toward bipedalism are seen in our earliest hominin finds. However, many specimens also indicate retained capabilities for climbing. Trends include a larger, more robust hallux; a more compact foot, with an arch; a robust, long femur, angled at the knee; a robust tibia; a bowl-shaped pelvis; and a more anterior foramen magnum. While the level of bipedality in Salehanthropus tchadenisis is debated since there are few fossils and no postcranial evidence, Orrorin tugenensis and Ardipithecus kadabba show clear indications of some of these bipedal trends. However, some retained ancestral traits, such as an opposable hallux in Ardipithecus, indicate some retention in climbing ability.
Derived Adaptations: Early Hominin Dention
The Importance of Teeth
Teeth are abundant in the fossil record, primarily because they are already highly mineralized as they are forming, far more so than even bone. Because of this, teeth preserve readily. And, because they preserve readily, they are well-studied and better understood than many skeletal elements. In the sparse hominin (and primate) fossil record, teeth are, in some cases, all we have.
Teeth also reveal a lot about the individual from whom they came. We can tell what they evolved to eat, to which other species they may be closely related, and even, to some extent, the level of sexual dimorphism, or general variability, within a given species. This is powerful information that can be contained in a single tooth. With a little more observation, the wearing patterns on a tooth can tell us about the diet of the individual in the weeks leading up to its death. Furthermore, the way in which a tooth is formed, and the timing of formation, can reveal information about changes in diet (or even mobility) over infancy and childhood, using isotopic analyses. When it comes to our earliest hominin relatives, this information is vital for understanding how they lived.
The purpose of comparing different hominin species is to better understand the functional morphology as it applies to dentition. In this, we mean that the morphology of the teeth or masticatory system (which includes jaws) can reveal something about the way in which they were used and, therefore, the kinds of foods these hominins ate. When comparing the features of hominin groups, it is worth considering modern analogues (i.e., animals with which to compare) to make more appropriate assumptions about diet. In this way, hominin dentition is often compared with that of chimpanzees and gorillas (our close ape relatives), as well as with that of modern humans.
The most divergent group, however, is humans. Humans around the world have incredibly varied diets. Among hunter-gatherers, it can vary from a honey- and plant-rich diet, as seen in the Hadza in Tanzania, to a diet almost entirely reliant on animal fat and protein, as seen in Inuits in polar regions of the world. We are therefore considered generalists, more general than the largely frugivorous (fruit-eating) chimpanzee or the folivorous (foliage-eating) gorilla, as discussed in Chapter 5.
One way in which all humans are similar is our reliance on the processing of our food. We cut up and tear meat with tools using our hands, instead of using our front teeth (incisors and canines). We smash and grind up hard seeds, instead of crushing them with our hind teeth (molars). This means that, unlike our ape relatives, we can rely more on developing tools to navigate our complex and varied diets. (We could say) Our brain, therefore, is our primary masticatory organ. Evolutionarily, our teeth have reduced in size and our faces are flatter, or more orthognathic, partially in response to our increased reliance on our hands and brain to process food. Similarly, a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat. These trends begin early on in our evolution. The link has been made between some of the earliest evidence for stone tool manufacture, the earliest members of our genus, and the features that we associate with these specimens.
General Dental Trends in Early Hominins
Several trends are visible in the dentition of early hominins. However, all tend to have the same dental formula. The dental formula tells us how many of each tooth type are present in each quadrant of the mouth. Going from the front of the mouth, this includes the square, flat incisors; the pointy canines; the small, flatter premolars; and the larger hind molars. In many primates, from Old World monkeys to great apes, the typical dental formula is 2:1:2:3. This means that if we divide the mouth into quadrants, each has two incisors, one canine, two premolars, and three molars. The eight teeth per quadrant total 32 teeth in all (although some humans have fewer teeth due to the absence of their wisdom teeth, or third molars).

The morphology of the individual teeth is where we see the most change. Among primates, large incisors are associated with food procurement or preparation (such as biting small fruits), while small incisors indicate a diet that may contain small seeds or leaves (where the preparation is primarily in the back of the mouth). Most hominins have relatively large, flat, vertically aligned incisors that occlude (touch) relatively well, forming a “bite.” This differs from, for instance, the orangutan, whose teeth stick out (i.e., are procumbent).
While the teeth are often aligned with diet, the canines may be misleading in that regard. We tend to associate pointy, large canines with the ripping required for meat, and the reduction (or, in some animals, the absence) of canines as indicative of herbivorous diets. In humans, our canines are often a similar size to our incisors and therefore considered incisiform (Figure 9.10). However, our closest relatives all have very long, pointy canines, particularly on their upper dentition. This is true even for the gorilla, which lives almost exclusively on plants. The canines in these instances reveal more about social structure and sexual dimorphism than diet, as large canines often signal dominance.
Early on in human evolution, we see a reduction in canine size. Sahelanthropus tchadensis and Orrorin tugenensis both have smaller canines than those in extant great apes, yet the canines are still larger and pointier than those in humans or more recent hominins. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. In Ardipithecus ramidus, there is no obvious difference between male and female canine size, yet they are still slightly larger and pointier than in modern humans. This implies a less sexually dimorphic social structure in the earlier hominins relative to modern-day chimpanzees and gorillas.
Along with a reduction in canine size is the reduction or elimination of a canine diastema: a gap between the teeth on the mandible that allows room for elongated teeth on the maxilla to “fit” in the mouth. Absence of a diastema is an excellent indication of a reduction in canine size. In animals with large canines (such as baboons), there is also often a honing P3, where the first premolar (also known as P3 for evolutionary reasons) is triangular in shape, “sharpened” by the extended canine from the upper dentition. This is also seen in some early hominins: Ardipithecus, for example, has small canines that are almost the same height as its incisors, although still larger than those in recent hominins.
The hind dentition, such as the bicuspid (two cusped) premolars or the much larger molars, are also highly indicative of a generalist diet in hominins. Among the earliest hominins, the molars are larger than we see in our genus, increasing in size to the back of the mouth and angled in such a way from the much smaller anterior dentition as to give these hominins a parabolic (V-shaped) dental arch. This differs from our living relatives and some early hominins, such as Sahelanthropus, whose molars and premolars are relatively parallel between the left and right sides of the mouth, creating a U-shape.
Among more recent early hominins, the molars are larger than those in the earliest hominins and far larger than those in our own genus, Homo. Large, short molars with thick enamel allowed our early cousins to grind fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing. In our genus, the hind dentition is far smaller than in these early hominins. Our teeth also have medium-size cusps, which allow for both efficient grinding and tearing/shearing meats.
Understanding the dental morphology has allowed researchers to extrapolate very specific behaviors of early hominins. It is worth noting that while teeth preserve well and are abundant, a slew of other morphological traits additionally provide evidence for many of these hypotheses. Yet there are some traits that are ambiguous. For instance, while there are definitely high levels of sexual dimorphism in Au. afarensis, discussed in the next section, the canine teeth are reduced in size, implying that while canines may be useful indicators for sexual dimorphism, it is also worth considering other evidence.
In summary, trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the ancestral dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
Special Topic: Contested Species
Many named species are highly debated and argued to have specimens associated with a more variable Au. afarensis or Au. anamensis species. Sometimes these specimens are dated to times when, or found in places in which, there are “gaps” in the palaeoanthropological record. These are argued to represent chronospecies or variants of Au. afarensis. However, it is possible that, with more discoveries, the distinct species types will hold.
Australopithecus bahrelghazali is dated to within the time period of Au. afarensis (3.6 mya; Brunet et al. 1995) and was the first Australopithecine to be discovered in Chad in central Africa. Researchers argue that the holotype, whom discoverers have named “Abel,” falls under the range of variation of Au. afarensis and therefore that A. bahrelghazali does not fall into a new species (Lebatard et al. 2008). If “Abel” is a member of Au. afarensis, the geographic range of the species would be greatly extended.
On a different note, Australopithecus deyiremada (meaning “close relative” in the Ethiopian language of Afar) is dated to 3.5 mya to 3.3 mya and is based on fossil mandible bones discovered in 2011 in Woranso-Mille (in the Afar region of Ethiopia) by Yohannes Haile-Selassie, an Ethiopian paleoanthropologist (Haile-Selassie et al. 2019). The discovery indicated, in contrast to Au. afarensis, smaller teeth with thicker enamel (potentially suggesting a harder diet) as well as a larger mandible and more projecting cheekbones. This find may be evidence that more than one closely related hominin species occupied the same region at the same temporal period (Haile-Selassie et al. 2015; Spoor 2015) or that other Au. afarensis specimens have been incorrectly designated. However, others have argued that this species has been prematurely identified and that more evidence is needed before splitting the taxa, since the variation appears subtle and may be due to slightly different niche occupations between populations over time.
Australopithecus garhi is another species found in the Middle Awash region of Ethiopia. It is currently dated to 2.5 mya (younger than Au. afarensis). Researchers have suggested it fills in a much-needed temporal “gap” between hominin finds in the region, with some anatomical differences, such as a relatively large cranial capacity (450 cc) and larger hind dentition than seen in other gracile Australopithecines. Similarly, the species has been argued to have longer hind limbs than Au. afarensis, although it was still able to move arboreally (Asfaw et al. 1999). However, this species is not well documented or understood and is based on only several fossil specimens. More astonishingly, crude stone tools resembling Oldowan (which will be described later) have been found in association with Au. garhi. While lacking some of the features of the Oldowan, this is one of the earliest technologies found in direct association with a hominin.
Kenyanthopus platyops (the name “platyops” refers to its flatter-faced appearance) is a highly contested genus/species designation of a specimen (KNM-WT 40000) from Lake Turkana in Kenya, discovered by Maeve Leakey in 1999 (Figure 9.11). Dated to between 3.5 mya and 3.2 mya, some have suggested this specimen is an Australopithecus, perhaps even Au. afarensis (with a brain size which is difficult to determine, yet appears small), while still others have placed this specimen in Homo (small dentition and flat-orthognathic face). While taxonomic placing of this species is quite divided, the discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis (Leakey et al. 2001). Some researchers have additionally associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this specimen.

The Genus Australopithecus
The Australopithecines are a diverse group of hominins, comprising various species. Australopithecus is the given group or genus name. It stems from the Latin word Australo, meaning “southern,” and the Greek word pithecus, meaning “ape.” Within this section, we will outline these differing species’ geological and temporal distributions across Africa, unique derived and/or shared traits, and importance in the fossil record.

Between 3 mya and 1 mya, there seems to be differences in dietary strategy between different species of hominins designated as Australopithecines. A pattern of larger posterior dentition (even relative to the incisors and canines in the front of the mouth), thick enamel, and cranial evidence for extremely large chewing muscles is far more pronounced in a group known as the robust australopithecines. This pattern is extremely relative to their earlier contemporaries or predecessors, the gracile australopithecines, and is certainly larger than those seen in early Homo, which emerged during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins (Figure 9.12).
Because of these differences, this section has been divided into “gracile” and “robust” Australopithecines, highlighting the morphological differences between the two groups (which many researchers have designated as separate genera: Australopithecus and Paranthropus, respectively) and then focusing on the individual species. It is worth noting, however, that not all researchers accept these clades as biologically or genetically distinct, with some researchers insisting that the relative gracile and robust features found in these species are due to parallel evolutionary events toward similar dietary niches.
Despite this genus’ ancestral traits and small cranial capacity, all members show evidence of bipedal locomotion. It is generally accepted that Australopithecus species display varying degrees of arborealism along with bipedality.
Gracile Australopithecines
This section describes individual species from across Africa. These species are called “gracile australopithecines” because of their smaller and less robust features compared to the divergent “robust” group. Numerous Australopithecine species have been named, but some are only based on a handful of fossil finds, whose designations are controversial.
East African Australopithecines
East African Australopithecines are found throughout the EARS, and they include the earliest species associated with this genus. Numerous fossil-yielding sites, such as Olduvai, Turkana, and Laetoli, have excellent, datable stratigraphy, owing to the layers of volcanic tufts that have accumulated over millions of years. These tufts may be dated using absolute dating techniques, such as Potassium-Argon dating (described in Chapter 7). This means that it is possible to know a relatively refined date for any fossil if the context (i.e., exact location) of that find is known. Similarly, comparisons between the faunal assemblages of these stratigraphic layers have allowed researchers to chronologically identify environmental changes.

The earliest known Australopithecine is dated to 4.2 mya to 3.8 mya. Australopithecus anamensis (after “Anam,” meaning “lake” from the Turkana region in Kenya; Leakey et al. 1995; Patterson and Howells 1967) is currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia; Figure 9.13). Recently, a 2019 find from Ethiopia, named MRD, after Miro Dora where it was found, was discovered by an Ethiopian herder named Ali Bereino. It is one of the most complete cranial finds of this species (Ward et al. 1999). A small brain size (370 cc), relatively large canines, projecting cheekbones, and earholes show more ancestral features as compared to those of more recent Australopithecines. The most important element discovered with this species is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking. Similarly, the earliest found hominin femur belongs to this species. Ancestral traits in the upper limb (such as the humerus) indicate some retained arboreal locomotion.
Some researchers suggest that Au. anamensis is an intermediate form of the chronospecies that becomes Au. afarensis, evolving from Ar. ramidus. However, this is debated, with other researchers suggesting morphological similarities and affinities with more recent species instead. Almost 100 specimens, representing over 20 individuals, have been found to date (Leakey et al. 1995; McHenry 2009; Ward et al. 1999).
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. Au. afarensis (which means “from the Afar region”) is dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia (Figure 9.14). The most famous individual from this species is a partial female skeleton discovered in Hadar (Ethiopia), later nicknamed “Lucy,” after the Beatles’ song “Lucy in the Sky with Diamonds,” which was played in celebration of the find (Johanson et al. 1978; Kimbel and Delezene 2009). This skeleton was found in 1974 by Donald Johanson and dates to approximately 3.2 mya. In addition, in 2002 a juvenile of the species was found by Zeresenay Alemseged and given the name “Selam” (meaning “peace,” DIK 1-1), though it is popularly known as “Lucy’s Child” or as the “Dikika Child” (Alemseged et al. 2006). Similarly, the “Laetoli Footprints” (discussed in Chapter 7; Hay and Leakey 1982; Leakey and Hay 1979) have drawn much attention.


The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans (indicative of a generalist diet); in addition, Au. afarensis has a prognathic face (the face below the eyes juts anteriorly) and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus. Despite a reduction in canine size in this species, large overall size variation indicates high levels of sexual dimorphism.
Skeletal evidence indicates that this species was bipedal, as its pelvis and lower limb demonstrate a humanlike femoral neck, valgus knee, and bowl-shaped hip (Figure 9.15). More evidence of bipedalism is found in the footprints of this species. Au. afarensis is associated with the Laetoli Footprints, a 24-meter trackway of hominin fossil footprints preserved in volcanic ash discovered by Mary Leakey in Tanzania and dated to 3.5 mya to 3 mya. This set of prints is thought to have been produced by three bipedal individuals as there are no knuckle imprints, no opposable big toes, and a clear arch is present. The infants of this species are thought to have been more arboreal than the adults, as discovered through analyses of the foot bones of the Dikika Child dated to 3.32 mya (Alemseged et al. 2006).
Although not found in direct association with stone tools, potential evidence for cut marks on bones, found at Dikika, and dated to 3.39 mya indicates a possible temporal/ geographic overlap between meat eating, tool use, and this species. However, this evidence is fiercely debated. Others have associated the cut marks with the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species.
South African Australopithecines
Since the discovery of the Taung Child, there have been numerous Australopithecine discoveries from the region known as “The Cradle of Humankind,” which was recently given UNESCO World Heritage Site status as “The Fossil Hominid Sites of South Africa.” The limestone caves found in the Cradle allow for the excellent preservation of fossils. Past animals navigating the landscape and falling into cave openings, or caves used as dens by carnivores, led to the accumulation of deposits over millions of years. Many of the hominin fossils, encased in breccia (hard, calcareous sedimentary rock), are recently exposed from limestone quarries mined in the previous century. This means that extracting fossils requires excellent and detailed exposed work, often by a team of skilled technicians.
While these sites have historically been difficult to date, with mixed assemblages accumulated over large time periods, advances in techniques such as uranium-series dating have allowed for greater accuracy. Historically, the excellent faunal record from East Africa has been used to compare sites based on relative dating, whereby environmental and faunal changes and extinction events allow us to know which hominin finds are relatively younger or older than others.
The discovery of the Taung Child in 1924 (discussed in the Special Topic box “The Taung Child” below) shifted the focus of palaeoanthropological research from Europe to Africa, although acceptance of this shift was slow (Broom 1947; Dart 1925). The species to which it is assigned, Australopithecus africanus (name meaning “Southern Ape of Africa”), is currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa (Figure 9.16). A relatively large brain (400 cc to 500 cc), small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits. Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism. However, the sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some ancestral features. Although not in direct association with stone tools, a 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities.

Another famous Au. africanus skull (the skull of “Mrs. Ples”) was previously attributed to Plesianthropus transvaalensis, meaning “near human from the Transvaal,” the old name for Gauteng Province, South Africa (Broom 1947, 1950). The name was shortened by contemporary journalists to “Ples” (Figure 9.17). Due to the prevailing mores of the time, the assumed female found herself married, at least in name, and has become widely known as “Mrs. Ples.” It was later reassigned to Au. africanus and is now argued by some to be a young male rather than an adult female cranium (Thackeray 2000, Thackeray et al. 2002).

In 2008, nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger, noted a clavicle bone in some leftover mining breccia in the Malapa Fossil Site (South Africa). After rigorous studies, the species, Australopithecus sediba (meaning “fountain” or “wellspring” in the South African language of Sesotho), was named in 2010 (Figure 9.18; Berger et al. 2010). The first type specimen belongs to a juvenile male, Karabo (MH1), but the species is known from at least six partial skeletons, from infants through adults. These specimens are currently dated to 1.97 mya (Dirks et al. 2010). The discoverers have argued that Au. sediba shows mosaic features between Au. africanus and the genus, Homo, which potentially indicates a transitional species, although this is heavily debated. These features include a small brain size (Australopithecus-like; 420 cc to 450 cc) but gracile mandible and small teeth (Homo-like). Similarly, the postcranial skeletons are also said to have mosaic features: scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. Some researchers have argued that Au. sediba shows a modern hand morphology (shorter fingers and a longer thumb), indicating that adaptations to tool manufacture and use may be present in this species.

Another famous Australopithecine find from South Africa is that of the nearly complete skeleton now known as “Little Foot” (Clarke 1998, 2013). Little Foot (StW 573) is potentially the earliest dated South African hominin fossil, dating to 3.7 mya, based on radiostopic techniques, although some argue that it is younger than 3 mya (Pickering and Kramers 2010). The name is jokingly in contrast to the cryptid species “bigfoot” and is named because the initial discovery of four ankle bones indicated bipedality. Little Foot was discovered by Ron Clarke in 1994, when he came across the ankle bones while sorting through monkey fossils in the University of Witwatersrand collections (Clarke and Tobias 1995). He asked Stephen Motsumi and Nkwane Molefe to identify the known records of the fossils, which allowed them to find the rest of the specimen within just days of searching the Sterkfontein Caves’ Silberberg Grotto.
The discoverers of Little Foot insist that other fossil finds, previously identified as Au. Africanus, be placed in this new species based on shared ancestral traits with older East African Australopithecines (Clarke and Kuman 2019). These include features such as a relatively large brain size (408 cc), robust zygomatic arch, and a flatter midface. Furthermore, the discoverers have argued that the heavy anterior dental wear patterns, relatively large anterior dentition, and smaller hind dentition of this specimen more closely resemble that of Au. anamensis or Au. afarensis. It has thus been placed in the species Australopithecus prometheus. This species name refers to a previously defunct taxon named by Raymond Dart. The species designation was, through analyzing Little Foot, revived by Ron Clarke, who insists that many other fossil hominin specimens have prematurely been placed into Au. africanus. Others say that it is more likely that Au. africanus is a more variable species and not representative of two distinct species.
Paranthropus “Robust” Australopithecines
In the robust australopithecines, the specialized nature of the teeth and masticatory system, such as flaring zygomatic arches (cheekbones), accommodate very large temporalis (chewing) muscles. These features also include a large, broad, dish-shaped face and and a large mandible with extremely large posterior dentition (referred to as megadonts) and hyper-thick enamel (Kimbel 2015; Lee-Thorp 2011; Wood 2010). Research has revolved around the shared adaptations of these “robust” australopithecines, linking their morphologies to a diet of hard and/or tough foods (Brain 1967; Rak 1988). Some argued that the diet of the robust australopithecines was so specific that any change in environment would have accelerated their extinction. The generalist nature of the teeth of the gracile australopithecines, and of early Homo, would have made them more capable of adapting to environmental change. However, some have suggested that the features of the robust australopithecines might have developed as an effective response to what are known as fallback foods in hard times rather than indicating a lack of adaptability.
There are currently three widely accepted robust australopithecus or, Paranthropus, species: P. aethiopicus, which has more ancestral traits, and P. boisei and P. robustus, which are more derived in their features (Strait et al. 1997; Wood and Schroer 2017). These three species have been grouped together by a majority of scholars as a single genus as they share more derived features (are more closely related to each other; or, in other words, are monophyletic) than the other australopithecines (Grine 1988; Hlazo 2015; Strait et al. 1997; Wood 2010 ). While researchers have mostly agreed to use the umbrella term Paranthropus, there are those who disagree (Constantino and Wood 2004, 2007; Wood 2010).
As a collective, this genus spans 2.7 mya to 1.0 mya, although the dates of the individual species differ. The earliest of the Paranthropus species, Paranthropus aethiopicus, is dated to between 2.7 mya and 2.3 mya and currently found in Tanzania, Kenya, and Ethiopia in the EARS system (Figure 9.19; Constantino and Wood 2007; Hlazo 2015; Kimbel 2015; Walker et al. 1986; White 1988). It is well known because of one specimen known as the “Black Skull” (KNM–WT 17000), so called because of the mineral manganese that stained it black during fossilization (Kimbel 2015). As with all robust Australopithecines, P. aethiopicus has the shared derived traits of large, flat premolars and molars; large, flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle); a sagittal crest (ridge on the top of the skull) for increased muscle attachment of the chewing muscles to the skull; and a robust mandible and supraorbital torus (brow ridge). However, only a few teeth have been found. A proximal tibia indicates bipedality and similar body size to Au. afarensis. In recent years, researchers have discovered and assigned a proximal tibia and juvenile cranium (L.338y-6) to the species (Wood and Boyle 2016).

First attributed as Zinjanthropus boisei (with the first discovery going by the nickname “Zinj” or sometimes “Nutcracker Man”), Paranthropus boisei was discovered in 1959 by Mary Leakey (see Figure 9.20 and 9.21; Hay 1990; Leakey 1959). This “robust” australopith species is distributed across countries in East Africa at sites such as Kenya (Koobi Fora, West Turkana, and Chesowanja), Malawi (Malema-Chiwondo), Tanzania (Olduvai Gorge and Peninj), and Ethiopia (Omo River Basin and Konso). The hypodigm, sample of fossils whose features define the group, has been found by researchers to date to roughly 2.4 mya to 1.4 mya. Due to the nature of its exaggerated, larger, and more robust features, P. boisei has been termed hyper-robust—that is, even more heavily built than other robust species, with very large, flat posterior dentition (Kimbel 2015). Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). Another famous specimen from this species is the Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu.


Paranthropus robustus was the first taxon to be discovered within the genus in Kromdraai B by a schoolboy named Gert Terblanche; subsequent fossil discoveries were made by researcher Robert Broom in 1938 (Figure 9.22; Broom 1938a, 1938b, 1950), with the holotype specimen TM 1517 (Broom 1938a, 1938b, 1950; Hlazo 2018). Paranthropus robustus dates approximately from 2.0 mya to 1 mya and is the only taxon from the genus to be discovered in South Africa. Several of these fossils are fragmentary in nature, distorted, and not well preserved because they have been recovered from quarry breccia using explosives. P. robustus features are neither as “hyper-robust” as P. boisei nor as ancestral as P. aethiopicus; instead, they have been described as being less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring; Rak 1983; Walker and Leakey 1988). Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick-enameled dentition.

Comparisons between Gracile and Robust Australopiths
Comparisons between gracile and robust australopithecines may indicate different phylogenetic groupings or parallel evolution in several species. In general, the robust australopithecines have large temporalis (chewing) muscles, as indicated by flaring zygomatic arches, sagittal crests, and robust mandibles (jawbones). Their hind dentition is large (megadont), with low cusps and thick enamel. Within the gracile australopithecines, researchers have debated the relatedness of the species, or even whether these species should be lumped together to represent more variable or polytypic species. Often researchers will attempt to draw chronospecific trajectories, with one taxon said to evolve into another over time.
Special Topic: The Taung Child

The well-known fossil of a juvenile Australopithecine, the “Taung Child,” was the first early hominin evidence ever discovered and was the first to demonstrate our common human heritage in Africa (Figure 9.23; Dart 1925). The tiny facial skeleton and natural endocast were discovered in 1924 by a local quarryman in the North West Province in South Africa and were painstakingly removed from the surrounding cement-like breccia by Raymond Dart using his wife’s knitting needles. When first shared with the scientific community in 1925, it was discounted as being nothing more than a young monkey of some kind. Prevailing biases of the time made it too difficult to contemplate that this small-brained hominin could have anything to do with our own history. The fact that it was discovered in Africa simply served to strengthen this bias.
Early Tool Use and Technology
Early Stone Age Technology (ESA)
The Early Stone Age (ESA) marks the beginning of recognizable technology made by our human ancestors. Stone-tool (or lithic) technology is defined by the fracturing of rocks and the manufacture of tools through a process called knapping. The Stone Age lasted for more than 3 million years and is broken up into chronological periods called the Early (ESA), Middle (MSA), and Later Stone Ages (LSA). Each period is further broken up into a different techno-complex, a term encompassing multiple assemblages (collections of artifacts) that share similar traits in terms of artifact production and morphology. The ESA spanned the largest technological time period of human innovation from over 3 million years ago to around 300,000 years ago and is associated almost entirely with hominin species prior to modern Homo sapiens. As the ESA advanced, stone tool makers (known as knappers) began to change the ways they detached flakes and eventually were able to shape artifacts into functional tools. These advances in technology go together with the developments in human evolution and cognition, dispersal of populations across the African continent and the world, and climatic changes.
In order to understand the ESA, it is important to consider that not all assemblages are exactly the same within each techno-complex: one can have multiple phases and traditions at different sites (Lombard et al. 2012). However, there is an overarching commonality between them. Within stone tool assemblages, both flakes or cores (the rocks from which flakes are removed) are used as tools. Large Cutting Tools (LCTs) are tools that are shaped to have functional edges. It is important to note that the information presented here is a small fraction of what is known about the ESA, and there are ongoing debates and discoveries within archaeology.
Currently, the oldest-known stone tools, which form the techno-complex the Lomekwian, date to 3.3 mya (Harmand et al. 2015; Toth 1985). They were found at a site called Lomekwi 3 in Kenya. This techno-complex is the most recently defined and pushed back the oldest-known date for lithic technology. There is only one known site thus far and, due to the age of the site, it is associated with species prior to Homo, such as Kenyanthropus platyops. Flakes were produced through indirect percussion, whereby the knappers held a rock and hit it against another rock resting on the ground. The pieces are very chunky and do not display the same fracture patterns seen in later techno-complexes. Lomekwian knappers likely aimed to get a sharp-edged piece on a flake, which would have been functional, although the specific function is currently unknown.
Stone tool use, however, is not only understood through the direct discovery of the tools. Cut marks on fossilized animal bones may illuminate the functionality of stone tools. In one controversial study in 2010, researchers argued that cut marks on a pair of animal bones from Dikika (Ethiopia), dated to 3.4 mya, were from stone tools. The discoverers suggested that they be more securely associated, temporally, with Au. afarensis. However, others have noted that these marks are consistent with teeth marks from crocodiles and other carnivores.

The Oldowan techno-complex is far more established in the scientific literature (Leakey 1971). It is called the Oldowan because it was originally discovered in Olduvai Gorge, Tanzania, but the oldest assemblage is from Gona in Ethiopia, dated to 2.6 mya (Semaw 2000). The techno-complex is defined as a core and flake industry. Like the Lomekwian, there was an aim to get sharp-edged flakes, but this was achieved through a different production method. Knappers were able to actively hold or manipulate the core being knapped, which they could directly hit using a hammerstone. This technique is known as free-hand percussion, and it demonstrates an understanding of fracture mechanics. It has long been argued that the Oldowan hominins were skillful in tool manufacture.
Because Oldowan knapping requires skill, earlier researchers have attributed these tools to members of our genus, Homo. However, some have argued that these tools are in more direct association with hominins in the genera described in this chapter (Figure 9.24).
Invisible Tool Manufacture and Use
The vast majority of our understanding of these early hominins comes from fossils and reconstructed paleoenvironments. It is only from 3 mya when we can start “looking into their minds” and lifestyles by analyzing their manufacture and use of stone tools. However, the vast majority of tool use in primates (and, one can argue, in humans) is not with durable materials like stone. All of our extant great ape relatives have been observed using sticks, leaves, and other materials for some secondary purpose (to wade across rivers, to “fish” for termites, or to absorb water for drinking). It is possible that the majority of early hominin tool use and manufacture may be invisible to us because of this preservation bias.
Chapter Summary
The fossil record of our earliest hominin relatives has allowed paleoanthropologists to unpack some of the mysteries of our evolution. We now know that traits associated with bipedalism evolved before other “human-like” traits, even though the first hominins were still very capable of arboreal locomotion. We also know that, for much of this time, hominin taxa were diverse in the way they looked and what they ate, and they were widely distributed across the African continent. And we know that the environments in which these hominins lived underwent many changes over this time during several warming and cooling phases.
Yet this knowledge has opened up many new mysteries. We still need to better differentiate some taxa. In addition, there are ongoing debates about why certain traits evolved and what they meant for the extinction of some of our relatives (like the robust australopiths). The capabilities of these early hominins with respect to tool use and manufacture is also still uncertain.
Hominin Species Summaries
Hominin |
Sahelanthropus tchadensis |
Dates |
7 mya to 6 mya |
Region(s) |
Chad |
Famous discoveries |
The initial discovery, made in 2001. |
Brain size |
360 cc average |
Dentition |
Smaller than in extant great apes; larger and pointier than in humans. Canines worn at the tips. |
Cranial features |
A short cranial base and a foramen magnum (hole in which the spinal cord enters the cranium) that is more humanlike in positioning; has been argued to indicate upright walking. |
Postcranial features |
Currently little published postcranial material. |
Culture |
N/A |
Other |
The extent to which this hominin was bipedal is currently heavily debated. If so, it would indicate an arboreal bipedal ancestor of hominins, not a knuckle-walker like chimpanzees. |
Hominin |
Orrorin tugenensis |
Dates |
6 mya to 5.7 mya |
Region(s) |
Tugen Hills (Kenya) |
Famous discoveries |
Original discovery in 2000. |
Brain size |
N/A |
Dentition |
Smaller cheek teeth (molars and premolars) than even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines. |
Cranial features |
Not many found |
Postcranial features |
Fragmentary leg, arm, and finger bones have been found. Indicates bipedal locomotion. |
Culture |
Potential toolmaking capability based on hand morphology, but nothing found directly. |
Other |
This is the earliest species that clearly indicates adaptations for bipedal locomotion. |
Hominin |
Ardipithecus kadabba |
Dates |
5.2 mya to 5.8 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
Discovered by Yohannes Haile-Selassie in 1997. |
Brain size |
N/A |
Dentition |
Larger hind dentition than in modern chimpanzees. Thick enamel and larger canines than in later hominins. |
Cranial features |
N/A |
Postcranial features |
A large hallux (big toe) bone indicates a bipedal “push off.” |
Culture |
N/A |
Other |
Faunal evidence indicates a mixed grassland/woodland environment. |
Hominin |
Ardipithecus ramidus |
Dates |
4.4 mya |
Region(s) |
Middle Awash region and Gona (Ethiopia) |
Famous discoveries |
A partial female skeleton nicknamed “Ardi” (ARA-VP-6/500) (found in 1994). |
Brain size |
300 cc to 350 cc |
Dentition |
Little differences between the canines of males and females (small sexual dimorphism). |
Cranial features |
Midfacial projection, slightly prognathic. Cheekbones less flared and robust than in later hominins. |
Postcranial features |
Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, an opposable big toe similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. |
Culture |
None directly associated |
Other |
Over 110 specimens from Aramis |
Hominin |
Australopithecus anamensis |
Dates |
4.2 mya to 3.8 mya |
Region(s) |
Turkana region (Kenya); Middle Awash (Ethiopia) |
Famous discoveries |
A 2019 find from Ethiopia, named MRD. |
Brain size |
370 cc |
Dentition |
Relatively large canines compared with more recent Australopithecines. |
Cranial features |
Projecting cheekbones and ancestral earholes. |
Postcranial features |
Lower limb bones (tibia and femur) indicate bipedality; arboreal features in upper limb bones (humerus) found. |
Culture |
N/A |
Other |
Almost 100 specimens, representing over 20 individuals, have been found to date. |
Hominin |
Australopithecus afarensis |
Dates |
3.9 mya to 2.9 mya |
Region(s) |
Afar Region, Omo, Maka, Fejej, and Belohdelie (Ethiopia); Laetoli (Tanzania); Koobi Fora (Kenya) |
Famous discoveries |
Lucy (discovery: 1974), Selam (Dikika Child, discovery: 2000), Laetoli Footprints (discovery: 1976). |
Brain size |
380 cc to 430 cc |
Dentition |
Reduced canines and molars relative to great apes but larger than in modern humans. |
Cranial features |
Prognathic face, facial features indicate relatively strong chewing musculature (compared with Homo) but less extreme than in Paranthropus. |
Postcranial features |
Clear evidence for bipedalism from lower limb postcranial bones. Laetoli Footprints indicate humanlike walking. Dikika Child bones indicate retained ancestral arboreal traits in the postcrania. |
Culture |
None directly, but close in age and proximity to controversial cut marks at Dikika and early tools in Lomekwi. |
Other |
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. |
Hominin |
Australopithecus bahrelghazali |
Dates |
3.6 mya |
Region(s) |
Chad |
Famous discoveries |
“Abel,” the holotype (discovery: 1995). |
Brain size |
N/A |
Dentition |
N/A |
Cranial features |
N/A |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Arguably within range of variation of Au. afarensis. |
Hominin |
Australopithecus prometheus |
Dates |
3.7 mya (debated) |
Region(s) |
Sterkfontein (South Africa) |
Famous discoveries |
“Little Foot” (StW 573) (discovery: 1994) |
Brain size |
408 cc (Little Foot estimate) |
Dentition |
Heavy anterior dental wear patterns, relatively large anterior dentition and smaller hind dentition, similar to Au. afarensis. |
Cranial features |
Relatively larger brain size, robust zygomatic arch, and a flatter midface. |
Postcranial features |
The initial discovery of four ankle bones indicated bipedality. |
Culture |
N/A |
Other |
Highly debated new species designation. |
Hominin |
Australopithecus deyiremada |
Dates |
3.5 mya to 3.3 mya |
Region(s) |
Woranso-Mille (Afar region, Ethiopia) |
Famous discoveries |
First fossil mandible bones were discovered in 2011 in the Afar region of Ethiopia by Yohannes Haile-Selassie. |
Brain size |
N/A |
Dentition |
Smaller teeth with thicker enamel than seen in Au. afarensis, with a potentially hardier diet. |
Cranial features |
Larger mandible and more projecting cheekbones than in Au. afarensis. |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Contested species designation; arguably a member of Au. afarensis. |
Hominin |
Kenyanthopus platyops |
Dates |
3.5 mya to 3.2 mya |
Region(s) |
Lake Turkana (Kenya) |
Famous discoveries |
KNM–WT 40000 (discovered 1999) |
Brain size |
Difficult to determine but appears within the range of Australopithecus afarensis. |
Dentition |
Small molars/dentition (Homo-like characteristic) |
Cranial features |
Flatter (i.e., orthognathic) face |
Postcranial features |
N/A |
Culture |
Some have associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species/specimen. |
Other |
Taxonomic placing of this species is quite divided. The discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis. |
Hominin |
Australopithecus africanus |
Dates |
3.3 mya to 2.1 mya |
Region(s) |
Sterkfontein, Taung, Makapansgat, Gladysvale (South Africa) |
Famous discoveries |
Taung Child (discovery in 1994), “Mrs. Ples” (discover in 1947), Little Foot (arguable; discovery in 1994). |
Brain size |
400 cc to 500 cc |
Dentition |
Smaller teeth (derived) relative to Au. afarensis. Small canines with no diastema. |
Cranial features |
A rounder skull compared with Au. afarensis in East Africa. A sloping face (ancestral). |
Postcranial features |
Similar postcranial evidence for bipedal locomotion (derived pelvis) with retained arboreal locomotion, e.g., curved phalanges (fingers), as seen in Au. afarensis. |
Culture |
None with direct evidence. |
Other |
A 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities. |
Hominin |
Australopithecus garhi |
Dates |
2.5 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
N/A |
Brain size |
450 cc |
Dentition |
Larger hind dentition than seen in other gracile Australopithecines. |
Cranial features |
N/A |
Postcranial features |
A femur of a fragmentary partial skeleton, argued to belong to Au. garhi, indicates this species may be longer-limbed than Au. afarensis, although still able to move arboreally. |
Culture |
Crude stone tools resembling Oldowan (described later) have been found in association with Au. garhi. |
Other |
This species is not well documented or understood and is based on only a few fossil specimens. |
Hominin |
Paranthropus aethiopicus |
Dates |
2.7 mya to 2.3 mya |
Region(s) |
West Turkana (Kenya); Laetoli (Tanzania); Omo River Basin (Ethiopia) |
Famous discoveries |
The “Black Skull” (KNM–WT 17000) (discovery 1985). |
Brain Size |
410 cc |
Dentition |
P. aethiopicus has the shared derived traits of large flat premolars and molars, although few teeth have been found. |
Cranial features |
Large flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle), a sagittal crest for increased muscle attachment of the chewing muscles to the skull, and a robust mandible and supraorbital torus (brow ridge). |
Postcranial features |
A proximal tibia indicates bipedality and similar size to Au. afarensis. |
Culture |
N/A |
Other |
The “Black Skull” is so called because of the mineral manganese that stained it black during fossilization. |
Hominin |
Paranthropus boisei |
Dates |
2.4 mya to 1.4 mya |
Region(s) |
Koobi Fora, West Turkana, and Chesowanja (Kenya); Malema-Chiwondo (Malawi), Olduvai Gorge and Peninj (Tanzania); and Omo River basin and Konso (Ethiopia) |
Famous discoveries |
“Zinj,” or sometimes “Nutcracker Man” (OH5), in 1959 by Mary Leakey. The Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu. |
Brain size |
500 cc to 550 cc |
Dentition |
Very large, flat posterior dentition (largest of all hominins currently known). Much smaller anterior dentition. Very thick dental enamel. |
Cranial features |
Indications of very large chewing muscles (e.g., flaring zygomatic arches and a large sagittal crest). |
Postcranial features |
Evidence for high variability and sexual dimorphism, with estimates of males at 1.37 meters tall and females at 1.24 meters. |
Culture |
Richard Leakey and Bernard Wood have both suggested that P. boisei could have made and used stone tools. Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. |
Other |
Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). This differs from what is seen in P. robustus. |
Hominin |
Australopithecus sediba |
Dates |
1.97 mya |
Region(s) |
Malapa Fossil Site (South Africa) |
Famous discoveries |
Karabo (MH1) (discovery in 2008) |
Brain size |
420 cc to 450 cc |
Dentition |
Small dentition with Australopithecine cusp-spacing. |
Cranial features |
Small brain size (Australopithecus-like) but gracile mandible (Homo-like). |
Postcranial features |
Scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (tree climbing, particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. |
Culture |
None of direct association, but some have argued that a modern hand morphology (shorter fingers and a longer thumb) means that adaptations to tool manufacture and use may be present in this species. |
Other |
It was first discovered through a clavicle bone in 2008 by nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger. |
Hominin |
Paranthropus robustus |
Dates |
2.3 mya to 1 mya |
Region(s) |
Kromdraai B, Swartkrans, Gondolin, Drimolen, and Coopers Cave (South Africa) |
Famous discoveries |
SK48 (original skull) |
Brain size |
410 cc to 530 cc |
Dentition |
Large posterior teeth with thick enamel, consistent with other Robust Australopithecines. Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick enameled dentition. |
Cranial features |
P. robustus features are neither as “hyper-robust” as P. boisei or as ancestral in features as P. aethiopicus. They have been described as less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring). |
Postcranial features |
Reconstructions indicate sexual dimorphism. |
Culture |
N/A |
Other |
Several of these fossils are fragmentary in nature, distorted, and not well preserved, because they have been recovered from quarry breccia using explosives. |
Review Questions
- What is the difference between a “derived” versus an “ancestral” trait? Give an example of both, seen in Au. afarensis.
- Which of the paleoenvironment hypotheses have been used to describe early hominin diversity, and which have been used to describe bipedalism?
- Which anatomical features for bipedalism do we see in early hominins?
- Describe the dentition of gracile and robust australopithecines. What might these tell us about their diets?
- List the hominin species argued to be associated with stone tool technologies. Are you convinced of these associations? Why/why not?
Key Terms
Arboreal: Related to trees or woodland.
Aridification: Becoming increasingly arid or dry, as related to the climate or environment.
Aridity Hypothesis: The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution.
Assemblage: A collection demonstrating a pattern. Often pertaining to a site or region.
Bipedalism: The locomotor ability to walk on two legs.
Breccia: Hard, calcareous sedimentary rock.
Canines: The pointy teeth just next to the incisors, in the front of the mouth.
Cheek teeth: Or hind dentition (molars and premolars).
Chronospecies: Species that are said to evolve into another species, in a linear fashion, over time.
Clade: A group of species or taxa with a shared common ancestor.
Cladistics: The field of grouping organisms into those with shared ancestry.
Context: As pertaining to palaeoanthropology, this term refers to the place where an artifact or fossil is found.
Cores: The remains of a rock that has been flaked or knapped.
Cusps: The ridges or “bumps” on the teeth.
Dental formula: A technique to describe the number of incisors, canines, premolars, and molars in each quadrant of the mouth.
Derived traits: Newly evolved traits that differ from those seen in the ancestor.
Diastema: A tooth gap between the incisors and canines.
Early Stone Age (ESA): The earliest-described archaeological period in which we start seeing stone-tool technology.
East African Rift System (EARS): This term is often used to refer to the Rift Valley, expanding from Malawi to Ethiopia. This active geological structure is responsible for much of the visibility of the paleoanthropological record in East Africa.
Enamel: The highly mineralized outer layer of the tooth.
Encephalization: Expansion of the brain.
Extant: Currently living—i.e., not extinct.
Fallback foods: Foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
Fauna: The animals of a particular region, habitat, or geological period.
Faunal assemblages: Collections of fossils of the animals found at a site.
Faunal turnover: The rate at which species go extinct and are replaced with new species.
Flake: The piece knocked off of a stone core during the manufacture of a tool, which may be used as a stone tool.
Flora: The plants of a particular region, habitat, or geological period.
Folivorous: Foliage-eating.
Foramen magnum: The large hole (foramen) at the base of the cranium, through which the spinal cord enters the skull.
Fossil: The remains or impression of an organism from the past.
Frugivorous: Fruit-eating.
Generalist: A species that can thrive in a wide variety of habitats and can have a varied diet.
Glacial: Colder, drier periods during an ice age when there is more ice trapped at the poles.
Gracile: Slender, less rugged, or pronounced features.
Hallux: The big toe.
Holotype: A single specimen from which a species or taxon is described or named.
Hominin: A primate category that includes humans and our fossil relatives since our divergence from extant great apes.
Honing P3: The mandibular premolar alongside the canine (in primates, the P3), which is angled to give space for (and sharpen) the upper canines.
Hyper-robust: Even more robust than considered normal in the Paranthropus genus.
Hypodigm: A sample (here, fossil) from which researchers extrapolate features of a population.
Incisiform: An adjective referring to a canine that appears more incisor-like in morphology.
Incisors: The teeth in the front of the mouth, used to bite off food.
Interglacial: A period of milder climate in between two glacial periods.
Isotopes: Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses.
Knappers: The people who fractured rocks in order to manufacture tools.
Knapping: The fracturing of rocks for the manufacture of tools.
Large Cutting Tool (LCT): A tool that is shaped to have functional edges.
Last Common Ancestor (LCA): The hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence.
Lithic: Relating to stone (here to stone tools).
Lumbar lordosis: The inward curving of the lower (lumbar) parts of the spine. The lower curve in the human S-shaped spine.
Lumpers: Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
Megadont: An organism with extremely large dentition compared with body size.
Metacarpals: The long bones of the hand that connect to the phalanges (finger bones).
Molars: The largest, most posterior of the hind dentition.
Monophyletic: A taxon or group of taxa descended from a common ancestor that is not shared with another taxon or group.
Morphology: The study of the form or size and shape of things; in this case, skeletal parts.
Mosaic evolution: The concept that evolutionary change does not occur homogeneously throughout the body in organisms.
Obligate bipedalism: Where the primary form of locomotion for an organism is bipedal.
Occlude: When the teeth from the maxilla come into contact with the teeth in the mandible.
Oldowan: Lower Paleolithic, the earliest stone tool culture.
Orthognathic: The face below the eyes is relatively flat and does not jut out anteriorly.
Paleoanthropologists: Researchers that study human evolution.
Paleoenvironment: An environment from a period in the Earth’s geological past.
Parabolic: Like a parabola (parabola-shaped).
Phalanges: Long bones in the hand and fingers.
Phylogenetics: The study of phylogeny.
Phylogeny: The study of the evolutionary relationships between groups of organisms.
Pliocene: A geological epoch between the Miocene and Pleistocene.
Polytypic: In reference to taxonomy, having two or more group variants capable of interacting and breeding biologically but having morphological population differences.
Postcranium: The skeleton below the cranium (head).
Premolars: The smallest of the hind teeth, behind the canines.
Procumbent: In reference to incisors, tilting forward.
Prognathic: In reference to the face, the area below the eyes juts anteriorly.
Quaternary Ice Age: The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles.
Relative dating: Dating techniques that refer to a temporal sequence (i.e., older or younger than others in the reference) and do not estimate actual or absolute dates.
Robust: Rugged or exaggerated features.
Site: A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
Specialist: A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
Splitters: Researchers who prefer to split a highly variable taxon into multiple groups or species.
Taxa: Plural of taxon, a taxonomic group such as species, genus, or family.
Taxonomy: The science of grouping and classifying organisms.
Techno-complex: A term encompassing multiple assemblages that share similar traits in terms of artifact production and morphology.
Thermoregulation: Maintaining body temperature through physiologically cooling or warming the body.
Ungulates: Hoofed mammals—e.g., cows and kudu.
Volcanic tufts: Rock made from ash from volcanic eruptions in the past.
Valgus knee: The angle of the knee between the femur and tibia, which allows for weight distribution to be angled closer to the point above the center of gravity (i.e., between the feet) in bipeds.
About the Authors
Kerryn Warren, Ph.D.
Grad Coach International, kerryn.warren@gmail.com
Kerryn Warren is a dissertation coach at Grad Coach International and is passionate about stimulating research thinking in students of all levels. She has lectured on multiple topics, including archaeology and human evolution, with her research and science communication interests including hybridization in the hominin fossil record (stemming from research from her Ph.D.) and understanding how evolution is taught in South African schools. She also worked as one of the “Underground Astronauts,” selected to excavate Homo naledi remains from the Rising Star Cave System in the Cradle of Humankind.
K. Lindsay Hunter, M.A., Ph.D. candidate
CARTA, k.lindsay.hunter@gmail.com
Lindsay Hunter is a trained palaeoanthropologist who uses her more than 15 years of experience to make sense of the distant past of our species to build a better future. She received her master’s degree in biological anthropology from the University of Iowa and is completing her Ph.D. in archaeology at the University of the Witwatersrand in Johannesburg, South Africa. She has studied fossil and human bone collections across five continents with major grant support from the National Science Foundation (United States) and the Wenner-Gren Foundation for Anthropological Research. As a National Geographic Explorer, Lindsay developed and managed the National Geographic–sponsored Umsuka Public Palaeoanthropology Project in the Cradle of Humankind World Heritage Site (CoH WHS) in South Africa from within Westbury Township, Johannesburg, between 2016–2019. She currently serves as the Community Engagement & Advancement Director for CARTA: The UC San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny in La Jolla, California.
Navashni Naidoo, M.Sc.
University of Cape Town, nnaidoo2@illinois.edu
Navashni Naidoo is a researcher at Nelson Mandela University, lecturing on physical geology. She completed her Master’s in Science in Archaeology in 2017 at the University of Cape Town. Her research interests include developing paleoenvironmental proxies suited to the African continent, behavioral ecology, and engaging with community-driven archaeological projects. She has excavated at Stone Age sites across Southern Africa and East Africa. Navashni is currently pursuing a PhD in the Department of Anthropology at the University of Illinois.
Silindokuhle Mavuso, M.Sc.
University of Witwatersrand, S.muvaso@ru.ac.za
Silindokuhle has always been curious about the world around him and how it has been shaped. He is a lecturer at Rhodes University of Witwatersrand (Wits), and conducts research on palaeoenvironmental reconstruction and change of the northeastern Turkana Basin’s Pleistocene sequence. Silindokuhle began his education with a B.Sc. (Geology, Archaeology, and Environmental and Geographical Sciences) from the University of Cape Town before moving to Wits for a B.Sc. Honors (geology and paleontology) and M.Sc. in geology. He is currently concluding his PhD Studies. During this time, he has gained more training as a Koobi Fora Fieldschool fellow (Kenya) as well as an Erasmus Mundus scholar (France). Silindokuhle is a Plio-Pleistocene geologist with a specific focus on identifying and explaining past environments that are associated with early human life and development through time. He is interested in a wide range of disciplines such as micromorphology, sedimentology, geochemistry, geochronology, and sequence stratigraphy. He has worked with teams from significant eastern and southern African hominid sites including Elandsfontein, Rising Star, Sterkfontein, Gondolin, Laetoli, Olduvai, and Koobi Fora.
For Further Exploration
The Smithsonian Institution website hosts descriptions of fossil species, an interactive timeline, and much more.
The Maropeng Museum website hosts a wealth of information regarding South African Fossil Bearing sites in the Cradle of Humankind.
This quick comparison between Homo naledi and Australopithecus sediba from the Perot Museum.
This explanation of the braided stream by the Perot Museum.
A collation of 3-D files for visualizing (or even 3-D printing) for homes, schools, and universities.
PBS learning materials, including videos and diagrams of the Laetoli footprints, bipedalism, and fossils.
A wealth of information from the Australian Museum website, including species descriptions, family trees, and explanations of bipedalism and diet.
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Acknowledgements
All of the authors in this section are students and early career researchers in paleoanthropology and related fields in South Africa (or at least have worked in South Africa). We wish to thank everyone who supports young and diverse talent in this field and would love to further acknowledge Black, African, and female academics who have helped pave the way for us.
Kerryn Warren, Ph.D., Grad Coach International
Lindsay Hunter, M.A., University of Iowa
Navashni Naidoo, M.Sc., University of Cape Town
Silindokuhle Mavuso, M.Sc., University of Witwatersrand
This chapter is a revision from "Chapter 9: Early Hominins" by Kerryn Warren, K. Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, and Nomawethu Hlazo. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Understand what is meant by “derived” and “ancestral” traits and why this is relevant for understanding early hominin evolution.
- Understand changing paleoclimates and paleoenvironments as potential factors influencing early hominin adaptations.
- Describe the anatomical changes associated with bipedalism and dentition in early hominins, as well as their implications..
- Describe early hominin genera and species, including their currently understood dates and geographic expanses.
- Describe the earliest stone tool techno-complexes and their impact on the transition from early hominins to our genus.
Defining Hominins
It is through our study of our hominin ancestors and relatives that we are exposed to a world of “might have beens”: of other paths not taken by our species, other ways of being human. But to better understand these different evolutionary trajectories, we must first define the terms we are using. If an imaginary line were drawn between ourselves and our closest relatives, the great apes, bipedalism (or habitually walking upright on two feet) is where that line would be. Hominin, then, means everyone on “our” side of the line: humans and all of our extinct bipedal ancestors and relatives since our divergence from the last common ancestor (LCA) we share with chimpanzees.
Historic interpretations of our evolution, prior to our finding of early hominin fossils, varied. Debates in the mid-1800s regarding hominin origins focused on two key issues:
- Where did we evolve?
- Which traits evolved first?
Charles Darwin hypothesized that we evolved in Africa, as he was convinced that we shared greater commonality with chimpanzees and gorillas on the continent (Darwin 1871). Others, such as Ernst Haeckel and Eugène Dubois, insisted that we were closer in affinity to orangutans and that we evolved in Eurasia where, until the discovery of the Taung Child in South Africa in 1924, all humanlike fossils (of Neanderthals and Homo erectus) had been found (Shipman 2002).
Within this conversation, naturalists and early paleoanthropologists (people who study human evolution) speculated about which human traits came first. These included the evolution of a big brain (encephalization), the evolution of the way in which we move about on two legs (bipedalism), and the evolution of our flat faces and small teeth (indications of dietary change). Original hypotheses suggested that, in order to be motivated to change diet and move about in a bipedal fashion, the large brain needed to have evolved first, as is seen in the fossil species mentioned above.
However, we now know that bipedal locomotion is one of the first things that evolved in our lineage, with early relatives having more apelike dentition and small brain sizes. While brain size expansion is seen primarily in our genus, Homo, earlier hominin brain sizes were highly variable between and within taxa, from 300 cc (cranial capacity, cm3), estimated in Ardipithecus, to 550 cc, estimated in Paranthropus boisei. The lower estimates are well within the range of variation of nonhuman extant great apes. In addition, body size variability also plays a role in the interpretation of whether brain size could be considered large or small for a particular species or specimen. In this chapter, we will tease out the details of early hominin evolution in terms of morphology (i.e. the study of the form, size, or shape of things; in this case, skeletal parts).
We also know that early human evolution occurred in a very complicated fashion. There were multiple species (multiple genera) that featured diversity in their diets and locomotion. Specimens have been found all along the East African Rift System (EARS); that is, in Ethiopia, Kenya, Tanzania, and Malawi; see Figure 9.1), in limestone caves in South Africa, and in Chad. Dates of these early relatives range from around 7 million years ago (mya) to around 1 mya, overlapping temporally with members of our genus, Homo.

Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another, and they consider which of these species were able to make and use tools. As a result, every site discovery in the patchy hominin fossil record tells us more about our evolution. In addition, recent scientific techniques (not available even ten years ago) provide new insights into the diets, environments, and lifestyles of these ancient relatives.
In the past, taxonomy was primarily based on morphology. Today it is tied to known relationships based on molecular phylogeny (e.g., based on DNA) or a combination of the two. This is complicated when applied to living taxa, but becomes much more difficult when we try to categorize ancestor-descendant relationships for long-extinct species whose molecular information is no longer preserved. We therefore find ourselves falling back on morphological comparisons, often of teeth and partially fossilized skeletal material.
It is here that we turn to the related concepts of cladistics and phylogenetics. Cladistics groups organisms according to their last common ancestors based on shared derived traits. In the case of early hominins, these are often morphological traits that differ from those seen in earlier populations. These new or modified traits provide evidence of evolutionary relationships, and organisms with the same derived traits are grouped in the same clade (Figure 9.2). For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade of birds. In this chapter, we will examine the grouping of the Robust Australopithecines, whose cranial and dental features differ from those of earlier hominins, and therefore are considered derived.

Dig Deeper: Problems Defining Hominin Species
It is worth noting that species designations for early hominin specimens are often highly contested. This is due to the fragmentary nature of the fossil record, the large timescale (millions of years) with which paleoanthropologists need to work, and the difficulty in evaluating whether morphological differences and similarities are due to meaningful phylogenetic or biological differences or subtle differences/variation in niche occupation or time. In other words, do morphological differences really indicate different species? How would classifying species in the paleoanthropological record compare with classifying living species today, for whom we can sequence genomes and observe lifestyles?
There are also broader philosophical differences among researchers when it comes to paleo-species designations. Some scientists, known as “lumpers,” argue that large variability is expected among multiple populations in a given species over time. These researchers will therefore prefer to “lump” specimens of subtle differences into single taxa. Others, known as “splitters,” argue that species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences. In general, splitters would consider geographic differences among populations as meaning that a species is polytypic (i.e., capable of interacting and breeding biologically but having morphological population differences). This is worth keeping in mind when learning about why species designations may be contested.

This further plays a role in evaluating ancestry. Debates over which species “gave rise” to which continue to this day. It is common to try to create “lineages” of species to determine when one species evolved into another over time. We refer to these as chronospecies (Figure 9.3). Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record. More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
Finally, it is worth considering the process of fossil discovery and publication. Some fossils are easily diagnostic to a species level and allow for easy and accurate interpretation. Some, however, are more controversial. This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species (e.g., a fossil of a patella or knee bone). Researchers often need to make several important claims when announcing or publishing a find: a secure date (if possible), clear association with other finds, and an adequate comparison among multiple species (both extant and fossil). Therefore, it is not uncommon that an important find was made years before it is scientifically published.
Paleoenvironment and Hominin Evolution
There is no doubt that one of the major selective pressures in hominin evolution is the environment. Large-scale changes in global and regional climate, as well as alterations to the environment, are (thought to be) all linked to (all) hominin diversification, dispersal, and extinction (Maslin et al. 2014). Environmental reconstructions often use modern analogues. Let us take, for instance, the hippopotamus. It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive. Such instances have occurred multiple times in the past, and the bones of some fauna (i.e., animals, like the hippopotamus) that are sensitive to these changes give us insights into these events.
Yet reconstructing a paleoenvironment relies on a range of techniques, which vary depending on whether research interests focus on local changes or more global environmental changes/reconstructions. For local environments (such as a single site or region), comparing the faunal assemblages (collections of fossils of animals found at a site) with animals found in certain modern environments allows us to determine if past environments mirror current ones in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes. Other techniques are also useful in this regard. Chemical analyses, for instance, can reveal the diets of individual fauna, providing clues as to the relative wetness or dryness of their environment (e.g., nitrogen isotopes; Kingston and Harrison 2007).
Global climatic changes in the distant past, which fluctuated between being colder and drier and warmer and wetter on average, would have global implications for environmental change (Figure 9.4). These can be studied by comparing marine core and terrestrial soil data across multiple sites. These techniques are based on chemical analysis, such as examination of the nitrogen and oxygen isotopes in shells and sediments. Similarly, analyzing pollen grains shows which kinds of flora survived in an environment at a specific time period. There are multiple lines of evidence that allow us to visualize global climate trends over millions of years (although it should be noted that the direction and extent of these changes could differ by geographic region).

Both local and global climatic/environmental changes have been used to understand factors affecting our evolution (DeHeinzelin et al. 1999; Kingston 2007). Environmental change acts as an important factor regarding the onset of several important hominin traits seen in early hominins and discussed in this chapter. Namely, the environment has been interpreted as the following:
- the driving force behind the evolution of bipedalism,
- the reason for change and variation in early hominin diets, and
- the diversification of multiple early hominin species.
There are numerous hypotheses regarding how climate has driven and continues to drive human evolution. Here, we will focus on just three popular hypotheses.
Savannah Hypothesis (or Aridity Hypothesis)
The hypothesis: This popular theory suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion (Figure 9.5). It was first proposed by Darwin (1871) and supported by anthropologists like Raymond Dart (1925). However, this idea was supported by little fossil or paleoenvironmental evidence and was later refined as the Aridity Hypothesis. This hypothesis states that the long-term aridification and, thereby, expansion of savannah biomes were drivers in diversification in early hominin evolution (deMenocal 2004; deMenocal and Bloemendal 1995). It advocates for periods of accelerated aridification leading to early hominin speciation events.

The evidence: While early bipedal hominins are often associated with wetter, more closed environments (i.e., not the Savannah Hypothesis), both marine and terrestrial records seem to support general cooling, drying conditions, with isotopic records indicating an increase in grasslands (i.e., colder and wetter climatic conditions) between 8 mya and 6 mya across the African continent (Cerling et al. 2011). This can be contrasted with later climatic changes derived from aeolian dust records (sediments transported to the site of interest by wind), which demonstrate increases in seasonal rainfall between 3 mya and 2.6 mya, 1.8 mya and 1.6 mya, and 1.2 mya and 0.8 mya (deMenocal 2004; deMenocal and Bloemendal 1995).
Interpretation(s): Despite a relatively scarce early hominin record, it is clear that two important factors occur around the time period in which we see increasing aridity. The first factor is the diversification of taxa, where high morphological variation between specimens has led to the naming of multiple hominin genera and species. The second factor is the observation that the earliest hominin fossils appear to have traits associated with bipedalism and are dated to around the drying period (as based on isotopic records). Some have argued that it is more accurately a combination of bipedalism and arboreal locomotion, which will be discussed later. However, the local environments in which these early specimens are found (as based on the faunal assemblages) do not appear to have been dry.
Turnover Pulse Hypothesis
The hypothesis: In 1985, paleontologist Elisabeth Vbra noticed that in periods of extreme and rapid climate change, ungulates (hoofed mammals of various kinds) that had generalized diets fared better than those with specialized diets (Vrba 1988, 1998). Specialist eaters (those who rely primarily on specific food types) faced extinction at greater rates than their generalist (those who can eat more varied and variable diets) counterparts because they were unable to adapt to new environments (Vrba 2000). Thus, periods with extreme climate change would be associated with high faunal turnover: that is, the extinction of many species and the speciation, diversification, and migration of many others to occupy various niches.
The evidence: The onset of the Quaternary Ice Age, between 2.5 mya and 3 mya, brought extreme global, cyclical interglacial and glacial periods (warmer, wetter periods with less ice at the poles, and colder, drier periods with more ice near the poles). Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites (Behrensmeyer et al. 1997; Bobe and Behrensmeyer 2004). Similarly, work in the Cape Floristic Belt of South Africa shows that extreme changes in climate play a role in extinction and migration in ungulates. While this theory was originally developed for ungulates, its proponents have argued that it can be applied to hominins as well. However, the link between climate and speciation is only vaguely understood (Faith and Behrensmeyer 2013).
Interpretation(s): While the evidence of rapid faunal turnover among ungulates during this time period appears clear, there is still some debate around its usefulness as applied to the paleoanthropological record. Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct.
Variability Selection Hypothesis
The hypothesis: This hypothesis was first articulated by paleoanthropologist Richard Potts (1998). It links the high amount of climatic variability over the last 7 million years to both behavioral and morphological changes. Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context (Potts 1998, 2013). The Variability Selection Hypothesis states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations (Potts 2013).
The evidence: The evidence for this theory is similar to that for the Turnover Pulse Hypothesis: large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
Interpretation(s): In this way, the Variability Selection Hypothesis allows for a more flexible interpretation of the evolution of bipedalism in hominins and a more fluid interpretation of the Turnover Pulse Hypothesis, where species turnover is meant to be more rapid. In some ways, this hypothesis accommodates both environmental data and our interpretations of an evolution toward greater variability among species and the survivability of generalists.
Paleoenvironment Summary
Some hypotheses presented in this section pay specific attention to habitat (Savannah Hypothesis) while others point to large-scale climatic forces (Variability Selection Hypothesis). Some may be interpreted to describe the evolution of traits such as bipedalism (Savannah Hypothesis), and others generally explain the diversification of early hominins (Turnover Pulse and Variability Selection Hypotheses). While there is no consensus as to how the environment drove our evolution, it is clear that the environment shaped both habitat and resource availability in ways that would have influenced our early ancestors physically and behaviorally.
Derived Adaptations: Bipedalism
The unique form of locomotion exhibited by modern humans, called obligate bipedalism, is important in distinguishing our species from the extant (living) great apes. The ability to walk habitually upright is thus considered one of the defining attributes of the hominin lineage. We also differ from other animals that walk bipedally (such as kangaroos) in that we do not have a tail to balance us as we move.
The origin of bipedalism in hominins has been debated in paleoanthropology, but at present there are two main ideas: (theories)
- early hominins initially lived in trees, but increasingly started living on the ground, so we were a product of an arboreal last common ancestor (LCA) or,
- our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
Most research supports the first theory of an arboreal LCA based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking. This would mean that both humans and chimpanzees can be considered “derived” in terms of locomotion since chimpanzees would have independently evolved knuckle-walking.
There are many current ideas regarding selective pressures that would lead to early hominins adapting upright posture and locomotion. Many of these selective pressures, as we have seen in the previous section, coincide with a shift in environmental conditions, supported by paleoenvironmental data. In general, however, it appears that, like extant great apes, early hominins thrived in forested regions with dense tree coverage, which would indicate an arboreal lifestyle. As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse such that bipedalism would become more important.
There are several proposed selective pressures for bipedalism:
- Energy conservation: Modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land. While chimpanzees, for instance, are faster than humans terrestrially, they expend large amounts of energy being so. Adaptations to bipedalism include “stacking” the majority of the weight of the body over a small area around the center of gravity (i.e., the head is above the chest, which is above the pelvis, which is over the knees, which are above the feet). This reduces the amount of muscle needed to be engaged during locomotion to “pull us up” and allows us to travel longer distances expending far less energy.
- Thermoregulation: Less surface area (i.e., only the head and shoulders) is exposed to direct sunlight during the hottest parts of the day (i.e., midday). This means that the body has less need to employ additional “cooling” mechanisms such as sweating, which additionally means less water loss.
- Bipedalism (Freeing of Hands): This method of locomotion freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use of tools.
These selective pressures are not mutually exclusive. Bipedality could have evolved from a combination of these selective pressures, in ways that increased the chances of early hominin survival.
Skeletal Adaptations for Bipedalism

Humans have highly specialized adaptations to facilitate obligate bipedalism (Figure 9.6). Many of these adaptations occur within the soft tissue of the body (e.g., muscles and tendons). However, when analyzing the paleoanthropological record for evidence of the emergence of bipedalism, all that remains is the fossilized bone. Interpretations of locomotion are therefore often based on comparative analyses between fossil remains and the skeletons of extant primates with known locomotor behaviors. These adaptations occur throughout the skeleton and are summarized in Figure 9.7.
The majority of these adaptations occur in the postcranium (the skeleton from below the head) and are outlined in Figure 9.7. In general, these adaptations allow for greater stability and strength in the lower limb, by allowing for more shock absorption, for a larger surface area for muscle attachment, and for the “stacking” of the skeleton directly over the center of gravity to reduce energy needed to be kept upright. These adaptations often mean less flexibility in areas such as the knee and foot.
However, these adaptations come at a cost. Evolving from a nonobligate bipedal ancestor means that the adaptations we have are evolutionary compromises. For instance, the valgus knee (angle at the knee) is an essential adaptation to balance the body weight above the ankle during bipedal locomotion. However, the strain and shock absorption at an angled knee eventually takes its toll. For example, runners often experience joint pain. Similarly, the long neck of the femur absorbs stress and accommodates for a larger pelvis, but it is a weak point, resulting in hip replacements being commonplace among the elderly, especially in cases where the bone additionally weakens through osteoporosis. Finally, the S-shaped curve in our spine allows us to stand upright, relative to the more curved C-shaped spine of an LCA. Yet the weaknesses in the curves can lead to pinching of nerves and back pain. Since many of these problems primarily are only seen in old age, they can potentially be seen as an evolutionary compromise.
Despite relatively few postcranial fragments, the fossil record in early hominins indicates a complex pattern of emergence of bipedalism. Key features, such as a more anteriorly placed foramen magnum, are argued to be seen even in the earliest discovered hominins, indicating an upright posture (Dart 1925). Some early species appear to have a mix of ancestral (arboreal) and derived (bipedal) traits, which indicates a mixed locomotion and a more mosaic evolution of the trait. Some early hominins appear to, for instance, have bowl-shaped pelvises (hip bones) and angled femurs suitable for bipedalism but also have retained an opposable hallux (big toe) or curved fingers and longer arms (for arboreal locomotion). These mixed morphologies may indicate that earlier hominins were not fully obligate bipeds and thus thrived in mosaic environments.
Yet the associations between postcranial and the more diagnostic cranial fossils and bones are not always clear, muddying our understanding of the specific species to which fossils belong (Grine et al. 2022).
Region | Feature | Obligate Biped (H. sapiens) | Nonobligate Biped |
Cranium | Position of the foramen magnum | Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground). | Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground. |
Post
cranium |
Body proportions | Shorter upper limb (not used for locomotion). | Longer upper limbs (used for locomotion). |
Post
cranium |
Spinal curvature | S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis). | C-curve. |
Post
cranium |
Vertebrae | Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission). | Gracile lumbar vertebrae compared to those of modern humans. |
Post
cranium |
Pelvis | Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces. | Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface. |
Post
cranium |
Lower limb | In general, longer, more robust lower limbs and more stable, larger joints.
|
In general, smaller, more gracile limbs with more flexible joints.
|
Post
cranium |
Foot | Rigid, robust foot, without a midtarsal break.
Nonopposable and large, robust big toe (for push off while walking) and large heel for shock absorbance. |
Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping. |
It is also worth noting that, while not directly related to bipedalism per se, other postcranial adaptations are evident in the hominin fossil record from some of the earlier hominins. For instance, the hand and finger morphologies of many of the earliest hominins indicate adaptations consistent with arboreality. These include longer hands, more curved metacarpals and phalanges (long bones in the hand and fingers, respectively), and a shorter, relatively weaker thumb. This allows for gripping onto curved surfaces during locomotion. The earliest hominins appear to have mixed morphologies for both bipedalism and arborealism. However, among Australopiths (members of the genus, Australopithecus), there are indications for greater reliance on bipedalism as the primary form of locomotion. Similarly, adaptations consistent with tool manufacture (shorter fingers and a longer, more robust thumb, in contrast to the features associated with arborealism) have been argued to appear before the genus Homo.
Special Topic: Fear of Snakes — A Cultural or Biological Response?

It is suggested that primates have three major predators: raptors, felines, and snakes; however, many studies show that of these carnivores, snakes were one of the first that mammals had to contend with alongside dinosaurs, as felines and raptors evolved at a much slower pace than their reptilian competition. Herpetologists trace the evolution of constricting snakes to about 100 million years ago, and by the time mammals arrived around 75 million years ago, constrictors were already well established as a formidable threat (Greene, 2017). Both co-existed for millennia and each sustained selective pressures requiring them to evolve specific traits to survive. When venomous snakes eventually emerged 55 to 65 million years ago, they posed yet an additional threat to proto-primates as they required less distance for the predator to kill (2017). Alongside camouflage and silent movement techniques, it was the development of the snake’s hollow fangs through which to deliver venom that was most transformative to primate evolution. As such, primates evolved their pre-conscious attention, and visual acuity to cope with this new threat; therefore, while snakes were adapting morphologically to feed themselves, they were unwittingly teaching proto-primates valuable lessons in predator detection and reacting appropriately in order to survive.
In a 2009 Harvard University study, Lynne A. Isbell hypothesizes that envenoming snakes are linked to being directly responsible for the origins of the evolving complex brains and superior visual capacity in the lineage of anthropoids leading to humans (Isbell, 2009). Forward-facing eyes for binocular vision, depth perception, enhanced visual acuity, stereoscopic and trichromatic colour vision, all traits necessary for snake detection; and the quick motor responses from the primate’s fight, flight, or freeze defence mechanism to circumvent a snake’s squeeze or bite. Numerous laboratory studies show that humans and primates both sense and visually detect snakes more rapidly than other threatening stimuli (Van Le Et al., 2013). These experiments show that snakes elicited the strongest, fastest responses (Van Le Et al., 2013). This is known as ‘Snake Detection Theory’ and is the evolution of the primate’s complex brain, visual acuity, and rapid motor responses towards snakes in its environment that are the adaptations needed to live successfully as arboreal beings. It is not fortuitous then, that primates that never coexisted with venomous snakes, such as lemurs in Madagascar, have less visual acuity, better olfaction and smaller brains. Within Isbell’s work, a collaborative study by a group of neuroscientists tested this hypothesis and found that, indeed, there is higher neural firing and activity in multiple areas of the primate brain, notably in the pulvinar, a region responsible for visual attention and oculomotor behaviour (Isbell, L., 2009).

Today, the fear of snakes is widespread in humans, often shown through avoidance and disgust. A study in The Journal of Ethnobiology and Ethnomedicine notes that snakes are over-hunted and excluded from conservation efforts worldwide (Ceríaco, 2012). While cultural factors shape our sentiments, instinct also plays a role—such as the developed avoidance behaviors toward threats like snakes. This blend of instinct and cultural influence is not only seen in behavior but also deeply embedded in the stories we tell. Many cultures depict mythological snakes as harbingers of death or chaos. In the Bible, Satan becomes a snake to tempt Eve. Norse mythology features Jörmungandr, the world serpent who signals the apocalypse. Egyptian myth tells of Apophis, who battles the sun god Ra nightly. Though sources vary, these myths consistently portray snakes as threats. As such, the widespread fear of snakes may reflect both evolutionary and cultural influences. Understood as an adaptive response inherited from primate ancestors—who developed avoidance behaviors toward potentially dangerous stimuli—and reinforced through myths and religious narratives, the enduring presence of snakes as potent figures of fear across human societies and primate groups highlights the complex intertwining of instinct and cultural meaning in shaping human behavior.
Early Hominins: Sahelanthropus and Orrorin
We see evidence for bipedalism in some of the earliest fossil hominins, dated from within our estimates of our divergence from chimpanzees. These hominins, however, also indicate evidence for arboreal locomotion.
The earliest dated hominin find (between 6 mya and 7 mya, based on radiometric dating of volcanic tufts) has been argued to come from Chad and is named Sahelanthropus tchadensis (Figure 9.8; Brunet et al. 1995). The initial discovery was made in 2001 by Ahounta Djimdoumalbaye and announced in Nature in 2002 by a team led by French paleontologist Michel Brunet. The find has a small cranial capacity (360 cc) and smaller canines than those in extant great apes, though they are larger and pointier than those in humans. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. A short cranial base and a foramen magnum that is more humanlike in positioning have been argued to indicate upright walking.

Initially, the inclusion of Sahelanthropus in the hominin family was debated by researchers, since the evidence for bipedalism is based on cranial evidence alone, which is not as convincing as postcranial evidence. Yet, a femur (thigh bone) and ulnae (upper arm bones) thought to belong to Sahelanthropus was discovered in 2001 (although not published until 2022). These bones may support the idea that the hominin was in fact a terrestrial biped with arboreal capabilities and behaviors (Daver et al. 2022).
Orrorin tugenensis (Orrorin meaning “original man”), dated to between 6 mya and 5.7 mya, was discovered near Tugen Hills in Kenya in 2000. Smaller cheek teeth (molars and premolars) than those in even more recent hominins, thick enamel, and reduced, but apelike, canines characterize this species. This is the first species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains. One of the most important elements discovered was a proximal femur, BAR 1002'00. The femur is the thigh bone, and the proximal part is that which articulates with the pelvis; this is very important for studying posture and locomotion. This femur indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins. Some have argued that features of the finger bones suggest potential tool-making capabilities, although many researchers argue that these features are also consistent with climbing.
Early Hominins: The Genus Ardipithecus
Another genus, Ardipithecus, is argued to be represented by at least two species: Ardipithecus (Ar.) ramidus and Ar. kadabba.
Ardipithecus ramidus (“ramid” means root in the Afar language) is currently the best-known of the earliest hominins (Figure 9.9). Unlike Sahelanthropus and Orrorin, this species has a large sample size of over 110 specimens from Aramis alone. Dated to 4.4 mya, Ar. ramidus was found in Ethiopia (in the Middle Awash region and in Gona). This species was announced in 1994 by American palaeoanthropologist Tim White, based on a partial female skeleton nicknamed “Ardi” (ARA-VP-6/500; White et al. 1994). Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, she had an opposable big toe (hallux), similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. A small brain (300 cc to 350 cc), midfacial projection, and slight prognathism show retained ancestral cranial features, but the cheek bones are less flared and robust than in later hominins.

Ardipithecus kadabba (the species name means “oldest ancestor” in the Afar language) is known from localities on the western margin of the Middle Awash region, the same locality where Ar. ramidus has been found. Specimens include mandibular fragments and isolated teeth as well as a few postcranial elements from the Asa Koma (5.5 mya to 5.77 mya) and Kuseralee Members (5.2 mya), well-dated and understood (but temporally separate) volcanic layers in East Africa. This species was discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie. Originally these specimens were referred to as a subspecies of Ar. ramidus. In 2002, six teeth were discovered at Asa Koma and the dental-wear patterns confirmed that this was a distinct species, named Ar. kadabba, in 2004. One of the postcranial remains recovered included a 5.2 million-year-old toe bone that demonstrated features that are associated with toeing off (pushing off the ground with the big toe leaving last) during walking, a characteristic unique to bipedal walkers. However, the toe bone was found in the Kuseralee Member, and therefore some doubt has been cast by researchers about its association with the teeth from the Asa Koma Member.
Bipedal Trends in Early Hominins: Summary
Trends toward bipedalism are seen in our earliest hominin finds. However, many specimens also indicate retained capabilities for climbing. Trends include a larger, more robust hallux; a more compact foot, with an arch; a robust, long femur, angled at the knee; a robust tibia; a bowl-shaped pelvis; and a more anterior foramen magnum. While the level of bipedality in Salehanthropus tchadenisis is debated since there are few fossils and no postcranial evidence, Orrorin tugenensis and Ardipithecus kadabba show clear indications of some of these bipedal trends. However, some retained ancestral traits, such as an opposable hallux in Ardipithecus, indicate some retention in climbing ability.
Derived Adaptations: Early Hominin Dention
The Importance of Teeth
Teeth are abundant in the fossil record, primarily because they are already highly mineralized as they are forming, far more so than even bone. Because of this, teeth preserve readily. And, because they preserve readily, they are well-studied and better understood than many skeletal elements. In the sparse hominin (and primate) fossil record, teeth are, in some cases, all we have.
Teeth also reveal a lot about the individual from whom they came. We can tell what they evolved to eat, to which other species they may be closely related, and even, to some extent, the level of sexual dimorphism, or general variability, within a given species. This is powerful information that can be contained in a single tooth. With a little more observation, the wearing patterns on a tooth can tell us about the diet of the individual in the weeks leading up to its death. Furthermore, the way in which a tooth is formed, and the timing of formation, can reveal information about changes in diet (or even mobility) over infancy and childhood, using isotopic analyses. When it comes to our earliest hominin relatives, this information is vital for understanding how they lived.
The purpose of comparing different hominin species is to better understand the functional morphology as it applies to dentition. In this, we mean that the morphology of the teeth or masticatory system (which includes jaws) can reveal something about the way in which they were used and, therefore, the kinds of foods these hominins ate. When comparing the features of hominin groups, it is worth considering modern analogues (i.e., animals with which to compare) to make more appropriate assumptions about diet. In this way, hominin dentition is often compared with that of chimpanzees and gorillas (our close ape relatives), as well as with that of modern humans.
The most divergent group, however, is humans. Humans around the world have incredibly varied diets. Among hunter-gatherers, it can vary from a honey- and plant-rich diet, as seen in the Hadza in Tanzania, to a diet almost entirely reliant on animal fat and protein, as seen in Inuits in polar regions of the world. We are therefore considered generalists, more general than the largely frugivorous (fruit-eating) chimpanzee or the folivorous (foliage-eating) gorilla, as discussed in Chapter 5.
One way in which all humans are similar is our reliance on the processing of our food. We cut up and tear meat with tools using our hands, instead of using our front teeth (incisors and canines). We smash and grind up hard seeds, instead of crushing them with our hind teeth (molars). This means that, unlike our ape relatives, we can rely more on developing tools to navigate our complex and varied diets. (We could say) Our brain, therefore, is our primary masticatory organ. Evolutionarily, our teeth have reduced in size and our faces are flatter, or more orthognathic, partially in response to our increased reliance on our hands and brain to process food. Similarly, a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat. These trends begin early on in our evolution. The link has been made between some of the earliest evidence for stone tool manufacture, the earliest members of our genus, and the features that we associate with these specimens.
General Dental Trends in Early Hominins
Several trends are visible in the dentition of early hominins. However, all tend to have the same dental formula. The dental formula tells us how many of each tooth type are present in each quadrant of the mouth. Going from the front of the mouth, this includes the square, flat incisors; the pointy canines; the small, flatter premolars; and the larger hind molars. In many primates, from Old World monkeys to great apes, the typical dental formula is 2:1:2:3. This means that if we divide the mouth into quadrants, each has two incisors, one canine, two premolars, and three molars. The eight teeth per quadrant total 32 teeth in all (although some humans have fewer teeth due to the absence of their wisdom teeth, or third molars).

The morphology of the individual teeth is where we see the most change. Among primates, large incisors are associated with food procurement or preparation (such as biting small fruits), while small incisors indicate a diet that may contain small seeds or leaves (where the preparation is primarily in the back of the mouth). Most hominins have relatively large, flat, vertically aligned incisors that occlude (touch) relatively well, forming a “bite.” This differs from, for instance, the orangutan, whose teeth stick out (i.e., are procumbent).
While the teeth are often aligned with diet, the canines may be misleading in that regard. We tend to associate pointy, large canines with the ripping required for meat, and the reduction (or, in some animals, the absence) of canines as indicative of herbivorous diets. In humans, our canines are often a similar size to our incisors and therefore considered incisiform (Figure 9.10). However, our closest relatives all have very long, pointy canines, particularly on their upper dentition. This is true even for the gorilla, which lives almost exclusively on plants. The canines in these instances reveal more about social structure and sexual dimorphism than diet, as large canines often signal dominance.
Early on in human evolution, we see a reduction in canine size. Sahelanthropus tchadensis and Orrorin tugenensis both have smaller canines than those in extant great apes, yet the canines are still larger and pointier than those in humans or more recent hominins. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. In Ardipithecus ramidus, there is no obvious difference between male and female canine size, yet they are still slightly larger and pointier than in modern humans. This implies a less sexually dimorphic social structure in the earlier hominins relative to modern-day chimpanzees and gorillas.
Along with a reduction in canine size is the reduction or elimination of a canine diastema: a gap between the teeth on the mandible that allows room for elongated teeth on the maxilla to “fit” in the mouth. Absence of a diastema is an excellent indication of a reduction in canine size. In animals with large canines (such as baboons), there is also often a honing P3, where the first premolar (also known as P3 for evolutionary reasons) is triangular in shape, “sharpened” by the extended canine from the upper dentition. This is also seen in some early hominins: Ardipithecus, for example, has small canines that are almost the same height as its incisors, although still larger than those in recent hominins.
The hind dentition, such as the bicuspid (two cusped) premolars or the much larger molars, are also highly indicative of a generalist diet in hominins. Among the earliest hominins, the molars are larger than we see in our genus, increasing in size to the back of the mouth and angled in such a way from the much smaller anterior dentition as to give these hominins a parabolic (V-shaped) dental arch. This differs from our living relatives and some early hominins, such as Sahelanthropus, whose molars and premolars are relatively parallel between the left and right sides of the mouth, creating a U-shape.
Among more recent early hominins, the molars are larger than those in the earliest hominins and far larger than those in our own genus, Homo. Large, short molars with thick enamel allowed our early cousins to grind fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing. In our genus, the hind dentition is far smaller than in these early hominins. Our teeth also have medium-size cusps, which allow for both efficient grinding and tearing/shearing meats.
Understanding the dental morphology has allowed researchers to extrapolate very specific behaviors of early hominins. It is worth noting that while teeth preserve well and are abundant, a slew of other morphological traits additionally provide evidence for many of these hypotheses. Yet there are some traits that are ambiguous. For instance, while there are definitely high levels of sexual dimorphism in Au. afarensis, discussed in the next section, the canine teeth are reduced in size, implying that while canines may be useful indicators for sexual dimorphism, it is also worth considering other evidence.
In summary, trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the ancestral dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
Special Topic: Contested Species
Many named species are highly debated and argued to have specimens associated with a more variable Au. afarensis or Au. anamensis species. Sometimes these specimens are dated to times when, or found in places in which, there are “gaps” in the palaeoanthropological record. These are argued to represent chronospecies or variants of Au. afarensis. However, it is possible that, with more discoveries, the distinct species types will hold.
Australopithecus bahrelghazali is dated to within the time period of Au. afarensis (3.6 mya; Brunet et al. 1995) and was the first Australopithecine to be discovered in Chad in central Africa. Researchers argue that the holotype, whom discoverers have named “Abel,” falls under the range of variation of Au. afarensis and therefore that A. bahrelghazali does not fall into a new species (Lebatard et al. 2008). If “Abel” is a member of Au. afarensis, the geographic range of the species would be greatly extended.
On a different note, Australopithecus deyiremada (meaning “close relative” in the Ethiopian language of Afar) is dated to 3.5 mya to 3.3 mya and is based on fossil mandible bones discovered in 2011 in Woranso-Mille (in the Afar region of Ethiopia) by Yohannes Haile-Selassie, an Ethiopian paleoanthropologist (Haile-Selassie et al. 2019). The discovery indicated, in contrast to Au. afarensis, smaller teeth with thicker enamel (potentially suggesting a harder diet) as well as a larger mandible and more projecting cheekbones. This find may be evidence that more than one closely related hominin species occupied the same region at the same temporal period (Haile-Selassie et al. 2015; Spoor 2015) or that other Au. afarensis specimens have been incorrectly designated. However, others have argued that this species has been prematurely identified and that more evidence is needed before splitting the taxa, since the variation appears subtle and may be due to slightly different niche occupations between populations over time.
Australopithecus garhi is another species found in the Middle Awash region of Ethiopia. It is currently dated to 2.5 mya (younger than Au. afarensis). Researchers have suggested it fills in a much-needed temporal “gap” between hominin finds in the region, with some anatomical differences, such as a relatively large cranial capacity (450 cc) and larger hind dentition than seen in other gracile Australopithecines. Similarly, the species has been argued to have longer hind limbs than Au. afarensis, although it was still able to move arboreally (Asfaw et al. 1999). However, this species is not well documented or understood and is based on only several fossil specimens. More astonishingly, crude stone tools resembling Oldowan (which will be described later) have been found in association with Au. garhi. While lacking some of the features of the Oldowan, this is one of the earliest technologies found in direct association with a hominin.
Kenyanthopus platyops (the name “platyops” refers to its flatter-faced appearance) is a highly contested genus/species designation of a specimen (KNM-WT 40000) from Lake Turkana in Kenya, discovered by Maeve Leakey in 1999 (Figure 9.11). Dated to between 3.5 mya and 3.2 mya, some have suggested this specimen is an Australopithecus, perhaps even Au. afarensis (with a brain size which is difficult to determine, yet appears small), while still others have placed this specimen in Homo (small dentition and flat-orthognathic face). While taxonomic placing of this species is quite divided, the discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis (Leakey et al. 2001). Some researchers have additionally associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this specimen.

The Genus Australopithecus
The Australopithecines are a diverse group of hominins, comprising various species. Australopithecus is the given group or genus name. It stems from the Latin word Australo, meaning “southern,” and the Greek word pithecus, meaning “ape.” Within this section, we will outline these differing species’ geological and temporal distributions across Africa, unique derived and/or shared traits, and importance in the fossil record.

Between 3 mya and 1 mya, there seems to be differences in dietary strategy between different species of hominins designated as Australopithecines. A pattern of larger posterior dentition (even relative to the incisors and canines in the front of the mouth), thick enamel, and cranial evidence for extremely large chewing muscles is far more pronounced in a group known as the robust australopithecines. This pattern is extremely relative to their earlier contemporaries or predecessors, the gracile australopithecines, and is certainly larger than those seen in early Homo, which emerged during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins (Figure 9.12).
Because of these differences, this section has been divided into “gracile” and “robust” Australopithecines, highlighting the morphological differences between the two groups (which many researchers have designated as separate genera: Australopithecus and Paranthropus, respectively) and then focusing on the individual species. It is worth noting, however, that not all researchers accept these clades as biologically or genetically distinct, with some researchers insisting that the relative gracile and robust features found in these species are due to parallel evolutionary events toward similar dietary niches.
Despite this genus’ ancestral traits and small cranial capacity, all members show evidence of bipedal locomotion. It is generally accepted that Australopithecus species display varying degrees of arborealism along with bipedality.
Gracile Australopithecines
This section describes individual species from across Africa. These species are called “gracile australopithecines” because of their smaller and less robust features compared to the divergent “robust” group. Numerous Australopithecine species have been named, but some are only based on a handful of fossil finds, whose designations are controversial.
East African Australopithecines
East African Australopithecines are found throughout the EARS, and they include the earliest species associated with this genus. Numerous fossil-yielding sites, such as Olduvai, Turkana, and Laetoli, have excellent, datable stratigraphy, owing to the layers of volcanic tufts that have accumulated over millions of years. These tufts may be dated using absolute dating techniques, such as Potassium-Argon dating (described in Chapter 7). This means that it is possible to know a relatively refined date for any fossil if the context (i.e., exact location) of that find is known. Similarly, comparisons between the faunal assemblages of these stratigraphic layers have allowed researchers to chronologically identify environmental changes.

The earliest known Australopithecine is dated to 4.2 mya to 3.8 mya. Australopithecus anamensis (after “Anam,” meaning “lake” from the Turkana region in Kenya; Leakey et al. 1995; Patterson and Howells 1967) is currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia; Figure 9.13). Recently, a 2019 find from Ethiopia, named MRD, after Miro Dora where it was found, was discovered by an Ethiopian herder named Ali Bereino. It is one of the most complete cranial finds of this species (Ward et al. 1999). A small brain size (370 cc), relatively large canines, projecting cheekbones, and earholes show more ancestral features as compared to those of more recent Australopithecines. The most important element discovered with this species is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking. Similarly, the earliest found hominin femur belongs to this species. Ancestral traits in the upper limb (such as the humerus) indicate some retained arboreal locomotion.
Some researchers suggest that Au. anamensis is an intermediate form of the chronospecies that becomes Au. afarensis, evolving from Ar. ramidus. However, this is debated, with other researchers suggesting morphological similarities and affinities with more recent species instead. Almost 100 specimens, representing over 20 individuals, have been found to date (Leakey et al. 1995; McHenry 2009; Ward et al. 1999).
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. Au. afarensis (which means “from the Afar region”) is dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia (Figure 9.14). The most famous individual from this species is a partial female skeleton discovered in Hadar (Ethiopia), later nicknamed “Lucy,” after the Beatles’ song “Lucy in the Sky with Diamonds,” which was played in celebration of the find (Johanson et al. 1978; Kimbel and Delezene 2009). This skeleton was found in 1974 by Donald Johanson and dates to approximately 3.2 mya. In addition, in 2002 a juvenile of the species was found by Zeresenay Alemseged and given the name “Selam” (meaning “peace,” DIK 1-1), though it is popularly known as “Lucy’s Child” or as the “Dikika Child” (Alemseged et al. 2006). Similarly, the “Laetoli Footprints” (discussed in Chapter 7; Hay and Leakey 1982; Leakey and Hay 1979) have drawn much attention.


The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans (indicative of a generalist diet); in addition, Au. afarensis has a prognathic face (the face below the eyes juts anteriorly) and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus. Despite a reduction in canine size in this species, large overall size variation indicates high levels of sexual dimorphism.
Skeletal evidence indicates that this species was bipedal, as its pelvis and lower limb demonstrate a humanlike femoral neck, valgus knee, and bowl-shaped hip (Figure 9.15). More evidence of bipedalism is found in the footprints of this species. Au. afarensis is associated with the Laetoli Footprints, a 24-meter trackway of hominin fossil footprints preserved in volcanic ash discovered by Mary Leakey in Tanzania and dated to 3.5 mya to 3 mya. This set of prints is thought to have been produced by three bipedal individuals as there are no knuckle imprints, no opposable big toes, and a clear arch is present. The infants of this species are thought to have been more arboreal than the adults, as discovered through analyses of the foot bones of the Dikika Child dated to 3.32 mya (Alemseged et al. 2006).
Although not found in direct association with stone tools, potential evidence for cut marks on bones, found at Dikika, and dated to 3.39 mya indicates a possible temporal/ geographic overlap between meat eating, tool use, and this species. However, this evidence is fiercely debated. Others have associated the cut marks with the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species.
South African Australopithecines
Since the discovery of the Taung Child, there have been numerous Australopithecine discoveries from the region known as “The Cradle of Humankind,” which was recently given UNESCO World Heritage Site status as “The Fossil Hominid Sites of South Africa.” The limestone caves found in the Cradle allow for the excellent preservation of fossils. Past animals navigating the landscape and falling into cave openings, or caves used as dens by carnivores, led to the accumulation of deposits over millions of years. Many of the hominin fossils, encased in breccia (hard, calcareous sedimentary rock), are recently exposed from limestone quarries mined in the previous century. This means that extracting fossils requires excellent and detailed exposed work, often by a team of skilled technicians.
While these sites have historically been difficult to date, with mixed assemblages accumulated over large time periods, advances in techniques such as uranium-series dating have allowed for greater accuracy. Historically, the excellent faunal record from East Africa has been used to compare sites based on relative dating, whereby environmental and faunal changes and extinction events allow us to know which hominin finds are relatively younger or older than others.
The discovery of the Taung Child in 1924 (discussed in the Special Topic box “The Taung Child” below) shifted the focus of palaeoanthropological research from Europe to Africa, although acceptance of this shift was slow (Broom 1947; Dart 1925). The species to which it is assigned, Australopithecus africanus (name meaning “Southern Ape of Africa”), is currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa (Figure 9.16). A relatively large brain (400 cc to 500 cc), small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits. Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism. However, the sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some ancestral features. Although not in direct association with stone tools, a 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities.

Another famous Au. africanus skull (the skull of “Mrs. Ples”) was previously attributed to Plesianthropus transvaalensis, meaning “near human from the Transvaal,” the old name for Gauteng Province, South Africa (Broom 1947, 1950). The name was shortened by contemporary journalists to “Ples” (Figure 9.17). Due to the prevailing mores of the time, the assumed female found herself married, at least in name, and has become widely known as “Mrs. Ples.” It was later reassigned to Au. africanus and is now argued by some to be a young male rather than an adult female cranium (Thackeray 2000, Thackeray et al. 2002).

In 2008, nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger, noted a clavicle bone in some leftover mining breccia in the Malapa Fossil Site (South Africa). After rigorous studies, the species, Australopithecus sediba (meaning “fountain” or “wellspring” in the South African language of Sesotho), was named in 2010 (Figure 9.18; Berger et al. 2010). The first type specimen belongs to a juvenile male, Karabo (MH1), but the species is known from at least six partial skeletons, from infants through adults. These specimens are currently dated to 1.97 mya (Dirks et al. 2010). The discoverers have argued that Au. sediba shows mosaic features between Au. africanus and the genus, Homo, which potentially indicates a transitional species, although this is heavily debated. These features include a small brain size (Australopithecus-like; 420 cc to 450 cc) but gracile mandible and small teeth (Homo-like). Similarly, the postcranial skeletons are also said to have mosaic features: scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. Some researchers have argued that Au. sediba shows a modern hand morphology (shorter fingers and a longer thumb), indicating that adaptations to tool manufacture and use may be present in this species.

Another famous Australopithecine find from South Africa is that of the nearly complete skeleton now known as “Little Foot” (Clarke 1998, 2013). Little Foot (StW 573) is potentially the earliest dated South African hominin fossil, dating to 3.7 mya, based on radiostopic techniques, although some argue that it is younger than 3 mya (Pickering and Kramers 2010). The name is jokingly in contrast to the cryptid species “bigfoot” and is named because the initial discovery of four ankle bones indicated bipedality. Little Foot was discovered by Ron Clarke in 1994, when he came across the ankle bones while sorting through monkey fossils in the University of Witwatersrand collections (Clarke and Tobias 1995). He asked Stephen Motsumi and Nkwane Molefe to identify the known records of the fossils, which allowed them to find the rest of the specimen within just days of searching the Sterkfontein Caves’ Silberberg Grotto.
The discoverers of Little Foot insist that other fossil finds, previously identified as Au. Africanus, be placed in this new species based on shared ancestral traits with older East African Australopithecines (Clarke and Kuman 2019). These include features such as a relatively large brain size (408 cc), robust zygomatic arch, and a flatter midface. Furthermore, the discoverers have argued that the heavy anterior dental wear patterns, relatively large anterior dentition, and smaller hind dentition of this specimen more closely resemble that of Au. anamensis or Au. afarensis. It has thus been placed in the species Australopithecus prometheus. This species name refers to a previously defunct taxon named by Raymond Dart. The species designation was, through analyzing Little Foot, revived by Ron Clarke, who insists that many other fossil hominin specimens have prematurely been placed into Au. africanus. Others say that it is more likely that Au. africanus is a more variable species and not representative of two distinct species.
Paranthropus “Robust” Australopithecines
In the robust australopithecines, the specialized nature of the teeth and masticatory system, such as flaring zygomatic arches (cheekbones), accommodate very large temporalis (chewing) muscles. These features also include a large, broad, dish-shaped face and and a large mandible with extremely large posterior dentition (referred to as megadonts) and hyper-thick enamel (Kimbel 2015; Lee-Thorp 2011; Wood 2010). Research has revolved around the shared adaptations of these “robust” australopithecines, linking their morphologies to a diet of hard and/or tough foods (Brain 1967; Rak 1988). Some argued that the diet of the robust australopithecines was so specific that any change in environment would have accelerated their extinction. The generalist nature of the teeth of the gracile australopithecines, and of early Homo, would have made them more capable of adapting to environmental change. However, some have suggested that the features of the robust australopithecines might have developed as an effective response to what are known as fallback foods in hard times rather than indicating a lack of adaptability.
There are currently three widely accepted robust australopithecus or, Paranthropus, species: P. aethiopicus, which has more ancestral traits, and P. boisei and P. robustus, which are more derived in their features (Strait et al. 1997; Wood and Schroer 2017). These three species have been grouped together by a majority of scholars as a single genus as they share more derived features (are more closely related to each other; or, in other words, are monophyletic) than the other australopithecines (Grine 1988; Hlazo 2015; Strait et al. 1997; Wood 2010 ). While researchers have mostly agreed to use the umbrella term Paranthropus, there are those who disagree (Constantino and Wood 2004, 2007; Wood 2010).
As a collective, this genus spans 2.7 mya to 1.0 mya, although the dates of the individual species differ. The earliest of the Paranthropus species, Paranthropus aethiopicus, is dated to between 2.7 mya and 2.3 mya and currently found in Tanzania, Kenya, and Ethiopia in the EARS system (Figure 9.19; Constantino and Wood 2007; Hlazo 2015; Kimbel 2015; Walker et al. 1986; White 1988). It is well known because of one specimen known as the “Black Skull” (KNM–WT 17000), so called because of the mineral manganese that stained it black during fossilization (Kimbel 2015). As with all robust Australopithecines, P. aethiopicus has the shared derived traits of large, flat premolars and molars; large, flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle); a sagittal crest (ridge on the top of the skull) for increased muscle attachment of the chewing muscles to the skull; and a robust mandible and supraorbital torus (brow ridge). However, only a few teeth have been found. A proximal tibia indicates bipedality and similar body size to Au. afarensis. In recent years, researchers have discovered and assigned a proximal tibia and juvenile cranium (L.338y-6) to the species (Wood and Boyle 2016).

First attributed as Zinjanthropus boisei (with the first discovery going by the nickname “Zinj” or sometimes “Nutcracker Man”), Paranthropus boisei was discovered in 1959 by Mary Leakey (see Figure 9.20 and 9.21; Hay 1990; Leakey 1959). This “robust” australopith species is distributed across countries in East Africa at sites such as Kenya (Koobi Fora, West Turkana, and Chesowanja), Malawi (Malema-Chiwondo), Tanzania (Olduvai Gorge and Peninj), and Ethiopia (Omo River Basin and Konso). The hypodigm, sample of fossils whose features define the group, has been found by researchers to date to roughly 2.4 mya to 1.4 mya. Due to the nature of its exaggerated, larger, and more robust features, P. boisei has been termed hyper-robust—that is, even more heavily built than other robust species, with very large, flat posterior dentition (Kimbel 2015). Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). Another famous specimen from this species is the Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu.


Paranthropus robustus was the first taxon to be discovered within the genus in Kromdraai B by a schoolboy named Gert Terblanche; subsequent fossil discoveries were made by researcher Robert Broom in 1938 (Figure 9.22; Broom 1938a, 1938b, 1950), with the holotype specimen TM 1517 (Broom 1938a, 1938b, 1950; Hlazo 2018). Paranthropus robustus dates approximately from 2.0 mya to 1 mya and is the only taxon from the genus to be discovered in South Africa. Several of these fossils are fragmentary in nature, distorted, and not well preserved because they have been recovered from quarry breccia using explosives. P. robustus features are neither as “hyper-robust” as P. boisei nor as ancestral as P. aethiopicus; instead, they have been described as being less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring; Rak 1983; Walker and Leakey 1988). Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick-enameled dentition.

Comparisons between Gracile and Robust Australopiths
Comparisons between gracile and robust australopithecines may indicate different phylogenetic groupings or parallel evolution in several species. In general, the robust australopithecines have large temporalis (chewing) muscles, as indicated by flaring zygomatic arches, sagittal crests, and robust mandibles (jawbones). Their hind dentition is large (megadont), with low cusps and thick enamel. Within the gracile australopithecines, researchers have debated the relatedness of the species, or even whether these species should be lumped together to represent more variable or polytypic species. Often researchers will attempt to draw chronospecific trajectories, with one taxon said to evolve into another over time.
Special Topic: The Taung Child

The well-known fossil of a juvenile Australopithecine, the “Taung Child,” was the first early hominin evidence ever discovered and was the first to demonstrate our common human heritage in Africa (Figure 9.23; Dart 1925). The tiny facial skeleton and natural endocast were discovered in 1924 by a local quarryman in the North West Province in South Africa and were painstakingly removed from the surrounding cement-like breccia by Raymond Dart using his wife’s knitting needles. When first shared with the scientific community in 1925, it was discounted as being nothing more than a young monkey of some kind. Prevailing biases of the time made it too difficult to contemplate that this small-brained hominin could have anything to do with our own history. The fact that it was discovered in Africa simply served to strengthen this bias.
Early Tool Use and Technology
Early Stone Age Technology (ESA)
The Early Stone Age (ESA) marks the beginning of recognizable technology made by our human ancestors. Stone-tool (or lithic) technology is defined by the fracturing of rocks and the manufacture of tools through a process called knapping. The Stone Age lasted for more than 3 million years and is broken up into chronological periods called the Early (ESA), Middle (MSA), and Later Stone Ages (LSA). Each period is further broken up into a different techno-complex, a term encompassing multiple assemblages (collections of artifacts) that share similar traits in terms of artifact production and morphology. The ESA spanned the largest technological time period of human innovation from over 3 million years ago to around 300,000 years ago and is associated almost entirely with hominin species prior to modern Homo sapiens. As the ESA advanced, stone tool makers (known as knappers) began to change the ways they detached flakes and eventually were able to shape artifacts into functional tools. These advances in technology go together with the developments in human evolution and cognition, dispersal of populations across the African continent and the world, and climatic changes.
In order to understand the ESA, it is important to consider that not all assemblages are exactly the same within each techno-complex: one can have multiple phases and traditions at different sites (Lombard et al. 2012). However, there is an overarching commonality between them. Within stone tool assemblages, both flakes or cores (the rocks from which flakes are removed) are used as tools. Large Cutting Tools (LCTs) are tools that are shaped to have functional edges. It is important to note that the information presented here is a small fraction of what is known about the ESA, and there are ongoing debates and discoveries within archaeology.
Currently, the oldest-known stone tools, which form the techno-complex the Lomekwian, date to 3.3 mya (Harmand et al. 2015; Toth 1985). They were found at a site called Lomekwi 3 in Kenya. This techno-complex is the most recently defined and pushed back the oldest-known date for lithic technology. There is only one known site thus far and, due to the age of the site, it is associated with species prior to Homo, such as Kenyanthropus platyops. Flakes were produced through indirect percussion, whereby the knappers held a rock and hit it against another rock resting on the ground. The pieces are very chunky and do not display the same fracture patterns seen in later techno-complexes. Lomekwian knappers likely aimed to get a sharp-edged piece on a flake, which would have been functional, although the specific function is currently unknown.
Stone tool use, however, is not only understood through the direct discovery of the tools. Cut marks on fossilized animal bones may illuminate the functionality of stone tools. In one controversial study in 2010, researchers argued that cut marks on a pair of animal bones from Dikika (Ethiopia), dated to 3.4 mya, were from stone tools. The discoverers suggested that they be more securely associated, temporally, with Au. afarensis. However, others have noted that these marks are consistent with teeth marks from crocodiles and other carnivores.

The Oldowan techno-complex is far more established in the scientific literature (Leakey 1971). It is called the Oldowan because it was originally discovered in Olduvai Gorge, Tanzania, but the oldest assemblage is from Gona in Ethiopia, dated to 2.6 mya (Semaw 2000). The techno-complex is defined as a core and flake industry. Like the Lomekwian, there was an aim to get sharp-edged flakes, but this was achieved through a different production method. Knappers were able to actively hold or manipulate the core being knapped, which they could directly hit using a hammerstone. This technique is known as free-hand percussion, and it demonstrates an understanding of fracture mechanics. It has long been argued that the Oldowan hominins were skillful in tool manufacture.
Because Oldowan knapping requires skill, earlier researchers have attributed these tools to members of our genus, Homo. However, some have argued that these tools are in more direct association with hominins in the genera described in this chapter (Figure 9.24).
Invisible Tool Manufacture and Use
The vast majority of our understanding of these early hominins comes from fossils and reconstructed paleoenvironments. It is only from 3 mya when we can start “looking into their minds” and lifestyles by analyzing their manufacture and use of stone tools. However, the vast majority of tool use in primates (and, one can argue, in humans) is not with durable materials like stone. All of our extant great ape relatives have been observed using sticks, leaves, and other materials for some secondary purpose (to wade across rivers, to “fish” for termites, or to absorb water for drinking). It is possible that the majority of early hominin tool use and manufacture may be invisible to us because of this preservation bias.
Chapter Summary
The fossil record of our earliest hominin relatives has allowed paleoanthropologists to unpack some of the mysteries of our evolution. We now know that traits associated with bipedalism evolved before other “human-like” traits, even though the first hominins were still very capable of arboreal locomotion. We also know that, for much of this time, hominin taxa were diverse in the way they looked and what they ate, and they were widely distributed across the African continent. And we know that the environments in which these hominins lived underwent many changes over this time during several warming and cooling phases.
Yet this knowledge has opened up many new mysteries. We still need to better differentiate some taxa. In addition, there are ongoing debates about why certain traits evolved and what they meant for the extinction of some of our relatives (like the robust australopiths). The capabilities of these early hominins with respect to tool use and manufacture is also still uncertain.
Hominin Species Summaries
Hominin |
Sahelanthropus tchadensis |
Dates |
7 mya to 6 mya |
Region(s) |
Chad |
Famous discoveries |
The initial discovery, made in 2001. |
Brain size |
360 cc average |
Dentition |
Smaller than in extant great apes; larger and pointier than in humans. Canines worn at the tips. |
Cranial features |
A short cranial base and a foramen magnum (hole in which the spinal cord enters the cranium) that is more humanlike in positioning; has been argued to indicate upright walking. |
Postcranial features |
Currently little published postcranial material. |
Culture |
N/A |
Other |
The extent to which this hominin was bipedal is currently heavily debated. If so, it would indicate an arboreal bipedal ancestor of hominins, not a knuckle-walker like chimpanzees. |
Hominin |
Orrorin tugenensis |
Dates |
6 mya to 5.7 mya |
Region(s) |
Tugen Hills (Kenya) |
Famous discoveries |
Original discovery in 2000. |
Brain size |
N/A |
Dentition |
Smaller cheek teeth (molars and premolars) than even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines. |
Cranial features |
Not many found |
Postcranial features |
Fragmentary leg, arm, and finger bones have been found. Indicates bipedal locomotion. |
Culture |
Potential toolmaking capability based on hand morphology, but nothing found directly. |
Other |
This is the earliest species that clearly indicates adaptations for bipedal locomotion. |
Hominin |
Ardipithecus kadabba |
Dates |
5.2 mya to 5.8 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
Discovered by Yohannes Haile-Selassie in 1997. |
Brain size |
N/A |
Dentition |
Larger hind dentition than in modern chimpanzees. Thick enamel and larger canines than in later hominins. |
Cranial features |
N/A |
Postcranial features |
A large hallux (big toe) bone indicates a bipedal “push off.” |
Culture |
N/A |
Other |
Faunal evidence indicates a mixed grassland/woodland environment. |
Hominin |
Ardipithecus ramidus |
Dates |
4.4 mya |
Region(s) |
Middle Awash region and Gona (Ethiopia) |
Famous discoveries |
A partial female skeleton nicknamed “Ardi” (ARA-VP-6/500) (found in 1994). |
Brain size |
300 cc to 350 cc |
Dentition |
Little differences between the canines of males and females (small sexual dimorphism). |
Cranial features |
Midfacial projection, slightly prognathic. Cheekbones less flared and robust than in later hominins. |
Postcranial features |
Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, an opposable big toe similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. |
Culture |
None directly associated |
Other |
Over 110 specimens from Aramis |
Hominin |
Australopithecus anamensis |
Dates |
4.2 mya to 3.8 mya |
Region(s) |
Turkana region (Kenya); Middle Awash (Ethiopia) |
Famous discoveries |
A 2019 find from Ethiopia, named MRD. |
Brain size |
370 cc |
Dentition |
Relatively large canines compared with more recent Australopithecines. |
Cranial features |
Projecting cheekbones and ancestral earholes. |
Postcranial features |
Lower limb bones (tibia and femur) indicate bipedality; arboreal features in upper limb bones (humerus) found. |
Culture |
N/A |
Other |
Almost 100 specimens, representing over 20 individuals, have been found to date. |
Hominin |
Australopithecus afarensis |
Dates |
3.9 mya to 2.9 mya |
Region(s) |
Afar Region, Omo, Maka, Fejej, and Belohdelie (Ethiopia); Laetoli (Tanzania); Koobi Fora (Kenya) |
Famous discoveries |
Lucy (discovery: 1974), Selam (Dikika Child, discovery: 2000), Laetoli Footprints (discovery: 1976). |
Brain size |
380 cc to 430 cc |
Dentition |
Reduced canines and molars relative to great apes but larger than in modern humans. |
Cranial features |
Prognathic face, facial features indicate relatively strong chewing musculature (compared with Homo) but less extreme than in Paranthropus. |
Postcranial features |
Clear evidence for bipedalism from lower limb postcranial bones. Laetoli Footprints indicate humanlike walking. Dikika Child bones indicate retained ancestral arboreal traits in the postcrania. |
Culture |
None directly, but close in age and proximity to controversial cut marks at Dikika and early tools in Lomekwi. |
Other |
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. |
Hominin |
Australopithecus bahrelghazali |
Dates |
3.6 mya |
Region(s) |
Chad |
Famous discoveries |
“Abel,” the holotype (discovery: 1995). |
Brain size |
N/A |
Dentition |
N/A |
Cranial features |
N/A |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Arguably within range of variation of Au. afarensis. |
Hominin |
Australopithecus prometheus |
Dates |
3.7 mya (debated) |
Region(s) |
Sterkfontein (South Africa) |
Famous discoveries |
“Little Foot” (StW 573) (discovery: 1994) |
Brain size |
408 cc (Little Foot estimate) |
Dentition |
Heavy anterior dental wear patterns, relatively large anterior dentition and smaller hind dentition, similar to Au. afarensis. |
Cranial features |
Relatively larger brain size, robust zygomatic arch, and a flatter midface. |
Postcranial features |
The initial discovery of four ankle bones indicated bipedality. |
Culture |
N/A |
Other |
Highly debated new species designation. |
Hominin |
Australopithecus deyiremada |
Dates |
3.5 mya to 3.3 mya |
Region(s) |
Woranso-Mille (Afar region, Ethiopia) |
Famous discoveries |
First fossil mandible bones were discovered in 2011 in the Afar region of Ethiopia by Yohannes Haile-Selassie. |
Brain size |
N/A |
Dentition |
Smaller teeth with thicker enamel than seen in Au. afarensis, with a potentially hardier diet. |
Cranial features |
Larger mandible and more projecting cheekbones than in Au. afarensis. |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Contested species designation; arguably a member of Au. afarensis. |
Hominin |
Kenyanthopus platyops |
Dates |
3.5 mya to 3.2 mya |
Region(s) |
Lake Turkana (Kenya) |
Famous discoveries |
KNM–WT 40000 (discovered 1999) |
Brain size |
Difficult to determine but appears within the range of Australopithecus afarensis. |
Dentition |
Small molars/dentition (Homo-like characteristic) |
Cranial features |
Flatter (i.e., orthognathic) face |
Postcranial features |
N/A |
Culture |
Some have associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species/specimen. |
Other |
Taxonomic placing of this species is quite divided. The discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis. |
Hominin |
Australopithecus africanus |
Dates |
3.3 mya to 2.1 mya |
Region(s) |
Sterkfontein, Taung, Makapansgat, Gladysvale (South Africa) |
Famous discoveries |
Taung Child (discovery in 1994), “Mrs. Ples” (discover in 1947), Little Foot (arguable; discovery in 1994). |
Brain size |
400 cc to 500 cc |
Dentition |
Smaller teeth (derived) relative to Au. afarensis. Small canines with no diastema. |
Cranial features |
A rounder skull compared with Au. afarensis in East Africa. A sloping face (ancestral). |
Postcranial features |
Similar postcranial evidence for bipedal locomotion (derived pelvis) with retained arboreal locomotion, e.g., curved phalanges (fingers), as seen in Au. afarensis. |
Culture |
None with direct evidence. |
Other |
A 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities. |
Hominin |
Australopithecus garhi |
Dates |
2.5 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
N/A |
Brain size |
450 cc |
Dentition |
Larger hind dentition than seen in other gracile Australopithecines. |
Cranial features |
N/A |
Postcranial features |
A femur of a fragmentary partial skeleton, argued to belong to Au. garhi, indicates this species may be longer-limbed than Au. afarensis, although still able to move arboreally. |
Culture |
Crude stone tools resembling Oldowan (described later) have been found in association with Au. garhi. |
Other |
This species is not well documented or understood and is based on only a few fossil specimens. |
Hominin |
Paranthropus aethiopicus |
Dates |
2.7 mya to 2.3 mya |
Region(s) |
West Turkana (Kenya); Laetoli (Tanzania); Omo River Basin (Ethiopia) |
Famous discoveries |
The “Black Skull” (KNM–WT 17000) (discovery 1985). |
Brain Size |
410 cc |
Dentition |
P. aethiopicus has the shared derived traits of large flat premolars and molars, although few teeth have been found. |
Cranial features |
Large flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle), a sagittal crest for increased muscle attachment of the chewing muscles to the skull, and a robust mandible and supraorbital torus (brow ridge). |
Postcranial features |
A proximal tibia indicates bipedality and similar size to Au. afarensis. |
Culture |
N/A |
Other |
The “Black Skull” is so called because of the mineral manganese that stained it black during fossilization. |
Hominin |
Paranthropus boisei |
Dates |
2.4 mya to 1.4 mya |
Region(s) |
Koobi Fora, West Turkana, and Chesowanja (Kenya); Malema-Chiwondo (Malawi), Olduvai Gorge and Peninj (Tanzania); and Omo River basin and Konso (Ethiopia) |
Famous discoveries |
“Zinj,” or sometimes “Nutcracker Man” (OH5), in 1959 by Mary Leakey. The Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu. |
Brain size |
500 cc to 550 cc |
Dentition |
Very large, flat posterior dentition (largest of all hominins currently known). Much smaller anterior dentition. Very thick dental enamel. |
Cranial features |
Indications of very large chewing muscles (e.g., flaring zygomatic arches and a large sagittal crest). |
Postcranial features |
Evidence for high variability and sexual dimorphism, with estimates of males at 1.37 meters tall and females at 1.24 meters. |
Culture |
Richard Leakey and Bernard Wood have both suggested that P. boisei could have made and used stone tools. Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. |
Other |
Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). This differs from what is seen in P. robustus. |
Hominin |
Australopithecus sediba |
Dates |
1.97 mya |
Region(s) |
Malapa Fossil Site (South Africa) |
Famous discoveries |
Karabo (MH1) (discovery in 2008) |
Brain size |
420 cc to 450 cc |
Dentition |
Small dentition with Australopithecine cusp-spacing. |
Cranial features |
Small brain size (Australopithecus-like) but gracile mandible (Homo-like). |
Postcranial features |
Scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (tree climbing, particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. |
Culture |
None of direct association, but some have argued that a modern hand morphology (shorter fingers and a longer thumb) means that adaptations to tool manufacture and use may be present in this species. |
Other |
It was first discovered through a clavicle bone in 2008 by nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger. |
Hominin |
Paranthropus robustus |
Dates |
2.3 mya to 1 mya |
Region(s) |
Kromdraai B, Swartkrans, Gondolin, Drimolen, and Coopers Cave (South Africa) |
Famous discoveries |
SK48 (original skull) |
Brain size |
410 cc to 530 cc |
Dentition |
Large posterior teeth with thick enamel, consistent with other Robust Australopithecines. Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick enameled dentition. |
Cranial features |
P. robustus features are neither as “hyper-robust” as P. boisei or as ancestral in features as P. aethiopicus. They have been described as less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring). |
Postcranial features |
Reconstructions indicate sexual dimorphism. |
Culture |
N/A |
Other |
Several of these fossils are fragmentary in nature, distorted, and not well preserved, because they have been recovered from quarry breccia using explosives. |
Review Questions
- What is the difference between a “derived” versus an “ancestral” trait? Give an example of both, seen in Au. afarensis.
- Which of the paleoenvironment hypotheses have been used to describe early hominin diversity, and which have been used to describe bipedalism?
- Which anatomical features for bipedalism do we see in early hominins?
- Describe the dentition of gracile and robust australopithecines. What might these tell us about their diets?
- List the hominin species argued to be associated with stone tool technologies. Are you convinced of these associations? Why/why not?
Key Terms
Arboreal: Related to trees or woodland.
Aridification: Becoming increasingly arid or dry, as related to the climate or environment.
Aridity Hypothesis: The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution.
Assemblage: A collection demonstrating a pattern. Often pertaining to a site or region.
Bipedalism: The locomotor ability to walk on two legs.
Breccia: Hard, calcareous sedimentary rock.
Canines: The pointy teeth just next to the incisors, in the front of the mouth.
Cheek teeth: Or hind dentition (molars and premolars).
Chronospecies: Species that are said to evolve into another species, in a linear fashion, over time.
Clade: A group of species or taxa with a shared common ancestor.
Cladistics: The field of grouping organisms into those with shared ancestry.
Context: As pertaining to palaeoanthropology, this term refers to the place where an artifact or fossil is found.
Cores: The remains of a rock that has been flaked or knapped.
Cusps: The ridges or “bumps” on the teeth.
Dental formula: A technique to describe the number of incisors, canines, premolars, and molars in each quadrant of the mouth.
Derived traits: Newly evolved traits that differ from those seen in the ancestor.
Diastema: A tooth gap between the incisors and canines.
Early Stone Age (ESA): The earliest-described archaeological period in which we start seeing stone-tool technology.
East African Rift System (EARS): This term is often used to refer to the Rift Valley, expanding from Malawi to Ethiopia. This active geological structure is responsible for much of the visibility of the paleoanthropological record in East Africa.
Enamel: The highly mineralized outer layer of the tooth.
Encephalization: Expansion of the brain.
Extant: Currently living—i.e., not extinct.
Fallback foods: Foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
Fauna: The animals of a particular region, habitat, or geological period.
Faunal assemblages: Collections of fossils of the animals found at a site.
Faunal turnover: The rate at which species go extinct and are replaced with new species.
Flake: The piece knocked off of a stone core during the manufacture of a tool, which may be used as a stone tool.
Flora: The plants of a particular region, habitat, or geological period.
Folivorous: Foliage-eating.
Foramen magnum: The large hole (foramen) at the base of the cranium, through which the spinal cord enters the skull.
Fossil: The remains or impression of an organism from the past.
Frugivorous: Fruit-eating.
Generalist: A species that can thrive in a wide variety of habitats and can have a varied diet.
Glacial: Colder, drier periods during an ice age when there is more ice trapped at the poles.
Gracile: Slender, less rugged, or pronounced features.
Hallux: The big toe.
Holotype: A single specimen from which a species or taxon is described or named.
Hominin: A primate category that includes humans and our fossil relatives since our divergence from extant great apes.
Honing P3: The mandibular premolar alongside the canine (in primates, the P3), which is angled to give space for (and sharpen) the upper canines.
Hyper-robust: Even more robust than considered normal in the Paranthropus genus.
Hypodigm: A sample (here, fossil) from which researchers extrapolate features of a population.
Incisiform: An adjective referring to a canine that appears more incisor-like in morphology.
Incisors: The teeth in the front of the mouth, used to bite off food.
Interglacial: A period of milder climate in between two glacial periods.
Isotopes: Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses.
Knappers: The people who fractured rocks in order to manufacture tools.
Knapping: The fracturing of rocks for the manufacture of tools.
Large Cutting Tool (LCT): A tool that is shaped to have functional edges.
Last Common Ancestor (LCA): The hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence.
Lithic: Relating to stone (here to stone tools).
Lumbar lordosis: The inward curving of the lower (lumbar) parts of the spine. The lower curve in the human S-shaped spine.
Lumpers: Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
Megadont: An organism with extremely large dentition compared with body size.
Metacarpals: The long bones of the hand that connect to the phalanges (finger bones).
Molars: The largest, most posterior of the hind dentition.
Monophyletic: A taxon or group of taxa descended from a common ancestor that is not shared with another taxon or group.
Morphology: The study of the form or size and shape of things; in this case, skeletal parts.
Mosaic evolution: The concept that evolutionary change does not occur homogeneously throughout the body in organisms.
Obligate bipedalism: Where the primary form of locomotion for an organism is bipedal.
Occlude: When the teeth from the maxilla come into contact with the teeth in the mandible.
Oldowan: Lower Paleolithic, the earliest stone tool culture.
Orthognathic: The face below the eyes is relatively flat and does not jut out anteriorly.
Paleoanthropologists: Researchers that study human evolution.
Paleoenvironment: An environment from a period in the Earth’s geological past.
Parabolic: Like a parabola (parabola-shaped).
Phalanges: Long bones in the hand and fingers.
Phylogenetics: The study of phylogeny.
Phylogeny: The study of the evolutionary relationships between groups of organisms.
Pliocene: A geological epoch between the Miocene and Pleistocene.
Polytypic: In reference to taxonomy, having two or more group variants capable of interacting and breeding biologically but having morphological population differences.
Postcranium: The skeleton below the cranium (head).
Premolars: The smallest of the hind teeth, behind the canines.
Procumbent: In reference to incisors, tilting forward.
Prognathic: In reference to the face, the area below the eyes juts anteriorly.
Quaternary Ice Age: The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles.
Relative dating: Dating techniques that refer to a temporal sequence (i.e., older or younger than others in the reference) and do not estimate actual or absolute dates.
Robust: Rugged or exaggerated features.
Site: A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
Specialist: A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
Splitters: Researchers who prefer to split a highly variable taxon into multiple groups or species.
Taxa: Plural of taxon, a taxonomic group such as species, genus, or family.
Taxonomy: The science of grouping and classifying organisms.
Techno-complex: A term encompassing multiple assemblages that share similar traits in terms of artifact production and morphology.
Thermoregulation: Maintaining body temperature through physiologically cooling or warming the body.
Ungulates: Hoofed mammals—e.g., cows and kudu.
Volcanic tufts: Rock made from ash from volcanic eruptions in the past.
Valgus knee: The angle of the knee between the femur and tibia, which allows for weight distribution to be angled closer to the point above the center of gravity (i.e., between the feet) in bipeds.
About the Authors
Kerryn Warren, Ph.D.
Grad Coach International, kerryn.warren@gmail.com
Kerryn Warren is a dissertation coach at Grad Coach International and is passionate about stimulating research thinking in students of all levels. She has lectured on multiple topics, including archaeology and human evolution, with her research and science communication interests including hybridization in the hominin fossil record (stemming from research from her Ph.D.) and understanding how evolution is taught in South African schools. She also worked as one of the “Underground Astronauts,” selected to excavate Homo naledi remains from the Rising Star Cave System in the Cradle of Humankind.
K. Lindsay Hunter, M.A., Ph.D. candidate
CARTA, k.lindsay.hunter@gmail.com
Lindsay Hunter is a trained palaeoanthropologist who uses her more than 15 years of experience to make sense of the distant past of our species to build a better future. She received her master’s degree in biological anthropology from the University of Iowa and is completing her Ph.D. in archaeology at the University of the Witwatersrand in Johannesburg, South Africa. She has studied fossil and human bone collections across five continents with major grant support from the National Science Foundation (United States) and the Wenner-Gren Foundation for Anthropological Research. As a National Geographic Explorer, Lindsay developed and managed the National Geographic–sponsored Umsuka Public Palaeoanthropology Project in the Cradle of Humankind World Heritage Site (CoH WHS) in South Africa from within Westbury Township, Johannesburg, between 2016–2019. She currently serves as the Community Engagement & Advancement Director for CARTA: The UC San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny in La Jolla, California.
Navashni Naidoo, M.Sc.
University of Cape Town, nnaidoo2@illinois.edu
Navashni Naidoo is a researcher at Nelson Mandela University, lecturing on physical geology. She completed her Master’s in Science in Archaeology in 2017 at the University of Cape Town. Her research interests include developing paleoenvironmental proxies suited to the African continent, behavioral ecology, and engaging with community-driven archaeological projects. She has excavated at Stone Age sites across Southern Africa and East Africa. Navashni is currently pursuing a PhD in the Department of Anthropology at the University of Illinois.
Silindokuhle Mavuso, M.Sc.
University of Witwatersrand, S.muvaso@ru.ac.za
Silindokuhle has always been curious about the world around him and how it has been shaped. He is a lecturer at Rhodes University of Witwatersrand (Wits), and conducts research on palaeoenvironmental reconstruction and change of the northeastern Turkana Basin’s Pleistocene sequence. Silindokuhle began his education with a B.Sc. (Geology, Archaeology, and Environmental and Geographical Sciences) from the University of Cape Town before moving to Wits for a B.Sc. Honors (geology and paleontology) and M.Sc. in geology. He is currently concluding his PhD Studies. During this time, he has gained more training as a Koobi Fora Fieldschool fellow (Kenya) as well as an Erasmus Mundus scholar (France). Silindokuhle is a Plio-Pleistocene geologist with a specific focus on identifying and explaining past environments that are associated with early human life and development through time. He is interested in a wide range of disciplines such as micromorphology, sedimentology, geochemistry, geochronology, and sequence stratigraphy. He has worked with teams from significant eastern and southern African hominid sites including Elandsfontein, Rising Star, Sterkfontein, Gondolin, Laetoli, Olduvai, and Koobi Fora.
For Further Exploration
The Smithsonian Institution website hosts descriptions of fossil species, an interactive timeline, and much more.
The Maropeng Museum website hosts a wealth of information regarding South African Fossil Bearing sites in the Cradle of Humankind.
This quick comparison between Homo naledi and Australopithecus sediba from the Perot Museum.
This explanation of the braided stream by the Perot Museum.
A collation of 3-D files for visualizing (or even 3-D printing) for homes, schools, and universities.
PBS learning materials, including videos and diagrams of the Laetoli footprints, bipedalism, and fossils.
A wealth of information from the Australian Museum website, including species descriptions, family trees, and explanations of bipedalism and diet.
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Acknowledgements
All of the authors in this section are students and early career researchers in paleoanthropology and related fields in South Africa (or at least have worked in South Africa). We wish to thank everyone who supports young and diverse talent in this field and would love to further acknowledge Black, African, and female academics who have helped pave the way for us.
Kerryn Warren, Ph.D., Grad Coach International
Lindsay Hunter, M.A., University of Iowa
Navashni Naidoo, M.Sc., University of Cape Town
Silindokuhle Mavuso, M.Sc., University of Witwatersrand
This chapter is a revision from "Chapter 9: Early Hominins" by Kerryn Warren, K. Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, and Nomawethu Hlazo. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Understand what is meant by “derived” and “ancestral” traits and why this is relevant for understanding early hominin evolution.
- Understand changing paleoclimates and paleoenvironments as potential factors influencing early hominin adaptations.
- Describe the anatomical changes associated with bipedalism and dentition in early hominins, as well as their implications..
- Describe early hominin genera and species, including their currently understood dates and geographic expanses.
- Describe the earliest stone tool techno-complexes and their impact on the transition from early hominins to our genus.
Defining Hominins
It is through our study of our hominin ancestors and relatives that we are exposed to a world of “might have beens”: of other paths not taken by our species, other ways of being human. But to better understand these different evolutionary trajectories, we must first define the terms we are using. If an imaginary line were drawn between ourselves and our closest relatives, the great apes, bipedalism (or habitually walking upright on two feet) is where that line would be. Hominin, then, means everyone on “our” side of the line: humans and all of our extinct bipedal ancestors and relatives since our divergence from the last common ancestor (LCA) we share with chimpanzees.
Historic interpretations of our evolution, prior to our finding of early hominin fossils, varied. Debates in the mid-1800s regarding hominin origins focused on two key issues:
- Where did we evolve?
- Which traits evolved first?
Charles Darwin hypothesized that we evolved in Africa, as he was convinced that we shared greater commonality with chimpanzees and gorillas on the continent (Darwin 1871). Others, such as Ernst Haeckel and Eugène Dubois, insisted that we were closer in affinity to orangutans and that we evolved in Eurasia where, until the discovery of the Taung Child in South Africa in 1924, all humanlike fossils (of Neanderthals and Homo erectus) had been found (Shipman 2002).
Within this conversation, naturalists and early paleoanthropologists (people who study human evolution) speculated about which human traits came first. These included the evolution of a big brain (encephalization), the evolution of the way in which we move about on two legs (bipedalism), and the evolution of our flat faces and small teeth (indications of dietary change). Original hypotheses suggested that, in order to be motivated to change diet and move about in a bipedal fashion, the large brain needed to have evolved first, as is seen in the fossil species mentioned above.
However, we now know that bipedal locomotion is one of the first things that evolved in our lineage, with early relatives having more apelike dentition and small brain sizes. While brain size expansion is seen primarily in our genus, Homo, earlier hominin brain sizes were highly variable between and within taxa, from 300 cc (cranial capacity, cm3), estimated in Ardipithecus, to 550 cc, estimated in Paranthropus boisei. The lower estimates are well within the range of variation of nonhuman extant great apes. In addition, body size variability also plays a role in the interpretation of whether brain size could be considered large or small for a particular species or specimen. In this chapter, we will tease out the details of early hominin evolution in terms of morphology (i.e. the study of the form, size, or shape of things; in this case, skeletal parts).
We also know that early human evolution occurred in a very complicated fashion. There were multiple species (multiple genera) that featured diversity in their diets and locomotion. Specimens have been found all along the East African Rift System (EARS); that is, in Ethiopia, Kenya, Tanzania, and Malawi; see Figure 9.1), in limestone caves in South Africa, and in Chad. Dates of these early relatives range from around 7 million years ago (mya) to around 1 mya, overlapping temporally with members of our genus, Homo.

Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another, and they consider which of these species were able to make and use tools. As a result, every site discovery in the patchy hominin fossil record tells us more about our evolution. In addition, recent scientific techniques (not available even ten years ago) provide new insights into the diets, environments, and lifestyles of these ancient relatives.
In the past, taxonomy was primarily based on morphology. Today it is tied to known relationships based on molecular phylogeny (e.g., based on DNA) or a combination of the two. This is complicated when applied to living taxa, but becomes much more difficult when we try to categorize ancestor-descendant relationships for long-extinct species whose molecular information is no longer preserved. We therefore find ourselves falling back on morphological comparisons, often of teeth and partially fossilized skeletal material.
It is here that we turn to the related concepts of cladistics and phylogenetics. Cladistics groups organisms according to their last common ancestors based on shared derived traits. In the case of early hominins, these are often morphological traits that differ from those seen in earlier populations. These new or modified traits provide evidence of evolutionary relationships, and organisms with the same derived traits are grouped in the same clade (Figure 9.2). For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade of birds. In this chapter, we will examine the grouping of the Robust Australopithecines, whose cranial and dental features differ from those of earlier hominins, and therefore are considered derived.

Dig Deeper: Problems Defining Hominin Species
It is worth noting that species designations for early hominin specimens are often highly contested. This is due to the fragmentary nature of the fossil record, the large timescale (millions of years) with which paleoanthropologists need to work, and the difficulty in evaluating whether morphological differences and similarities are due to meaningful phylogenetic or biological differences or subtle differences/variation in niche occupation or time. In other words, do morphological differences really indicate different species? How would classifying species in the paleoanthropological record compare with classifying living species today, for whom we can sequence genomes and observe lifestyles?
There are also broader philosophical differences among researchers when it comes to paleo-species designations. Some scientists, known as “lumpers,” argue that large variability is expected among multiple populations in a given species over time. These researchers will therefore prefer to “lump” specimens of subtle differences into single taxa. Others, known as “splitters,” argue that species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences. In general, splitters would consider geographic differences among populations as meaning that a species is polytypic (i.e., capable of interacting and breeding biologically but having morphological population differences). This is worth keeping in mind when learning about why species designations may be contested.

This further plays a role in evaluating ancestry. Debates over which species “gave rise” to which continue to this day. It is common to try to create “lineages” of species to determine when one species evolved into another over time. We refer to these as chronospecies (Figure 9.3). Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record. More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
Finally, it is worth considering the process of fossil discovery and publication. Some fossils are easily diagnostic to a species level and allow for easy and accurate interpretation. Some, however, are more controversial. This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species (e.g., a fossil of a patella or knee bone). Researchers often need to make several important claims when announcing or publishing a find: a secure date (if possible), clear association with other finds, and an adequate comparison among multiple species (both extant and fossil). Therefore, it is not uncommon that an important find was made years before it is scientifically published.
Paleoenvironment and Hominin Evolution
There is no doubt that one of the major selective pressures in hominin evolution is the environment. Large-scale changes in global and regional climate, as well as alterations to the environment, are (thought to be) all linked to (all) hominin diversification, dispersal, and extinction (Maslin et al. 2014). Environmental reconstructions often use modern analogues. Let us take, for instance, the hippopotamus. It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive. Such instances have occurred multiple times in the past, and the bones of some fauna (i.e., animals, like the hippopotamus) that are sensitive to these changes give us insights into these events.
Yet reconstructing a paleoenvironment relies on a range of techniques, which vary depending on whether research interests focus on local changes or more global environmental changes/reconstructions. For local environments (such as a single site or region), comparing the faunal assemblages (collections of fossils of animals found at a site) with animals found in certain modern environments allows us to determine if past environments mirror current ones in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes. Other techniques are also useful in this regard. Chemical analyses, for instance, can reveal the diets of individual fauna, providing clues as to the relative wetness or dryness of their environment (e.g., nitrogen isotopes; Kingston and Harrison 2007).
Global climatic changes in the distant past, which fluctuated between being colder and drier and warmer and wetter on average, would have global implications for environmental change (Figure 9.4). These can be studied by comparing marine core and terrestrial soil data across multiple sites. These techniques are based on chemical analysis, such as examination of the nitrogen and oxygen isotopes in shells and sediments. Similarly, analyzing pollen grains shows which kinds of flora survived in an environment at a specific time period. There are multiple lines of evidence that allow us to visualize global climate trends over millions of years (although it should be noted that the direction and extent of these changes could differ by geographic region).

Both local and global climatic/environmental changes have been used to understand factors affecting our evolution (DeHeinzelin et al. 1999; Kingston 2007). Environmental change acts as an important factor regarding the onset of several important hominin traits seen in early hominins and discussed in this chapter. Namely, the environment has been interpreted as the following:
- the driving force behind the evolution of bipedalism,
- the reason for change and variation in early hominin diets, and
- the diversification of multiple early hominin species.
There are numerous hypotheses regarding how climate has driven and continues to drive human evolution. Here, we will focus on just three popular hypotheses.
Savannah Hypothesis (or Aridity Hypothesis)
The hypothesis: This popular theory suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion (Figure 9.5). It was first proposed by Darwin (1871) and supported by anthropologists like Raymond Dart (1925). However, this idea was supported by little fossil or paleoenvironmental evidence and was later refined as the Aridity Hypothesis. This hypothesis states that the long-term aridification and, thereby, expansion of savannah biomes were drivers in diversification in early hominin evolution (deMenocal 2004; deMenocal and Bloemendal 1995). It advocates for periods of accelerated aridification leading to early hominin speciation events.

The evidence: While early bipedal hominins are often associated with wetter, more closed environments (i.e., not the Savannah Hypothesis), both marine and terrestrial records seem to support general cooling, drying conditions, with isotopic records indicating an increase in grasslands (i.e., colder and wetter climatic conditions) between 8 mya and 6 mya across the African continent (Cerling et al. 2011). This can be contrasted with later climatic changes derived from aeolian dust records (sediments transported to the site of interest by wind), which demonstrate increases in seasonal rainfall between 3 mya and 2.6 mya, 1.8 mya and 1.6 mya, and 1.2 mya and 0.8 mya (deMenocal 2004; deMenocal and Bloemendal 1995).
Interpretation(s): Despite a relatively scarce early hominin record, it is clear that two important factors occur around the time period in which we see increasing aridity. The first factor is the diversification of taxa, where high morphological variation between specimens has led to the naming of multiple hominin genera and species. The second factor is the observation that the earliest hominin fossils appear to have traits associated with bipedalism and are dated to around the drying period (as based on isotopic records). Some have argued that it is more accurately a combination of bipedalism and arboreal locomotion, which will be discussed later. However, the local environments in which these early specimens are found (as based on the faunal assemblages) do not appear to have been dry.
Turnover Pulse Hypothesis
The hypothesis: In 1985, paleontologist Elisabeth Vbra noticed that in periods of extreme and rapid climate change, ungulates (hoofed mammals of various kinds) that had generalized diets fared better than those with specialized diets (Vrba 1988, 1998). Specialist eaters (those who rely primarily on specific food types) faced extinction at greater rates than their generalist (those who can eat more varied and variable diets) counterparts because they were unable to adapt to new environments (Vrba 2000). Thus, periods with extreme climate change would be associated with high faunal turnover: that is, the extinction of many species and the speciation, diversification, and migration of many others to occupy various niches.
The evidence: The onset of the Quaternary Ice Age, between 2.5 mya and 3 mya, brought extreme global, cyclical interglacial and glacial periods (warmer, wetter periods with less ice at the poles, and colder, drier periods with more ice near the poles). Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites (Behrensmeyer et al. 1997; Bobe and Behrensmeyer 2004). Similarly, work in the Cape Floristic Belt of South Africa shows that extreme changes in climate play a role in extinction and migration in ungulates. While this theory was originally developed for ungulates, its proponents have argued that it can be applied to hominins as well. However, the link between climate and speciation is only vaguely understood (Faith and Behrensmeyer 2013).
Interpretation(s): While the evidence of rapid faunal turnover among ungulates during this time period appears clear, there is still some debate around its usefulness as applied to the paleoanthropological record. Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct.
Variability Selection Hypothesis
The hypothesis: This hypothesis was first articulated by paleoanthropologist Richard Potts (1998). It links the high amount of climatic variability over the last 7 million years to both behavioral and morphological changes. Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context (Potts 1998, 2013). The Variability Selection Hypothesis states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations (Potts 2013).
The evidence: The evidence for this theory is similar to that for the Turnover Pulse Hypothesis: large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
Interpretation(s): In this way, the Variability Selection Hypothesis allows for a more flexible interpretation of the evolution of bipedalism in hominins and a more fluid interpretation of the Turnover Pulse Hypothesis, where species turnover is meant to be more rapid. In some ways, this hypothesis accommodates both environmental data and our interpretations of an evolution toward greater variability among species and the survivability of generalists.
Paleoenvironment Summary
Some hypotheses presented in this section pay specific attention to habitat (Savannah Hypothesis) while others point to large-scale climatic forces (Variability Selection Hypothesis). Some may be interpreted to describe the evolution of traits such as bipedalism (Savannah Hypothesis), and others generally explain the diversification of early hominins (Turnover Pulse and Variability Selection Hypotheses). While there is no consensus as to how the environment drove our evolution, it is clear that the environment shaped both habitat and resource availability in ways that would have influenced our early ancestors physically and behaviorally.
Derived Adaptations: Bipedalism
The unique form of locomotion exhibited by modern humans, called obligate bipedalism, is important in distinguishing our species from the extant (living) great apes. The ability to walk habitually upright is thus considered one of the defining attributes of the hominin lineage. We also differ from other animals that walk bipedally (such as kangaroos) in that we do not have a tail to balance us as we move.
The origin of bipedalism in hominins has been debated in paleoanthropology, but at present there are two main ideas: (theories)
- early hominins initially lived in trees, but increasingly started living on the ground, so we were a product of an arboreal last common ancestor (LCA) or,
- our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
Most research supports the first theory of an arboreal LCA based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking. This would mean that both humans and chimpanzees can be considered “derived” in terms of locomotion since chimpanzees would have independently evolved knuckle-walking.
There are many current ideas regarding selective pressures that would lead to early hominins adapting upright posture and locomotion. Many of these selective pressures, as we have seen in the previous section, coincide with a shift in environmental conditions, supported by paleoenvironmental data. In general, however, it appears that, like extant great apes, early hominins thrived in forested regions with dense tree coverage, which would indicate an arboreal lifestyle. As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse such that bipedalism would become more important.
There are several proposed selective pressures for bipedalism:
- Energy conservation: Modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land. While chimpanzees, for instance, are faster than humans terrestrially, they expend large amounts of energy being so. Adaptations to bipedalism include “stacking” the majority of the weight of the body over a small area around the center of gravity (i.e., the head is above the chest, which is above the pelvis, which is over the knees, which are above the feet). This reduces the amount of muscle needed to be engaged during locomotion to “pull us up” and allows us to travel longer distances expending far less energy.
- Thermoregulation: Less surface area (i.e., only the head and shoulders) is exposed to direct sunlight during the hottest parts of the day (i.e., midday). This means that the body has less need to employ additional “cooling” mechanisms such as sweating, which additionally means less water loss.
- Bipedalism (Freeing of Hands): This method of locomotion freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use of tools.
These selective pressures are not mutually exclusive. Bipedality could have evolved from a combination of these selective pressures, in ways that increased the chances of early hominin survival.
Skeletal Adaptations for Bipedalism

Humans have highly specialized adaptations to facilitate obligate bipedalism (Figure 9.6). Many of these adaptations occur within the soft tissue of the body (e.g., muscles and tendons). However, when analyzing the paleoanthropological record for evidence of the emergence of bipedalism, all that remains is the fossilized bone. Interpretations of locomotion are therefore often based on comparative analyses between fossil remains and the skeletons of extant primates with known locomotor behaviors. These adaptations occur throughout the skeleton and are summarized in Figure 9.7.
The majority of these adaptations occur in the postcranium (the skeleton from below the head) and are outlined in Figure 9.7. In general, these adaptations allow for greater stability and strength in the lower limb, by allowing for more shock absorption, for a larger surface area for muscle attachment, and for the “stacking” of the skeleton directly over the center of gravity to reduce energy needed to be kept upright. These adaptations often mean less flexibility in areas such as the knee and foot.
However, these adaptations come at a cost. Evolving from a nonobligate bipedal ancestor means that the adaptations we have are evolutionary compromises. For instance, the valgus knee (angle at the knee) is an essential adaptation to balance the body weight above the ankle during bipedal locomotion. However, the strain and shock absorption at an angled knee eventually takes its toll. For example, runners often experience joint pain. Similarly, the long neck of the femur absorbs stress and accommodates for a larger pelvis, but it is a weak point, resulting in hip replacements being commonplace among the elderly, especially in cases where the bone additionally weakens through osteoporosis. Finally, the S-shaped curve in our spine allows us to stand upright, relative to the more curved C-shaped spine of an LCA. Yet the weaknesses in the curves can lead to pinching of nerves and back pain. Since many of these problems primarily are only seen in old age, they can potentially be seen as an evolutionary compromise.
Despite relatively few postcranial fragments, the fossil record in early hominins indicates a complex pattern of emergence of bipedalism. Key features, such as a more anteriorly placed foramen magnum, are argued to be seen even in the earliest discovered hominins, indicating an upright posture (Dart 1925). Some early species appear to have a mix of ancestral (arboreal) and derived (bipedal) traits, which indicates a mixed locomotion and a more mosaic evolution of the trait. Some early hominins appear to, for instance, have bowl-shaped pelvises (hip bones) and angled femurs suitable for bipedalism but also have retained an opposable hallux (big toe) or curved fingers and longer arms (for arboreal locomotion). These mixed morphologies may indicate that earlier hominins were not fully obligate bipeds and thus thrived in mosaic environments.
Yet the associations between postcranial and the more diagnostic cranial fossils and bones are not always clear, muddying our understanding of the specific species to which fossils belong (Grine et al. 2022).
Region | Feature | Obligate Biped (H. sapiens) | Nonobligate Biped |
Cranium | Position of the foramen magnum | Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground). | Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground. |
Post
cranium |
Body proportions | Shorter upper limb (not used for locomotion). | Longer upper limbs (used for locomotion). |
Post
cranium |
Spinal curvature | S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis). | C-curve. |
Post
cranium |
Vertebrae | Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission). | Gracile lumbar vertebrae compared to those of modern humans. |
Post
cranium |
Pelvis | Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces. | Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface. |
Post
cranium |
Lower limb | In general, longer, more robust lower limbs and more stable, larger joints.
|
In general, smaller, more gracile limbs with more flexible joints.
|
Post
cranium |
Foot | Rigid, robust foot, without a midtarsal break.
Nonopposable and large, robust big toe (for push off while walking) and large heel for shock absorbance. |
Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping. |
It is also worth noting that, while not directly related to bipedalism per se, other postcranial adaptations are evident in the hominin fossil record from some of the earlier hominins. For instance, the hand and finger morphologies of many of the earliest hominins indicate adaptations consistent with arboreality. These include longer hands, more curved metacarpals and phalanges (long bones in the hand and fingers, respectively), and a shorter, relatively weaker thumb. This allows for gripping onto curved surfaces during locomotion. The earliest hominins appear to have mixed morphologies for both bipedalism and arborealism. However, among Australopiths (members of the genus, Australopithecus), there are indications for greater reliance on bipedalism as the primary form of locomotion. Similarly, adaptations consistent with tool manufacture (shorter fingers and a longer, more robust thumb, in contrast to the features associated with arborealism) have been argued to appear before the genus Homo.
Special Topic: Fear of Snakes — A Cultural or Biological Response/Adaptation?

It is suggested that primates have three major predators: raptors, felines, and snakes; however, many studies show that of these carnivores, snakes were one of the first that mammals had to contend with alongside dinosaurs, as felines and raptors evolved at a much slower pace than their reptilian competition. Herpetologists trace the evolution of constricting snakes to about 100 million years ago, and by the time mammals arrived around 75 million years ago, constrictors were already well established as a formidable threat (Greene, 2017). Both co-existed for millennia and each sustained selective pressures requiring them to evolve specific traits to survive. When venomous snakes eventually emerged 55 to 65 million years ago, they posed yet an additional threat to proto-primates as they required less distance for the predator to kill (2017). Alongside camouflage and silent movement techniques, it was the development of the snake’s hollow fangs through which to deliver venom that was most transformative to primate evolution. As such, primates evolved their pre-conscious attention, and visual acuity to cope with this new threat; therefore, while snakes were adapting morphologically to feed themselves, they were unwittingly teaching proto-primates valuable lessons in predator detection and reacting appropriately in order to survive.
In a 2009 Harvard University study, Lynne A. Isbell hypothesizes that envenoming snakes are linked to being directly responsible for the origins of the evolving complex brains and superior visual capacity in the lineage of anthropoids leading to humans (Isbell, 2009). Forward-facing eyes for binocular vision, depth perception, enhanced visual acuity, stereoscopic and trichromatic colour vision, all traits necessary for snake detection; and the quick motor responses from the primate’s fight, flight, or freeze defence mechanism to circumvent a snake’s squeeze or bite. Numerous laboratory studies show that humans and primates both sense and visually detect snakes more rapidly than other threatening stimuli (Van Le Et al., 2013). These experiments show that snakes elicited the strongest, fastest responses (Van Le Et al., 2013). This is known as ‘Snake Detection Theory’ and is the evolution of the primate’s complex brain, visual acuity, and rapid motor responses towards snakes in its environment that are the adaptations needed to live successfully as arboreal beings. It is not fortuitous then, that primates that never coexisted with venomous snakes, such as lemurs in Madagascar, have less visual acuity, better olfaction and smaller brains. Within Isbell’s work, a collaborative study by a group of neuroscientists tested this hypothesis and found that, indeed, there is higher neural firing and activity in multiple areas of the primate brain, notably in the pulvinar, a region responsible for visual attention and oculomotor behaviour (Isbell, L., 2009).

Today, the fear of snakes is widespread in humans, often shown through avoidance and disgust. A study in The Journal of Ethnobiology and Ethnomedicine notes that snakes are over-hunted and excluded from conservation efforts worldwide (Ceríaco, 2012). While cultural factors shape our sentiments, instinct also plays a role—such as the developed avoidance behaviors toward threats like snakes. This blend of instinct and cultural influence is not only seen in behavior but also deeply embedded in the stories we tell. Many cultures depict mythological snakes as harbingers of death or chaos. In the Bible, Satan becomes a snake to tempt Eve. Norse mythology features Jörmungandr, the world serpent who signals the apocalypse. Egyptian myth tells of Apophis, who battles the sun god Ra nightly. Though sources vary, these myths consistently portray snakes as threats. As such, the widespread fear of snakes may reflect both evolutionary and cultural influences. Understood as an adaptive response inherited from primate ancestors—who developed avoidance behaviors toward potentially dangerous stimuli—and reinforced through myths and religious narratives, the enduring presence of snakes as potent figures of fear across human societies and primate groups highlights the complex intertwining of instinct and cultural meaning in shaping human behavior.
Early Hominins: Sahelanthropus and Orrorin
We see evidence for bipedalism in some of the earliest fossil hominins, dated from within our estimates of our divergence from chimpanzees. These hominins, however, also indicate evidence for arboreal locomotion.
The earliest dated hominin find (between 6 mya and 7 mya, based on radiometric dating of volcanic tufts) has been argued to come from Chad and is named Sahelanthropus tchadensis (Figure 9.8; Brunet et al. 1995). The initial discovery was made in 2001 by Ahounta Djimdoumalbaye and announced in Nature in 2002 by a team led by French paleontologist Michel Brunet. The find has a small cranial capacity (360 cc) and smaller canines than those in extant great apes, though they are larger and pointier than those in humans. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. A short cranial base and a foramen magnum that is more humanlike in positioning have been argued to indicate upright walking.

Initially, the inclusion of Sahelanthropus in the hominin family was debated by researchers, since the evidence for bipedalism is based on cranial evidence alone, which is not as convincing as postcranial evidence. Yet, a femur (thigh bone) and ulnae (upper arm bones) thought to belong to Sahelanthropus was discovered in 2001 (although not published until 2022). These bones may support the idea that the hominin was in fact a terrestrial biped with arboreal capabilities and behaviors (Daver et al. 2022).
Orrorin tugenensis (Orrorin meaning “original man”), dated to between 6 mya and 5.7 mya, was discovered near Tugen Hills in Kenya in 2000. Smaller cheek teeth (molars and premolars) than those in even more recent hominins, thick enamel, and reduced, but apelike, canines characterize this species. This is the first species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains. One of the most important elements discovered was a proximal femur, BAR 1002'00. The femur is the thigh bone, and the proximal part is that which articulates with the pelvis; this is very important for studying posture and locomotion. This femur indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins. Some have argued that features of the finger bones suggest potential tool-making capabilities, although many researchers argue that these features are also consistent with climbing.
Early Hominins: The Genus Ardipithecus
Another genus, Ardipithecus, is argued to be represented by at least two species: Ardipithecus (Ar.) ramidus and Ar. kadabba.
Ardipithecus ramidus (“ramid” means root in the Afar language) is currently the best-known of the earliest hominins (Figure 9.9). Unlike Sahelanthropus and Orrorin, this species has a large sample size of over 110 specimens from Aramis alone. Dated to 4.4 mya, Ar. ramidus was found in Ethiopia (in the Middle Awash region and in Gona). This species was announced in 1994 by American palaeoanthropologist Tim White, based on a partial female skeleton nicknamed “Ardi” (ARA-VP-6/500; White et al. 1994). Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, she had an opposable big toe (hallux), similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. A small brain (300 cc to 350 cc), midfacial projection, and slight prognathism show retained ancestral cranial features, but the cheek bones are less flared and robust than in later hominins.

Ardipithecus kadabba (the species name means “oldest ancestor” in the Afar language) is known from localities on the western margin of the Middle Awash region, the same locality where Ar. ramidus has been found. Specimens include mandibular fragments and isolated teeth as well as a few postcranial elements from the Asa Koma (5.5 mya to 5.77 mya) and Kuseralee Members (5.2 mya), well-dated and understood (but temporally separate) volcanic layers in East Africa. This species was discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie. Originally these specimens were referred to as a subspecies of Ar. ramidus. In 2002, six teeth were discovered at Asa Koma and the dental-wear patterns confirmed that this was a distinct species, named Ar. kadabba, in 2004. One of the postcranial remains recovered included a 5.2 million-year-old toe bone that demonstrated features that are associated with toeing off (pushing off the ground with the big toe leaving last) during walking, a characteristic unique to bipedal walkers. However, the toe bone was found in the Kuseralee Member, and therefore some doubt has been cast by researchers about its association with the teeth from the Asa Koma Member.
Bipedal Trends in Early Hominins: Summary
Trends toward bipedalism are seen in our earliest hominin finds. However, many specimens also indicate retained capabilities for climbing. Trends include a larger, more robust hallux; a more compact foot, with an arch; a robust, long femur, angled at the knee; a robust tibia; a bowl-shaped pelvis; and a more anterior foramen magnum. While the level of bipedality in Salehanthropus tchadenisis is debated since there are few fossils and no postcranial evidence, Orrorin tugenensis and Ardipithecus kadabba show clear indications of some of these bipedal trends. However, some retained ancestral traits, such as an opposable hallux in Ardipithecus, indicate some retention in climbing ability.
Derived Adaptations: Early Hominin Dention
The Importance of Teeth
Teeth are abundant in the fossil record, primarily because they are already highly mineralized as they are forming, far more so than even bone. Because of this, teeth preserve readily. And, because they preserve readily, they are well-studied and better understood than many skeletal elements. In the sparse hominin (and primate) fossil record, teeth are, in some cases, all we have.
Teeth also reveal a lot about the individual from whom they came. We can tell what they evolved to eat, to which other species they may be closely related, and even, to some extent, the level of sexual dimorphism, or general variability, within a given species. This is powerful information that can be contained in a single tooth. With a little more observation, the wearing patterns on a tooth can tell us about the diet of the individual in the weeks leading up to its death. Furthermore, the way in which a tooth is formed, and the timing of formation, can reveal information about changes in diet (or even mobility) over infancy and childhood, using isotopic analyses. When it comes to our earliest hominin relatives, this information is vital for understanding how they lived.
The purpose of comparing different hominin species is to better understand the functional morphology as it applies to dentition. In this, we mean that the morphology of the teeth or masticatory system (which includes jaws) can reveal something about the way in which they were used and, therefore, the kinds of foods these hominins ate. When comparing the features of hominin groups, it is worth considering modern analogues (i.e., animals with which to compare) to make more appropriate assumptions about diet. In this way, hominin dentition is often compared with that of chimpanzees and gorillas (our close ape relatives), as well as with that of modern humans.
The most divergent group, however, is humans. Humans around the world have incredibly varied diets. Among hunter-gatherers, it can vary from a honey- and plant-rich diet, as seen in the Hadza in Tanzania, to a diet almost entirely reliant on animal fat and protein, as seen in Inuits in polar regions of the world. We are therefore considered generalists, more general than the largely frugivorous (fruit-eating) chimpanzee or the folivorous (foliage-eating) gorilla, as discussed in Chapter 5.
One way in which all humans are similar is our reliance on the processing of our food. We cut up and tear meat with tools using our hands, instead of using our front teeth (incisors and canines). We smash and grind up hard seeds, instead of crushing them with our hind teeth (molars). This means that, unlike our ape relatives, we can rely more on developing tools to navigate our complex and varied diets. (We could say) Our brain, therefore, is our primary masticatory organ. Evolutionarily, our teeth have reduced in size and our faces are flatter, or more orthognathic, partially in response to our increased reliance on our hands and brain to process food. Similarly, a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat. These trends begin early on in our evolution. The link has been made between some of the earliest evidence for stone tool manufacture, the earliest members of our genus, and the features that we associate with these specimens.
General Dental Trends in Early Hominins
Several trends are visible in the dentition of early hominins. However, all tend to have the same dental formula. The dental formula tells us how many of each tooth type are present in each quadrant of the mouth. Going from the front of the mouth, this includes the square, flat incisors; the pointy canines; the small, flatter premolars; and the larger hind molars. In many primates, from Old World monkeys to great apes, the typical dental formula is 2:1:2:3. This means that if we divide the mouth into quadrants, each has two incisors, one canine, two premolars, and three molars. The eight teeth per quadrant total 32 teeth in all (although some humans have fewer teeth due to the absence of their wisdom teeth, or third molars).

The morphology of the individual teeth is where we see the most change. Among primates, large incisors are associated with food procurement or preparation (such as biting small fruits), while small incisors indicate a diet that may contain small seeds or leaves (where the preparation is primarily in the back of the mouth). Most hominins have relatively large, flat, vertically aligned incisors that occlude (touch) relatively well, forming a “bite.” This differs from, for instance, the orangutan, whose teeth stick out (i.e., are procumbent).
While the teeth are often aligned with diet, the canines may be misleading in that regard. We tend to associate pointy, large canines with the ripping required for meat, and the reduction (or, in some animals, the absence) of canines as indicative of herbivorous diets. In humans, our canines are often a similar size to our incisors and therefore considered incisiform (Figure 9.10). However, our closest relatives all have very long, pointy canines, particularly on their upper dentition. This is true even for the gorilla, which lives almost exclusively on plants. The canines in these instances reveal more about social structure and sexual dimorphism than diet, as large canines often signal dominance.
Early on in human evolution, we see a reduction in canine size. Sahelanthropus tchadensis and Orrorin tugenensis both have smaller canines than those in extant great apes, yet the canines are still larger and pointier than those in humans or more recent hominins. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. In Ardipithecus ramidus, there is no obvious difference between male and female canine size, yet they are still slightly larger and pointier than in modern humans. This implies a less sexually dimorphic social structure in the earlier hominins relative to modern-day chimpanzees and gorillas.
Along with a reduction in canine size is the reduction or elimination of a canine diastema: a gap between the teeth on the mandible that allows room for elongated teeth on the maxilla to “fit” in the mouth. Absence of a diastema is an excellent indication of a reduction in canine size. In animals with large canines (such as baboons), there is also often a honing P3, where the first premolar (also known as P3 for evolutionary reasons) is triangular in shape, “sharpened” by the extended canine from the upper dentition. This is also seen in some early hominins: Ardipithecus, for example, has small canines that are almost the same height as its incisors, although still larger than those in recent hominins.
The hind dentition, such as the bicuspid (two cusped) premolars or the much larger molars, are also highly indicative of a generalist diet in hominins. Among the earliest hominins, the molars are larger than we see in our genus, increasing in size to the back of the mouth and angled in such a way from the much smaller anterior dentition as to give these hominins a parabolic (V-shaped) dental arch. This differs from our living relatives and some early hominins, such as Sahelanthropus, whose molars and premolars are relatively parallel between the left and right sides of the mouth, creating a U-shape.
Among more recent early hominins, the molars are larger than those in the earliest hominins and far larger than those in our own genus, Homo. Large, short molars with thick enamel allowed our early cousins to grind fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing. In our genus, the hind dentition is far smaller than in these early hominins. Our teeth also have medium-size cusps, which allow for both efficient grinding and tearing/shearing meats.
Understanding the dental morphology has allowed researchers to extrapolate very specific behaviors of early hominins. It is worth noting that while teeth preserve well and are abundant, a slew of other morphological traits additionally provide evidence for many of these hypotheses. Yet there are some traits that are ambiguous. For instance, while there are definitely high levels of sexual dimorphism in Au. afarensis, discussed in the next section, the canine teeth are reduced in size, implying that while canines may be useful indicators for sexual dimorphism, it is also worth considering other evidence.
In summary, trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the ancestral dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
Special Topic: Contested Species
Many named species are highly debated and argued to have specimens associated with a more variable Au. afarensis or Au. anamensis species. Sometimes these specimens are dated to times when, or found in places in which, there are “gaps” in the palaeoanthropological record. These are argued to represent chronospecies or variants of Au. afarensis. However, it is possible that, with more discoveries, the distinct species types will hold.
Australopithecus bahrelghazali is dated to within the time period of Au. afarensis (3.6 mya; Brunet et al. 1995) and was the first Australopithecine to be discovered in Chad in central Africa. Researchers argue that the holotype, whom discoverers have named “Abel,” falls under the range of variation of Au. afarensis and therefore that A. bahrelghazali does not fall into a new species (Lebatard et al. 2008). If “Abel” is a member of Au. afarensis, the geographic range of the species would be greatly extended.
On a different note, Australopithecus deyiremada (meaning “close relative” in the Ethiopian language of Afar) is dated to 3.5 mya to 3.3 mya and is based on fossil mandible bones discovered in 2011 in Woranso-Mille (in the Afar region of Ethiopia) by Yohannes Haile-Selassie, an Ethiopian paleoanthropologist (Haile-Selassie et al. 2019). The discovery indicated, in contrast to Au. afarensis, smaller teeth with thicker enamel (potentially suggesting a harder diet) as well as a larger mandible and more projecting cheekbones. This find may be evidence that more than one closely related hominin species occupied the same region at the same temporal period (Haile-Selassie et al. 2015; Spoor 2015) or that other Au. afarensis specimens have been incorrectly designated. However, others have argued that this species has been prematurely identified and that more evidence is needed before splitting the taxa, since the variation appears subtle and may be due to slightly different niche occupations between populations over time.
Australopithecus garhi is another species found in the Middle Awash region of Ethiopia. It is currently dated to 2.5 mya (younger than Au. afarensis). Researchers have suggested it fills in a much-needed temporal “gap” between hominin finds in the region, with some anatomical differences, such as a relatively large cranial capacity (450 cc) and larger hind dentition than seen in other gracile Australopithecines. Similarly, the species has been argued to have longer hind limbs than Au. afarensis, although it was still able to move arboreally (Asfaw et al. 1999). However, this species is not well documented or understood and is based on only several fossil specimens. More astonishingly, crude stone tools resembling Oldowan (which will be described later) have been found in association with Au. garhi. While lacking some of the features of the Oldowan, this is one of the earliest technologies found in direct association with a hominin.
Kenyanthopus platyops (the name “platyops” refers to its flatter-faced appearance) is a highly contested genus/species designation of a specimen (KNM-WT 40000) from Lake Turkana in Kenya, discovered by Maeve Leakey in 1999 (Figure 9.11). Dated to between 3.5 mya and 3.2 mya, some have suggested this specimen is an Australopithecus, perhaps even Au. afarensis (with a brain size which is difficult to determine, yet appears small), while still others have placed this specimen in Homo (small dentition and flat-orthognathic face). While taxonomic placing of this species is quite divided, the discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis (Leakey et al. 2001). Some researchers have additionally associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this specimen.

The Genus Australopithecus
The Australopithecines are a diverse group of hominins, comprising various species. Australopithecus is the given group or genus name. It stems from the Latin word Australo, meaning “southern,” and the Greek word pithecus, meaning “ape.” Within this section, we will outline these differing species’ geological and temporal distributions across Africa, unique derived and/or shared traits, and importance in the fossil record.

Between 3 mya and 1 mya, there seems to be differences in dietary strategy between different species of hominins designated as Australopithecines. A pattern of larger posterior dentition (even relative to the incisors and canines in the front of the mouth), thick enamel, and cranial evidence for extremely large chewing muscles is far more pronounced in a group known as the robust australopithecines. This pattern is extremely relative to their earlier contemporaries or predecessors, the gracile australopithecines, and is certainly larger than those seen in early Homo, which emerged during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins (Figure 9.12).
Because of these differences, this section has been divided into “gracile” and “robust” Australopithecines, highlighting the morphological differences between the two groups (which many researchers have designated as separate genera: Australopithecus and Paranthropus, respectively) and then focusing on the individual species. It is worth noting, however, that not all researchers accept these clades as biologically or genetically distinct, with some researchers insisting that the relative gracile and robust features found in these species are due to parallel evolutionary events toward similar dietary niches.
Despite this genus’ ancestral traits and small cranial capacity, all members show evidence of bipedal locomotion. It is generally accepted that Australopithecus species display varying degrees of arborealism along with bipedality.
Gracile Australopithecines
This section describes individual species from across Africa. These species are called “gracile australopithecines” because of their smaller and less robust features compared to the divergent “robust” group. Numerous Australopithecine species have been named, but some are only based on a handful of fossil finds, whose designations are controversial.
East African Australopithecines
East African Australopithecines are found throughout the EARS, and they include the earliest species associated with this genus. Numerous fossil-yielding sites, such as Olduvai, Turkana, and Laetoli, have excellent, datable stratigraphy, owing to the layers of volcanic tufts that have accumulated over millions of years. These tufts may be dated using absolute dating techniques, such as Potassium-Argon dating (described in Chapter 7). This means that it is possible to know a relatively refined date for any fossil if the context (i.e., exact location) of that find is known. Similarly, comparisons between the faunal assemblages of these stratigraphic layers have allowed researchers to chronologically identify environmental changes.

The earliest known Australopithecine is dated to 4.2 mya to 3.8 mya. Australopithecus anamensis (after “Anam,” meaning “lake” from the Turkana region in Kenya; Leakey et al. 1995; Patterson and Howells 1967) is currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia; Figure 9.13). Recently, a 2019 find from Ethiopia, named MRD, after Miro Dora where it was found, was discovered by an Ethiopian herder named Ali Bereino. It is one of the most complete cranial finds of this species (Ward et al. 1999). A small brain size (370 cc), relatively large canines, projecting cheekbones, and earholes show more ancestral features as compared to those of more recent Australopithecines. The most important element discovered with this species is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking. Similarly, the earliest found hominin femur belongs to this species. Ancestral traits in the upper limb (such as the humerus) indicate some retained arboreal locomotion.
Some researchers suggest that Au. anamensis is an intermediate form of the chronospecies that becomes Au. afarensis, evolving from Ar. ramidus. However, this is debated, with other researchers suggesting morphological similarities and affinities with more recent species instead. Almost 100 specimens, representing over 20 individuals, have been found to date (Leakey et al. 1995; McHenry 2009; Ward et al. 1999).
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. Au. afarensis (which means “from the Afar region”) is dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia (Figure 9.14). The most famous individual from this species is a partial female skeleton discovered in Hadar (Ethiopia), later nicknamed “Lucy,” after the Beatles’ song “Lucy in the Sky with Diamonds,” which was played in celebration of the find (Johanson et al. 1978; Kimbel and Delezene 2009). This skeleton was found in 1974 by Donald Johanson and dates to approximately 3.2 mya. In addition, in 2002 a juvenile of the species was found by Zeresenay Alemseged and given the name “Selam” (meaning “peace,” DIK 1-1), though it is popularly known as “Lucy’s Child” or as the “Dikika Child” (Alemseged et al. 2006). Similarly, the “Laetoli Footprints” (discussed in Chapter 7; Hay and Leakey 1982; Leakey and Hay 1979) have drawn much attention.


The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans (indicative of a generalist diet); in addition, Au. afarensis has a prognathic face (the face below the eyes juts anteriorly) and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus. Despite a reduction in canine size in this species, large overall size variation indicates high levels of sexual dimorphism.
Skeletal evidence indicates that this species was bipedal, as its pelvis and lower limb demonstrate a humanlike femoral neck, valgus knee, and bowl-shaped hip (Figure 9.15). More evidence of bipedalism is found in the footprints of this species. Au. afarensis is associated with the Laetoli Footprints, a 24-meter trackway of hominin fossil footprints preserved in volcanic ash discovered by Mary Leakey in Tanzania and dated to 3.5 mya to 3 mya. This set of prints is thought to have been produced by three bipedal individuals as there are no knuckle imprints, no opposable big toes, and a clear arch is present. The infants of this species are thought to have been more arboreal than the adults, as discovered through analyses of the foot bones of the Dikika Child dated to 3.32 mya (Alemseged et al. 2006).
Although not found in direct association with stone tools, potential evidence for cut marks on bones, found at Dikika, and dated to 3.39 mya indicates a possible temporal/ geographic overlap between meat eating, tool use, and this species. However, this evidence is fiercely debated. Others have associated the cut marks with the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species.
South African Australopithecines
Since the discovery of the Taung Child, there have been numerous Australopithecine discoveries from the region known as “The Cradle of Humankind,” which was recently given UNESCO World Heritage Site status as “The Fossil Hominid Sites of South Africa.” The limestone caves found in the Cradle allow for the excellent preservation of fossils. Past animals navigating the landscape and falling into cave openings, or caves used as dens by carnivores, led to the accumulation of deposits over millions of years. Many of the hominin fossils, encased in breccia (hard, calcareous sedimentary rock), are recently exposed from limestone quarries mined in the previous century. This means that extracting fossils requires excellent and detailed exposed work, often by a team of skilled technicians.
While these sites have historically been difficult to date, with mixed assemblages accumulated over large time periods, advances in techniques such as uranium-series dating have allowed for greater accuracy. Historically, the excellent faunal record from East Africa has been used to compare sites based on relative dating, whereby environmental and faunal changes and extinction events allow us to know which hominin finds are relatively younger or older than others.
The discovery of the Taung Child in 1924 (discussed in the Special Topic box “The Taung Child” below) shifted the focus of palaeoanthropological research from Europe to Africa, although acceptance of this shift was slow (Broom 1947; Dart 1925). The species to which it is assigned, Australopithecus africanus (name meaning “Southern Ape of Africa”), is currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa (Figure 9.16). A relatively large brain (400 cc to 500 cc), small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits. Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism. However, the sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some ancestral features. Although not in direct association with stone tools, a 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities.

Another famous Au. africanus skull (the skull of “Mrs. Ples”) was previously attributed to Plesianthropus transvaalensis, meaning “near human from the Transvaal,” the old name for Gauteng Province, South Africa (Broom 1947, 1950). The name was shortened by contemporary journalists to “Ples” (Figure 9.17). Due to the prevailing mores of the time, the assumed female found herself married, at least in name, and has become widely known as “Mrs. Ples.” It was later reassigned to Au. africanus and is now argued by some to be a young male rather than an adult female cranium (Thackeray 2000, Thackeray et al. 2002).

In 2008, nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger, noted a clavicle bone in some leftover mining breccia in the Malapa Fossil Site (South Africa). After rigorous studies, the species, Australopithecus sediba (meaning “fountain” or “wellspring” in the South African language of Sesotho), was named in 2010 (Figure 9.18; Berger et al. 2010). The first type specimen belongs to a juvenile male, Karabo (MH1), but the species is known from at least six partial skeletons, from infants through adults. These specimens are currently dated to 1.97 mya (Dirks et al. 2010). The discoverers have argued that Au. sediba shows mosaic features between Au. africanus and the genus, Homo, which potentially indicates a transitional species, although this is heavily debated. These features include a small brain size (Australopithecus-like; 420 cc to 450 cc) but gracile mandible and small teeth (Homo-like). Similarly, the postcranial skeletons are also said to have mosaic features: scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. Some researchers have argued that Au. sediba shows a modern hand morphology (shorter fingers and a longer thumb), indicating that adaptations to tool manufacture and use may be present in this species.

Another famous Australopithecine find from South Africa is that of the nearly complete skeleton now known as “Little Foot” (Clarke 1998, 2013). Little Foot (StW 573) is potentially the earliest dated South African hominin fossil, dating to 3.7 mya, based on radiostopic techniques, although some argue that it is younger than 3 mya (Pickering and Kramers 2010). The name is jokingly in contrast to the cryptid species “bigfoot” and is named because the initial discovery of four ankle bones indicated bipedality. Little Foot was discovered by Ron Clarke in 1994, when he came across the ankle bones while sorting through monkey fossils in the University of Witwatersrand collections (Clarke and Tobias 1995). He asked Stephen Motsumi and Nkwane Molefe to identify the known records of the fossils, which allowed them to find the rest of the specimen within just days of searching the Sterkfontein Caves’ Silberberg Grotto.
The discoverers of Little Foot insist that other fossil finds, previously identified as Au. Africanus, be placed in this new species based on shared ancestral traits with older East African Australopithecines (Clarke and Kuman 2019). These include features such as a relatively large brain size (408 cc), robust zygomatic arch, and a flatter midface. Furthermore, the discoverers have argued that the heavy anterior dental wear patterns, relatively large anterior dentition, and smaller hind dentition of this specimen more closely resemble that of Au. anamensis or Au. afarensis. It has thus been placed in the species Australopithecus prometheus. This species name refers to a previously defunct taxon named by Raymond Dart. The species designation was, through analyzing Little Foot, revived by Ron Clarke, who insists that many other fossil hominin specimens have prematurely been placed into Au. africanus. Others say that it is more likely that Au. africanus is a more variable species and not representative of two distinct species.
Paranthropus “Robust” Australopithecines
In the robust australopithecines, the specialized nature of the teeth and masticatory system, such as flaring zygomatic arches (cheekbones), accommodate very large temporalis (chewing) muscles. These features also include a large, broad, dish-shaped face and and a large mandible with extremely large posterior dentition (referred to as megadonts) and hyper-thick enamel (Kimbel 2015; Lee-Thorp 2011; Wood 2010). Research has revolved around the shared adaptations of these “robust” australopithecines, linking their morphologies to a diet of hard and/or tough foods (Brain 1967; Rak 1988). Some argued that the diet of the robust australopithecines was so specific that any change in environment would have accelerated their extinction. The generalist nature of the teeth of the gracile australopithecines, and of early Homo, would have made them more capable of adapting to environmental change. However, some have suggested that the features of the robust australopithecines might have developed as an effective response to what are known as fallback foods in hard times rather than indicating a lack of adaptability.
There are currently three widely accepted robust australopithecus or, Paranthropus, species: P. aethiopicus, which has more ancestral traits, and P. boisei and P. robustus, which are more derived in their features (Strait et al. 1997; Wood and Schroer 2017). These three species have been grouped together by a majority of scholars as a single genus as they share more derived features (are more closely related to each other; or, in other words, are monophyletic) than the other australopithecines (Grine 1988; Hlazo 2015; Strait et al. 1997; Wood 2010 ). While researchers have mostly agreed to use the umbrella term Paranthropus, there are those who disagree (Constantino and Wood 2004, 2007; Wood 2010).
As a collective, this genus spans 2.7 mya to 1.0 mya, although the dates of the individual species differ. The earliest of the Paranthropus species, Paranthropus aethiopicus, is dated to between 2.7 mya and 2.3 mya and currently found in Tanzania, Kenya, and Ethiopia in the EARS system (Figure 9.19; Constantino and Wood 2007; Hlazo 2015; Kimbel 2015; Walker et al. 1986; White 1988). It is well known because of one specimen known as the “Black Skull” (KNM–WT 17000), so called because of the mineral manganese that stained it black during fossilization (Kimbel 2015). As with all robust Australopithecines, P. aethiopicus has the shared derived traits of large, flat premolars and molars; large, flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle); a sagittal crest (ridge on the top of the skull) for increased muscle attachment of the chewing muscles to the skull; and a robust mandible and supraorbital torus (brow ridge). However, only a few teeth have been found. A proximal tibia indicates bipedality and similar body size to Au. afarensis. In recent years, researchers have discovered and assigned a proximal tibia and juvenile cranium (L.338y-6) to the species (Wood and Boyle 2016).

First attributed as Zinjanthropus boisei (with the first discovery going by the nickname “Zinj” or sometimes “Nutcracker Man”), Paranthropus boisei was discovered in 1959 by Mary Leakey (see Figure 9.20 and 9.21; Hay 1990; Leakey 1959). This “robust” australopith species is distributed across countries in East Africa at sites such as Kenya (Koobi Fora, West Turkana, and Chesowanja), Malawi (Malema-Chiwondo), Tanzania (Olduvai Gorge and Peninj), and Ethiopia (Omo River Basin and Konso). The hypodigm, sample of fossils whose features define the group, has been found by researchers to date to roughly 2.4 mya to 1.4 mya. Due to the nature of its exaggerated, larger, and more robust features, P. boisei has been termed hyper-robust—that is, even more heavily built than other robust species, with very large, flat posterior dentition (Kimbel 2015). Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). Another famous specimen from this species is the Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu.


Paranthropus robustus was the first taxon to be discovered within the genus in Kromdraai B by a schoolboy named Gert Terblanche; subsequent fossil discoveries were made by researcher Robert Broom in 1938 (Figure 9.22; Broom 1938a, 1938b, 1950), with the holotype specimen TM 1517 (Broom 1938a, 1938b, 1950; Hlazo 2018). Paranthropus robustus dates approximately from 2.0 mya to 1 mya and is the only taxon from the genus to be discovered in South Africa. Several of these fossils are fragmentary in nature, distorted, and not well preserved because they have been recovered from quarry breccia using explosives. P. robustus features are neither as “hyper-robust” as P. boisei nor as ancestral as P. aethiopicus; instead, they have been described as being less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring; Rak 1983; Walker and Leakey 1988). Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick-enameled dentition.

Comparisons between Gracile and Robust Australopiths
Comparisons between gracile and robust australopithecines may indicate different phylogenetic groupings or parallel evolution in several species. In general, the robust australopithecines have large temporalis (chewing) muscles, as indicated by flaring zygomatic arches, sagittal crests, and robust mandibles (jawbones). Their hind dentition is large (megadont), with low cusps and thick enamel. Within the gracile australopithecines, researchers have debated the relatedness of the species, or even whether these species should be lumped together to represent more variable or polytypic species. Often researchers will attempt to draw chronospecific trajectories, with one taxon said to evolve into another over time.
Special Topic: The Taung Child

The well-known fossil of a juvenile Australopithecine, the “Taung Child,” was the first early hominin evidence ever discovered and was the first to demonstrate our common human heritage in Africa (Figure 9.23; Dart 1925). The tiny facial skeleton and natural endocast were discovered in 1924 by a local quarryman in the North West Province in South Africa and were painstakingly removed from the surrounding cement-like breccia by Raymond Dart using his wife’s knitting needles. When first shared with the scientific community in 1925, it was discounted as being nothing more than a young monkey of some kind. Prevailing biases of the time made it too difficult to contemplate that this small-brained hominin could have anything to do with our own history. The fact that it was discovered in Africa simply served to strengthen this bias.
Early Tool Use and Technology
Early Stone Age Technology (ESA)
The Early Stone Age (ESA) marks the beginning of recognizable technology made by our human ancestors. Stone-tool (or lithic) technology is defined by the fracturing of rocks and the manufacture of tools through a process called knapping. The Stone Age lasted for more than 3 million years and is broken up into chronological periods called the Early (ESA), Middle (MSA), and Later Stone Ages (LSA). Each period is further broken up into a different techno-complex, a term encompassing multiple assemblages (collections of artifacts) that share similar traits in terms of artifact production and morphology. The ESA spanned the largest technological time period of human innovation from over 3 million years ago to around 300,000 years ago and is associated almost entirely with hominin species prior to modern Homo sapiens. As the ESA advanced, stone tool makers (known as knappers) began to change the ways they detached flakes and eventually were able to shape artifacts into functional tools. These advances in technology go together with the developments in human evolution and cognition, dispersal of populations across the African continent and the world, and climatic changes.
In order to understand the ESA, it is important to consider that not all assemblages are exactly the same within each techno-complex: one can have multiple phases and traditions at different sites (Lombard et al. 2012). However, there is an overarching commonality between them. Within stone tool assemblages, both flakes or cores (the rocks from which flakes are removed) are used as tools. Large Cutting Tools (LCTs) are tools that are shaped to have functional edges. It is important to note that the information presented here is a small fraction of what is known about the ESA, and there are ongoing debates and discoveries within archaeology.
Currently, the oldest-known stone tools, which form the techno-complex the Lomekwian, date to 3.3 mya (Harmand et al. 2015; Toth 1985). They were found at a site called Lomekwi 3 in Kenya. This techno-complex is the most recently defined and pushed back the oldest-known date for lithic technology. There is only one known site thus far and, due to the age of the site, it is associated with species prior to Homo, such as Kenyanthropus platyops. Flakes were produced through indirect percussion, whereby the knappers held a rock and hit it against another rock resting on the ground. The pieces are very chunky and do not display the same fracture patterns seen in later techno-complexes. Lomekwian knappers likely aimed to get a sharp-edged piece on a flake, which would have been functional, although the specific function is currently unknown.
Stone tool use, however, is not only understood through the direct discovery of the tools. Cut marks on fossilized animal bones may illuminate the functionality of stone tools. In one controversial study in 2010, researchers argued that cut marks on a pair of animal bones from Dikika (Ethiopia), dated to 3.4 mya, were from stone tools. The discoverers suggested that they be more securely associated, temporally, with Au. afarensis. However, others have noted that these marks are consistent with teeth marks from crocodiles and other carnivores.

The Oldowan techno-complex is far more established in the scientific literature (Leakey 1971). It is called the Oldowan because it was originally discovered in Olduvai Gorge, Tanzania, but the oldest assemblage is from Gona in Ethiopia, dated to 2.6 mya (Semaw 2000). The techno-complex is defined as a core and flake industry. Like the Lomekwian, there was an aim to get sharp-edged flakes, but this was achieved through a different production method. Knappers were able to actively hold or manipulate the core being knapped, which they could directly hit using a hammerstone. This technique is known as free-hand percussion, and it demonstrates an understanding of fracture mechanics. It has long been argued that the Oldowan hominins were skillful in tool manufacture.
Because Oldowan knapping requires skill, earlier researchers have attributed these tools to members of our genus, Homo. However, some have argued that these tools are in more direct association with hominins in the genera described in this chapter (Figure 9.24).
Invisible Tool Manufacture and Use
The vast majority of our understanding of these early hominins comes from fossils and reconstructed paleoenvironments. It is only from 3 mya when we can start “looking into their minds” and lifestyles by analyzing their manufacture and use of stone tools. However, the vast majority of tool use in primates (and, one can argue, in humans) is not with durable materials like stone. All of our extant great ape relatives have been observed using sticks, leaves, and other materials for some secondary purpose (to wade across rivers, to “fish” for termites, or to absorb water for drinking). It is possible that the majority of early hominin tool use and manufacture may be invisible to us because of this preservation bias.
Chapter Summary
The fossil record of our earliest hominin relatives has allowed paleoanthropologists to unpack some of the mysteries of our evolution. We now know that traits associated with bipedalism evolved before other “human-like” traits, even though the first hominins were still very capable of arboreal locomotion. We also know that, for much of this time, hominin taxa were diverse in the way they looked and what they ate, and they were widely distributed across the African continent. And we know that the environments in which these hominins lived underwent many changes over this time during several warming and cooling phases.
Yet this knowledge has opened up many new mysteries. We still need to better differentiate some taxa. In addition, there are ongoing debates about why certain traits evolved and what they meant for the extinction of some of our relatives (like the robust australopiths). The capabilities of these early hominins with respect to tool use and manufacture is also still uncertain.
Hominin Species Summaries
Hominin |
Sahelanthropus tchadensis |
Dates |
7 mya to 6 mya |
Region(s) |
Chad |
Famous discoveries |
The initial discovery, made in 2001. |
Brain size |
360 cc average |
Dentition |
Smaller than in extant great apes; larger and pointier than in humans. Canines worn at the tips. |
Cranial features |
A short cranial base and a foramen magnum (hole in which the spinal cord enters the cranium) that is more humanlike in positioning; has been argued to indicate upright walking. |
Postcranial features |
Currently little published postcranial material. |
Culture |
N/A |
Other |
The extent to which this hominin was bipedal is currently heavily debated. If so, it would indicate an arboreal bipedal ancestor of hominins, not a knuckle-walker like chimpanzees. |
Hominin |
Orrorin tugenensis |
Dates |
6 mya to 5.7 mya |
Region(s) |
Tugen Hills (Kenya) |
Famous discoveries |
Original discovery in 2000. |
Brain size |
N/A |
Dentition |
Smaller cheek teeth (molars and premolars) than even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines. |
Cranial features |
Not many found |
Postcranial features |
Fragmentary leg, arm, and finger bones have been found. Indicates bipedal locomotion. |
Culture |
Potential toolmaking capability based on hand morphology, but nothing found directly. |
Other |
This is the earliest species that clearly indicates adaptations for bipedal locomotion. |
Hominin |
Ardipithecus kadabba |
Dates |
5.2 mya to 5.8 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
Discovered by Yohannes Haile-Selassie in 1997. |
Brain size |
N/A |
Dentition |
Larger hind dentition than in modern chimpanzees. Thick enamel and larger canines than in later hominins. |
Cranial features |
N/A |
Postcranial features |
A large hallux (big toe) bone indicates a bipedal “push off.” |
Culture |
N/A |
Other |
Faunal evidence indicates a mixed grassland/woodland environment. |
Hominin |
Ardipithecus ramidus |
Dates |
4.4 mya |
Region(s) |
Middle Awash region and Gona (Ethiopia) |
Famous discoveries |
A partial female skeleton nicknamed “Ardi” (ARA-VP-6/500) (found in 1994). |
Brain size |
300 cc to 350 cc |
Dentition |
Little differences between the canines of males and females (small sexual dimorphism). |
Cranial features |
Midfacial projection, slightly prognathic. Cheekbones less flared and robust than in later hominins. |
Postcranial features |
Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, an opposable big toe similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. |
Culture |
None directly associated |
Other |
Over 110 specimens from Aramis |
Hominin |
Australopithecus anamensis |
Dates |
4.2 mya to 3.8 mya |
Region(s) |
Turkana region (Kenya); Middle Awash (Ethiopia) |
Famous discoveries |
A 2019 find from Ethiopia, named MRD. |
Brain size |
370 cc |
Dentition |
Relatively large canines compared with more recent Australopithecines. |
Cranial features |
Projecting cheekbones and ancestral earholes. |
Postcranial features |
Lower limb bones (tibia and femur) indicate bipedality; arboreal features in upper limb bones (humerus) found. |
Culture |
N/A |
Other |
Almost 100 specimens, representing over 20 individuals, have been found to date. |
Hominin |
Australopithecus afarensis |
Dates |
3.9 mya to 2.9 mya |
Region(s) |
Afar Region, Omo, Maka, Fejej, and Belohdelie (Ethiopia); Laetoli (Tanzania); Koobi Fora (Kenya) |
Famous discoveries |
Lucy (discovery: 1974), Selam (Dikika Child, discovery: 2000), Laetoli Footprints (discovery: 1976). |
Brain size |
380 cc to 430 cc |
Dentition |
Reduced canines and molars relative to great apes but larger than in modern humans. |
Cranial features |
Prognathic face, facial features indicate relatively strong chewing musculature (compared with Homo) but less extreme than in Paranthropus. |
Postcranial features |
Clear evidence for bipedalism from lower limb postcranial bones. Laetoli Footprints indicate humanlike walking. Dikika Child bones indicate retained ancestral arboreal traits in the postcrania. |
Culture |
None directly, but close in age and proximity to controversial cut marks at Dikika and early tools in Lomekwi. |
Other |
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. |
Hominin |
Australopithecus bahrelghazali |
Dates |
3.6 mya |
Region(s) |
Chad |
Famous discoveries |
“Abel,” the holotype (discovery: 1995). |
Brain size |
N/A |
Dentition |
N/A |
Cranial features |
N/A |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Arguably within range of variation of Au. afarensis. |
Hominin |
Australopithecus prometheus |
Dates |
3.7 mya (debated) |
Region(s) |
Sterkfontein (South Africa) |
Famous discoveries |
“Little Foot” (StW 573) (discovery: 1994) |
Brain size |
408 cc (Little Foot estimate) |
Dentition |
Heavy anterior dental wear patterns, relatively large anterior dentition and smaller hind dentition, similar to Au. afarensis. |
Cranial features |
Relatively larger brain size, robust zygomatic arch, and a flatter midface. |
Postcranial features |
The initial discovery of four ankle bones indicated bipedality. |
Culture |
N/A |
Other |
Highly debated new species designation. |
Hominin |
Australopithecus deyiremada |
Dates |
3.5 mya to 3.3 mya |
Region(s) |
Woranso-Mille (Afar region, Ethiopia) |
Famous discoveries |
First fossil mandible bones were discovered in 2011 in the Afar region of Ethiopia by Yohannes Haile-Selassie. |
Brain size |
N/A |
Dentition |
Smaller teeth with thicker enamel than seen in Au. afarensis, with a potentially hardier diet. |
Cranial features |
Larger mandible and more projecting cheekbones than in Au. afarensis. |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Contested species designation; arguably a member of Au. afarensis. |
Hominin |
Kenyanthopus platyops |
Dates |
3.5 mya to 3.2 mya |
Region(s) |
Lake Turkana (Kenya) |
Famous discoveries |
KNM–WT 40000 (discovered 1999) |
Brain size |
Difficult to determine but appears within the range of Australopithecus afarensis. |
Dentition |
Small molars/dentition (Homo-like characteristic) |
Cranial features |
Flatter (i.e., orthognathic) face |
Postcranial features |
N/A |
Culture |
Some have associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species/specimen. |
Other |
Taxonomic placing of this species is quite divided. The discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis. |
Hominin |
Australopithecus africanus |
Dates |
3.3 mya to 2.1 mya |
Region(s) |
Sterkfontein, Taung, Makapansgat, Gladysvale (South Africa) |
Famous discoveries |
Taung Child (discovery in 1994), “Mrs. Ples” (discover in 1947), Little Foot (arguable; discovery in 1994). |
Brain size |
400 cc to 500 cc |
Dentition |
Smaller teeth (derived) relative to Au. afarensis. Small canines with no diastema. |
Cranial features |
A rounder skull compared with Au. afarensis in East Africa. A sloping face (ancestral). |
Postcranial features |
Similar postcranial evidence for bipedal locomotion (derived pelvis) with retained arboreal locomotion, e.g., curved phalanges (fingers), as seen in Au. afarensis. |
Culture |
None with direct evidence. |
Other |
A 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities. |
Hominin |
Australopithecus garhi |
Dates |
2.5 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
N/A |
Brain size |
450 cc |
Dentition |
Larger hind dentition than seen in other gracile Australopithecines. |
Cranial features |
N/A |
Postcranial features |
A femur of a fragmentary partial skeleton, argued to belong to Au. garhi, indicates this species may be longer-limbed than Au. afarensis, although still able to move arboreally. |
Culture |
Crude stone tools resembling Oldowan (described later) have been found in association with Au. garhi. |
Other |
This species is not well documented or understood and is based on only a few fossil specimens. |
Hominin |
Paranthropus aethiopicus |
Dates |
2.7 mya to 2.3 mya |
Region(s) |
West Turkana (Kenya); Laetoli (Tanzania); Omo River Basin (Ethiopia) |
Famous discoveries |
The “Black Skull” (KNM–WT 17000) (discovery 1985). |
Brain Size |
410 cc |
Dentition |
P. aethiopicus has the shared derived traits of large flat premolars and molars, although few teeth have been found. |
Cranial features |
Large flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle), a sagittal crest for increased muscle attachment of the chewing muscles to the skull, and a robust mandible and supraorbital torus (brow ridge). |
Postcranial features |
A proximal tibia indicates bipedality and similar size to Au. afarensis. |
Culture |
N/A |
Other |
The “Black Skull” is so called because of the mineral manganese that stained it black during fossilization. |
Hominin |
Paranthropus boisei |
Dates |
2.4 mya to 1.4 mya |
Region(s) |
Koobi Fora, West Turkana, and Chesowanja (Kenya); Malema-Chiwondo (Malawi), Olduvai Gorge and Peninj (Tanzania); and Omo River basin and Konso (Ethiopia) |
Famous discoveries |
“Zinj,” or sometimes “Nutcracker Man” (OH5), in 1959 by Mary Leakey. The Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu. |
Brain size |
500 cc to 550 cc |
Dentition |
Very large, flat posterior dentition (largest of all hominins currently known). Much smaller anterior dentition. Very thick dental enamel. |
Cranial features |
Indications of very large chewing muscles (e.g., flaring zygomatic arches and a large sagittal crest). |
Postcranial features |
Evidence for high variability and sexual dimorphism, with estimates of males at 1.37 meters tall and females at 1.24 meters. |
Culture |
Richard Leakey and Bernard Wood have both suggested that P. boisei could have made and used stone tools. Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. |
Other |
Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). This differs from what is seen in P. robustus. |
Hominin |
Australopithecus sediba |
Dates |
1.97 mya |
Region(s) |
Malapa Fossil Site (South Africa) |
Famous discoveries |
Karabo (MH1) (discovery in 2008) |
Brain size |
420 cc to 450 cc |
Dentition |
Small dentition with Australopithecine cusp-spacing. |
Cranial features |
Small brain size (Australopithecus-like) but gracile mandible (Homo-like). |
Postcranial features |
Scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (tree climbing, particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. |
Culture |
None of direct association, but some have argued that a modern hand morphology (shorter fingers and a longer thumb) means that adaptations to tool manufacture and use may be present in this species. |
Other |
It was first discovered through a clavicle bone in 2008 by nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger. |
Hominin |
Paranthropus robustus |
Dates |
2.3 mya to 1 mya |
Region(s) |
Kromdraai B, Swartkrans, Gondolin, Drimolen, and Coopers Cave (South Africa) |
Famous discoveries |
SK48 (original skull) |
Brain size |
410 cc to 530 cc |
Dentition |
Large posterior teeth with thick enamel, consistent with other Robust Australopithecines. Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick enameled dentition. |
Cranial features |
P. robustus features are neither as “hyper-robust” as P. boisei or as ancestral in features as P. aethiopicus. They have been described as less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring). |
Postcranial features |
Reconstructions indicate sexual dimorphism. |
Culture |
N/A |
Other |
Several of these fossils are fragmentary in nature, distorted, and not well preserved, because they have been recovered from quarry breccia using explosives. |
Review Questions
- What is the difference between a “derived” versus an “ancestral” trait? Give an example of both, seen in Au. afarensis.
- Which of the paleoenvironment hypotheses have been used to describe early hominin diversity, and which have been used to describe bipedalism?
- Which anatomical features for bipedalism do we see in early hominins?
- Describe the dentition of gracile and robust australopithecines. What might these tell us about their diets?
- List the hominin species argued to be associated with stone tool technologies. Are you convinced of these associations? Why/why not?
Key Terms
Arboreal: Related to trees or woodland.
Aridification: Becoming increasingly arid or dry, as related to the climate or environment.
Aridity Hypothesis: The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution.
Assemblage: A collection demonstrating a pattern. Often pertaining to a site or region.
Bipedalism: The locomotor ability to walk on two legs.
Breccia: Hard, calcareous sedimentary rock.
Canines: The pointy teeth just next to the incisors, in the front of the mouth.
Cheek teeth: Or hind dentition (molars and premolars).
Chronospecies: Species that are said to evolve into another species, in a linear fashion, over time.
Clade: A group of species or taxa with a shared common ancestor.
Cladistics: The field of grouping organisms into those with shared ancestry.
Context: As pertaining to palaeoanthropology, this term refers to the place where an artifact or fossil is found.
Cores: The remains of a rock that has been flaked or knapped.
Cusps: The ridges or “bumps” on the teeth.
Dental formula: A technique to describe the number of incisors, canines, premolars, and molars in each quadrant of the mouth.
Derived traits: Newly evolved traits that differ from those seen in the ancestor.
Diastema: A tooth gap between the incisors and canines.
Early Stone Age (ESA): The earliest-described archaeological period in which we start seeing stone-tool technology.
East African Rift System (EARS): This term is often used to refer to the Rift Valley, expanding from Malawi to Ethiopia. This active geological structure is responsible for much of the visibility of the paleoanthropological record in East Africa.
Enamel: The highly mineralized outer layer of the tooth.
Encephalization: Expansion of the brain.
Extant: Currently living—i.e., not extinct.
Fallback foods: Foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
Fauna: The animals of a particular region, habitat, or geological period.
Faunal assemblages: Collections of fossils of the animals found at a site.
Faunal turnover: The rate at which species go extinct and are replaced with new species.
Flake: The piece knocked off of a stone core during the manufacture of a tool, which may be used as a stone tool.
Flora: The plants of a particular region, habitat, or geological period.
Folivorous: Foliage-eating.
Foramen magnum: The large hole (foramen) at the base of the cranium, through which the spinal cord enters the skull.
Fossil: The remains or impression of an organism from the past.
Frugivorous: Fruit-eating.
Generalist: A species that can thrive in a wide variety of habitats and can have a varied diet.
Glacial: Colder, drier periods during an ice age when there is more ice trapped at the poles.
Gracile: Slender, less rugged, or pronounced features.
Hallux: The big toe.
Holotype: A single specimen from which a species or taxon is described or named.
Hominin: A primate category that includes humans and our fossil relatives since our divergence from extant great apes.
Honing P3: The mandibular premolar alongside the canine (in primates, the P3), which is angled to give space for (and sharpen) the upper canines.
Hyper-robust: Even more robust than considered normal in the Paranthropus genus.
Hypodigm: A sample (here, fossil) from which researchers extrapolate features of a population.
Incisiform: An adjective referring to a canine that appears more incisor-like in morphology.
Incisors: The teeth in the front of the mouth, used to bite off food.
Interglacial: A period of milder climate in between two glacial periods.
Isotopes: Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses.
Knappers: The people who fractured rocks in order to manufacture tools.
Knapping: The fracturing of rocks for the manufacture of tools.
Large Cutting Tool (LCT): A tool that is shaped to have functional edges.
Last Common Ancestor (LCA): The hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence.
Lithic: Relating to stone (here to stone tools).
Lumbar lordosis: The inward curving of the lower (lumbar) parts of the spine. The lower curve in the human S-shaped spine.
Lumpers: Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
Megadont: An organism with extremely large dentition compared with body size.
Metacarpals: The long bones of the hand that connect to the phalanges (finger bones).
Molars: The largest, most posterior of the hind dentition.
Monophyletic: A taxon or group of taxa descended from a common ancestor that is not shared with another taxon or group.
Morphology: The study of the form or size and shape of things; in this case, skeletal parts.
Mosaic evolution: The concept that evolutionary change does not occur homogeneously throughout the body in organisms.
Obligate bipedalism: Where the primary form of locomotion for an organism is bipedal.
Occlude: When the teeth from the maxilla come into contact with the teeth in the mandible.
Oldowan: Lower Paleolithic, the earliest stone tool culture.
Orthognathic: The face below the eyes is relatively flat and does not jut out anteriorly.
Paleoanthropologists: Researchers that study human evolution.
Paleoenvironment: An environment from a period in the Earth’s geological past.
Parabolic: Like a parabola (parabola-shaped).
Phalanges: Long bones in the hand and fingers.
Phylogenetics: The study of phylogeny.
Phylogeny: The study of the evolutionary relationships between groups of organisms.
Pliocene: A geological epoch between the Miocene and Pleistocene.
Polytypic: In reference to taxonomy, having two or more group variants capable of interacting and breeding biologically but having morphological population differences.
Postcranium: The skeleton below the cranium (head).
Premolars: The smallest of the hind teeth, behind the canines.
Procumbent: In reference to incisors, tilting forward.
Prognathic: In reference to the face, the area below the eyes juts anteriorly.
Quaternary Ice Age: The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles.
Relative dating: Dating techniques that refer to a temporal sequence (i.e., older or younger than others in the reference) and do not estimate actual or absolute dates.
Robust: Rugged or exaggerated features.
Site: A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
Specialist: A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
Splitters: Researchers who prefer to split a highly variable taxon into multiple groups or species.
Taxa: Plural of taxon, a taxonomic group such as species, genus, or family.
Taxonomy: The science of grouping and classifying organisms.
Techno-complex: A term encompassing multiple assemblages that share similar traits in terms of artifact production and morphology.
Thermoregulation: Maintaining body temperature through physiologically cooling or warming the body.
Ungulates: Hoofed mammals—e.g., cows and kudu.
Volcanic tufts: Rock made from ash from volcanic eruptions in the past.
Valgus knee: The angle of the knee between the femur and tibia, which allows for weight distribution to be angled closer to the point above the center of gravity (i.e., between the feet) in bipeds.
About the Authors
Kerryn Warren, Ph.D.
Grad Coach International, kerryn.warren@gmail.com
Kerryn Warren is a dissertation coach at Grad Coach International and is passionate about stimulating research thinking in students of all levels. She has lectured on multiple topics, including archaeology and human evolution, with her research and science communication interests including hybridization in the hominin fossil record (stemming from research from her Ph.D.) and understanding how evolution is taught in South African schools. She also worked as one of the “Underground Astronauts,” selected to excavate Homo naledi remains from the Rising Star Cave System in the Cradle of Humankind.
K. Lindsay Hunter, M.A., Ph.D. candidate
CARTA, k.lindsay.hunter@gmail.com
Lindsay Hunter is a trained palaeoanthropologist who uses her more than 15 years of experience to make sense of the distant past of our species to build a better future. She received her master’s degree in biological anthropology from the University of Iowa and is completing her Ph.D. in archaeology at the University of the Witwatersrand in Johannesburg, South Africa. She has studied fossil and human bone collections across five continents with major grant support from the National Science Foundation (United States) and the Wenner-Gren Foundation for Anthropological Research. As a National Geographic Explorer, Lindsay developed and managed the National Geographic–sponsored Umsuka Public Palaeoanthropology Project in the Cradle of Humankind World Heritage Site (CoH WHS) in South Africa from within Westbury Township, Johannesburg, between 2016–2019. She currently serves as the Community Engagement & Advancement Director for CARTA: The UC San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny in La Jolla, California.
Navashni Naidoo, M.Sc.
University of Cape Town, nnaidoo2@illinois.edu
Navashni Naidoo is a researcher at Nelson Mandela University, lecturing on physical geology. She completed her Master’s in Science in Archaeology in 2017 at the University of Cape Town. Her research interests include developing paleoenvironmental proxies suited to the African continent, behavioral ecology, and engaging with community-driven archaeological projects. She has excavated at Stone Age sites across Southern Africa and East Africa. Navashni is currently pursuing a PhD in the Department of Anthropology at the University of Illinois.
Silindokuhle Mavuso, M.Sc.
University of Witwatersrand, S.muvaso@ru.ac.za
Silindokuhle has always been curious about the world around him and how it has been shaped. He is a lecturer at Rhodes University of Witwatersrand (Wits), and conducts research on palaeoenvironmental reconstruction and change of the northeastern Turkana Basin’s Pleistocene sequence. Silindokuhle began his education with a B.Sc. (Geology, Archaeology, and Environmental and Geographical Sciences) from the University of Cape Town before moving to Wits for a B.Sc. Honors (geology and paleontology) and M.Sc. in geology. He is currently concluding his PhD Studies. During this time, he has gained more training as a Koobi Fora Fieldschool fellow (Kenya) as well as an Erasmus Mundus scholar (France). Silindokuhle is a Plio-Pleistocene geologist with a specific focus on identifying and explaining past environments that are associated with early human life and development through time. He is interested in a wide range of disciplines such as micromorphology, sedimentology, geochemistry, geochronology, and sequence stratigraphy. He has worked with teams from significant eastern and southern African hominid sites including Elandsfontein, Rising Star, Sterkfontein, Gondolin, Laetoli, Olduvai, and Koobi Fora.
For Further Exploration
The Smithsonian Institution website hosts descriptions of fossil species, an interactive timeline, and much more.
The Maropeng Museum website hosts a wealth of information regarding South African Fossil Bearing sites in the Cradle of Humankind.
This quick comparison between Homo naledi and Australopithecus sediba from the Perot Museum.
This explanation of the braided stream by the Perot Museum.
A collation of 3-D files for visualizing (or even 3-D printing) for homes, schools, and universities.
PBS learning materials, including videos and diagrams of the Laetoli footprints, bipedalism, and fossils.
A wealth of information from the Australian Museum website, including species descriptions, family trees, and explanations of bipedalism and diet.
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Acknowledgements
All of the authors in this section are students and early career researchers in paleoanthropology and related fields in South Africa (or at least have worked in South Africa). We wish to thank everyone who supports young and diverse talent in this field and would love to further acknowledge Black, African, and female academics who have helped pave the way for us.
Sarah S. King, Ph.D., Cerro Coso Community College
Kara Jones, M.A., Ph.D. student, University of Nevada Las Vegas
This chapter is a revision from "Chapter 7: Understanding the Fossil Context” by Sarah King and Lee Anne Zajicek. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Identify the different types of fossils and describe how they are formed.
- Discuss relative and chronometric dating methods, the type of material they analyze, and their applications.
- Describe the methods used to reconstruct past environments.
- Interpret a site using the methods described in this chapter.
Fossil Study: An Evolving Process
Mary Anning and the Age of Wonder

Mary Anning (1799–1847) is likely the most famous fossil hunter you’ve never heard of (Figure 7.1). Anning lived her entire life in Lyme Regis on the Dorset coast in England. As a woman, born to a poor family, with minimal education (even by 19th-century standards), the odds were against Anning becoming a scientist (Emling 2009, xii). It was remarkable that Anning was eventually able to influence the great scientists of the day with her fossil discoveries and her subsequent hypotheses regarding evolution.
The time when Anning lived was a remarkable period in human history because of the Industrial Revolution in Britain. Moreover, the scientific discoveries of the 18th and 19th centuries set the stage for great leaps of knowledge and understanding about humans and the natural world. Barely a century earlier, Sir Isaac Newton had developed his theories on physics and become the president of the Royal Society of London (Dolnick 2011, 5). In this framework, the pursuit of intellectual and scientific discovery became a popular avocation for many individuals, the vast majority of whom were wealthy men (Figure 7.2).

In spite of the expectations of Georgian English society to the contrary, Anning became a highly successful fossil hunter as well as a self-educated geologist and anatomist. The geology of Lyme Regis, with its limestone cliffs, provided a fortuitous backdrop for Anning’s lifework. Now called the “Jurassic Coast,” Lyme Regis has always been a rich source for fossilized remains (Figure 7.3). Continuing her father’s passion for fossil hunting, Anning scoured the crumbling cliffs after storms for fossilized remains and shells. The work was physically demanding and downright dangerous. In 1833, while searching for fossils, Anning lost her beloved dog in a landslide and nearly lost her own life in the process (Emling 2009).

Around the age of ten, Anning located and excavated a complete fossilized skeleton of an ichthyosaurus (“fish lizard”). She eventually found Pterodactylus macronyx and a 2.7-meter Plesiosaurus, considered by many to be her greatest discovery (Figure 7.4). These discoveries proved that there had been significant changes in the way living things appeared throughout the history of the world. Like many of her peers, including Darwin, Anning had strong religious convictions. However, the evidence that was being found in the fossil record was contradictory to the Genesis story in the Bible. In The Fossil Hunter: Dinosaurs, Evolution, and the Woman Whose Discoveries Changed the World, Anning’s biographer Shelley Emling (2009, 38) notes, “the puzzling attributes of Mary’s fossil [ichthyosaurus] struck a blow at this belief and eventually helped pave the way for a real understanding of life before the age of humans.”

Intellectual and scientific debate now had physical evidence to support the theory of evolution, which would eventually result in Darwin’s seminal work, On the Origin of Species (1859). Anning’s discoveries and theories were appreciated and advocated by her friends, intellectual men who were associated with the Geological Society of London. Regrettably, this organization was closed to women, and Anning received little official recognition for her contributions to the fields of natural history and paleontology. It is clear that Anning’s knowledge, diligence, and uncanny luck in finding magnificent specimens of fossils earned her unshakeable credibility and made her a peer to many antiquarians (Emling 2009).
Fossil hunting is still providing evidence and a narrative of the story of Earth. Mary Anning recognized the value of fossils in understanding natural history and relentlessly championed her theories to the brightest minds of her day. Anning’s ability to creatively think “outside the box”—skillfully assimilating knowledge from multiple academic fields—was her gift to our present understanding of the fossil record. Given how profoundly Anning has shaped how we, in the modern day, think about the origins of life, it is surprising that her contributions have been so marginalized. Anning’s name should be on the tip of everyone’s tongue. Fortunately, at least in one sense of the word, it is. The well-known tongue twister, below, may have been written about Mary Anning:
She sells sea-shells on the sea-shore.
The shells she sells are sea-shells, I’m sure.
For if she sells sea-shells on the sea-shore
Then I’m sure she sells sea-shore shells.
—T. Sullivan (1908)
Developing Modern Methods
As Mary Anning’s story suggests, scientists in Europe were working at a time dominated by western Christian tradition. Literal interpretations of the bible did not allow for the long, slow processes of geological or evolutionary change to operate. However, many scientists were making observations that did not fit the biblical narrative. During the 18th century, Scotsman James Hutton’s work on the formation of Earth provided a much longer timeline of events than previous biblical interpretations would allow. Hutton’s theory of Deep Time was crucial to the understanding of fossils. Deep Time gave the history of Earth enough time—4.543 billion years—to encompass continental drift, the evolution of species, and the fossilization process. A second Scotsman, Charles Lyell, propelled Hutton’s work into his own theory of uniformitarianism, the doctrine that Earth’s geologic formations are the work of slow geologic forces. Lyell’s three-volume work, Principles of Geology (1830–1833), was influential to naturalist Charles Darwin (see Chapter 2 for more information on Darwin’s work). In fact, Lyell’s first volume accompanied Darwin on his five-year voyage around the world on the HMS Beagle (1831–1836). The concepts proposed by Lyell gave Darwin an opportunity to apply his working theories of evolution by natural selection and a greater length of time with which to work. These resulting theories were important scientific discoveries and paved the way for the “Age of Wonder” (Holmes 2010, xvi).

The work of Anning, Darwin, Lyell, and many others laid the foundation for the modern methods we use today. Though anthropology is focused on humans and our primate relatives (and not on dinosaurs, as many people wrongly assume), you will see that methods developed in paleontology, geology, chemistry, biology, and physics are often applied in anthropological research. In this chapter, you will learn about the primary methods and techniques employed by biological anthropologists to answer questions about fossils, the mineralized copies of once-living organisms (Figure 7.5). Ultimately, these answers provide insights into human evolution. Pay close attention to ways in which modern biological anthropologists use other disciplines to analyze evidence and reconstruct past activities and environments.
Earth: It's Older than Dirt
Scientists have developed precise and accurate dating methods based on work in the fields of physics and chemistry. Using these methods, scientists are able to establish the age of Earth as well as approximate ages of the organisms that have lived here. Earth is roughly 4.6 billion years old, give or take a few hundred million years. The first evidence for a living organism appeared around 3.5 billion years ago (bya). The scale of geologic time can seem downright overwhelming. In order to organize and make sense of Earth’s past, geologists break up that time into subunits, which are human-made divisions along Earth’s timeline. The largest subunit is the eon. An eon is further divided into eras, and eras are divided into periods. Finally, periods are divided into epochs (see Figure 7.6; Williams 2004, 37). Currently, we are living in the Phanerozoic eon, Cenozoic era, Quaternary period, and probably the Holocene epoch—though there is academic debate about the current epoch (see below).

These divisions are based on major changes and events recorded in the geologic record. Events like significant shifts in climate or mass extinctions can be used to mark the end of one geologic time unit and the beginning of another. However, it is important to remember that these borders are not real in a physical sense; they are helpful organizational guidelines for scientific research. There can be debate regarding how the boundaries are defined. Additionally, the methods we use to establish these dates are refined over time, occasionally leading to shifts in established chronology (see the discussion on calibration in the radiocarbon dating section below). For instance, the current epoch has been traditionally known as the Holocene. It began almost twelve thousand years ago (kya) during the warming period after that last major ice age. Today, there is evidence to indicate human-driven climate change is warming the world and changing the environmental patterns faster than the natural cyclical processes. This has led some scientists within the stratigraphic community to argue for a new epoch beginning around 1950 with the Nuclear Age called the Anthropocene (Monastersky 2015; Waters et al. 2016). Nobel Laureate Paul Crutzen places the beginning of the Anthropocene much earlier—at the dawn of the Industrial Revolution, with its polluting effects of burning coal (Crutzen and Stoermer 2000, 17–18). Geologist William Ruddiman argues that the epoch began 5,000–8,000 years ago with the advent of agriculture and the buildup of early methane gasses (Ruddiman et al. 2008). Regardless of when the Anthropocene started, the major event that marks the boundary is the warming temperatures and mass extinction of nonhuman species caused by human activity (Figure 7.7). Researchers now declare that “human activity now rivals geologic forces in influencing the trajectory of the Earth System” (Steffen et al. 2018, 1).

Fossils: The Taphonomic Process
Most of the evidence of human evolution comes from the study of the dead. To obtain as much information as possible from the remains of once-living creatures, one must understand the processes that occur after death. This is where taphonomy comes in (Figure 7.8). Taphonomy is the study of what happens to an organism after death (Komar and Buikstra 2008, 189; Stodder 2008). It includes the study of how an organism becomes a fossil. However, as you’ll see throughout this book, the majority of organisms never make it through the full fossilization process.

Taphonomy is important in biological anthropology, especially in subdisciplines like bioarchaeology (the study of human remains in the archaeological record) and zooarchaeology (the study of faunal remains from archaeological sites). It is so important that many scientists have recreated a variety of burial and decay experiments to track taphonomic change in modern contexts. These contexts can then be used to understand the taphonomic patterns seen in the fossil record (see Reitz and Wing 1999, 122–141).
Taphonomic analysis can also give us important insights into the development of complex thought and ritual in human evolution. In Chapter 11, you will see the first evidence of recognized burial practices in hominins. Taphonomy helped to establish whether these burials were simply the result of natural processes or intentionally constructed by humans (Klein 1999, 395; Straus 1989). Deliberate burials often include the body placed in a specific position, such as supine (on the back) with arms crossed over the chest or in a flexed position (think fetal position) facing a particular direction. If bones have evidence of a carnivore or rodent gnawing on them, it can be inferred that the remains were exposed to scavengers after death.
Going back further in time, taphonomic evidence may tell us how our ancestors died. For instance, several australopithecine fossils show evidence of carnivore tooth marks and even punctures from saber-toothed cats, indicating that we weren’t always the top of the food chain. The Bodo Cranium, a Homo erectus cranium from Middle Awash Valley, Ethiopia, shows cut marks made by stone tools, indicating an early example of possible defleshing activity in our human ancestors (White 1986). At the archaeological site of Zhoukoudian, researchers used taphonomy to show that the highly fragmented remains of at least 51 Homo erectus individuals were scavenged by Pleistocene cave hyenas (Boaz et al. 2004). The damage on Skull VI was described as “elongated, raking bite marks, isolated puncture bite marks, and perimortem breakage consistent with patterns of modern hyaenid bone modification” (Boaz et al. 2004). Additionally, a fresh burnt equid cranium was discovered which supports the theory of mobile hominid scavenging and fire use at the site (Boaz et al. 2004).
Special Topic: Bog Bodies and Mummies (Add a picture to show how well preserved they are!)
Preservation is a key topic in anthropological research, since we can only study the evidence that gets left behind in the fossil and archaeological record. This chapter is concerned with the fossil record; however, there are other forms of preserved remains that provide anthropologists with information about the past. You’ve undoubtedly heard of mummification, likely in the context of Egyptian or South American mummies. However, bog bodies and ice mummies are further examples of how remains can be preserved in special circumstances. It is important to note that fossilization is a process that takes much longer than the preservation of bog bodies or mummies.
Bog bodies are good examples of wetland preservation. Peat bogs are formed by the slow accumulation of vegetation and silts in ponds and lakes. Individuals were buried in bogs throughout Europe as far back as 10 kya, with a proliferation of activity from 1,600 to 3,200 years ago (Giles 2020; Ravn 2010). When they were found thousands of years later, they resembled recent burials. Their hair, skin, clothing, and organs were exceptionally well preserved, in addition to their bones and teeth (Eisenbeiss 2016; Ravn 2010). Preservation was so good in fact that archaeologists could identify the individuals’ last meals and re-create tattoos found on their skin.
Extreme cold can also halt the natural decay process. A well-known ice mummy is Ötzi, a Copper Age man dating to around 5,200 years ago found in the Alps (Vanzetti et al. 2012; Vidale et al. 2016). As with the bog bodies, his hair, skin, clothing, and organs were all well preserved. Recently, archaeologists were able to identify his last meal (Maixner et al. 2018). It was high in fat, which makes sense considering the extremely cold environment in which he lived, as meals high in fat assist in cold tolerance (Fumagalli et al. 2015).
In the Andes, ancient peoples would bury human sacrifices throughout the high peaks in a sacred ritual called Capacocha (Wilson et al. 2007). The best-preserved mummy to date is called the “Maiden” or “Sarita” because she was found at the summit of Sara Sara Volcano. Her remains are over 500 years old, but she still looks like the 15-year-old girl she was at the time of her death, as if she had just been sleeping for 500 years (Reinhard 2006).
Finally, arid environments can also contribute to the preservation of organic remains. As discussed with waterlogged sites, much of the bacteria that is active in breaking down bodies is already present in our gut and begins the putrefaction process shortly after death. Arid environments deplete organic material of the moisture that putrefactive bacteria need to function (Booth et al. 2015). When that occurs, the soft tissue like skin, hair, and organs can be preserved. It is similar to the way a food dehydrator works to preserve meat, fruit, and vegetables for long-term storage. There are several examples of arid environments spontaneously preserving human remains, including catacomb burials in Austria and Italy (Aufderheide 2003, 170, 192–205).
Fossilization
Fossils only represent a tiny fraction of creatures that existed in the past. It is extremely difficult for an organism to become a fossil. After all, organisms are designed to deteriorate after they die. Bacteria, insects, scavengers, weather, and environment all aid in the process that breaks down organisms so their elements can be returned to Earth to maintain ecosystems (Stodder 2008). Fossilization, therefore, is the preservation of an organism against these natural decay processes (Figure 7.9).

For fossilization to occur, several important things must happen. First, the organism must be protected from things like bacterial activity, scavengers, and temperature and moisture fluctuations. A stable environment is important. This means that the organism should not be exposed to significant fluctuations in temperature, humidity, and weather patterns. Changes to moisture and temperature cause the organic tissues to expand and contract repeatedly, which will eventually cause microfractures and break down (Stodder 2008). Soft tissue like organs, muscle, and skin are more easily broken down in the decay process; therefore, they are less likely to be preserved. Bones and teeth, however, last much longer and are more common in the fossil record (Williams 2004, 207).
Wetlands are a particularly good area for preservation because they allow for rapid permanent burial and a stable moisture environment. That is why many fossils are found in and around ancient lakes and river systems. Waterlogged sites can also be naturally anaerobic (without oxygen). Much of the bacteria that causes decay is already present in our gut and can begin the decomposition process shortly after death during putrefaction (Booth et al. 2015). Since oxygen is necessary for the body’s bacteria to break down organic material, the decay process is significantly slowed or halted in anaerobic conditions.
The next step in the fossilization process is sediment accumulation. The sediments cover and protect the organism from the environment. They, along with water, provide the minerals that will eventually become the fossil (Williams 2004, 31). Sediment accumulation also provides the pressure needed for mineralization to take place. Lithification is when the weight and pressure of the sediments squeeze out extra fluids and replace the voids that appear with minerals from the surrounding sediments. Finally, we have permineralization. This is when the organism is fully replaced by minerals from the sediments. A fossil is really a mineral copy of the original organism (Williams 2004, 31).
Types of Fossils
Plants

Plants make up the majority of fossilized materials. One of the most common plants existing today, the fern, has been found in fossilized form many times. Other plants that no longer exist or the early ancestors of modern plants come in fossilized forms as well. It is through these fossils that we can discover how plants evolved and learn about the climate of Earth over different periods of time.
Another type of fossilized plant is petrified wood. This fossil is created when actual pieces of wood—such as the trunk of a tree—mineralize and turn into rock. Petrified wood is a combination of silica, calcite, and quartz, and it is both heavy and brittle. Petrified wood can be colorful and is generally aesthetically pleasing because all the features of the original tree’s composition are illuminated through mineralization (Figure 7.10). There are a number of places all over the world where petrified wood “forests” can be found, but there is an excellent assemblage in Arizona, at the Petrified Forest National Park. At this site, evidence relating to the environment of the area some 225 mya is on display.
Human/Animal Remains

We are more familiar with the fossils of early animals because natural history museums have exhibits of dinosaurs and extinct mammals. However, there are a number of fossilized hominin remains that provide a picture of the fossil record over the course of our evolution from primates. The term hominins includes all human ancestors who existed after the evolutionary split from chimpanzees and bonobos, some six to seven mya. Modern humans are Homo sapiens, but hominins can include much earlier versions of humans. One such hominin is “Lucy” (AL 288-1), the 3.2 million-year-old fossil of Australopithecus afarensis that was discovered in Ethiopia in 1974 (Figure 7.11). Until recently, Lucy was the most complete and oldest hominin fossil, with 40% of her skeleton preserved (see Chapter 9 for more information about Lucy). In 1994, an Australopithecus fossil nicknamed “Little Foot” (Stw 573) was located in the World Heritage Site at Sterkfontein Caves (“the Cradle of Humankind”) in South Africa. Little Foot is more complete than Lucy and possibly the oldest fossil that has so far been found, dating to at least 3.6 million years (Granger et al. 2015). The ankle bones of the fossil were extricated from the matrix of concrete-like rock, revealing that the bones of the ankles and feet indicate bipedalism (University of Witwatersrand 2017).
Both the Lucy and Little Foot fossils date back to the Pliocene (5.8 to 2.3 mya). Older hominin fossils from the late Miocene (7.25 to 5.5 mya) have been located, although they are much less complete. The oldest hominin fossil is a fragmentary skull named Sahelanthropus tchadensis, found in Northern Chad and dating to circa seven mya (Lebatard et al. 2008). It is through the discovery, dating, and study of primate and early hominin fossils that we find physical evidence of the evolutionary timeline of humans.
Asphalt


Asphalt, a form of crude oil, can also yield fossilized remains. Asphalt is commonly referred to in error as tar because of its viscous nature and dark color. A famous fossil site from California is La Brea Tar Pits in downtown Los Angeles (Figure 7.12). In the middle of the busy city on Wilshire Boulevard, asphalt (not tar) bubbles up through seeps (cracks) in the sidewalk. The La Brea Tar Pits Museum provides an incredible look at the both extinct and extant animals that lived in the Los Angeles Basin 40,000–11,000 years ago. These animals became entrapped in the asphalt during the Pleistocene and perished in place. Ongoing excavations have yielded millions of fossils, including megafauna such as American mastodons and incomplete skeletons of extinct species of dire wolves, Canis dirus, and the saber-toothed cat, Smilodon fatalis (Figure 7.13). Fossilized remains of plants have also been found in the asphalt. The remains of one person have also been found at the tar pits. Referred to as La Brea Woman, the remains were found in 1914 and were subsequently dated to around 10,250 years ago. The La Brea Woman was a likely female individual who was 17–28 years old at the time of her death, with a height of under five feet (Spray 2022). She is thought to have died from blunt force trauma to her head, famously making her Los Angeles’s first documented homicide victim (Spray 2022). (Learn more about her in the Special Topic box, “Necropolitics,” below.) Between the fossils of animals and those of plants, paleontologists have a good idea of the way the Los Angeles Basin looked and what the climate in the area was like many thousands of years ago.
Igneous Rock
Most fossils are found in sedimentary rock. This type of rock has been formed from deposits of minerals over millions of years in bodies of water on Earth’s surface. Some examples include shale, limestone, and siltstone. Sedimentary rock typically has a layered appearance. However, fossils have been found in igneous rock as well. Igneous rock is volcanic rock that is created from cooled molten lava. It is rare for fossils to survive molten lava, and it is estimated that only 2% of all fossils have been found in igneous rock (Ingber 2012). Part of a giant rhinocerotid skull dating back 9.2 mya to the Miocene was discovered in Cappadocia, Turkey, in 2010. The fossil was a remarkable find because the eruption of the Çardak caldera was so sudden that it simply dehydrated and “baked” the animal (Antoine et al. 2012).
Trace Fossils
Depending on the specific circumstances of weather and time, even footprints can become fossilized. Footprints fall into the category of trace fossils, which includes other evidence of biological activity such as nests, burrows, tooth marks, and shells. A well-known example of trace fossils are the Laetoli footprints in Tanzania (Figure 7.14). More recently, archaeological investigations in North America have revealed fossil footprints which rewrite the history of people in the Americas at White Sands, New Mexico. You can read more about the Laetoli and White Sands footprints in the Dig Deeper box below.

Other fossilized footprints have been discovered around the world. At Pech Merle cave in the Dordogne region of France, archaeologists discovered two fossilized footprints. They then brought in indigenous trackers from Namibia to look for other footprints. The approach worked, as many other footprints belonging to as many as five individuals were discovered with the expert eyes of the trackers (Pastoors et al. 2017). These footprints date back 12,000 years (Granger Historical Picture Archive 2018).
Some of the more unappealing but still-fascinating trace fossils are bezoars and coprolite. Bezoars are hard, concrete-like substances found in the intestines of fossilized creatures. Bezoars start off like the hair balls that cats and rabbits accumulate from grooming, but they become hard, concrete-like substances in the intestines. If an animal with a hairball dies before expelling the hair ball mass and the organism becomes fossilized, that mass becomes a bezoar.
Coprolite is fossilized dung. One of the best collections of coprolites is affectionately known as the “Poozeum.” The collection includes a huge coprolite named “Precious” (Figure 7.15). Coprolite, like all fossilized materials, can be in matrix—meaning that the fossil is embedded in secondary rock. As unpleasant as it may seem to work with coprolites, remember that the organic material in dung has mineralized or has started to mineralize; therefore, it is no longer soft and is generally not smelly. Also, just as a doctor can tell a lot about health and diet from a stool sample, anthropologists can glean a great deal of information from coprolite about the diets of ancient animals and the environment in which the food sources existed. For instance, 65 million-year-old grass phytoliths (microscopic silica in plants) found in dinosaur coprolite in India revealed that grasses had been in existence much earlier than scientists initially believed (Taylor and O’Dea 2014, 133).

Pseudofossils
Pseudofossils are not to be mistaken for fake fossils, which have vexed scientists from time to time. A fake fossil is an item that is deliberately manipulated or manufactured to mislead scientists and the general public. In contrast, pseudofossils are not misrepresentations but rather misinterpretations of rocks that look like true fossilized remains (S. Brubaker, personal communication, March 9, 2018). Pseudofossils are the result of impressions or markings on rock, or even the way other inorganic materials react with the rock. A common example is dendrites, the crystallized deposits of black minerals that resemble plant growth (Figure 7.16). Other examples of pseudofossils are unusual or odd-shaped rocks that include various concretions and nodules. An expert can examine a potential fossil to see if there is the requisite internal structure of organic material such as bone or wood that would qualify the item as a fossil.

Dig Deeper: Trace Fossils The Power of Poop
Coprolites found in Paisley Caves, Oregon, in the United States are shedding new light on some of the earliest occupants in North America. Human coprolites are distinguished from animal coprolites through the identification of fecal biomarkers using lipids, or fats, and bile acids (Shillito et al. 2020a). Paisley Caves have 16,000 years of anthropogenic, or human-caused, deposition, with some coprolites having been dated as old as 12.8kya (Blong et al. 2020). Over 285 radiocarbon dates have been recorded from the site (Shillito et al. 2020a), making Paisley Caves one of the most well-dated archaeological sites in the United States. Coprolite analysis can be summarized in three levels, macroscopic, microscopic, and molecular. This can also be understood as analyzing the morphology (macroscopic), contents (microscopic), and residues (molecular) (Shillito et al. 2020b). Each of these levels adds a different layer of information. Coprolite shape is informative through what can be seen macroscopically, such as ingestions of basketry or cordage, small gravels and grains, and general shape. The contents of coprolites may be of the most interest to scientists because certain plants and animals can signal past environments as well as food procurement methods. Coprolites from Paisley Caves have included small pebbles and obsidian chips from butchering game, grinding plants, and general food preparation as well as small bits of fire cracked rock likely from cooking in hearths (Blong 2020). Additionally, rodent bones in coprolites included crania and vertebrae, which suggests whole consumption (Taylor et al. 2020). Insect remains are present in the coprolites as well, such as ants, Jerusalem crickets, June beetles, and darkling beetles (Blong 2020). In all, the coprolites of Paisley Caves have provided an invaluable resource to anthropologists to study the past climate and lifeways of early humans in the Americas.
Coprolites can also signal past health, which is a study known as paleopathology. A study by Katelyn McDonough and colleagues (2022) focused on the identification of parasites in coprolites at Bonneville Estates Rockshelter in eastern Nevada and their link to the greater Great Basin during the Archaic, a period of time spanning 8,000–5,000 years ago. According to the study, parasites such as Acanthocephalans (thorny-headed worms) have been affecting the Great Basin for at least the last 10,000 years. Acanthocephalans are endoparasites, meaning parasites that live inside of their hosts. They are found worldwide and seem to have been concentrated in the Great Basin in the past. Bonneville Estates Rockshelter has been visited by humans for over 13,000 years, with parasite identification going back to nearly 7,000 years. The species identified at Bonneville Estates is Moniliformis clarki. This species parasitizes crickets and insects, a popular food source during the Archaic in the Great Basin. The parasite uses intermediate hosts to get to mammals and birds as definitive hosts. Crickets and beetles have been recorded as food materials in Paisley Caves as well. Insects have remained an important dietary staple for people of the Great Basin and are consumed raw, dried, brined, or ground into flour. Insects that remain uncooked or undercooked have a higher risk for transmission of parasites. Symptoms associated with Acanthocephalans infection are intense intestinal discomfort, anemia, and anorexia, leading to death. It is hypothesized that the consumption of basketry, cordage, and charcoal (which was also identified at Paisley Caves), sometimes associated with parasite-infected coprolites, may have been a method of treatment for the infection. Interestingly, present day infections from this parasite are rising after remaining quite rare, as detection of the parasite is occurring in insect farms.
Walking to the Past
In 1974, British anthropologist Mary Leakey discovered fossilized animal tracks at Laetoli (Figure 7.17), not far from the important paleoanthropological site at Olduvai Gorge in Tanzania. A few years later, a 27-meter trail of hominin footprints were discovered at the same site. These 70 footprints, now referred to as the Laetoli Footprints, were created when early humans walked in wet volcanic ash. Before the impressions were obscured, more volcanic ash and rain fell, sealing the footprints. These series of environmental events were truly extraordinary, but they fortunately resulted in some of the most famous and revealing trace fossils ever found. Dating of the footprints indicate that they were made 3.6 mya (Smithsonian National Museum of Natural History 2018).

Just as forensic scientists can use footprints to identify the approximate build of a potential suspect in a crime, archaeologists have read the Laetoli Footprints for clues to these early humans. The footprints clearly indicate bipedal hominins who had similar feet to those of modern humans. Analysis of the gait through computer simulation revealed that the hominins at Laetoli walked similarly to the way we walk today (Crompton 2012). More recent analyses confirm the similarity to modern humans but also indicate a gait that involved more of a flexed limb than that of modern humans (Hatala et al. 2016; Raichlen and Gordon 2017). The relatively short stride implies that these hominins had short legs—unlike the longer legs of later early humans who migrated out of Africa (Smithsonian National Museum of Natural History 2018). In the context of Olduvai Gorge, where fossils of Australopithecus afarensis have been located and dated to the same timeframe as the footprints, it is likely that these newly discovered impressions were left by these same hominins.
The footprints at Laetoli were made by a small group of as many as three Australopithecus afarensis, walking in close proximity, not unlike what we would see on a modern street or sidewalk. Two trails of footprints have been positively identified with the third set of prints appearing smaller and set in the tracks left by one of the larger individuals. While scientific methods have given us the ability to date the footprints and understand the body mechanics of the hominin, additional consideration of the footprints can lead to other implications. For instance, the close proximity of the individuals implies a close relationship existed between them, not unlike that of a family. Due to the size variation and the depth of impression, the footprints seem to have been made by two larger adults and possibly one child. Scientists theorize that the weight being carried by one of the larger individuals is a young child or a baby (Masao et al. 2016). Excavation continues at Laetoli today, resulting in the discovery of two more footprints in 2015, also believed to have been made by Au. afarensis (Masao et al. 2016).

But it is not just human evolution studies that can benefit from the analysis of fossil footprints. A recent discovery of fossilized footprints has rewritten what we know about the peopling of the Americas. It was originally thought that humans had been in the Americas for at least the last 15,000 years by crossing through the ice-free corridor (IFC) between the Cordilleran and Laurentide ice sheets in present-day Alaska and Canada. However, fossil footprints from the Tularosa Basin of New Mexico (see Figure 7.18) discovered in 2021 have challenged this theory. The footprints, dated between 22,860 (∓320) and 21,130 (∓250) years ago (nps.gov) based on Ruppia cirrhosa grass seeds located above and below the footprints, have shown humans have been in the Americas for much longer than previously thought. These footprints represent an adolescent individual and toddler walking through the lakebed at White Sands (see Figure 7.19), New Mexico, alongside both giant ground sloths and mammoths (Barras 2022; Wade 2021). Also present in the lakebed are footprints of camels and dire wolves (nps.gov 2022; Wade 2021).

The IFC model was upheld by a group of theorists known as “Clovis First,” who believed the migration of people into the Americas was recent and was represented archaeologically through the Clovis projectile point toolkit. Subsequent discoveries at sites such as Cactus Hill on the east coast of the United States and Monte Verde, Chile, have demonstrated that this model wouldn’t have worked. Because these sites are as old as 20,000 years and 18,500 years respectively, the IFC would have been frozen over and impassable (Gruhn 2020). Other models have been adopted to account for this, such as the coastal migration model down the west coast of North America. The more-likely migration scenario seems to be neither of these as more discoveries or antiquity continue to emerge. People may instead have migrated into the Americas before the last glacial maximum began, around 25,500–19,000 years ago. According to Indigenous knowledge, they have always been here. With the discovery of the White Sands footprints, it is known that humans have been in the Americas for at least 20,000 years.
This discovery also reveals the importance of recognizing knowledge beyond that which is produced by the European scientific tradition. Rather than framing science in a way that runs counter to Indigenous knowledge, it can be thought that science is catching up with it. For instance, the Acoma Pueblo people have the word for camel in their vocabulary. This was dismissed by scientists who assumed the word was for describing camels that were introduced to the United States in the past 100 years. However, the discovery of the White Sands footprints also included the footprints of Pleistocene camels in the same strata. Therefore, the fact that the Acoma Pueblo people have had a word for camel likely refers the Pleistocene-age megafauna camel, Camelops hesternus, rather than Camelus dromedarius or Camelus bactrianus, two present-day camel species (which are actually descendants of Camelops hesternus). Therefore, the existence of the Acoma Pueblo word for camel is not like an anomaly but rather a testament to the fact that Acoma Pueblo ancestors walked beside C. hesternus on this continent 20,000 years ago. These footprints challenge the “ice-free corridor” expansion model, as the bridge connecting present-day Alaska and Russia into Canada would have been covered in an impenetrable ice sheet at this time. The discovery of these footprints urges scientists to reconsider further investigations at well-known Terminal Pleistocene/Early Holocene dry lake beds in the Southwestern and Mojave deserts—and to include Indigenous knowledge in their work rather than ignore it.
Special Topic: Necropolitics
What are necropolitics? Necropolitics is an application of critical theory that describes how “governments assign differential value to human life” and similarly how someone is treated after they die (Verghese 2021). How is someone’s death political?
Consider the La Brea Woman example from the section on asphalt above. The La Brea Woman’s discovery was controversial, not because she is the only person to be found in the tar pits or because of her age but also because of necropolitics. The La Brea Woman was collected in 1914 and her body was housed on display at the George C. Page Museum in Los Angeles against the wishes of the Chumash and the Tongva, two tribes whose ancestral lands include Los Angeles. The museum decided to display a skull cast instead to meet the request of the tribes which included a separate postcranial skeleton from a different individual. The updated display itself was wrought with other ethical issues, as a cast of her skull was “attached to the ancient remains of a Pakistani female that was dyed dark bronze, the femurs shortened to approximate the stature of native people” (Cooper 2010). In both cases, neither the individuals or their descendent communities consented to the display or grotesque modification of human remains. According to an interview conducted by LA Weekly (Cooper 2010) with Cindi Alvitre, former chair of the Gabrielino-Tongva Tribal Council, the display of Indigenous human remains is akin to voyeurism. She states “It's disheartening to me because it's very inappropriate to display any human remains. The things we do to fill the imagination of visitors. It violates human rights.” It is important to listen to the wishes of Indigenous people and center their values when conducting work with their ancestors. A good source for considering places to look for archaeological research ethics before conducting fieldwork (and ideally during your research design) is the Society for American Archaeology’s ethics principle list, as well as following the Indigenous Archaeology Collective.
Indigenous remains are now protected in the United States due to legislation such as Native American Graves Protection and Repatriation Act (NAGPRA). You can read more about this in Chapter 15: Bioarchaeology and Forensic Anthropology. Before the passing of NAGPRA, tribes had little agency over how the bodies of their ancestors were treated by anthropologists and museums, including decisions about sampling and destructive tests. Now when archaeological field work is conducted on federal land, tribes must be consulted before work begins. This consultation process often includes what to do if human remains are encountered. Indigenous tribes are multifaceted and multivocal; each has its own rules about how to handle the remains of their ancestors. In some cases, all work on the project must be halted after the discovery of human remains. Other tribes allow for work to continue if the remains are moved and reburied. Some tribes are open to radiometric dating if it aligns with their beliefs in the afterlife. Each tribe is different, and each tribe deserves to have its wishes respected.
Voices From the Past: What Fossils Can Tell Us
Given that so few organisms ever become fossilized, any anthropologist or fossil hunter will tell you that finding a fossil is extremely exciting. But this is just the beginning of a fantastic mystery. With the creative application of scientific methods and deductive reasoning, a great deal can be learned about the fossilized organism and the environment in which it lived, leading to enhanced understanding of the world around us.
Dating Methods
Context is a crucial concept in paleoanthropology and archaeology. Objects and fossils are interesting in and of themselves, but without context there is only so much we can learn from them. One of the most important contextual pieces is the dating of an object or fossil. By being able to place it in time, we can compare it more accurately with other contemporary fossils and artifacts or we can better analyze the evolution of a fossil species or artifacts. To answer the question “How do we know what we know?,” you have to know how archaeologists and paleoanthropologists establish dates for artifacts, fossils, and sites.
Though accurate dating is important for context and analysis, we must consider the impact. Many of the chronometric dating methods used by anthropologists require the removal of small samples from artifacts, bones, soils, and rock. Thus these techniques are considered destructive. How much of an artifact are you willing to destroy to get your date? Sharon Clough, a Senior Environmental Officer at Cotswold Archaeology, addressed this issue in a case study from her research. She stated that “the benefit of a date did not outweigh the destruction of a valuable and finite resource” (Clough 2020). The resource in question was human remains. When considering our dating options, we want to be sure that we do as little harm as possible, especially in the case of human remains (read more about this issue in the Special Topic box, “Necropolitics”).
Dating techniques are divided into two broad categories: relative dating methods and chronometric (sometimes called absolute) dating methods.
Relative Dating
Relative dating methods are used first because they rely on simple observational skills. In the 1820s, Christian Jürgensen Thomsen at the National Museum of Denmark in Copenhagen developed the “three-age” system still used in European archaeology today (Feder 2017, 17). He categorized the artifacts at the museum based on the idea that simpler tools and materials were most likely older than more complex tools and materials. Stone tools must predate metal tools because they do not require special technology to develop. Copper and bronze tools must predate iron because they can be smelted or worked at lower temperatures, etc. Based on these observations, he categorized the artifacts into Stone Age, Bronze Age, and Iron Age.
The restriction of relative dating is that you don’t know specific dates or how much time passed between different sites or artifacts. You simply know that one artifact or fossil is older than another. Thomsen knew that Stone Age artifacts were older than Bronze Age artifacts, but he couldn’t tell if they were hundreds of years older or thousands of years older. The same is true with fossils that have differences of ages into the hundreds of millions of years.
The first relative dating technique is stratigraphy (Figure 7.20). You might have already heard this term if you have watched documentaries on archaeological excavations. That’s because this method is still being used today. It provides a solid foundation for other dating techniques and gives important context to artifacts and fossils found at a site.

Stratigraphy is based on the Law of Superposition first proposed by Nicholas Steno in 1669 and further explored by James Hutton (the previously mentioned “Father” of Deep Time). Essentially, superposition tells us that things on the bottom are older than things on the top (Williams 2004, 28). Notice on Figure 7.20 that there are distinctive layers piled on top of each other. It stands to reason that each layer is older than the one immediately on top of it (Hester et al. 1997, 338). Think of a pile of laundry on the floor. Over the course of a week, as dirty clothes get tossed on that pile, the shirt tossed down on Monday will be at the bottom of the pile while the shirt tossed down on Friday will be at the top. Assuming that the laundry pile was undisturbed throughout the week, if the clothes were picked up layer by layer, the clothing choices that week could be reconstructed in the order that they were worn.
Another relative dating technique is biostratigraphy. This form of dating looks at the context of a fossil or artifact and compares it to the other fossils and biological remains (plant and animal) found in the same stratigraphic layers. For instance, if an artifact is found in the same layer as wooly mammoth remains, you know that it must date to around the last ice age, when wooly mammoths were still abundant on Earth. In the absence of more specific dating techniques, early archaeologists could prove the great antiquity of stone tools because of their association with extinct animals. The application of this relative dating technique in archaeology was used at the Folsom site in New Mexico. In 1927, a stone spear point was discovered embedded in the rib of an extinct species of bison. Because of the undeniable association between the artifact and the ancient animal, there was scientific evidence that people had occupied the North American continent since antiquity (Cook 1928).
Similar to biostratigraphic dating is cultural dating (Figure 7.21). This relative dating technique is used to identify the chronological relationships between human-made artifacts. Cultural dating is based on artifact types and styles (Hester et al. 1997, 338). For instance, a pocket knife by itself is difficult to date. However, if the same pocket knife is discovered surrounded by cassette tapes and VHS tapes, it is logical to assume that the artifact came from the late 20th century like the cassette and VHS tapes. The pocket knife could not be dated earlier than the late 20th century because the tapes were made no earlier than 1977. In the Thomsen example above, he was able to identify a relative chronology of ancient European tools based on the artifact styles, manufacturing techniques, and raw materials. Cultural dating can be used with any human-made artifacts. Both cultural dating and biostratigraphy are most effective when researchers are already familiar with the time periods for the artifacts and animals. They are still used today to identify general time periods for sites.

Chemical dating was developed in the 19th century and represents one of the early attempts to use soil composition and chemistry to date artifacts. A specific type of chemical dating is fluorine dating, and it is commonly used to compare the age of the soil around bone, antler, and teeth located in close proximity (Cook and Ezra-Cohn 1959; Goodrum and Olson 2009). While this technique is based on chemical dating, it only provides the relative dates of items rather than their absolute ages. For this reason, fluorine dating is considered a hybrid form of relative and chronometric dating methods (which will be discussed next).
Soils contain different amounts of chemicals, and those chemicals, such as fluorine, can be absorbed by human and animal bones buried in the soil. The longer the remains are in the soil, the more fluorine they will absorb (Cook and Ezra-Cohn 1959; Goodrum and Olson 2009). A sample of the bone or antler can be processed and measured for its fluorine content. Unfortunately, this absorption rate is highly sensitive to temperature, soil pH, and varying fluorine levels in local soil and groundwater (Goodrum and Olson 2009; Haddy and Hanson 1982). This makes it difficult to get an accurate date for the remains or to compare remains between two sites. However, this technique is particularly useful for determining whether different artifacts come from the same burial context. If they were buried in the same soil for the same length of time, their fluorine signatures would match.
Chronometric Dating
Unlike relative dating methods, chronometric dating methods provide specific dates and time ranges. Many of the chronometric techniques we will discuss are based on work in other disciplines such as chemistry and physics. The modern developments in studying radioactive materials are accurate and precise in establishing dates for ancient sites and remains.
Many of the chronometric dating methods are based on the measurement of radioactive decay of particular elements. Elements are materials that cannot be broken down into more simple materials without losing their chemical identity (Brown et al. 2018, 48). Each element consists of an atom that has a specific number of protons (positively charged particles) and electrons (negatively charged particles) as well as varying numbers of neutrons (particles with no charge). The protons and neutrons are located in the densely compacted nucleus of the atom, but the majority of the volume of an atom is space outside the nucleus around which the electrons orbit (see Figure 7.22).

Elements are classified based on the number of protons in the nucleus. For example, carbon has six protons, giving it an atomic number 6. Uranium has 92 protons, which means that it has an atomic number 92. While the number of protons in the atom of an element do not vary, the number of neutrons may. Atoms of a given element that have different numbers of neutrons are known as isotopes.
The majority of an atom’s mass is determined by the protons and neutrons, which have more than a thousand times the mass of an electron. Due to the different numbers of neutrons in the nucleus, isotopes vary by nuclear/atomic weight (Brown et al. 2018, 94). For instance, isotopes of carbon include carbon 12 (12C), carbon 13 (13C), and carbon 14 (14C). Carbon always has six protons, but 12C has six neutrons whereas 14C has eight neutrons. Because 14C has more neutrons, it has a greater mass than 12C (Brown et al. 2018, 95).
Most isotopes in nature are considered stable isotopes and will remain in their normal structure indefinitely. However, some isotopes are considered unstable isotopes (sometimes called radioisotopes) because they spontaneously release energy and particles, transforming into stable isotopes (Brown et al. 2018, 946; Flowers et al. 2018, section 21.1). The process of transforming the atom by spontaneously releasing energy is called radioactive decay. This change occurs at a predictable rate for nearly all radioisotopes of elements, allowing scientists to use unstable isotopes to measure time passage from a few hundred to a few billion years with a large degree of accuracy and precision.
The leading chronometric method for archaeology is radiocarbon dating (Figure 7.23). This method is based on the decay of 14C, which is an unstable isotope of carbon. It is created when nitrogen 14 (14N) interacts with cosmic rays, which causes it to capture a neutron and convert to 14C. Carbon 14 in our atmosphere is absorbed by plants during photosynthesis, a process by which light energy is turned into chemical energy to sustain life in plants, algae, and some bacteria. Plants absorb carbon dioxide from the atmosphere and use the energy from light to convert it into sugar that fuels the plant (Campbell and Reece 2005, 181–200). Though 14C is an unstable isotope, plants can use it in the same way that they use the stable isotopes of carbon.

Animals get 14C by eating the plants. Humans take it in by eating plants and animals. After death, organisms stop taking in new carbon, and the unstable 14C will begin to decay. Carbon 14 has a half-life of 5,730 years (Hester et al. 1997, 324). That means that in 5,730 years, half the amount of 14C will convert back into 14N. Because the pattern of radioactive decay is so reliable, we can use 14C to accurately date sites up to 55,000 years old (Hajdas et al. 2021). However, 14C can only be used on the remains of biological organisms. This includes charcoal, shell, wood, plant material, and bone. This method involves destroying a small sample of the material. Earlier methods of radiocarbon dating required at least 1 gram of material, but with the introduction of accelerator mass spectrometry (AMS), sample sizes as small as 1 milligram can now be used (Hajdas et al. 2021). This significantly reduces the destructive nature of this method.
The use of radiocarbon dating at Denisova Cave in modern-day Russia revealed an astounding find, the first dated first-generation individual with a Neanderthal mother and Denisovan father. Vivian Slon and colleagues (2018) sequenced the genome, which revealed the individual's hybrid genetic background, and radiocarbon dated the remains, revealing the sub-adult was over 50,000 years old (Slon et al. 2018).
As mentioned before, 14C is unstable and ultimately decays back into 14N. This decay is happening at a constant rate (even now, inside your own body!). However, as long as an organism is alive and taking in food, 14C is being replenished in the body. As soon as an organism dies, it no longer takes in new 14C. We can then use the rate of decay to measure how long it has been since the organism died (Hester et al. 1997, 324). However, the amount of 14C in the atmosphere is not stable over time. It fluctuates based on changes to the earth’s magnetic field and solar activity. In order to turn 14C results into accurate calendar years, they must be calibrated using data from other sources. Annual tree rings (see discussion of dendrochronology below), foraminifera from stratified marine sediments, and microfossils from lake sediments can be used to chart the changes in 14C as “calibration curves.” The radiocarbon date obtained from the sample is compared to the established curve and then adjusted to reflect a more accurate calendar date (see Figure 7.24). The curves are updated over time with more data so that we can continue to refine radiocarbon dates (Törnqvist et al. 2016). The most recent calibration curves were released in 2020 and may change the dates for some existing sites by hundreds of years (Jones 2020).

As you will see in the hominin chapters (Chapters 9–12), 55,000 years is only a tiny fragment of human evolutionary history. It is insignificant in the context of the age of our planet. In order to date even older fossils, other methods are necessary.
Potassium-argon (K-Ar) dating and argon-argon (Ar-Ar) dating can reach further back into the past than radiocarbon dating. Used to date volcanic rock, these techniques are based on the decay of unstable potassium 40 (40K) into argon 40 (40Ar) gas, which gets trapped in the crystalline structures of volcanic material. It is a method of indirect dating. Instead of dating the fossil itself, K-Ar and Ar-Ar dates volcanic layers around the fossil. It will tell you when the volcanic eruption that deposited the layers occurred. This is where stratigraphy becomes important. The date of the surrounding layers can give you a minimum and maximum age of the fossil based on where it is in relation to those layers. This technique was used at Gesher Benot Ya'aqo in the Jordan Valley, dating early stratigraphic deposits of basalt flows to 100,000 years old (Bar-Yosef and Belmaker 2011). The site is unique because early layers of occupation with an Acheulean handaxe industry were made primarily of basalt, which is an uncommon material for this tool technology (see Chapter 10 for a full discussion of this tool technology). The benefit of this dating technique is that 40K has a half-life of circa 1.3 billion years, so it can be used on sites as young as 100 kya and as old as the age of Earth. As you will see in later chapters, it is particularly useful in dating early hominin sites in Africa (Michels 1972, 120; Renfrew and Bahn 2016, 155). Another benefit to this technique is that it does not damage precious fossils because the samples are taken from the surrounding rock instead. However, this method is not without its flaws. A study by J. G. Funkhouser and colleagues (1966) and Raymond Bradley (2015) demonstrated that igneous rocks with fluid inclusions, such as those found in Hawai‘i, can release gasses including radiogenic argon when crushed, leading to incorrectly older dates. This is an example of why it is important to use multiple dating methods in research to detect anomalies.
Uranium series dating is based on the decay chain of unstable isotopes of uranium. It uses mass spectrometry to detect the ratios of uranium 238 (238U), uranium 234(234U), and thorium 230 (230Th) in carbonates (Wendt et al. 2021). Thorium accumulates in the carbonate sample through radiometric decay. Thus, the age of the sample is calculated from the difference between a known initial ratio and the ratio present in the sample to be dated. This makes uranium series ideal for dating carbonate rich deposits such as carbonate cements from glacial moraine deposits, speleothems (deposits of secondary minerals that form on the walls, floors, and ceilings of caves, like stalactites and stalagmites), marine and lacustrine carbonates from corals, caliche, and tufa, as well as bones and teeth (University of Arizona, n.d.; van Calsteren and Thomas 2006). Due to the timing of the decay process, this dating technique can be used from a few years up to 650k (Wendt et al. 2021). Since many early hominin sites occur in cave environments, this dating technique can be very powerful. This method has also been used to develop more accurate calibration curves for radiocarbon dating. However, the accuracy of this method depends on knowing the initial ratios of the elements and ruling out possible contamination (Wendt et al. 2021). It also involves the destruction of a small sample of material.
Fission track dating is another useful dating technique for sites that are millions of years old. This is based on the decay of radioactive uranium 238 (238U). The unstable atom of 238U fissions at a predictable rate. The fission takes a lot of energy and causes damage to the surrounding rock. For instance, in volcanic glasses we can see this damage as trails in the glass. Researchers in the lab take a sample of the glass and count the number of fission trails using an optical microscope. As 238U has a half-life of 4,500 million years, it can be used to date rock and mineral material starting at just a few decades and extending back to the age of Earth. As with K-Ar, archaeologists are not dating artifacts directly. They are dating the layers around the artifacts in which they are interested (Laurenzi et al. 2007).
Luminescence dating, which includes thermoluminescence and a related technique called optically stimulated luminescence, is based on the naturally occurring background radiation in soils. Pottery, baked clay, and sediments that include quartz and feldspar are bombarded by radiation from the soils surrounding it. Electrons in the material get displaced from their orbit and trapped in the crystalline structure of the pottery, rock, or sediment. When a sample of the material is heated to 500°C (thermoluminescence) or exposed to particular light wavelengths (optically stimulated luminescence) in the laboratory, this energy gets released in the form of light and heat and can be measured (Cochrane et al. 2013; Renfrew and Bahn 2016, 160). You can use this method to date artifacts like pottery and burnt flint directly. When attempting to date fossils, you may use this method on the crystalline grains of quartz and feldspar in the surrounding soils (Cochrane et al. 2013). The important thing to remember with this form of dating is that heating the artifact or soils will reset the clock. The method is not necessarily dating when the object was last made or used but when it was last heated to 500°C or more (pottery) or exposed to sunlight (sediments). Luminescence dating can be used on sites from less than 100 years to over 100,000 years (Duller 2008, 4). As with all archaeological data, context is crucial to understanding the information.
Like thermoluminescence dating, electron spin resonance dating is based on the measurement of accumulated background radiation from the burial environment. It is used on artifacts and rocks with crystalline structures, including tooth enamel, shell, and rock—those for which thermoluminescence would not work. The radiation causes electrons to become dislodged from their normal orbit. They become trapped in the crystalline matrix and affect the electromagnetic energy of the object. This energy can be measured and used to estimate the length of time in the burial environment. This technique works well for remains as old as two million years (Carvajal et al. 2011, 115–116). It has the added benefit of being nondestructive, which is an important consideration when dealing with irreplaceable material.
Not all chronometric dating methods are based on unstable isotopes and their rates of decay. There are several other methods that make use of other natural biological and geologic processes. One such method is known as dendrochronology (Figure 7.25), which is based on the natural growth patterns of trees. Trees create concentric rings as they grow; the width of those rings depends on environmental conditions and season. The age of a tree can be determined by counting its rings, which also show records of rainfall, droughts, and forest fires.

Tree rings can be used to date wood artifacts and ecofacts from archaeological sites. This first requires the creation of a profile of trees in a particular area. The Laboratory of Tree-Ring Research at the University of Arizona has a comprehensive and ongoing catalog of tree profiles (see University of Arizona n.d.). Archaeologists can then compare wood artifacts and ecofacts with existing timelines, provided the tree rings are visible, and find where their artifacts fit in the pattern. Dendrochronology has been in use since the early 20th century (Dean 2009, 25). The Northern Hemisphere chronology stretches back nearly 14,000 years (Reimer et al. 2013, 1870) and has been used successfully to date southwestern U.S. sites such as Pueblo Bonito and Aztec Ruin (Dean 2009, 26). Dendrochronological evidence has helped calibrate radiocarbon dates and even provided direct evidence of global warming (Dean 2009, 26–27).
In Australia, dendrochronology, along with other environmental reconstruction methods, has been used to show that the Indigenous people had sophisticated land management systems before the arrival of British invaders. According to the work of Michael-Shawn Fletcher and colleagues (2021), there was a significant encroachment of the rainforests and tree species into grasslands after the British invasion. Prior to this time, Indigenous people managed the landscape through controlled burns at regular intervals. This practice created climate-resistant grasslands that were biodiverse and provided predictable food supplies for humans and other animals. Under European land management, there have been negative impacts on biodiversity and climate resilience and an increase in catastrophic wildfires (Fletcher et al. 2021).
This dating method does have its difficulties. Some issues are interrupted ring growth, microclimates, and species growth variations. This is addressed through using multiple samples, statistical analysis, and calibration with other dating methods. Despite these limitations, dendrochronology can be a powerful tool in dating archaeological sites (Hillam et al. 1990; Kuniholm and Striker 1987).
Environmental Reconstruction
As you read in Chapter 2, Charles Darwin, Jean-Baptiste Lamarck, Alfred Russel Wallace, and others recognized the importance of the environment in shaping the evolutionary course of animal species. To understand what selective processes might be shaping evolutionary change, we must be able to reconstruct the environment in which the organism was living.
One of the ways to do that is to look at the plant species that lived in the same time range as the species in which you are interested. One way to identify ancient flora is to analyze sediment cores from water and other protected sources. Pollen gets released into the air and some of that pollen will fall on wetlands, lakes, caves, and so forth. Eventually it sinks to the bottom of the lake and forms part of the sediment. This happens year after year, so subsequent layers of pollen build up in an area, creating strata. By taking a core sample and analyzing the pollen and other organic material, an archaeologist can build a timeline of plant types and see changes in the vegetation of the area (Hester et al. 1997, 284). This can even be done over large areas by studying ocean bed cores, which accumulate pollen and dust from large swaths of neighboring continents.
While sediment coring is one of the more common ways to reconstruct past environments, there are a few other methods. These have been recently employed at Holocene Lake Ivanpah, a paleolake that straddles the California and Nevada border in the United States. This lake was originally thought to have been completely dry around 9,300–7,800 kya (Sims and Spaulding 2017). However, analyzing core samples using soil identification, sediment chemistry, subsurface stratigraphy, and geomorphology (the study of the physical characteristics of the Earth’s surface) revealed deposition of three recent lake fillings during this period in the forms of additional hardpan, or lake bottom, playas, bedded or layered fine-grained (wetland) sediments, and buried beaches below the surface (Sims and Spaulding 2017; Spaulding and Sims 2018). These discoveries are important because they have not been integrated into interpretation of the local archaeological record, as it was assumed that the lake had been dry for thousands of years. Sedimentological analyses such as coring and those listed above can provide great insight into past climates and are accomplished in a minimally destructive way.
Another way of reconstructing past environments is by using stable isotopes. Unlike unstable isotopes, stable isotopes remain constant in the environment throughout time. Plants take in the isotopes through photosynthesis and ground water absorption. Animals take in isotopes by drinking local water and eating plants. Stable isotopes can be powerful tools for identifying where an organism grew up and what kind of food the organism ate throughout its life. They can even be used to identify global temperature fluctuations.
Global Temperature Reconstruction
Oxygen isotopes are a powerful tool in tracking global temperature fluctuations throughout time. The isotopes of Oxygen 18 (18O) and Oxygen 16 (16O) occur naturally in Earth’s water. Both are stable isotopes, but 18O has a heavier atomic weight. In the normal water cycle, evaporation takes water molecules from the surface to the atmosphere. Because 16O is lighter, it is more likely to be part of this evaporation process. The moisture gathers in the atmosphere as clouds that eventually may produce rain or snow and release the water back to the surface of the planet. During cool periods like glacial periods (ice ages), the evaporated water often comes down to Earth’s surface as snow. The snow piles up in the winter but, because of the cooler summers, does not melt off. Instead, it gets compacted and layered year after year, eventually resulting in large glaciers or ice sheets covering parts of Earth. Since 16O, with the lighter atomic weight, is more likely to be absorbed in the evaporation process, it gets locked up in glacier formation. The waters left in oceans would have a higher ratio of 18O during these periods of cooler global temperatures (Potts 2012, 154–156; see Figure 7.26).

The microorganisms that live in the oceans, foraminifera, absorb the water from their environment and use the oxygen isotopes in their body structures. When these organisms die, they sink to the ocean floor, contributing to the layers of sediment. Scientists can extract these ocean cores and sample the remains of foraminifera for their 18O and 16O ratios. These ratios give us a good approximation of global temperatures deep into the past. Cooler temperatures indicate higher ratios of 18O (Potts 2012, 154–156).
Diet Reconstruction
You may be familiar with the saying “you are what you eat.” When it comes to your teeth and bones, this adage is literal. Stable isotopes can also be used to reconstruct animal diet and migration patterns. Living organisms absorb elements from ingested plants and water. These elements are used in tissues like bones, teeth, skin, hair, and so on. By analyzing the stable isotopes in the bones and teeth of humans and other animals, we can identify the types of food they ate at different stages of their lives.
Plants take in carbon dioxide from the atmosphere during photosynthesis. We’ve already discussed this using the example of the unstable isotope 14C; however, this absorption also takes place with the stable isotopes of 12C and 13C. During photosynthesis, some plants incorporate carbon dioxide as a three-carbon molecule (C3 plants) and some as a four-carbon molecule (C4 plants). On the one hand, C3 plants include certain types of trees and shrubs that are found in relatively wet environments and have lower ratios of 13C compared to 12C. C4 plants, on the other hand, include plants from drier environments like savannahs and grasslands. C4 plants have higher ratios of 13C to 12C than C3 plants (Renfrew and Bahn 2016, 312). These ratios remain stable as you go up the food chain. Therefore, you can analyze the bones and teeth of an animal to identify the 13C/12C ratios and identify the types of plants that animal was eating.
The ratios of stable nitrogen isotopes 15N and 14N can also give information about the diet of fossilized or deceased organisms. Though initially absorbed from water and soils by plants, the nitrogen ratios change depending on the primary diet of the organism. An animal who has a mostly vegetarian diet will have lower ratios of 15N to 14N, while those further up the food chain, like carnivores, will have higher ratios of 15N. Interestingly, breastfeeding infants have a higher nitrogen ratio than their mothers, because they are getting all of their nutrients through their mother’s milk. So nitrogen can be used to track life events like weaning (Jay et al. 2008, 2). A marine versus terrestrial diet will also affect the nitrogen signatures. Terrestrial diets have lower ratios of 15N than marine diets. In the course of human evolution, this type of analysis can help us identify important changes in human nutrition. It can help anthropologists figure out when meat became a primary part of the ancient human diet or when marine resources began to be used. The ratios of stable nitrogen isotopes can also be used to determine a change in status, as in the case of the Llullaillaco children (the “ice mummies”) found in the Andes Mountains. For instance, the nitrogen values in hair from the Llullaillaco Maiden showed a significant positive shift that is associated with increased meat consumption in the last 12 months of her life (Wilson et al. 2007). Although the two younger children had little changes in their diets in the last year of their short lives, the changes in their nitrogen values were significant enough to suggest that the improvement in their diets may have been attributed to the Incas’ desire to sacrifice healthy, high-status children” (Faux 2012, 6).
Migration
Stable isotopes can also tell us a great deal about where an individual lived and whether they migrated during their lifetime. The geology of Earth varies because rocks and soils have different amounts or ratios of certain elements in them. These variations in the ratios of isotopes of certain elements are called isotopic signatures. They are like a chemical fingerprint for a geographical region. These isotopes get into the groundwater and are absorbed by plants and animals living in that area. Elements like strontium, oxygen, and nitrogen, among others, are then used by the body to build bones and teeth. If you ate and drank local water all of your life, your bones and teeth would have the same isotopic signature as the geographical region in which you lived.
However, many people (and animals) move around during their lifetimes. Isotopic signatures can be used to identify migration patterns in organisms (Montgomery et al. 2005). Teeth develop in early childhood. If the isotopes of teeth are analyzed, these isotopes would resemble those found in the geographic area where an individual lived as a child. Bones, however, are a different story. Bones are constantly changing throughout life. Old cells are removed and new cells are deposited to respond to growth, healing, activity change, and general deterioration. Therefore, the isotopic signature of bones will reflect the geographical area in which an individual spent the last seven to ten years of life. If an individual has different isotopic signatures for their bones and teeth, it could indicate a migration some time during their life after childhood.

Recent work involving stable isotope analysis has been done on the cremation burials from Stonehenge, in Wessex, England (Figure 7.27). Much of the archaeological work at Stonehenge in the past focused on the building and development of the monument itself. That is partly because most of the burials at the monument were cremated remains, which are difficult to study because of their fragmentary nature and the chemical alterations that bone and teeth undergo when heated. The cremation process complicates the oxygen and carbon isotopes. However, the researchers determined that strontium would not be affected by heating and could still be analyzed in cranial fragments. Using the remains of 25 individuals, they compared their strontium signatures to the geology of Wessex and other regions of the UK. Fifteen of those individuals had strontium signatures that matched the local geology. This means that in the last ten or so years of their lives, they lived and ate food from around Stonehenge. However, ten of the individuals did not match the local geologic signature. These individuals had strontium ratios more closely aligned with the geology of west Wales. Archaeologists find this particularly interesting because in the early phases of Stonehenge’s construction, the smaller “blue stones” were brought 200 km from Wales in a feat of early engineering. These larger regional connections show that Stonehenge was not just a site of local importance. It dominated a much larger region of influence and drew people from all over ancient Britain (Snoeck et al. 2018).
Special Topic: Cold Case Naia

In 2007, cave divers exploring the Sistema Sac Actun in the Yucatán Peninsula in Mexico (see Figure 7.28 and 7.29) discovered the bones of a 15- to 16-year-old female human along with the bones of various extinct animals from the Pleistocene (Collins et al. 2015). The site was named Hoyo Negro (“Black Hole”). The human bones belonged to a Paleo-American, later named “Naia” after a Greek water nymph. Examination of the partially fossilized remains revealed a great deal about Naia’s life, and the radiocarbon dating of her tooth enamel indicated that she lived some 13,000 years ago (Chatters et al. 2014). Naia’s arms were not overly developed, so her daily activities did not involve heavy carrying or grinding of grain or seeds. Her legs, however, were quite muscular, implying that Naia was used to walking long distances. Naia’s teeth and bones indicate habitually poor nutrition. There is evidence of violent injury during the course of Naia’s life from a healed spiral fracture of her left forearm. Naia also suffered from tooth decay and osteoporosis even though she appeared young and undersized. Dr. Jim Chatters hypothesizes that Naia entered the cave at a time when it was not flooded, probably looking for water. She may have become disoriented and fell off a high ledge to her death. The trauma to her pelvis is consistent with such an injury (Watson 2017).
Naia’s skeleton is remarkably complete given its age. As divers were able to locate her skull, Naia’s physical appearance in life could be interpreted. Surprisingly, in examining the skull, it was determined that Naia did not resemble modern Indigenous peoples in the region. However, the mitochondrial DNA (mtDNA) recovered from a tooth indicates that Naia shares her DNA with modern Indigenous peoples (Chatters et al. 2014). Though Naia’s burial environment made chemical analysis difficult, researchers were able to recover carbon isotopes from her remains. The isotopes from Naia’s tooth enamel suggest a diet of “cool-season grasses and/or broad-leaf vegetation” (Chatters et al. 2022, 68). Naia’s teeth also displayed numerous dental caries and only light dental wear. Coupled with the isotopic data, she likely had a “softer, more sugar-rich diet” (Chatters et al. 2022, 68).

Summary
With a timeline that extends back some 4.6 billion years, Earth has witnessed continental drift, environmental changes, and a growing complexity of life. Fossils, the mineralized remains of living organisms, provide physical evidence of life and the environment on the planet over the course of billions of years. In order to better understand the fossil record, anthropologists rely on the collaboration of numerous academic fields and disciplines. Anthropologists use a variety of scientific methods, both relative and chronometric, to analyze fossils to determine age, origins, and migration patterns as well as to provide insight into the health and diet of the fossilized organism. While each method has its advantages, disadvantages, and limited applications, these tools enable anthropologists to theorize how all living organisms evolved, including the evolution of early humans into modern humans, H. sapiens. The fossil record is far from complete, but our expanding understanding of the fossil context, with exciting new discoveries and improved scientific methods, enables us to document the history of our planet and the evolution of life on Earth.
Dating Methods Quick Guide
Method |
Material |
Effective date range |
Stratigraphy |
Soil layers |
Relative |
Biostratigraphy |
Plant and animal remains |
Relative |
Cultural dating |
Human-made objects |
Relative |
Fluorine |
Bone, antler, teeth |
Relative |
Radiocarbon |
Organic carbon bearing material (bones, teeth, antler, plant material, shell, charcoal) |
Younger than 55,000 years |
Potassium-argon and argon-argon |
Volcanic rock |
Older than 100,000 years |
Uranium series |
Carbonates such as stalactites, stalagmites, corals, caliche, and tufa |
Younger than 650,000 years |
Fission track |
Volcanic glasses and crystalline minerals |
Spans age of Earth |
Luminescence |
Pottery, baked clay, sediments |
100 to older than 100,000 years |
Electron spin resonance dating |
Tooth enamel, shell, rock with crystalline structures |
Younger than 2 million years |
Dendrochronology |
Wood (where tree rings are identifiable) |
Dependent on location and available chronologies |
Review Questions
- How do remains become fossils? What conditions are necessary for the fossilization process?
- What kind of information could you acquire from a single fossil? What could it tell you about the broader environment?
- What factors would you take into consideration when deciding which dating method to use for a particular artifact?
- What methods do anthropologists use to reconstruct past environments and lifestyles?
Key Terms
Anaerobic: An oxygen-free environment.
Anthropocene: The proposed name for our current geologic epoch based on human-driven climate change.
Argon-argon (Ar-Ar) dating: A chronometric dating method that measures the ratio of argon gas in volcanic rock to estimate time elapsed since the volcanic rock cooled and solidified. See also potassium-argon dating.
Atom: A small building block of matter.
Bezoars: Hard, concrete-like substances found in the intestines of fossil creatures.
Biostratigraphy: A relative dating method that uses other plant and animal remains occurring in the stratigraphic context to establish time depth.
Bya: Billion years ago.
Chronometric dating: Dating methods that give estimated numbers of years for artifacts and sites.
Continental drift: The slow movement of continents over time.
Coprolite: Fossilized poop.
Cultural dating: The relative dating method that arranges human-made artifacts in a time frame from oldest to youngest based on material, production technique, style, and other features.
Deep Time: James Hutton’s theory that the world was much older than biblical explanations allowed. This age could be determined by gradual natural processes like soil erosion.
Dendrochronology: A chronometric dating method that uses the annual growth of trees to build a timeline into the past.
Electron spin resonance dating: A chronometric dating method that measures the background radiation accumulated in material over time.
Element: Matter that cannot be broken down into smaller matter.
Eon: The largest unit of geologic time, spanning billions of years and divided into subunits called eras, periods, and epochs.
Epochs: The smallest units of geologic time, spanning thousands to millions of years.
Eras: Units of geologic time that span millions to billions of years and that are subdivided into periods and epochs.
Fission track dating: A chronometric dating method that is based on the fission of 283U.
Fluorine dating: A relative dating method that analyzes the absorption of fluorine in bones from the surrounding soils.
Foraminifera: Single-celled marine organisms with shells.
Fossilization: The process by which an organism becomes a fossil.
Fossils: Mineralized copies of organisms or activity imprints.
Geomorphology: The study of the physical characteristics of the Earth’s surface.
Glacial periods: Periods characterized by low global temperatures and the expansion of ice sheets on Earth’s surface.
Holocene: The geologic epoch from 10 kya to present. (See the discussion on “the Anthropocene” for the debate regarding the current epoch name.)
Hominin: The term used for humans and their ancestors after the split with chimpanzees and bonobos.
In matrix: When a fossil is embedded in a substance, such as igneous rock.
Isotopes: Variants of elements.
Kya: Thousand years ago.
Law of Superposition: The scientific law that states that rock and soil are deposited in layers, with the youngest layers on top and the oldest layers on the bottom.
Lithification: The process by which the pressure of sediments squeeze extra water out of decaying remains and replace the voids that appear with minerals from the surrounding soil and groundwater.
Luminescence dating: The chronometric dating method based on the buildup of background radiation in pottery, clay, and soils.
Megafauna: Large animals such as mammoths and mastodons.
Mitochondrial DNA: DNA located in the mitochondria of a cell that is only passed down from biological mother to child.
Mya: Million years ago.
Paleopathology: Study of ancient diseases and injuries identified through examining remains.
Periods: Geologic time units that span millions of years and are subdivided into epochs.
Permineralization: When minerals from water impregnate or replace organic remains, leaving a fossilized copy of the organism.
Petrified wood: A fossilized piece of wood in which the original organism is completely replaced by minerals through petrifaction.
Potassium-argon (K-Ar) dating: A chronometric dating method that measures the ratio of argon gas in volcanic rock to estimate time elapsed since the volcanic rock cooled and solidified. See also argon-argon dating.
Pseudofossils: Natural rocks or mineral formations that can be mistaken for fossils.
Radioactive decay: The process of transforming the atom by spontaneously releasing energy.
Radiocarbon dating: The chronometric dating method based on the radioactive decay of 14C in organic remains.
Relative dating: Dating methods that do not result in numbers of years but, rather, in relative timelines wherein some organisms or artifacts are older or younger than others.
Sediment cores: Core samples taken from lake beds or other water sources for analysis of their pollen.
Stable isotopes: Variants of elements that do not change over time without outside interference.
Stratigraphy: A relative dating method that is based on ordered layers or (strata) that build up over time.
Taphonomy: The study of what happens to an organism after death.
Trace fossils: Fossilized remains of activity such as footprints.
Uniformitarianism: The theoretical perspective that the geologic processes observed today are the same as the processes operating in the past.
Unstable isotopes: Variants of elements that spontaneously change into stable isotopes over time.
Uranium series dating: A radiometric dating method based on the decay chain of unstable isotopes of 238U and 235U.
About the Authors
Sarah S. King, Ph.D.
Cerro Coso Community College, sarah.king1@cerrocoso.edu
Dr. Sarah S. King is an anthropology/sociology professor at Cerro Coso Community College in California. She completed her Ph.D. work at the Division of Archaeological, Geographical and Environmental Sciences at the University of Bradford in West Yorkshire, England. Her thesis was entitled “What Makes War?: Assessing Iron Age Warfare through Mortuary Behavior and Osteological Patterns of Violence.” She also holds anthropology degrees from the University of California, Santa Cruz (B.A. hons., 2004), and the University of New Mexico, Albuquerque (M.A., 2006).
Kara Jones, M.A.
PhD student at University of Nevada, Las Vegas, jonesk44@unlv.nevada.edu
Kara Jones received their B.A. in anthropology at California State University, Bakersfield (2018) and their M.A. from University of Nevada, Las Vegas (2023, summer). Their master’s thesis is titled “Rockin’ at the Lake: Toolstone Use and Procurement along Holocene Lake Ivanpah, CA.” Mx Jones is a Mojave Desert archaeologist specializing in stone tool use and manufacture, focusing further on Holocene lakeshore adaptations.
For Further Exploration
Books
Bjornerud, Marcia. 2006. Reading the Rocks: The Autobiography of the Earth. New York: Basic Books.
Hazen, Robert M. 2013. The Story of Earth: The First 4.5 Billion Years, From Stardust to Living Planet. New York: Viking Penguin.
Holmes, Richard. 2010. The Age of Wonder: The Romantic Generation and the Discovery of the Beauty and Terror of Science. New York: Vintage.
Palmer, Douglas. 2005. Earth Time: Exploring the Deep Past from Victorian England to the Grand Canyon. New York: John Wiley & Sons.
Prothero, Donald R. 2015. The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonder of Evolution. New York: Columbia University Press.
Pyne, Lydia. 2016. Seven Skeletons: The Evolution of the World’s Most Famous Human Fossils. New York: Viking Books.
Repcheck, Jack. 2009. The Man Who Found Time: James Hutton and the Discovery of the Earth’s Antiquity. New York: Basic Books.
Taylor, Paul D., Aaron O’Dea. 2014. A History of Life in 100 Fossils. Washington, DC: Smithsonian Books.
Ward, David. 2002. Smithsonian Handbooks: Fossils. Washington, DC: Smithsonian Books.
Winchester, Simon. 2009. The Map That Changed the World: William Smith and the Birth of Modern Geology. New York: Harper Perennial.
Websites
East Tennessee State University Center of Excellence in Paleontology
Granger Historical Picture Archive
Indigenous Archaeology Collective
Natural History Museum (London), on Mary Anning
Petrified Forest National Park (NE Arizona)
Poozeum: The No. 2 Wonder of the World
Smithsonian National Museum of Natural History, Department of Paleobiology
Smithsonian National Museum of Natural History, on “What Does It Mean to be Human”
Society for American Archaeology, on “Ethics in Professional Archaeology”
Society for American Archaeology, “Principles of Archaeological Ethics”
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Acknowledgments
We are grateful to Lee Anne Zajicek, who coauthored the first edition. Her original contributions continue to be an integral part of this chapter. We thank the staff of the Maturango Museum, Ridgecrest, California. Specifically, for their generous help with photography and fossil images, we acknowledge Debbie Benson, executive director; Alexander K. Rogers, former archaeology curator; Sherry Brubaker, natural history curator; and Elaine Wiley, history curator. We thank Sharlene Paxton, a librarian at Cerro Coso Community College, Ridgecrest, California, for her guidance and expertise with OER and open-source images, and John Stenger-Smith and Claudia Sellers from Cerro Coso Community College, Ridgecrest, California, for their feedback on the chemistry and plant biology content. Finally, we thank William Zajicek and Lauren Zajicek, our community college students, for providing their impressions and extensive feedback on early drafts of the chapter.
Kerryn Warren, Ph.D., Grad Coach International
Lindsay Hunter, M.A., University of Iowa
Navashni Naidoo, M.Sc., University of Cape Town
Silindokuhle Mavuso, M.Sc., University of Witwatersrand
This chapter is a revision from "Chapter 9: Early Hominins" by Kerryn Warren, K. Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, and Nomawethu Hlazo. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Understand what is meant by “derived” and “ancestral” traits and why this is relevant for understanding early hominin evolution.
- Understand changing paleoclimates and paleoenvironments as potential factors influencing early hominin adaptations.
- Describe the anatomical changes associated with bipedalism and dentition in early hominins, as well as their implications..
- Describe early hominin genera and species, including their currently understood dates and geographic expanses.
- Describe the earliest stone tool techno-complexes and their impact on the transition from early hominins to our genus.
Defining Hominins
It is through our study of our hominin ancestors and relatives that we are exposed to a world of “might have beens”: of other paths not taken by our species, other ways of being human. But to better understand these different evolutionary trajectories, we must first define the terms we are using. If an imaginary line were drawn between ourselves and our closest relatives, the great apes, bipedalism (or habitually walking upright on two feet) is where that line would be. Hominin, then, means everyone on “our” side of the line: humans and all of our extinct bipedal ancestors and relatives since our divergence from the last common ancestor (LCA) we share with chimpanzees.
Historic interpretations of our evolution, prior to our finding of early hominin fossils, varied. Debates in the mid-1800s regarding hominin origins focused on two key issues:
- Where did we evolve?
- Which traits evolved first?
Charles Darwin hypothesized that we evolved in Africa, as he was convinced that we shared greater commonality with chimpanzees and gorillas on the continent (Darwin 1871). Others, such as Ernst Haeckel and Eugène Dubois, insisted that we were closer in affinity to orangutans and that we evolved in Eurasia where, until the discovery of the Taung Child in South Africa in 1924, all humanlike fossils (of Neanderthals and Homo erectus) had been found (Shipman 2002). (and refer to chapter)
Within this conversation, naturalists and early paleoanthropologists (people who study human evolution) speculated about which human traits came first. These included the evolution of a big brain (encephalization), the evolution of the way in which we move about on two legs (bipedalism), and the evolution of our flat faces and small teeth (indications of dietary change). Original hypotheses suggested that, in order to be motivated to change diet and move about in a bipedal fashion, the large brain needed to have evolved first, as is seen in the fossil species mentioned above.
However, we now know that bipedal locomotion is one of the first things that evolved in our lineage, with early relatives having more apelike dentition and small brain sizes. While brain size expansion is seen primarily in our genus, Homo, earlier hominin brain sizes were highly variable between and within taxa, from 300 cc (cranial capacity, cm3), estimated in Ardipithecus, to 550 cc, estimated in Paranthropus boisei. The lower estimates are well within the range of variation of nonhuman extant great apes. In addition, body size variability also plays a role in the interpretation of whether brain size could be considered large or small for a particular species or specimen. In this chapter, we will tease out the details of early hominin evolution in terms of morphology (i.e. the study of the form, size, or shape of things; in this case, skeletal parts).
We also know that early human evolution occurred in a very complicated fashion. There were multiple species (multiple genera) that featured diversity in their diets and locomotion. Specimens have been found all along the East African Rift System (EARS); that is, in Ethiopia, Kenya, Tanzania, and Malawi; see Figure 9.1), in limestone caves in South Africa, and in Chad. Dates of these early relatives range from around 7 million years ago (mya) to around 1 mya, overlapping temporally with members of our genus, Homo.

Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another, and they consider which of these species were able to make and use tools. As a result, every site discovery in the patchy hominin fossil record tells us more about our evolution. In addition, recent scientific techniques (not available even ten years ago) provide new insights into the diets, environments, and lifestyles of these ancient relatives.
In the past, taxonomy was primarily based on morphology. Today it is tied to known relationships based on molecular phylogeny (e.g., based on DNA) or a combination of the two. This is complicated when applied to living taxa, but becomes much more difficult when we try to categorize ancestor-descendant relationships for long-extinct species whose molecular information is no longer preserved. We therefore find ourselves falling back on morphological comparisons, often of teeth and partially fossilized skeletal material.
It is here that we turn to the related concepts of cladistics and phylogenetics. Cladistics groups organisms according to their last common ancestors based on shared derived traits. In the case of early hominins, these are often morphological traits that differ from those seen in earlier populations. These new or modified traits provide evidence of evolutionary relationships, and organisms with the same derived traits are grouped in the same clade (Figure 9.2). For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade of birds. In this chapter, we will examine the grouping of the Robust Australopithecines, whose cranial and dental features differ from those of earlier hominins, and therefore are considered derived.

Dig Deeper: Problems Defining Hominin Species
It is worth noting that species designations for early hominin specimens are often highly contested. This is due to the fragmentary nature of the fossil record, the large timescale (millions of years) with which paleoanthropologists need to work, and the difficulty in evaluating whether morphological differences and similarities are due to meaningful phylogenetic or biological differences or subtle differences/variation in niche occupation or time. In other words, do morphological differences really indicate different species? How would classifying species in the paleoanthropological record compare with classifying living species today, for whom we can sequence genomes and observe lifestyles?
There are also broader philosophical differences among researchers when it comes to paleo-species designations. Some scientists, known as “lumpers,” argue that large variability is expected among multiple populations in a given species over time. These researchers will therefore prefer to “lump” specimens of subtle differences into single taxa. Others, known as “splitters,” argue that species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences. In general, splitters would consider geographic differences among populations as meaning that a species is polytypic (i.e., capable of interacting and breeding biologically but having morphological population differences). This is worth keeping in mind when learning about why species designations may be contested.

This further plays a role in evaluating ancestry. Debates over which species “gave rise” to which continue to this day. It is common to try to create “lineages” of species to determine when one species evolved into another over time. We refer to these as chronospecies (Figure 9.3). Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record. More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
Finally, it is worth considering the process of fossil discovery and publication. Some fossils are easily diagnostic to a species level and allow for easy and accurate interpretation. Some, however, are more controversial. This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species (e.g., a fossil of a patella or knee bone). Researchers often need to make several important claims when announcing or publishing a find: a secure date (if possible), clear association with other finds, and an adequate comparison among multiple species (both extant and fossil). Therefore, it is not uncommon that an important find was made years before it is scientifically published.
Paleoenvironment and Hominin Evolution
There is no doubt that one of the major selective pressures in hominin evolution is the environment. Large-scale changes in global and regional climate, as well as alterations to the environment, are (partially or have a great part) all linked to hominin diversification, dispersal, and extinction (Maslin et al. 2014). Environmental reconstructions often use modern analogues. Let us take, for instance, the hippopotamus. It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive. Such instances have occurred multiple times in the past, and the bones of some fauna (i.e., animals, like the hippopotamus) that are sensitive to these changes give us insights into these events.
Yet reconstructing a paleoenvironment relies on a range of techniques, which vary depending on whether research interests focus on local changes or more global environmental changes/reconstructions. For local environments (such as a single site or region), comparing the faunal assemblages (collections of fossils of animals found at a site) with animals found in certain modern environments allows us to determine if past environments mirror current ones in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes. Other techniques are also useful in this regard. Chemical analyses, for instance, can reveal the diets of individual fauna, providing clues as to the relative wetness or dryness of their environment (e.g., nitrogen isotopes; Kingston and Harrison 2007).
Global climatic changes in the distant past, which fluctuated between being colder and drier and warmer and wetter on average, would have global implications for environmental change (Figure 9.4). These can be studied by comparing marine core and terrestrial soil data across multiple sites. These techniques are based on chemical analysis, such as examination of the nitrogen and oxygen isotopes in shells and sediments. Similarly, analyzing pollen grains shows which kinds of flora survived in an environment at a specific time period. There are multiple lines of evidence that allow us to visualize global climate trends over millions of years (although it should be noted that the direction and extent of these changes could differ by geographic region).

Both local and global climatic/environmental changes have been used to understand factors affecting our evolution (DeHeinzelin et al. 1999; Kingston 2007). Environmental change acts as an important factor regarding the onset of several important hominin traits seen in early hominins and discussed in this chapter. Namely, the environment has been interpreted as the following:
- the driving force behind the evolution of bipedalism,
- the reason for change and variation in early hominin diets, and
- the diversification of multiple early hominin species.
There are numerous hypotheses regarding how climate has driven and continues to drive human evolution. Here, we will focus on just three popular hypotheses.
Savannah Hypothesis (or Aridity Hypothesis)
The hypothesis: This popular theory suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion (Figure 9.5). It was first proposed by Darwin (1871) and supported by anthropologists like Raymond Dart (1925). However, this idea was supported by little fossil or paleoenvironmental evidence and was later refined as the Aridity Hypothesis. This hypothesis states that the long-term aridification and, thereby, expansion of savannah biomes were drivers in diversification in early hominin evolution (deMenocal 2004; deMenocal and Bloemendal 1995). It advocates for periods of accelerated aridification leading to early hominin speciation events.

The evidence: While early bipedal hominins are often associated with wetter, more closed environments (i.e., not the Savannah Hypothesis), both marine and terrestrial records seem to support general cooling, drying conditions, with isotopic records indicating an increase in grasslands (i.e., colder and wetter climatic conditions) between 8 mya and 6 mya across the African continent (Cerling et al. 2011). This can be contrasted with later climatic changes derived from aeolian dust records (sediments transported to the site of interest by wind), which demonstrate increases in seasonal rainfall between 3 mya and 2.6 mya, 1.8 mya and 1.6 mya, and 1.2 mya and 0.8 mya (deMenocal 2004; deMenocal and Bloemendal 1995).
Interpretation(s): Despite a relatively scarce early hominin record, it is clear that two important factors occur around the time period in which we see increasing aridity. The first factor is the diversification of taxa, where high morphological variation between specimens has led to the naming of multiple hominin genera and species. The second factor is the observation that the earliest hominin fossils appear to have traits associated with bipedalism and are dated to around the drying period (as based on isotopic records). Some have argued that it is more accurately a combination of bipedalism and arboreal locomotion, which will be discussed later. However, the local environments in which these early specimens are found (as based on the faunal assemblages) do not appear to have been dry.
Turnover Pulse Hypothesis
The hypothesis: In 1985, paleontologist Elisabeth Vbra noticed that in periods of extreme and rapid climate change, ungulates (hoofed mammals of various kinds) that had generalized diets fared better than those with specialized diets (Vrba 1988, 1998). Specialist eaters (those who rely primarily on specific food types) faced extinction at greater rates than their generalist (those who can eat more varied and variable diets) counterparts because they were unable to adapt to new environments (Vrba 2000). Thus, periods with extreme climate change would be associated with high faunal turnover: that is, the extinction of many species and the speciation, diversification, and migration of many others to occupy various niches.
The evidence: The onset of the Quaternary Ice Age, between 2.5 mya and 3 mya, brought extreme global, cyclical interglacial and glacial periods (warmer, wetter periods with less ice at the poles, and colder, drier periods with more ice near the poles). Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites (Behrensmeyer et al. 1997; Bobe and Behrensmeyer 2004). Similarly, work in the Cape Floristic Belt of South Africa shows that extreme changes in climate play a role in extinction and migration in ungulates. While this theory was originally developed for ungulates, its proponents have argued that it can be applied to hominins as well. However, the link between climate and speciation is only vaguely understood (Faith and Behrensmeyer 2013).
Interpretation(s): While the evidence of rapid faunal turnover among ungulates during this time period appears clear, there is still some debate around its usefulness as applied to the paleoanthropological record. Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct.
Variability Selection Hypothesis
The hypothesis: This hypothesis was first articulated by paleoanthropologist Richard Potts (1998). It links the high amount of climatic variability over the last 7 million years to both behavioral and morphological changes. Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context (Potts 1998, 2013). The Variability Selection Hypothesis states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations (Potts 2013).
The evidence: The evidence for this theory is similar to that for the Turnover Pulse Hypothesis: large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
Interpretation(s): In this way, the Variability Selection Hypothesis allows for a more flexible interpretation of the evolution of bipedalism in hominins and a more fluid interpretation of the Turnover Pulse Hypothesis, where species turnover is meant to be more rapid. In some ways, this hypothesis accommodates both environmental data and our interpretations of an evolution toward greater variability among species and the survivability of generalists.
Paleoenvironment Summary
Some hypotheses presented in this section pay specific attention to habitat (Savannah Hypothesis) while others point to large-scale climatic forces (Variability Selection Hypothesis). Some may be interpreted to describe the evolution of traits such as bipedalism (Savannah Hypothesis), and others generally explain the diversification of early hominins (Turnover Pulse and Variability Selection Hypotheses). While there is no consensus as to how the environment drove our evolution, it is clear that the environment shaped both habitat and resource availability in ways that would have influenced our early ancestors physically and behaviorally.
Derived Adaptations: Bipedalism
The unique form of locomotion exhibited by modern humans, called obligate bipedalism, is important in distinguishing our species from the extant (living) great apes. The ability to walk habitually upright is thus considered one of the defining attributes of the hominin lineage. We also differ from other animals that walk bipedally (such as kangaroos) in that we do not have a tail to balance us as we move.
The origin of bipedalism in hominins has been debated in paleoanthropology, but at present there are two main ideas: (theories)
- early hominins initially lived in trees, but increasingly started living on the ground, so we were a product of an arboreal last common ancestor (LCA) or,
- our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
Most research supports the first theory of an arboreal LCA based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking. This would mean that both humans and chimpanzees can be considered “derived” in terms of locomotion since chimpanzees would have independently evolved knuckle-walking.
There are many current ideas regarding selective pressures that would lead to early hominins adapting upright posture and locomotion. Many of these selective pressures, as we have seen in the previous section, coincide with a shift in environmental conditions, supported by paleoenvironmental data. In general, however, it appears that, like extant great apes, early hominins thrived in forested regions with dense tree coverage, which would indicate an arboreal lifestyle. As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse such that bipedalism would become more important.
There are several proposed selective pressures for bipedalism:
- Energy conservation: Modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land. While chimpanzees, for instance, are faster than humans terrestrially, they expend large amounts of energy being so. Adaptations to bipedalism include “stacking” the majority of the weight of the body over a small area around the center of gravity (i.e., the head is above the chest, which is above the pelvis, which is over the knees, which are above the feet). This reduces the amount of muscle needed to be engaged during locomotion to “pull us up” and allows us to travel longer distances expending far less energy.
- Thermoregulation: Less surface area (i.e., only the head and shoulders) is exposed to direct sunlight during the hottest parts of the day (i.e., midday). This means that the body has less need to employ additional “cooling” mechanisms such as sweating, which additionally means less water loss.
- Bipedalism (Freeing of Hands): This method of locomotion freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use of tools.
These selective pressures are not mutually exclusive. Bipedality could have evolved from a combination of these selective pressures, in ways that increased the chances of early hominin survival.
Skeletal Adaptations for Bipedalism

Humans have highly specialized adaptations to facilitate obligate bipedalism (Figure 9.6). Many of these adaptations occur within the soft tissue of the body (e.g., muscles and tendons). However, when analyzing the paleoanthropological record for evidence of the emergence of bipedalism, all that remains is the fossilized bone. Interpretations of locomotion are therefore often based on comparative analyses between fossil remains and the skeletons of extant primates with known locomotor behaviors. These adaptations occur throughout the skeleton and are summarized in Figure 9.7.
The majority of these adaptations occur in the postcranium (the skeleton from below the head) and are outlined in Figure 9.7. In general, these adaptations allow for greater stability and strength in the lower limb, by allowing for more shock absorption, for a larger surface area for muscle attachment, and for the “stacking” of the skeleton directly over the center of gravity to reduce energy needed to be kept upright. These adaptations often mean less flexibility in areas such as the knee and foot.
However, these adaptations come at a cost. Evolving from a nonobligate bipedal ancestor means that the adaptations we have are evolutionary compromises. For instance, the valgus knee (angle at the knee) is an essential adaptation to balance the body weight above the ankle during bipedal locomotion. However, the strain and shock absorption at an angled knee eventually takes its toll. For example, runners often experience joint pain. Similarly, the long neck of the femur absorbs stress and accommodates for a larger pelvis, but it is a weak point, resulting in hip replacements being commonplace among the elderly, especially in cases where the bone additionally weakens through osteoporosis. Finally, the S-shaped curve in our spine allows us to stand upright, relative to the more curved C-shaped spine of an LCA. Yet the weaknesses in the curves can lead to pinching of nerves and back pain. Since many of these problems primarily are only seen in old age, they can potentially be seen as an evolutionary compromise.
Despite relatively few postcranial fragments, the fossil record in early hominins indicates a complex pattern of emergence of bipedalism. Key features, such as a more anteriorly placed foramen magnum, are argued to be seen even in the earliest discovered hominins, indicating an upright posture (Dart 1925). Some early species appear to have a mix of ancestral (arboreal) and derived (bipedal) traits, which indicates a mixed locomotion and a more mosaic evolution of the trait. Some early hominins appear to, for instance, have bowl-shaped pelvises (hip bones) and angled femurs suitable for bipedalism but also have retained an opposable hallux (big toe) or curved fingers and longer arms (for arboreal locomotion). These mixed morphologies may indicate that earlier hominins were not fully obligate bipeds and thus thrived in mosaic environments.
Yet the associations between postcranial and the more diagnostic cranial fossils and bones are not always clear, muddying our understanding of the specific species to which fossils belong (Grine et al. 2022).
Region | Feature | Obligate Biped (H. sapiens) | Nonobligate Biped |
Cranium | Position of the foramen magnum | Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground). | Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground. |
Post
cranium |
Body proportions | Shorter upper limb (not used for locomotion). | Longer upper limbs (used for locomotion). |
Post
cranium |
Spinal curvature | S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis). | C-curve. |
Post
cranium |
Vertebrae | Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission). | Gracile lumbar vertebrae compared to those of modern humans. |
Post
cranium |
Pelvis | Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces. | Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface. |
Post
cranium |
Lower limb | In general, longer, more robust lower limbs and more stable, larger joints.
|
In general, smaller, more gracile limbs with more flexible joints.
|
Post
cranium |
Foot | Rigid, robust foot, without a midtarsal break.
Nonopposable and large, robust big toe (for push off while walking) and large heel for shock absorbance. |
Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping. |
It is also worth noting that, while not directly related to bipedalism per se, other postcranial adaptations are evident in the hominin fossil record from some of the earlier hominins. For instance, the hand and finger morphologies of many of the earliest hominins indicate adaptations consistent with arboreality. These include longer hands, more curved metacarpals and phalanges (long bones in the hand and fingers, respectively), and a shorter, relatively weaker thumb. This allows for gripping onto curved surfaces during locomotion. The earliest hominins appear to have mixed morphologies for both bipedalism and arborealism. However, among Australopiths (members of the genus, Australopithecus), there are indications for greater reliance on bipedalism as the primary form of locomotion. Similarly, adaptations consistent with tool manufacture (shorter fingers and a longer, more robust thumb, in contrast to the features associated with arborealism) have been argued to appear before the genus Homo.
Early Hominins: Sahelanthropus and Orrorin
We see evidence for bipedalism in some of the earliest fossil hominins, dated from within our estimates of our divergence from chimpanzees. These hominins, however, also indicate evidence for arboreal locomotion.
The earliest dated hominin find (between 6 mya and 7 mya, based on radiometric dating of volcanic tufts) has been argued to come from Chad and is named Sahelanthropus tchadensis (Figure 9.8; Brunet et al. 1995). The initial discovery was made in 2001 by Ahounta Djimdoumalbaye and announced in Nature in 2002 by a team led by French paleontologist Michel Brunet. The find has a small cranial capacity (360 cc) and smaller canines than those in extant great apes, though they are larger and pointier than those in humans. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. A short cranial base and a foramen magnum that is more humanlike in positioning have been argued to indicate upright walking.

Initially, the inclusion of Sahelanthropus in the hominin family was debated by researchers, since the evidence for bipedalism is based on cranial evidence alone, which is not as convincing as postcranial evidence. Yet, a femur (thigh bone) and ulnae (upper arm bones) thought to belong to Sahelanthropus was discovered in 2001 (although not published until 2022). These bones may support the idea that the hominin was in fact a terrestrial biped with arboreal capabilities and behaviors (Daver et al. 2022).
Orrorin tugenensis (Orrorin meaning “original man”), dated to between 6 mya and 5.7 mya, was discovered near Tugen Hills in Kenya in 2000. Smaller cheek teeth (molars and premolars) than those in even more recent hominins, thick enamel, and reduced, but apelike, canines characterize this species. This is the first species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains. One of the most important elements discovered was a proximal femur, BAR 1002'00. The femur is the thigh bone, and the proximal part is that which articulates with the pelvis; this is very important for studying posture and locomotion. This femur indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins. Some have argued that features of the finger bones suggest potential tool-making capabilities, although many researchers argue that these features are also consistent with climbing.
Early Hominins: The Genus Ardipithecus
Another genus, Ardipithecus, is argued to be represented by at least two species: Ardipithecus (Ar.) ramidus and Ar. kadabba.
Ardipithecus ramidus (“ramid” means root in the Afar language) is currently the best-known of the earliest hominins (Figure 9.9). Unlike Sahelanthropus and Orrorin, this species has a large sample size of over 110 specimens from Aramis alone. Dated to 4.4 mya, Ar. ramidus was found in Ethiopia (in the Middle Awash region and in Gona). This species was announced in 1994 by American palaeoanthropologist Tim White, based on a partial female skeleton nicknamed “Ardi” (ARA-VP-6/500; White et al. 1994). Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, she had an opposable big toe (hallux), similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. A small brain (300 cc to 350 cc), midfacial projection, and slight prognathism show retained ancestral cranial features, but the cheek bones are less flared and robust than in later hominins.

Ardipithecus kadabba (the species name means “oldest ancestor” in the Afar language) is known from localities on the western margin of the Middle Awash region, the same locality where Ar. ramidus has been found. Specimens include mandibular fragments and isolated teeth as well as a few postcranial elements from the Asa Koma (5.5 mya to 5.77 mya) and Kuseralee Members (5.2 mya), well-dated and understood (but temporally separate) volcanic layers in East Africa. This species was discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie. Originally these specimens were referred to as a subspecies of Ar. ramidus. In 2002, six teeth were discovered at Asa Koma and the dental-wear patterns confirmed that this was a distinct species, named Ar. kadabba, in 2004. One of the postcranial remains recovered included a 5.2 million-year-old toe bone that demonstrated features that are associated with toeing off (pushing off the ground with the big toe leaving last) during walking, a characteristic unique to bipedal walkers. However, the toe bone was found in the Kuseralee Member, and therefore some doubt has been cast by researchers about its association with the teeth from the Asa Koma Member.
Bipedal Trends in Early Hominins: Summary
Trends toward bipedalism are seen in our earliest hominin finds. However, many specimens also indicate retained capabilities for climbing. Trends include a larger, more robust hallux; a more compact foot, with an arch; a robust, long femur, angled at the knee; a robust tibia; a bowl-shaped pelvis; and a more anterior foramen magnum. While the level of bipedality in Salehanthropus tchadenisis is debated since there are few fossils and no postcranial evidence, Orrorin tugenensis and Ardipithecus kadabba show clear indications of some of these bipedal trends. However, some retained ancestral traits, such as an opposable hallux in Ardipithecus, indicate some retention in climbing ability.
Derived Adaptations: Early Hominin Dention
The Importance of Teeth
Teeth are abundant in the fossil record, primarily because they are already highly mineralized as they are forming, far more so than even bone. Because of this, teeth preserve readily. And, because they preserve readily, they are well-studied and better understood than many skeletal elements. In the sparse hominin (and primate) fossil record, teeth are, in some cases, all we have.
Teeth also reveal a lot about the individual from whom they came. We can tell what they evolved to eat, to which other species they may be closely related, and even, to some extent, the level of sexual dimorphism, or general variability, within a given species. This is powerful information that can be contained in a single tooth. With a little more observation, the wearing patterns on a tooth can tell us about the diet of the individual in the weeks leading up to its death. Furthermore, the way in which a tooth is formed, and the timing of formation, can reveal information about changes in diet (or even mobility) over infancy and childhood, using isotopic analyses. When it comes to our earliest hominin relatives, this information is vital for understanding how they lived.
The purpose of comparing different hominin species is to better understand the functional morphology as it applies to dentition. In this, we mean that the morphology of the teeth or masticatory system (which includes jaws) can reveal something about the way in which they were used and, therefore, the kinds of foods these hominins ate. When comparing the features of hominin groups, it is worth considering modern analogues (i.e., animals with which to compare) to make more appropriate assumptions about diet. In this way, hominin dentition is often compared with that of chimpanzees and gorillas (our close ape relatives), as well as with that of modern humans.
The most divergent group, however, is humans. Humans around the world have incredibly varied diets. Among hunter-gatherers, it can vary from a honey- and plant-rich diet, as seen in the Hadza in Tanzania, to a diet almost entirely reliant on animal fat and protein, as seen in Inuits in polar regions of the world. We are therefore considered generalists, more general than the largely frugivorous (fruit-eating) chimpanzee or the folivorous (foliage-eating) gorilla, as discussed in Chapter 5.
One way in which all humans are similar is our reliance on the processing of our food. We cut up and tear meat with tools using our hands, instead of using our front teeth (incisors and canines). We smash and grind up hard seeds, instead of crushing them with our hind teeth (molars). This means that, unlike our ape relatives, we can rely more on developing tools to navigate our complex and varied diets. (We could say) Our brain, therefore, is our primary masticatory organ. Evolutionarily, our teeth have reduced in size and our faces are flatter, or more orthognathic, partially in response to our increased reliance on our hands and brain to process food. Similarly, a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat. These trends begin early on in our evolution. The link has been made between some of the earliest evidence for stone tool manufacture, the earliest members of our genus, and the features that we associate with these specimens.
General Dental Trends in Early Hominins
Several trends are visible in the dentition of early hominins. However, all tend to have the same dental formula. The dental formula tells us how many of each tooth type are present in each quadrant of the mouth. Going from the front of the mouth, this includes the square, flat incisors; the pointy canines; the small, flatter premolars; and the larger hind molars. In many primates, from Old World monkeys to great apes, the typical dental formula is 2:1:2:3. This means that if we divide the mouth into quadrants, each has two incisors, one canine, two premolars, and three molars. The eight teeth per quadrant total 32 teeth in all (although some humans have fewer teeth due to the absence of their wisdom teeth, or third molars).

The morphology of the individual teeth is where we see the most change. Among primates, large incisors are associated with food procurement or preparation (such as biting small fruits), while small incisors indicate a diet that may contain small seeds or leaves (where the preparation is primarily in the back of the mouth). Most hominins have relatively large, flat, vertically aligned incisors that occlude (touch) relatively well, forming a “bite.” This differs from, for instance, the orangutan, whose teeth stick out (i.e., are procumbent).
While the teeth are often aligned with diet, the canines may be misleading in that regard. We tend to associate pointy, large canines with the ripping required for meat, and the reduction (or, in some animals, the absence) of canines as indicative of herbivorous diets. In humans, our canines are often a similar size to our incisors and therefore considered incisiform (Figure 9.10). However, our closest relatives all have very long, pointy canines, particularly on their upper dentition. This is true even for the gorilla, which lives almost exclusively on plants. The canines in these instances reveal more about social structure and sexual dimorphism than diet, as large canines often signal dominance.
Early on in human evolution, we see a reduction in canine size. Sahelanthropus tchadensis and Orrorin tugenensis both have smaller canines than those in extant great apes, yet the canines are still larger and pointier than those in humans or more recent hominins. This implies strongly that, over evolutionary time, the need for display and dominance among males has reduced, as has our sexual dimorphism. In Ardipithecus ramidus, there is no obvious difference between male and female canine size, yet they are still slightly larger and pointier than in modern humans. This implies a less sexually dimorphic social structure in the earlier hominins relative to modern-day chimpanzees and gorillas.
Along with a reduction in canine size is the reduction or elimination of a canine diastema: a gap between the teeth on the mandible that allows room for elongated teeth on the maxilla to “fit” in the mouth. Absence of a diastema is an excellent indication of a reduction in canine size. In animals with large canines (such as baboons), there is also often a honing P3, where the first premolar (also known as P3 for evolutionary reasons) is triangular in shape, “sharpened” by the extended canine from the upper dentition. This is also seen in some early hominins: Ardipithecus, for example, has small canines that are almost the same height as its incisors, although still larger than those in recent hominins.
The hind dentition, such as the bicuspid (two cusped) premolars or the much larger molars, are also highly indicative of a generalist diet in hominins. Among the earliest hominins, the molars are larger than we see in our genus, increasing in size to the back of the mouth and angled in such a way from the much smaller anterior dentition as to give these hominins a parabolic (V-shaped) dental arch. This differs from our living relatives and some early hominins, such as Sahelanthropus, whose molars and premolars are relatively parallel between the left and right sides of the mouth, creating a U-shape.
Among more recent early hominins, the molars are larger than those in the earliest hominins and far larger than those in our own genus, Homo. Large, short molars with thick enamel allowed our early cousins to grind fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing. In our genus, the hind dentition is far smaller than in these early hominins. Our teeth also have medium-size cusps, which allow for both efficient grinding and tearing/shearing meats.
Understanding the dental morphology has allowed researchers to extrapolate very specific behaviors of early hominins. It is worth noting that while teeth preserve well and are abundant, a slew of other morphological traits additionally provide evidence for many of these hypotheses. Yet there are some traits that are ambiguous. For instance, while there are definitely high levels of sexual dimorphism in Au. afarensis, discussed in the next section, the canine teeth are reduced in size, implying that while canines may be useful indicators for sexual dimorphism, it is also worth considering other evidence.
In summary, trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the ancestral dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
Special Topic: Contested Species
Many named species are highly debated and argued to have specimens associated with a more variable Au. afarensis or Au. anamensis species. Sometimes these specimens are dated to times when, or found in places in which, there are “gaps” in the palaeoanthropological record. These are argued to represent chronospecies or variants of Au. afarensis. However, it is possible that, with more discoveries, the distinct species types will hold.
Australopithecus bahrelghazali is dated to within the time period of Au. afarensis (3.6 mya; Brunet et al. 1995) and was the first Australopithecine to be discovered in Chad in central Africa. Researchers argue that the holotype, whom discoverers have named “Abel,” falls under the range of variation of Au. afarensis and therefore that A. bahrelghazali does not fall into a new species (Lebatard et al. 2008). If “Abel” is a member of Au. afarensis, the geographic range of the species would be greatly extended.
On a different note, Australopithecus deyiremada (meaning “close relative” in the Ethiopian language of Afar) is dated to 3.5 mya to 3.3 mya and is based on fossil mandible bones discovered in 2011 in Woranso-Mille (in the Afar region of Ethiopia) by Yohannes Haile-Selassie, an Ethiopian paleoanthropologist (Haile-Selassie et al. 2019). The discovery indicated, in contrast to Au. afarensis, smaller teeth with thicker enamel (potentially suggesting a harder diet) as well as a larger mandible and more projecting cheekbones. This find may be evidence that more than one closely related hominin species occupied the same region at the same temporal period (Haile-Selassie et al. 2015; Spoor 2015) or that other Au. afarensis specimens have been incorrectly designated. However, others have argued that this species has been prematurely identified and that more evidence is needed before splitting the taxa, since the variation appears subtle and may be due to slightly different niche occupations between populations over time.
Australopithecus garhi is another species found in the Middle Awash region of Ethiopia. It is currently dated to 2.5 mya (younger than Au. afarensis). Researchers have suggested it fills in a much-needed temporal “gap” between hominin finds in the region, with some anatomical differences, such as a relatively large cranial capacity (450 cc) and larger hind dentition than seen in other gracile Australopithecines. Similarly, the species has been argued to have longer hind limbs than Au. afarensis, although it was still able to move arboreally (Asfaw et al. 1999). However, this species is not well documented or understood and is based on only several fossil specimens. More astonishingly, crude stone tools resembling Oldowan (which will be described later) have been found in association with Au. garhi. While lacking some of the features of the Oldowan, this is one of the earliest technologies found in direct association with a hominin.
Kenyanthopus platyops (the name “platyops” refers to its flatter-faced appearance) is a highly contested genus/species designation of a specimen (KNM-WT 40000) from Lake Turkana in Kenya, discovered by Maeve Leakey in 1999 (Figure 9.11). Dated to between 3.5 mya and 3.2 mya, some have suggested this specimen is an Australopithecus, perhaps even Au. afarensis (with a brain size which is difficult to determine, yet appears small), while still others have placed this specimen in Homo (small dentition and flat-orthognathic face). While taxonomic placing of this species is quite divided, the discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis (Leakey et al. 2001). Some researchers have additionally associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this specimen.

The Genus Australopithecus
The Australopithecines are a diverse group of hominins, comprising various species. Australopithecus is the given group or genus name. It stems from the Latin word Australo, meaning “southern,” and the Greek word pithecus, meaning “ape.” Within this section, we will outline these differing species’ geological and temporal distributions across Africa, unique derived and/or shared traits, and importance in the fossil record.

Between 3 mya and 1 mya, there seems to be differences in dietary strategy between different species of hominins designated as Australopithecines. A pattern of larger posterior dentition (even relative to the incisors and canines in the front of the mouth), thick enamel, and cranial evidence for extremely large chewing muscles is far more pronounced in a group known as the robust australopithecines. This pattern is extremely relative to their earlier contemporaries or predecessors, the gracile australopithecines, and is certainly larger than those seen in early Homo, which emerged during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins (Figure 9.12).
Because of these differences, this section has been divided into “gracile” and “robust” Australopithecines, highlighting the morphological differences between the two groups (which many researchers have designated as separate genera: Australopithecus and Paranthropus, respectively) and then focusing on the individual species. It is worth noting, however, that not all researchers accept these clades as biologically or genetically distinct, with some researchers insisting that the relative gracile and robust features found in these species are due to parallel evolutionary events toward similar dietary niches.
Despite this genus’ ancestral traits and small cranial capacity, all members show evidence of bipedal locomotion. It is generally accepted that Australopithecus species display varying degrees of arborealism along with bipedality.
Gracile Australopithecines
This section describes individual species from across Africa. These species are called “gracile australopithecines” because of their smaller and less robust features compared to the divergent “robust” group. Numerous Australopithecine species have been named, but some are only based on a handful of fossil finds, whose designations are controversial.
East African Australopithecines
East African Australopithecines are found throughout the EARS, and they include the earliest species associated with this genus. Numerous fossil-yielding sites, such as Olduvai, Turkana, and Laetoli, have excellent, datable stratigraphy, owing to the layers of volcanic tufts that have accumulated over millions of years. These tufts may be dated using absolute dating techniques, such as Potassium-Argon dating (described in Chapter 7). This means that it is possible to know a relatively refined date for any fossil if the context (i.e., exact location) of that find is known. Similarly, comparisons between the faunal assemblages of these stratigraphic layers have allowed researchers to chronologically identify environmental changes.

The earliest known Australopithecine is dated to 4.2 mya to 3.8 mya. Australopithecus anamensis (after “Anam,” meaning “lake” from the Turkana region in Kenya; Leakey et al. 1995; Patterson and Howells 1967) is currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia; Figure 9.13). Recently, a 2019 find from Ethiopia, named MRD, after Miro Dora where it was found, was discovered by an Ethiopian herder named Ali Bereino. It is one of the most complete cranial finds of this species (Ward et al. 1999). A small brain size (370 cc), relatively large canines, projecting cheekbones, and earholes show more ancestral features as compared to those of more recent Australopithecines. The most important element discovered with this species is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking. Similarly, the earliest found hominin femur belongs to this species. Ancestral traits in the upper limb (such as the humerus) indicate some retained arboreal locomotion.
Some researchers suggest that Au. anamensis is an intermediate form of the chronospecies that becomes Au. afarensis, evolving from Ar. ramidus. However, this is debated, with other researchers suggesting morphological similarities and affinities with more recent species instead. Almost 100 specimens, representing over 20 individuals, have been found to date (Leakey et al. 1995; McHenry 2009; Ward et al. 1999).
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. Au. afarensis (which means “from the Afar region”) is dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia (Figure 9.14). The most famous individual from this species is a partial female skeleton discovered in Hadar (Ethiopia), later nicknamed “Lucy,” after the Beatles’ song “Lucy in the Sky with Diamonds,” which was played in celebration of the find (Johanson et al. 1978; Kimbel and Delezene 2009). This skeleton was found in 1974 by Donald Johanson and dates to approximately 3.2 mya. In addition, in 2002 a juvenile of the species was found by Zeresenay Alemseged and given the name “Selam” (meaning “peace,” DIK 1-1), though it is popularly known as “Lucy’s Child” or as the “Dikika Child” (Alemseged et al. 2006). Similarly, the “Laetoli Footprints” (discussed in Chapter 7; Hay and Leakey 1982; Leakey and Hay 1979) have drawn much attention.


The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans (indicative of a generalist diet); in addition, Au. afarensis has a prognathic face (the face below the eyes juts anteriorly) and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus. Despite a reduction in canine size in this species, large overall size variation indicates high levels of sexual dimorphism.
Skeletal evidence indicates that this species was bipedal, as its pelvis and lower limb demonstrate a humanlike femoral neck, valgus knee, and bowl-shaped hip (Figure 9.15). More evidence of bipedalism is found in the footprints of this species. Au. afarensis is associated with the Laetoli Footprints, a 24-meter trackway of hominin fossil footprints preserved in volcanic ash discovered by Mary Leakey in Tanzania and dated to 3.5 mya to 3 mya. This set of prints is thought to have been produced by three bipedal individuals as there are no knuckle imprints, no opposable big toes, and a clear arch is present. The infants of this species are thought to have been more arboreal than the adults, as discovered through analyses of the foot bones of the Dikika Child dated to 3.32 mya (Alemseged et al. 2006).
Although not found in direct association with stone tools, potential evidence for cut marks on bones, found at Dikika, and dated to 3.39 mya indicates a possible temporal/ geographic overlap between meat eating, tool use, and this species. However, this evidence is fiercely debated. Others have associated the cut marks with the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species.
South African Australopithecines
Since the discovery of the Taung Child, there have been numerous Australopithecine discoveries from the region known as “The Cradle of Humankind,” which was recently given UNESCO World Heritage Site status as “The Fossil Hominid Sites of South Africa.” The limestone caves found in the Cradle allow for the excellent preservation of fossils. Past animals navigating the landscape and falling into cave openings, or caves used as dens by carnivores, led to the accumulation of deposits over millions of years. Many of the hominin fossils, encased in breccia (hard, calcareous sedimentary rock), are recently exposed from limestone quarries mined in the previous century. This means that extracting fossils requires excellent and detailed exposed work, often by a team of skilled technicians.
While these sites have historically been difficult to date, with mixed assemblages accumulated over large time periods, advances in techniques such as uranium-series dating have allowed for greater accuracy. Historically, the excellent faunal record from East Africa has been used to compare sites based on relative dating, whereby environmental and faunal changes and extinction events allow us to know which hominin finds are relatively younger or older than others.
The discovery of the Taung Child in 1924 (discussed in the Special Topic box “The Taung Child” below) shifted the focus of palaeoanthropological research from Europe to Africa, although acceptance of this shift was slow (Broom 1947; Dart 1925). The species to which it is assigned, Australopithecus africanus (name meaning “Southern Ape of Africa”), is currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa (Figure 9.16). A relatively large brain (400 cc to 500 cc), small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits. Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism. However, the sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some ancestral features. Although not in direct association with stone tools, a 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities.

Another famous Au. africanus skull (the skull of “Mrs. Ples”) was previously attributed to Plesianthropus transvaalensis, meaning “near human from the Transvaal,” the old name for Gauteng Province, South Africa (Broom 1947, 1950). The name was shortened by contemporary journalists to “Ples” (Figure 9.17). Due to the prevailing mores of the time, the assumed female found herself married, at least in name, and has become widely known as “Mrs. Ples.” It was later reassigned to Au. africanus and is now argued by some to be a young male rather than an adult female cranium (Thackeray 2000, Thackeray et al. 2002).

In 2008, nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger, noted a clavicle bone in some leftover mining breccia in the Malapa Fossil Site (South Africa). After rigorous studies, the species, Australopithecus sediba (meaning “fountain” or “wellspring” in the South African language of Sesotho), was named in 2010 (Figure 9.18; Berger et al. 2010). The first type specimen belongs to a juvenile male, Karabo (MH1), but the species is known from at least six partial skeletons, from infants through adults. These specimens are currently dated to 1.97 mya (Dirks et al. 2010). The discoverers have argued that Au. sediba shows mosaic features between Au. africanus and the genus, Homo, which potentially indicates a transitional species, although this is heavily debated. These features include a small brain size (Australopithecus-like; 420 cc to 450 cc) but gracile mandible and small teeth (Homo-like). Similarly, the postcranial skeletons are also said to have mosaic features: scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. Some researchers have argued that Au. sediba shows a modern hand morphology (shorter fingers and a longer thumb), indicating that adaptations to tool manufacture and use may be present in this species.

Another famous Australopithecine find from South Africa is that of the nearly complete skeleton now known as “Little Foot” (Clarke 1998, 2013). Little Foot (StW 573) is potentially the earliest dated South African hominin fossil, dating to 3.7 mya, based on radiostopic techniques, although some argue that it is younger than 3 mya (Pickering and Kramers 2010). The name is jokingly in contrast to the cryptid species “bigfoot” and is named because the initial discovery of four ankle bones indicated bipedality. Little Foot was discovered by Ron Clarke in 1994, when he came across the ankle bones while sorting through monkey fossils in the University of Witwatersrand collections (Clarke and Tobias 1995). He asked Stephen Motsumi and Nkwane Molefe to identify the known records of the fossils, which allowed them to find the rest of the specimen within just days of searching the Sterkfontein Caves’ Silberberg Grotto.
The discoverers of Little Foot insist that other fossil finds, previously identified as Au. Africanus, be placed in this new species based on shared ancestral traits with older East African Australopithecines (Clarke and Kuman 2019). These include features such as a relatively large brain size (408 cc), robust zygomatic arch, and a flatter midface. Furthermore, the discoverers have argued that the heavy anterior dental wear patterns, relatively large anterior dentition, and smaller hind dentition of this specimen more closely resemble that of Au. anamensis or Au. afarensis. It has thus been placed in the species Australopithecus prometheus. This species name refers to a previously defunct taxon named by Raymond Dart. The species designation was, through analyzing Little Foot, revived by Ron Clarke, who insists that many other fossil hominin specimens have prematurely been placed into Au. africanus. Others say that it is more likely that Au. africanus is a more variable species and not representative of two distinct species.
Paranthropus “Robust” Australopithecines
In the robust australopithecines, the specialized nature of the teeth and masticatory system, such as flaring zygomatic arches (cheekbones), accommodate very large temporalis (chewing) muscles. These features also include a large, broad, dish-shaped face and and a large mandible with extremely large posterior dentition (referred to as megadonts) and hyper-thick enamel (Kimbel 2015; Lee-Thorp 2011; Wood 2010). Research has revolved around the shared adaptations of these “robust” australopithecines, linking their morphologies to a diet of hard and/or tough foods (Brain 1967; Rak 1988). Some argued that the diet of the robust australopithecines was so specific that any change in environment would have accelerated their extinction. The generalist nature of the teeth of the gracile australopithecines, and of early Homo, would have made them more capable of adapting to environmental change. However, some have suggested that the features of the robust australopithecines might have developed as an effective response to what are known as fallback foods in hard times rather than indicating a lack of adaptability.
There are currently three widely accepted robust australopithecus or, Paranthropus, species: P. aethiopicus, which has more ancestral traits, and P. boisei and P. robustus, which are more derived in their features (Strait et al. 1997; Wood and Schroer 2017). These three species have been grouped together by a majority of scholars as a single genus as they share more derived features (are more closely related to each other; or, in other words, are monophyletic) than the other australopithecines (Grine 1988; Hlazo 2015; Strait et al. 1997; Wood 2010 ). While researchers have mostly agreed to use the umbrella term Paranthropus, there are those who disagree (Constantino and Wood 2004, 2007; Wood 2010).
As a collective, this genus spans 2.7 mya to 1.0 mya, although the dates of the individual species differ. The earliest of the Paranthropus species, Paranthropus aethiopicus, is dated to between 2.7 mya and 2.3 mya and currently found in Tanzania, Kenya, and Ethiopia in the EARS system (Figure 9.19; Constantino and Wood 2007; Hlazo 2015; Kimbel 2015; Walker et al. 1986; White 1988). It is well known because of one specimen known as the “Black Skull” (KNM–WT 17000), so called because of the mineral manganese that stained it black during fossilization (Kimbel 2015). As with all robust Australopithecines, P. aethiopicus has the shared derived traits of large, flat premolars and molars; large, flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle); a sagittal crest (ridge on the top of the skull) for increased muscle attachment of the chewing muscles to the skull; and a robust mandible and supraorbital torus (brow ridge). However, only a few teeth have been found. A proximal tibia indicates bipedality and similar body size to Au. afarensis. In recent years, researchers have discovered and assigned a proximal tibia and juvenile cranium (L.338y-6) to the species (Wood and Boyle 2016).

First attributed as Zinjanthropus boisei (with the first discovery going by the nickname “Zinj” or sometimes “Nutcracker Man”), Paranthropus boisei was discovered in 1959 by Mary Leakey (see Figure 9.20 and 9.21; Hay 1990; Leakey 1959). This “robust” australopith species is distributed across countries in East Africa at sites such as Kenya (Koobi Fora, West Turkana, and Chesowanja), Malawi (Malema-Chiwondo), Tanzania (Olduvai Gorge and Peninj), and Ethiopia (Omo River Basin and Konso). The hypodigm, sample of fossils whose features define the group, has been found by researchers to date to roughly 2.4 mya to 1.4 mya. Due to the nature of its exaggerated, larger, and more robust features, P. boisei has been termed hyper-robust—that is, even more heavily built than other robust species, with very large, flat posterior dentition (Kimbel 2015). Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). Another famous specimen from this species is the Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu.


Paranthropus robustus was the first taxon to be discovered within the genus in Kromdraai B by a schoolboy named Gert Terblanche; subsequent fossil discoveries were made by researcher Robert Broom in 1938 (Figure 9.22; Broom 1938a, 1938b, 1950), with the holotype specimen TM 1517 (Broom 1938a, 1938b, 1950; Hlazo 2018). Paranthropus robustus dates approximately from 2.0 mya to 1 mya and is the only taxon from the genus to be discovered in South Africa. Several of these fossils are fragmentary in nature, distorted, and not well preserved because they have been recovered from quarry breccia using explosives. P. robustus features are neither as “hyper-robust” as P. boisei nor as ancestral as P. aethiopicus; instead, they have been described as being less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring; Rak 1983; Walker and Leakey 1988). Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick-enameled dentition.

Comparisons between Gracile and Robust Australopiths
Comparisons between gracile and robust australopithecines may indicate different phylogenetic groupings or parallel evolution in several species. In general, the robust australopithecines have large temporalis (chewing) muscles, as indicated by flaring zygomatic arches, sagittal crests, and robust mandibles (jawbones). Their hind dentition is large (megadont), with low cusps and thick enamel. Within the gracile australopithecines, researchers have debated the relatedness of the species, or even whether these species should be lumped together to represent more variable or polytypic species. Often researchers will attempt to draw chronospecific trajectories, with one taxon said to evolve into another over time.
Special Topic: The Taung Child

The well-known fossil of a juvenile Australopithecine, the “Taung Child,” was the first early hominin evidence ever discovered and was the first to demonstrate our common human heritage in Africa (Figure 9.23; Dart 1925). The tiny facial skeleton and natural endocast were discovered in 1924 by a local quarryman in the North West Province in South Africa and were painstakingly removed from the surrounding cement-like breccia by Raymond Dart using his wife’s knitting needles. When first shared with the scientific community in 1925, it was discounted as being nothing more than a young monkey of some kind. Prevailing biases of the time made it too difficult to contemplate that this small-brained hominin could have anything to do with our own history. The fact that it was discovered in Africa simply served to strengthen this bias.
Early Tool Use and Technology
Early Stone Age Technology (ESA)
The Early Stone Age (ESA) marks the beginning of recognizable technology made by our human ancestors. Stone-tool (or lithic) technology is defined by the fracturing of rocks and the manufacture of tools through a process called knapping. The Stone Age lasted for more than 3 million years and is broken up into chronological periods called the Early (ESA), Middle (MSA), and Later Stone Ages (LSA). Each period is further broken up into a different techno-complex, a term encompassing multiple assemblages (collections of artifacts) that share similar traits in terms of artifact production and morphology. The ESA spanned the largest technological time period of human innovation from over 3 million years ago to around 300,000 years ago and is associated almost entirely with hominin species prior to modern Homo sapiens. As the ESA advanced, stone tool makers (known as knappers) began to change the ways they detached flakes and eventually were able to shape artifacts into functional tools. These advances in technology go together with the developments in human evolution and cognition, dispersal of populations across the African continent and the world, and climatic changes.
In order to understand the ESA, it is important to consider that not all assemblages are exactly the same within each techno-complex: one can have multiple phases and traditions at different sites (Lombard et al. 2012). However, there is an overarching commonality between them. Within stone tool assemblages, both flakes or cores (the rocks from which flakes are removed) are used as tools. Large Cutting Tools (LCTs) are tools that are shaped to have functional edges. It is important to note that the information presented here is a small fraction of what is known about the ESA, and there are ongoing debates and discoveries within archaeology.
Currently, the oldest-known stone tools, which form the techno-complex the Lomekwian, date to 3.3 mya (Harmand et al. 2015; Toth 1985). They were found at a site called Lomekwi 3 in Kenya. This techno-complex is the most recently defined and pushed back the oldest-known date for lithic technology. There is only one known site thus far and, due to the age of the site, it is associated with species prior to Homo, such as Kenyanthropus platyops. Flakes were produced through indirect percussion, whereby the knappers held a rock and hit it against another rock resting on the ground. The pieces are very chunky and do not display the same fracture patterns seen in later techno-complexes. Lomekwian knappers likely aimed to get a sharp-edged piece on a flake, which would have been functional, although the specific function is currently unknown.
Stone tool use, however, is not only understood through the direct discovery of the tools. Cut marks on fossilized animal bones may illuminate the functionality of stone tools. In one controversial study in 2010, researchers argued that cut marks on a pair of animal bones from Dikika (Ethiopia), dated to 3.4 mya, were from stone tools. The discoverers suggested that they be more securely associated, temporally, with Au. afarensis. However, others have noted that these marks are consistent with teeth marks from crocodiles and other carnivores.

The Oldowan techno-complex is far more established in the scientific literature (Leakey 1971). It is called the Oldowan because it was originally discovered in Olduvai Gorge, Tanzania, but the oldest assemblage is from Gona in Ethiopia, dated to 2.6 mya (Semaw 2000). The techno-complex is defined as a core and flake industry. Like the Lomekwian, there was an aim to get sharp-edged flakes, but this was achieved through a different production method. Knappers were able to actively hold or manipulate the core being knapped, which they could directly hit using a hammerstone. This technique is known as free-hand percussion, and it demonstrates an understanding of fracture mechanics. It has long been argued that the Oldowan hominins were skillful in tool manufacture.
Because Oldowan knapping requires skill, earlier researchers have attributed these tools to members of our genus, Homo. However, some have argued that these tools are in more direct association with hominins in the genera described in this chapter (Figure 9.24).
Invisible Tool Manufacture and Use
The vast majority of our understanding of these early hominins comes from fossils and reconstructed paleoenvironments. It is only from 3 mya when we can start “looking into their minds” and lifestyles by analyzing their manufacture and use of stone tools. However, the vast majority of tool use in primates (and, one can argue, in humans) is not with durable materials like stone. All of our extant great ape relatives have been observed using sticks, leaves, and other materials for some secondary purpose (to wade across rivers, to “fish” for termites, or to absorb water for drinking). It is possible that the majority of early hominin tool use and manufacture may be invisible to us because of this preservation bias.
Chapter Summary
The fossil record of our earliest hominin relatives has allowed paleoanthropologists to unpack some of the mysteries of our evolution. We now know that traits associated with bipedalism evolved before other “human-like” traits, even though the first hominins were still very capable of arboreal locomotion. We also know that, for much of this time, hominin taxa were diverse in the way they looked and what they ate, and they were widely distributed across the African continent. And we know that the environments in which these hominins lived underwent many changes over this time during several warming and cooling phases.
Yet this knowledge has opened up many new mysteries. We still need to better differentiate some taxa. In addition, there are ongoing debates about why certain traits evolved and what they meant for the extinction of some of our relatives (like the robust australopiths). The capabilities of these early hominins with respect to tool use and manufacture is also still uncertain.
Hominin Species Summaries
Hominin |
Sahelanthropus tchadensis |
Dates |
7 mya to 6 mya |
Region(s) |
Chad |
Famous discoveries |
The initial discovery, made in 2001. |
Brain size |
360 cc average |
Dentition |
Smaller than in extant great apes; larger and pointier than in humans. Canines worn at the tips. |
Cranial features |
A short cranial base and a foramen magnum (hole in which the spinal cord enters the cranium) that is more humanlike in positioning; has been argued to indicate upright walking. |
Postcranial features |
Currently little published postcranial material. |
Culture |
N/A |
Other |
The extent to which this hominin was bipedal is currently heavily debated. If so, it would indicate an arboreal bipedal ancestor of hominins, not a knuckle-walker like chimpanzees. |
Hominin |
Orrorin tugenensis |
Dates |
6 mya to 5.7 mya |
Region(s) |
Tugen Hills (Kenya) |
Famous discoveries |
Original discovery in 2000. |
Brain size |
N/A |
Dentition |
Smaller cheek teeth (molars and premolars) than even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines. |
Cranial features |
Not many found |
Postcranial features |
Fragmentary leg, arm, and finger bones have been found. Indicates bipedal locomotion. |
Culture |
Potential toolmaking capability based on hand morphology, but nothing found directly. |
Other |
This is the earliest species that clearly indicates adaptations for bipedal locomotion. |
Hominin |
Ardipithecus kadabba |
Dates |
5.2 mya to 5.8 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
Discovered by Yohannes Haile-Selassie in 1997. |
Brain size |
N/A |
Dentition |
Larger hind dentition than in modern chimpanzees. Thick enamel and larger canines than in later hominins. |
Cranial features |
N/A |
Postcranial features |
A large hallux (big toe) bone indicates a bipedal “push off.” |
Culture |
N/A |
Other |
Faunal evidence indicates a mixed grassland/woodland environment. |
Hominin |
Ardipithecus ramidus |
Dates |
4.4 mya |
Region(s) |
Middle Awash region and Gona (Ethiopia) |
Famous discoveries |
A partial female skeleton nicknamed “Ardi” (ARA-VP-6/500) (found in 1994). |
Brain size |
300 cc to 350 cc |
Dentition |
Little differences between the canines of males and females (small sexual dimorphism). |
Cranial features |
Midfacial projection, slightly prognathic. Cheekbones less flared and robust than in later hominins. |
Postcranial features |
Ardi demonstrates a mosaic of ancestral and derived characteristics in the postcrania. For instance, an opposable big toe similar to chimpanzees (i.e., more ancestral), which could have aided in climbing trees effectively. However, the pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status. |
Culture |
None directly associated |
Other |
Over 110 specimens from Aramis |
Hominin |
Australopithecus anamensis |
Dates |
4.2 mya to 3.8 mya |
Region(s) |
Turkana region (Kenya); Middle Awash (Ethiopia) |
Famous discoveries |
A 2019 find from Ethiopia, named MRD. |
Brain size |
370 cc |
Dentition |
Relatively large canines compared with more recent Australopithecines. |
Cranial features |
Projecting cheekbones and ancestral earholes. |
Postcranial features |
Lower limb bones (tibia and femur) indicate bipedality; arboreal features in upper limb bones (humerus) found. |
Culture |
N/A |
Other |
Almost 100 specimens, representing over 20 individuals, have been found to date. |
Hominin |
Australopithecus afarensis |
Dates |
3.9 mya to 2.9 mya |
Region(s) |
Afar Region, Omo, Maka, Fejej, and Belohdelie (Ethiopia); Laetoli (Tanzania); Koobi Fora (Kenya) |
Famous discoveries |
Lucy (discovery: 1974), Selam (Dikika Child, discovery: 2000), Laetoli Footprints (discovery: 1976). |
Brain size |
380 cc to 430 cc |
Dentition |
Reduced canines and molars relative to great apes but larger than in modern humans. |
Cranial features |
Prognathic face, facial features indicate relatively strong chewing musculature (compared with Homo) but less extreme than in Paranthropus. |
Postcranial features |
Clear evidence for bipedalism from lower limb postcranial bones. Laetoli Footprints indicate humanlike walking. Dikika Child bones indicate retained ancestral arboreal traits in the postcrania. |
Culture |
None directly, but close in age and proximity to controversial cut marks at Dikika and early tools in Lomekwi. |
Other |
Au. afarensis is one of the oldest and most well-known australopithecine species and consists of a large number of fossil remains. |
Hominin |
Australopithecus bahrelghazali |
Dates |
3.6 mya |
Region(s) |
Chad |
Famous discoveries |
“Abel,” the holotype (discovery: 1995). |
Brain size |
N/A |
Dentition |
N/A |
Cranial features |
N/A |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Arguably within range of variation of Au. afarensis. |
Hominin |
Australopithecus prometheus |
Dates |
3.7 mya (debated) |
Region(s) |
Sterkfontein (South Africa) |
Famous discoveries |
“Little Foot” (StW 573) (discovery: 1994) |
Brain size |
408 cc (Little Foot estimate) |
Dentition |
Heavy anterior dental wear patterns, relatively large anterior dentition and smaller hind dentition, similar to Au. afarensis. |
Cranial features |
Relatively larger brain size, robust zygomatic arch, and a flatter midface. |
Postcranial features |
The initial discovery of four ankle bones indicated bipedality. |
Culture |
N/A |
Other |
Highly debated new species designation. |
Hominin |
Australopithecus deyiremada |
Dates |
3.5 mya to 3.3 mya |
Region(s) |
Woranso-Mille (Afar region, Ethiopia) |
Famous discoveries |
First fossil mandible bones were discovered in 2011 in the Afar region of Ethiopia by Yohannes Haile-Selassie. |
Brain size |
N/A |
Dentition |
Smaller teeth with thicker enamel than seen in Au. afarensis, with a potentially hardier diet. |
Cranial features |
Larger mandible and more projecting cheekbones than in Au. afarensis. |
Postcranial features |
N/A |
Culture |
N/A |
Other |
Contested species designation; arguably a member of Au. afarensis. |
Hominin |
Kenyanthopus platyops |
Dates |
3.5 mya to 3.2 mya |
Region(s) |
Lake Turkana (Kenya) |
Famous discoveries |
KNM–WT 40000 (discovered 1999) |
Brain size |
Difficult to determine but appears within the range of Australopithecus afarensis. |
Dentition |
Small molars/dentition (Homo-like characteristic) |
Cranial features |
Flatter (i.e., orthognathic) face |
Postcranial features |
N/A |
Culture |
Some have associated the earliest tool finds from Lomekwi, Kenya, temporally (3.3 mya) and in close geographic proximity to this species/specimen. |
Other |
Taxonomic placing of this species is quite divided. The discoverers have argued that this species is ancestral to Homo, in particular to Homo ruldolfensis. |
Hominin |
Australopithecus africanus |
Dates |
3.3 mya to 2.1 mya |
Region(s) |
Sterkfontein, Taung, Makapansgat, Gladysvale (South Africa) |
Famous discoveries |
Taung Child (discovery in 1994), “Mrs. Ples” (discover in 1947), Little Foot (arguable; discovery in 1994). |
Brain size |
400 cc to 500 cc |
Dentition |
Smaller teeth (derived) relative to Au. afarensis. Small canines with no diastema. |
Cranial features |
A rounder skull compared with Au. afarensis in East Africa. A sloping face (ancestral). |
Postcranial features |
Similar postcranial evidence for bipedal locomotion (derived pelvis) with retained arboreal locomotion, e.g., curved phalanges (fingers), as seen in Au. afarensis. |
Culture |
None with direct evidence. |
Other |
A 2015 study noted that the trabecular bone morphology of the hand was consistent with forceful tool manufacture and use, suggesting potential early tool abilities. |
Hominin |
Australopithecus garhi |
Dates |
2.5 mya |
Region(s) |
Middle Awash (Ethiopia) |
Famous discoveries |
N/A |
Brain size |
450 cc |
Dentition |
Larger hind dentition than seen in other gracile Australopithecines. |
Cranial features |
N/A |
Postcranial features |
A femur of a fragmentary partial skeleton, argued to belong to Au. garhi, indicates this species may be longer-limbed than Au. afarensis, although still able to move arboreally. |
Culture |
Crude stone tools resembling Oldowan (described later) have been found in association with Au. garhi. |
Other |
This species is not well documented or understood and is based on only a few fossil specimens. |
Hominin |
Paranthropus aethiopicus |
Dates |
2.7 mya to 2.3 mya |
Region(s) |
West Turkana (Kenya); Laetoli (Tanzania); Omo River Basin (Ethiopia) |
Famous discoveries |
The “Black Skull” (KNM–WT 17000) (discovery 1985). |
Brain Size |
410 cc |
Dentition |
P. aethiopicus has the shared derived traits of large flat premolars and molars, although few teeth have been found. |
Cranial features |
Large flaring zygomatic arches for accommodating large chewing muscles (the temporalis muscle), a sagittal crest for increased muscle attachment of the chewing muscles to the skull, and a robust mandible and supraorbital torus (brow ridge). |
Postcranial features |
A proximal tibia indicates bipedality and similar size to Au. afarensis. |
Culture |
N/A |
Other |
The “Black Skull” is so called because of the mineral manganese that stained it black during fossilization. |
Hominin |
Paranthropus boisei |
Dates |
2.4 mya to 1.4 mya |
Region(s) |
Koobi Fora, West Turkana, and Chesowanja (Kenya); Malema-Chiwondo (Malawi), Olduvai Gorge and Peninj (Tanzania); and Omo River basin and Konso (Ethiopia) |
Famous discoveries |
“Zinj,” or sometimes “Nutcracker Man” (OH5), in 1959 by Mary Leakey. The Peninj mandible from Tanzania, found in 1964 by Kimoya Kimeu. |
Brain size |
500 cc to 550 cc |
Dentition |
Very large, flat posterior dentition (largest of all hominins currently known). Much smaller anterior dentition. Very thick dental enamel. |
Cranial features |
Indications of very large chewing muscles (e.g., flaring zygomatic arches and a large sagittal crest). |
Postcranial features |
Evidence for high variability and sexual dimorphism, with estimates of males at 1.37 meters tall and females at 1.24 meters. |
Culture |
Richard Leakey and Bernard Wood have both suggested that P. boisei could have made and used stone tools. Tools dated to 2.5 mya in Ethiopia have been argued to possibly belong to this species. |
Other |
Despite the cranial features of P. boisei indicating a tough diet of tubers, nuts, and seeds, isotopes indicate a diet high in C4 foods (e.g., grasses, such as sedges). This differs from what is seen in P. robustus. |
Hominin |
Australopithecus sediba |
Dates |
1.97 mya |
Region(s) |
Malapa Fossil Site (South Africa) |
Famous discoveries |
Karabo (MH1) (discovery in 2008) |
Brain size |
420 cc to 450 cc |
Dentition |
Small dentition with Australopithecine cusp-spacing. |
Cranial features |
Small brain size (Australopithecus-like) but gracile mandible (Homo-like). |
Postcranial features |
Scientists have interpreted this mixture of traits (such as a robust ankle but evidence for an arch in the foot) as a transitional phase between a body previously adapted to arborealism (tree climbing, particularly in evidence from the bones of the wrist) to one that adapted to bipedal ground walking. |
Culture |
None of direct association, but some have argued that a modern hand morphology (shorter fingers and a longer thumb) means that adaptations to tool manufacture and use may be present in this species. |
Other |
It was first discovered through a clavicle bone in 2008 by nine-year-old Matthew Berger, son of paleoanthropologist Lee Berger. |
Hominin |
Paranthropus robustus |
Dates |
2.3 mya to 1 mya |
Region(s) |
Kromdraai B, Swartkrans, Gondolin, Drimolen, and Coopers Cave (South Africa) |
Famous discoveries |
SK48 (original skull) |
Brain size |
410 cc to 530 cc |
Dentition |
Large posterior teeth with thick enamel, consistent with other Robust Australopithecines. Enamel hypoplasia is also common in this species, possibly because of instability in the development of large, thick enameled dentition. |
Cranial features |
P. robustus features are neither as “hyper-robust” as P. boisei or as ancestral in features as P. aethiopicus. They have been described as less derived, more general features that are shared with both East African species (e.g., the sagittal crest and zygomatic flaring). |
Postcranial features |
Reconstructions indicate sexual dimorphism. |
Culture |
N/A |
Other |
Several of these fossils are fragmentary in nature, distorted, and not well preserved, because they have been recovered from quarry breccia using explosives. |
Review Questions
- What is the difference between a “derived” versus an “ancestral” trait? Give an example of both, seen in Au. afarensis.
- Which of the paleoenvironment hypotheses have been used to describe early hominin diversity, and which have been used to describe bipedalism?
- Which anatomical features for bipedalism do we see in early hominins?
- Describe the dentition of gracile and robust australopithecines. What might these tell us about their diets?
- List the hominin species argued to be associated with stone tool technologies. Are you convinced of these associations? Why/why not?
Key Terms
Arboreal: Related to trees or woodland.
Aridification: Becoming increasingly arid or dry, as related to the climate or environment.
Aridity Hypothesis: The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution.
Assemblage: A collection demonstrating a pattern. Often pertaining to a site or region.
Bipedalism: The locomotor ability to walk on two legs.
Breccia: Hard, calcareous sedimentary rock.
Canines: The pointy teeth just next to the incisors, in the front of the mouth.
Cheek teeth: Or hind dentition (molars and premolars).
Chronospecies: Species that are said to evolve into another species, in a linear fashion, over time.
Clade: A group of species or taxa with a shared common ancestor.
Cladistics: The field of grouping organisms into those with shared ancestry.
Context: As pertaining to palaeoanthropology, this term refers to the place where an artifact or fossil is found.
Cores: The remains of a rock that has been flaked or knapped.
Cusps: The ridges or “bumps” on the teeth.
Dental formula: A technique to describe the number of incisors, canines, premolars, and molars in each quadrant of the mouth.
Derived traits: Newly evolved traits that differ from those seen in the ancestor.
Diastema: A tooth gap between the incisors and canines.
Early Stone Age (ESA): The earliest-described archaeological period in which we start seeing stone-tool technology.
East African Rift System (EARS): This term is often used to refer to the Rift Valley, expanding from Malawi to Ethiopia. This active geological structure is responsible for much of the visibility of the paleoanthropological record in East Africa.
Enamel: The highly mineralized outer layer of the tooth.
Encephalization: Expansion of the brain.
Extant: Currently living—i.e., not extinct.
Fallback foods: Foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
Fauna: The animals of a particular region, habitat, or geological period.
Faunal assemblages: Collections of fossils of the animals found at a site.
Faunal turnover: The rate at which species go extinct and are replaced with new species.
Flake: The piece knocked off of a stone core during the manufacture of a tool, which may be used as a stone tool.
Flora: The plants of a particular region, habitat, or geological period.
Folivorous: Foliage-eating.
Foramen magnum: The large hole (foramen) at the base of the cranium, through which the spinal cord enters the skull.
Fossil: The remains or impression of an organism from the past.
Frugivorous: Fruit-eating.
Generalist: A species that can thrive in a wide variety of habitats and can have a varied diet.
Glacial: Colder, drier periods during an ice age when there is more ice trapped at the poles.
Gracile: Slender, less rugged, or pronounced features.
Hallux: The big toe.
Holotype: A single specimen from which a species or taxon is described or named.
Hominin: A primate category that includes humans and our fossil relatives since our divergence from extant great apes.
Honing P3: The mandibular premolar alongside the canine (in primates, the P3), which is angled to give space for (and sharpen) the upper canines.
Hyper-robust: Even more robust than considered normal in the Paranthropus genus.
Hypodigm: A sample (here, fossil) from which researchers extrapolate features of a population.
Incisiform: An adjective referring to a canine that appears more incisor-like in morphology.
Incisors: The teeth in the front of the mouth, used to bite off food.
Interglacial: A period of milder climate in between two glacial periods.
Isotopes: Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses.
Knappers: The people who fractured rocks in order to manufacture tools.
Knapping: The fracturing of rocks for the manufacture of tools.
Large Cutting Tool (LCT): A tool that is shaped to have functional edges.
Last Common Ancestor (LCA): The hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence.
Lithic: Relating to stone (here to stone tools).
Lumbar lordosis: The inward curving of the lower (lumbar) parts of the spine. The lower curve in the human S-shaped spine.
Lumpers: Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
Megadont: An organism with extremely large dentition compared with body size.
Metacarpals: The long bones of the hand that connect to the phalanges (finger bones).
Molars: The largest, most posterior of the hind dentition.
Monophyletic: A taxon or group of taxa descended from a common ancestor that is not shared with another taxon or group.
Morphology: The study of the form or size and shape of things; in this case, skeletal parts.
Mosaic evolution: The concept that evolutionary change does not occur homogeneously throughout the body in organisms.
Obligate bipedalism: Where the primary form of locomotion for an organism is bipedal.
Occlude: When the teeth from the maxilla come into contact with the teeth in the mandible.
Oldowan: Lower Paleolithic, the earliest stone tool culture.
Orthognathic: The face below the eyes is relatively flat and does not jut out anteriorly.
Paleoanthropologists: Researchers that study human evolution.
Paleoenvironment: An environment from a period in the Earth’s geological past.
Parabolic: Like a parabola (parabola-shaped).
Phalanges: Long bones in the hand and fingers.
Phylogenetics: The study of phylogeny.
Phylogeny: The study of the evolutionary relationships between groups of organisms.
Pliocene: A geological epoch between the Miocene and Pleistocene.
Polytypic: In reference to taxonomy, having two or more group variants capable of interacting and breeding biologically but having morphological population differences.
Postcranium: The skeleton below the cranium (head).
Premolars: The smallest of the hind teeth, behind the canines.
Procumbent: In reference to incisors, tilting forward.
Prognathic: In reference to the face, the area below the eyes juts anteriorly.
Quaternary Ice Age: The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles.
Relative dating: Dating techniques that refer to a temporal sequence (i.e., older or younger than others in the reference) and do not estimate actual or absolute dates.
Robust: Rugged or exaggerated features.
Site: A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
Specialist: A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
Splitters: Researchers who prefer to split a highly variable taxon into multiple groups or species.
Taxa: Plural of taxon, a taxonomic group such as species, genus, or family.
Taxonomy: The science of grouping and classifying organisms.
Techno-complex: A term encompassing multiple assemblages that share similar traits in terms of artifact production and morphology.
Thermoregulation: Maintaining body temperature through physiologically cooling or warming the body.
Ungulates: Hoofed mammals—e.g., cows and kudu.
Volcanic tufts: Rock made from ash from volcanic eruptions in the past.
Valgus knee: The angle of the knee between the femur and tibia, which allows for weight distribution to be angled closer to the point above the center of gravity (i.e., between the feet) in bipeds.
About the Authors
Kerryn Warren, Ph.D.
Grad Coach International, kerryn.warren@gmail.com
Kerryn Warren is a dissertation coach at Grad Coach International and is passionate about stimulating research thinking in students of all levels. She has lectured on multiple topics, including archaeology and human evolution, with her research and science communication interests including hybridization in the hominin fossil record (stemming from research from her Ph.D.) and understanding how evolution is taught in South African schools. She also worked as one of the “Underground Astronauts,” selected to excavate Homo naledi remains from the Rising Star Cave System in the Cradle of Humankind.
K. Lindsay Hunter, M.A., Ph.D. candidate
CARTA, k.lindsay.hunter@gmail.com
Lindsay Hunter is a trained palaeoanthropologist who uses her more than 15 years of experience to make sense of the distant past of our species to build a better future. She received her master’s degree in biological anthropology from the University of Iowa and is completing her Ph.D. in archaeology at the University of the Witwatersrand in Johannesburg, South Africa. She has studied fossil and human bone collections across five continents with major grant support from the National Science Foundation (United States) and the Wenner-Gren Foundation for Anthropological Research. As a National Geographic Explorer, Lindsay developed and managed the National Geographic–sponsored Umsuka Public Palaeoanthropology Project in the Cradle of Humankind World Heritage Site (CoH WHS) in South Africa from within Westbury Township, Johannesburg, between 2016–2019. She currently serves as the Community Engagement & Advancement Director for CARTA: The UC San Diego/Salk Institute Center for Academic Research and Training in Anthropogeny in La Jolla, California.
Navashni Naidoo, M.Sc.
University of Cape Town, nnaidoo2@illinois.edu
Navashni Naidoo is a researcher at Nelson Mandela University, lecturing on physical geology. She completed her Master’s in Science in Archaeology in 2017 at the University of Cape Town. Her research interests include developing paleoenvironmental proxies suited to the African continent, behavioral ecology, and engaging with community-driven archaeological projects. She has excavated at Stone Age sites across Southern Africa and East Africa. Navashni is currently pursuing a PhD in the Department of Anthropology at the University of Illinois.
Silindokuhle Mavuso, M.Sc.
University of Witwatersrand, S.muvaso@ru.ac.za
Silindokuhle has always been curious about the world around him and how it has been shaped. He is a lecturer at Rhodes University of Witwatersrand (Wits), and conducts research on palaeoenvironmental reconstruction and change of the northeastern Turkana Basin’s Pleistocene sequence. Silindokuhle began his education with a B.Sc. (Geology, Archaeology, and Environmental and Geographical Sciences) from the University of Cape Town before moving to Wits for a B.Sc. Honors (geology and paleontology) and M.Sc. in geology. He is currently concluding his PhD Studies. During this time, he has gained more training as a Koobi Fora Fieldschool fellow (Kenya) as well as an Erasmus Mundus scholar (France). Silindokuhle is a Plio-Pleistocene geologist with a specific focus on identifying and explaining past environments that are associated with early human life and development through time. He is interested in a wide range of disciplines such as micromorphology, sedimentology, geochemistry, geochronology, and sequence stratigraphy. He has worked with teams from significant eastern and southern African hominid sites including Elandsfontein, Rising Star, Sterkfontein, Gondolin, Laetoli, Olduvai, and Koobi Fora.
For Further Exploration
The Smithsonian Institution website hosts descriptions of fossil species, an interactive timeline, and much more.
The Maropeng Museum website hosts a wealth of information regarding South African Fossil Bearing sites in the Cradle of Humankind.
This quick comparison between Homo naledi and Australopithecus sediba from the Perot Museum.
This explanation of the braided stream by the Perot Museum.
A collation of 3-D files for visualizing (or even 3-D printing) for homes, schools, and universities.
PBS learning materials, including videos and diagrams of the Laetoli footprints, bipedalism, and fossils.
A wealth of information from the Australian Museum website, including species descriptions, family trees, and explanations of bipedalism and diet.
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Acknowledgements
All of the authors in this section are students and early career researchers in paleoanthropology and related fields in South Africa (or at least have worked in South Africa). We wish to thank everyone who supports young and diverse talent in this field and would love to further acknowledge Black, African, and female academics who have helped pave the way for us.
Large animals such as mammoths and mastodons.
Bonnie Yoshida-Levine Ph.D., Grossmont College
This chapter is a revision from "Chapter 10: Early Members of the Genus Homo" by Bonnie Yoshida-Levine. In Explorations: An Open Invitation to Biological Anthropology, first edition, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff, which is licensed under CC BY-NC 4.0.
Learning Objectives
- Describe how early Pleistocene climate change influenced the evolution of the genus Homo.
- Identify the characteristics that define the genus Homo.
- Describe the skeletal anatomy of Homo habilis and Homo erectus based on the fossil evidence.
- Assess opposing points of view about how early Homo should be classified.
The boy was no older than nine years when he perished by the swampy shores of the lake. After death, his slender, long-limbed body sank into the mud of the lake shallows. His bones fossilized and lay undisturbed for 1.5 million years. In the 1980s, fossil hunter Kamoya Kimeu, working on the western shore of Lake Turkana, Kenya, glimpsed a dark-colored piece of bone eroding in a hillside. This small skull fragment led to the discovery of what is arguably the world’s most complete early hominin fossil—a youth identified as a member of the species Homo erectus. Now known as Nariokotome Boy, after the nearby lake village, the skeleton has provided a wealth of information about the early evolution of our own genus, Homo (see Figure 10.1). Today, a stone monument with an inscription in three languages—English, Swahili, and the local Turkana language—marks the site of this momentous fossil discovery.

Chapter 9 described our oldest human ancestors, primarily members of the genus Australopithecus, who lived between 2 million and 4 million years ago. This chapter introduces the earliest members of the genus Homo, focusing on Homo habilis and Homo erectus.
Defining the Genus Homo
Because Anthropology is fundamentally concerned with what makes us human, defining our own genus takes on special significance for anthropologists. Ever since scientists acknowledged the existence of extinct species of humans, they have debated which of them display sufficient “humanness” to merit classification in the genus Homo. When grouping species into a common genus, biologists consider criteria such as physical characteristics (morphology), evidence of recent common ancestry, and adaptive strategy (use of the environment). However, there is disagreement about which of those criteria should be prioritized, as well as how specific fossils should be interpreted in light of the criteria.
Nevertheless, there is general agreement that species classified as Homo should share characteristics that are broadly similar within our species. These include the following:
- a relatively large brain size,
indicating a high degree of intelligence; - a smaller and flatter face
- smaller jaws and teeth
- increased reliance on culture, particularly the use of stone tools, to exploit a greater diversity of environments (adaptive zone).
Some researchers would include larger overall body size and limb proportions (longer legs/shorter arms) in this list. While these criteria seem relatively clear-cut, evaluating them in the fossil record has proved more difficult, particularly for the earliest members of the genus. There are several reasons for this. First, many fossil specimens dating to this time period are incomplete and poorly preserved. Second, early Homo fossils appear quite variable in brain size, facial features, and teeth and body size, and there is not yet consensus about how to best make sense of this diversity. Finally, there is growing evidence that the evolution of the genus Homo proceeded in a mosaic pattern: in other words, these characteristics did not appear all at once in a single species; rather, they were patchily distributed in different species from different regions and time periods. Consequently, different researchers have come up with conflicting classification schemes depending on which criteria they think are most important.
In this chapter, we will take several pathways toward examining the origin and evolution of the genus Homo. First, we will explore the environmental conditions of the Pleistocene epoch in which the genus Homo evolved. Next we will examine the fossil evidence for the two principal species traditionally identified as early Homo: Homo habilis and Homo erectus. Then we will use data from fossils and archaeological sites to reconstruct the behavior of early members of Homo, including tool manufacture, subsistence practices, migratory patterns, and social structure. Finally, we will consider these together in an attempt to characterize the key adaptive strategies of early Homo and how they put our early ancestors on the trajectory that led to our own species, Homo sapiens.
Climate Change and Human Evolution
A key goal in the study of human origins is to learn about the environmental pressures that may have shaped human evolution. As indicated in Chapter 7, scientists use a variety of techniques to reconstruct ancient environments. These include stable isotopes, core samples from oceans and lakes, windblown dust, analysis of geological formations and volcanoes, and fossils of ancient plant and animal communities. Such studies have provided valuable information about the environmental context of early Homo.
The early hominin species covered in Chapter 9, such as Ardipithecus ramidus and Australopithecus afarensis, evolved during the late Pliocene epoch. The Pliocene (5.3 million to 2.6 million years ago) was marked by cooler and drier conditions, with ice caps forming permanently at the poles. Still, Earth’s climate during the Pliocene was considerably warmer and wetter than at present.
The subsequent Pleistocene epoch (2.6 million years to 11,000 years ago) ushered in major environmental change. The Pleistocene is popularly referred to as the Ice Age. Since the term “Ice Age” tends to conjure up images of glaciers and woolly mammoths, one would naturally assume that this was a period of uniformly cold climate around the globe. But this is not actually the case. Instead, climate became much more variable, cycling abruptly between warm/wet (interglacial) and cold/dry (glacial) cycles. These patterns were influenced by changes in Earth’s elliptical orbit around the sun. As is shown in Figure 10.2, each cycle averaged about 41,000 years during the early Pleistocene; the cycles then lengthened to about 100,000 years starting around 1.25 million years ago. Since mountain ranges, wind patterns, ocean currents, and volcanic activity can all influence climate patterns, there were wide-ranging regional and local effects.

Data on ancient geography and climate help us understand how our ancestors moved and migrated to different parts of the world—as well as the constraints under which they operated. When periods of global cooling dominated, sea levels were lower as more water was captured as glacial ice. This exposed continental margins and opened pathways between land masses. During glacial periods, the large Indonesian islands of Sumatra, Java, and Borneo were connected to the Southeast Asian mainland, while New Guinea was part of the southern landmass of greater Australia. There was a land bridge connection between Britain and continental Europe, and an icy, treeless plain known as Beringia connected Northern Asia and Alaska. At the same time, glaciation made some northern areas inaccessible to human habitation. For example, there is evidence that hominin species were in Britain 950,000 years ago, but it does not appear that Britain was continuously occupied during this period. (It is speculated) These early humans may have died out or been forced to abandon the region during glacial periods.
In Africa, paleoclimate research has determined that grasslands (shown in Figure 10.3) expanded and shrank multiple times during this period, even as they expanded over the long term (deMenocal 2014). From studies of fossils, paleontologists have been able to reconstruct Pleistocene animal communities and to consider how they were affected by the changing climate. Among the African animal populations, the number of grazing animal species such as antelope increased. Although the African and Eurasian continents are connected by land, the Sahara desert and the mountainous topography of North Africa serve as natural barriers to crossing. But the fossil record shows that at different times animal species have moved back and forth between Africa and Eurasia. During the early Pleistocene, there is evidence of African mammal species such as baboons, hippos, antelope, and African buffalo migrating out of Africa into Eurasia during periods of aridity (Belmaker 2010).

This changing environment was undoubtedly challenging for our ancestors, but it offered new opportunities to make a living. One solution adopted by some hominins was to specialize in feeding on the new types of plants growing in this landscape. The robust australopithecines (described in Chapter 9) likely developed their large molar teeth with thick enamel in order to exploit this particular dietary niche.
Members of the genus Homo took a different route. Faced with the unstable African climate and shifting landscape, they evolved bigger brains that enabled them to rely on cultural solutions such as crafting stone tools that opened up new foraging opportunities. This strategy of behavioral flexibility served them well during this unpredictable time and led to new innovations such as increased meat-eating, cooperative hunting, and the exploitation of new environments outside Africa.
Homo habilis: The Earliest Members of Our Genus
Homo habilis has traditionally been considered the earliest species placed in the genus Homo. However, as we will see, there is substantial disagreement among paleoanthropologists about the fossils classified as Homo habilis, including whether they come from a single species or multiple, or even whether they should be part of the genus Homo at all.
Homo habilis has a somewhat larger brain size—an average of 650 cubic centimeters (cc)—compared to Australopithecus with less than 500 cc. Additionally, the skull is more rounded and the face less prognathic. However, the postcranial remains show a body size and proportions similar to Australopithecus.
Known dates for fossils identified as Homo habilis range from about 2.5 million years ago to 1.7 million years ago. Recently, a partial lower jaw dated to 2.8 million years from the site of Ledi-Gararu in Ethiopia has been tentatively identified as belonging to the genus Homo (Villmoare et al. 2015). If this classification holds up, it would push the origins of our genus back even further.

Discovery and Naming (just add paragraph not own section)
The first fossils to be named Homo habilis were discovered at the site of Olduvai Gorge in Tanzania, East Africa, by members of a team led by Louis and Mary Leakey (Figure 10.4). The Leakey family had been conducting fieldwork in the area since the 1930s and had discovered other hominin fossils at the site, such as the robust Paranthropos boisei. The key specimen, a juvenile individual, was actually found by their 20-year-old son Jonathan Leakey. Louis Leakey invited South African paleoanthropologist Philip Tobias and British anatomist John Napier to reconstruct and analyze the remains. The fossil of the juvenile shown in Figure 10.5 (now known as OH-7) consisted of a lower jaw, parts of the parietal bones of the skull, and some hand and finger bones. The fossil was dated by potassium-argon dating to about 1.75 million years. In 1964, the team published their findings in the scientific journal Nature (Leakey et al. 1964). As described in the publication, the new fossils had smaller molar teeth that were less “bulgy” than australopithecine teeth. Although the primary specimen was not yet fully grown, an estimate of its anticipated adult brain size would make it somewhat larger-brained than australopithecines such as Austalopithecus africanus. The hand bones were capable of a precision grip like a human’s hand. This increased the likelihood that stone tools found earlier at Olduvai Gorge were made by this group of hominins. Based on these findings, the authors inferred that it was a new species that should be classified in the genus Homo. They gave it the name Homo habilis, meaning “handy” or “skilled.”

Controversies over Classification of Homo habilis
Since its initial discovery, many more Homo habilis were discovered in East and South African sites during the 1970s and 1980s (Figure 10.6). As more fossils joined the ranks of Homo habilis, several trends became apparent. First, the fossils were quite variable. While some resembled the fossil specimen first published by Leakey and colleagues, others had larger cranial capacity and tooth size. A well-preserved fossil skull from East Lake Turkana labeled KNM-ER-1470 displayed a larger cranial size along with a strikingly wide face. The diversity of the Homo habilis fossils prompted some scientists to question whether they displayed too much variation to all belong to the same species. They proposed splitting the fossils into at least two groups. The first group resembling the original small-brained specimen would retain the species name Homo habilis; the second group consisting of the larger-brained fossils such as KNM-ER-1470 would be assigned the new name of Homo rudolfensis (see Figure 10.7). Researchers who favored keeping all fossils in Homo habilis argued that sexual dimorphism, adaptation to local environments, or developmental plasticity could be the cause of the differences. For example, modern human body size and body proportions are influenced by variations in climates and nutritional circumstances.
Location of Fossils |
Dates |
|
Ledi-Gararu, Ethiopia |
2.8 mya |
Partial lower jaw with evidence of both Australopithecus and Homo traits; tentatively considered oldest Early Homo fossil evidence. |
Olduvai Gorge, Tanzania |
1.7 mya to 1.8 mya |
Several different specimens classified as Homo habilis, including the type specimen found by Leakey, a relatively complete foot, and a skull with a cranial capacity of about 600 cc. |
Koobi Fora, Lake Turkana Basin, Kenya |
1.9 mya |
Several fossils from the Lake Turkana basin show considerable size differences, leading some anthropologists to classify the larger specimen (KNM-ER-1470) as a separate species, Homo rudolfensis. |
Sterkfontein and other possible South African cave sites |
about 1.7 mya |
South African caves have yielded fragmentary remains identified as Homo habilis, but secure dates and specifics about the fossils are lacking. |

Given the incomplete and fragmentary fossil record from this time period, it is not surprising that classification has proved contentious. As a scholarly consensus has not yet emerged on the classification status of early Homo, this chapter makes use of the single (inclusive) Homo habilis species designation.
There is also disagreement on whether Homo habilis legitimately belongs in the genus Homo. Most of the fossils first classified as Homo habilis were skulls and teeth. When arm, leg, and foot bones were later found, making it possible to estimate body size, the specimens turned out to be quite small in stature with long arms and short legs. Analysis of the relative strength of limb bones suggested that the species, though bipedal, was much more adapted to arboreal climbing than Homo erectus and Homo sapiens (Ruff 2009). This has prompted some scientists to assert that Homo habilis behaved more like an australopithecine—with a shorter gait and the ability to move around in the trees (Wood and Collard 1999). They were also skeptical of the claim that the brain size of Homo habilis was much larger than that of Australopithecus. They have proposed reclassifying some or all of the Homo habilis fossils into the genus Australopithecus, or even placing them into a newly created genus (Wood 2014).
Other scholars have interpreted the fossil evidence differently. A recent reanalysis of Homo habilis/rudolfensis fossils concluded that they sort into the genus Homo rather than Australopithecus (see Hominin Species Summaries at chapter end). In particular, statistical analysis performed indicates that the Homo habilis fossils differ significantly in average cranial capacity from the australopithecines. They also note that some australopithecine species such as the recently discovered Australopithecus sediba have relatively long legs, so body size may not have been as significant as brain- and tooth-size differences (Anton et al. 2014).
Special Topic: Kamoya Kimeu
Kamoya Kimeu (1938–2022) is arguably the most prolific fossil hunter in the history of paleoanthropology (Figure 10.8). In addition to his many decades of work as a field excavator and project supervisor in East Africa, he also trained field workers and scholars and has served as curator for prehistoric sites for the National Museum of Kenya.

Kamoya Kimeu was born in 1938 in rural southeastern Kenya. Despite a formal education that did not go past the sixth grade, he had an aptitude for languages and familiarity with the plants and animals in the East African bush that led him to a job in Tanzania as a field excavator for Louis and Mary Leakey in 1960. In the years that followed, Kimeu found dozens of major hominin fossils. These included a Paranthropus boisei mandible at Olduvai Gorge, Homo habilis specimen KNM-ER-1813 from the Turkana Basin (shown in Figure 10.5), and a key early modern Homo sapiens fossil from the Omo Valley, Ethiopia. Kimeu’s most famous fossil discovery was the skeleton of a young Homo erectus by the Nariokotome river bed in 1984. This finding was highly significant because it was a nearly complete early hominin skeleton and provided insight into child development within this species. In recognition of his work, Kimeu was awarded the National Geographic Society La Gorce Medal by U.S. President Ronald Reagan in 1985.
Traditionally, there has been a divide between African field workers and foreign research scientists, who would typically conduct seasonal field work in Africa, then travel back to their home institutions to publish their findings. Although Kimeu received widespread acclaim for the Nariokotome discovery, as well as a personal acknowledgement in the publication of the find in the journal Nature, he was not credited as an author. More recently, Kimeu’s intellectual contributions to the field of paleoanthropology have been recognized. In 2021, he received an honorary doctorate degree from Case Western Reserve University in Ohio. Kimeu’s most lasting legacy may be his mentorship of countless field workers and students. Today, there are a small but growing number of Black African paleoanthropologists taking on principal roles in the science of human origins.
Homo habilis Culture and Lifeways
Early Stone Tools
The larger brains and smaller teeth of early Homo are linked to a different adaptive strategy than that of earlier hominins: one dependent on modifying rocks to make stone tools and exploit new food sources. As discussed in Chapter 9, the 3.3-million-year-old stone tools from the Lomekwi 3 site in Kenya were made by earlier hominin species than Homo. However, stone tools become more frequent at sites dating to about 2 million years ago, the time of Homo habilis (Roche et al. 2009). This suggests that these hominins were increasingly reliant on stone tools to make a living.
Stone tools are assigned a good deal of importance in the study of human origins. Examining the form of the tools, the raw materials selected, and how they were made and used can provide insight into the thought processes of early humans and how they modified their environment in order to survive. Paleoanthropologists have traditionally classified collections of stone tools into industries, based on their form and mode of manufacture. There is not an exact correspondence between a tool industry and a hominin species; however, some general associations can be made between tool industries and particular hominins, locations, and time periods.
The Oldowan tool industry is named after the site of Olduvai Gorge in Tanzania where the tools were first discovered. The time period of the Oldowan is generally estimated to be 2.5 mya to 1.6 mya. The tools of this industry are described as “flake and chopper” tools—the choppers consisting of stone cobbles with a few flakes struck off them (Figure 10.9). To a casual observer, these tools might not look much different from randomly broken rocks. However, they are harder to make than their crude appearance suggests. The rock selected as the core must be struck by the rock serving as a hammerstone at just the right angle so that one or more flat flakes are removed. This requires selecting rocks that will fracture predictably instead of chunking, as well as the ability to plan ahead and envision the steps needed to create the finished product. The process leaves both the core and the flakes with sharp cutting edges that can be used for a variety of purposes.

Stone Tool Use and the Diet of Early Homo
What were the hominins doing with the tools? One key activity seems to have been butchering animals. Studies of animal bones at the site show cut marks on bones, and leg bones are often cracked open, suggesting that they were extracting the marrow from the bone cavities. It is interesting to consider whether the hominins hunted these animals or acquired them through other means. The butchered bones come from a variety of African mammals, ranging from small antelope to animals as big as wildebeest and elephants! It is difficult to envision slow, small-bodied Homo habilis with their Oldowan tools bringing down such large animals. One possibility is that the hominins were scavenging carcasses from lions and other large cats. Paleoanthropologist Robert Blumenschine has investigated this hypothesis by observing the behavior of present-day animal carnivores and scavengers on the African savanna. When lions abandon a kill after eating their fill, scavenging animals arrive almost immediately to pick apart the carcass. By the time slow-footed hominins arrived on the scene, the carcass would be mostly stripped of meat. However, if hominins could use stone tools to break into the leg bone cavities, they could get to the marrow, a fatty, calorie-dense source of protein (Blumenschine et al. 1987). Reconstructing activities that happened millions of years ago is obviously a difficult undertaking, and paleoanthropologists continue to debate whether scavenging or hunting was more commonly practiced during this time.
Regardless of how they were acquiring the meat, these activities suggest an important dietary shift from the way that the australopithecines were eating. The Oldowan toolmakers were exploiting a new ecological niche that provided them with more protein and calories. And it was not just limited to meat-eating—stone tool use could have made available numerous other subsistence opportunities. A study of microscopic wear patterns on a sample of Oldowan tools indicates that they were used for processing plant materials such as wood, roots or tubers, and grass seeds and stems (Lemorini et al. 2014). In fact, it has been pointed out that the Oldowan toolmakers’ cutting ability (whether for the purposes of consuming meat and plants or for making tools, shelters, or clothing) represents a new and unique innovation, never seen before in the natural world (Roche et al. 2009).
Overall, increasing the use of stone tools allowed hominins to expand their ecological niche and exert more control over their environment. As we’ll see shortly, this pattern continued and became more pronounced with Homo erectus.
Homo erectus: Biological and Cultural Innovations
Two million years ago, a new hominin appeared on the scene. Known as Homo erectus, the prevailing scientific view was that this species was much more like us. These hominins were equipped with bigger brains and large bodies with limb proportions similar to our own. Perhaps most importantly, their way of life is now one that is recognizably human, with more advanced tools, hunting, use of fire, and colonizing new environments outside of Africa.
As will be apparent below, new data suggests that the story is not quite as simple. The fossil record for Homo erectus is much more abundant than that of Homo habilis, but it is also more complex and varied—both with regard to the fossils as well as the geographic context in which they are found. We will first summarize the anatomical characteristics that define Homo erectus, and then discuss the fossil evidence from Africa and the primary geographic regions outside Africa where the species has been located.
Homo erectus Anatomy

Compared to Homo habilis, Homo erectus showed increased brain size, smaller teeth, and a larger body. However, it also displayed key differences from later hominin species including our own. Although the head of Homo erectus was less ape-like in appearance than the australopithecines, it did not resemble modern humans (Figure 10.10). Compared to Homo habilis, Homo erectus had a larger brain size: an average of about 900 cc compared to 650 cc to 750 cc. Instead of a rounded shape like our skulls, the erectus skull was long and low like a football, with a receding forehead, and a horizontal ridge called an occipital torus that gave the back of the skull a squared-off appearance. The cranial bones are thicker than those of modern humans, and some Homo erectus skulls have a slight thickening along the sagittal suture called a sagittal keel. Large, shelf-like brow ridges hang over the eyes. The face shows less prognathism, and the back teeth are smaller than those of Homo habilis. Instead of a pointed chin, like ours, the mandible of Homo erectus recedes back.
Apart from these features, there is significant variation among Homo erectus fossils from different regions. Scientists have long noted differences between the fossils from Africa and those from Indonesia and China. For example, the Asian fossils tend to have a thicker skull and larger brow ridges than the African specimens, and the sagittal keel described above is more pronounced. Homo erectus fossils from the Republic of Georgia (described in the next section) also display distinctive characteristics. As with Homo habilis, this diversity has prompted a classification debate about whether or not Homo erectus should be split into multiple species. When African Homo erectus is characterized as a separate species, it is called Homo ergaster, while the Asian variant retains the erectus species name because it was discovered first. Here, the species name Homo erectus will be used for both variants.
Homo erectus was thought to have a body size and proportions more similar to modern humans. Unlike Homo habilis and the australopithecines, both of whom were small-statured with long arms and short legs, Homo erectus shows evidence of being fully committed to life on the ground. This meant long, powerfully muscled legs that enabled these hominins to cover more ground efficiently. Indeed, studies of the Homo erectus body form have linked several characteristics of the species to long-distance running in the more open savanna environment (Bramble and Lieberman 2004). Many experts think that hominins around this time had lost much of their body hair, were particularly efficient at sweating, and had darker-pigmented skin—all traits that would support the active lifestyle of such a large-bodied hominin (see Special Topic box, “How We Became Sweaty, Hairless Primates”).
Special Topic: How We Became Hairless, Sweaty Primates (include here)
Much of the information about the body form of Homo erectus comes from the Nariokotome fossil of the Homo erectus youth, described at the beginning of the chapter (see Figure 10.1). However, Homo erectus fossils are turning out to be more varied than previously thought. Homo erectus fossils from sites in Africa, as well as from Dmanisi, Georgia, show smaller body sizes than the Nariokotome boy. Even the Nariokotome skeleton itself has been reassessed: some now predict he would have been about 5 feet and 4 inches when fully grown rather than over 6 feet as initially hypothesized, although there is still disagreement about which measurement is more accurate. One explanation for the range of body sizes could be adaptation to a range of different local environments, just as humans today show reduced body size in poor nutritional environments (Anton and Snodgrass 2012).
Homo erectus in Africa
Although the earliest discoveries of Homo erectus fossils were from Asia, the greatest quantity and best-preserved fossils of the species come from East African sites. The earliest fossils in Africa identified as Homo erectus come from the East African site of Koobi Fora, around Lake Turkana in Kenya, and are dated to about 1.8 million years ago. Other fossil remains have been found in East African sites in Kenya, Tanzania, and Ethiopia. Other notable African Homo erectus finds are a female pelvis from the site of Gona, Ethiopia (Simpson et al. 2008), and a cranium with massive brow ridges from Olduvai Gorge known as Olduvai 9, thought to be about 1.4 million years old.
Until recently, Homo erectus’ presence in southern Africa has not been well documented. However, work at the Drimolen cave site in South Africa has yielded new fossils of Paranthropus robustus, and the cranium of a 2–3 year old child tentatively identified as Homo erectus, dated to about 2 million years (Herries et al. 2020). If substantiated, this would be the oldest discovery to date of Homo erectus anywhere.
Regional Discoveries Outside Africa
It is generally agreed that Homo erectus was the first hominin to migrate out of Africa and colonize Asia and later Europe (although recent discoveries in Asia may challenge this view). Key locations and discoveries of Homo erectus fossils, along with the fossils’ estimated ages, are summarized in Figures 10.11 and 10.12.

Region
|
Sites
|
Dates
|
Significance of Fossils
|
East Africa |
East and West Lake Turkana, Kenya; Olduvai Gorge, Tanzania |
1.8 to 1.4 mya |
Earliest evidence of H. erectus; significant variation in skull and facial features. |
South Africa |
Drimolen Cave, South Africa |
2 mya |
Recent find of a 2–3 year old child would be oldest H. erectus anywhere to date. |
Western Eurasia |
Dmanisi, Republic of Georgia |
1.75 mya |
Smaller brains and bodies than H. erectus from other regions. |
Western Europe |
Atapuerca, Spain (Sima del Elefante and Gran Dolina caves) |
1.2 mya– 400,000 ya |
Partial jaw from Atapuerca is oldest evidence of H. erectus in Western Europe. Fossils from Gran Dolina (dated to about 800,000 years) sometimes referred to as H. antecessor. |
Indonesia |
Ngandong, Java; Sangiran, Java |
1.6 mya |
Early dispersal of H. erectus to East Asia; Asian H. erectus features. |
China |
Zhoukoudian, China; Loess Plateau (Lantian) |
780,000– 400,000 ya; 2.1 mya |
Large sample of H. erectus fossils and artifacts. Recent evidence of stone tools from Loess Plateau suggests great antiquity of Homo in East Asia. |
Indonesia
The first discovery of Homo erectus was in the late 1800s in Java, Indonesia. A Dutch anatomist named Eugene Dubois searched for human fossils with the belief that since orangutans lived there, it might be a good place to look for remains of early humans. He discovered a portion of a skull, a femur, and other bone fragments on a riverbank. While the femur looked human, the top of the skull was smaller and thicker than that of a modern person. Dubois named the fossil Pithecanthropus erectus (“upright ape-man”), popularized in the media at the time as “Java Man.” After later discoveries of similar fossils in China and Africa, they were combined into a single species (retaining the erectus name) under the genus Homo.
Although Homo erectus has a long history in Indonesia, the region’s geology has complicated the dating of fossils and sites. Fossils from the Sangiran Dome, Java, had previously been estimated to be as old as 1.8 million years, but scientists using new dating methods have arrived at a later date of about 1.3 mya (Matsu’ura et al. 2020). On the recent end of the timeline, a cache of H. erectus fossils from the site of Ngandong in Java has yielded a surprisingly young date of 43,000 years, although a newer study with different dating methods concluded that they were between 117,000 to 108,000 years old (Rizal et al. 2020).
China
There is evidence of Homo erectus in China from several regions and time periods. Homo erectus fossils from northern China, collectively known as “Peking Man,” are some of the most famous human fossils in the world. Dated to about 400,000–700,000 years ago, they were excavated from the site of Zhoukoudian, near the outskirts of Beijing. Hundreds of bones and teeth, including six nearly complete skulls, were excavated from a cave in the 1920s and 1930s. Much of the fossils’ fame comes from the fact that they disappeared under mysterious circumstances. As Japan advanced into China during World War II, Chinese authorities, concerned for the security of the fossils, packed up the boxes and arranged for them to be transported to the United States. But in the chaos of the war, they vanished and were never heard about again. Fortunately, an anatomist named Frans Weidenreich had previously studied the bones and made casts and measurements of the skulls, so this valuable information was not lost. More recent excavations at Longgushan “Dragon Bone Cave” at Zhoukoudian—of tools, living sites, and food remains—have revealed much about the lifestyle of Homo erectus during this time.
Despite this long history of research, China, compared to Africa, was perceived as somewhat peripheral to the study of hominin evolution. Although Homo erectus fossils have been found at several sites in China, with dates that make them comparable to those of Indonesian Homo erectus, none seemed to approximate the antiquity of African sites. The notable finds at sites like Nariokotome and Olorgesaille took center stage during the 1970s and 1980s, as scientists focused on elucidating the species’ anatomy and adaptations in its African homeland. In contrast, fewer research projects were focused on East Asian sites (Dennell and Roebroeks 2005; Qiu 2016).
However, isolated claims of very ancient hominin occupation kept cropping up from different locations in Asia. While some were dismissed because of problems with dating methods or stratigraphic context, the 2018 publication of the discovery of 2.1-million-year-old stone tools from China caught everyone’s attention. Based on paleomagnetic techniques that date the associated soils and windblown dust, these tools indicate that hominins in Asia predated those from the Georgian site of Dmanisi by at least 300,000 years (Zhu et al. 2018). In fact, the tools are older than any Homo erectus fossils anywhere. Since no fossils were found with the tools, it isn’t known which species made them, but it opens up the intriguing possibility that hominins could have migrated out of Africa earlier than Homo erectus. These new discoveries are shaking up previously held views of the East Asian human fossil record.
Western Eurasia
An extraordinary collection of fossils from the site of Dmanisi in the Republic of Georgia has revealed the presence of Homo erectus in Western Eurasia between 1.75 million and 1.86 million years ago. Dmanisi is located in the Caucasus mountains in Georgia. When archaeologists began excavating a medieval settlement near the town in the 1980s and came across the bones of extinct animals, they shifted their focus from the historic to the prehistoric era, but they probably did not anticipate going back quite so far in time. The first hominin fossils were discovered in the early 1990s, and since that time, at least five relatively well-preserved crania have been excavated.
There are several surprising things about the Dmanisi fossils. Compared to African Homo erectus, they have smaller brains and bodies. However, despite the small brain size, they show clear signs of Homo erectus traits such as heavy brow ridges and reduced facial prognathism. Paleoanthropologists have pointed to some aspects of their anatomy (such as the shoulders) that appear rather primitive, although their body proportions seem fully committed to terrestrial bipedalism. One explanation for these differences could be that the Dmanisi hominins represent a very early form of Homo erectus that left Africa before increases in brain and body size evolved in the African population.
Second, although the fossils at this location are from the same geological context, they show a great deal of variation in brain size and in facial features. One skull (Skull 5) has a cranial capacity of only 550 cc, smaller than many Homo habilis fossils, along with larger teeth and a protruding face. Scientists disagree on what these differences mean. Some contend that the Dmanisi fossils cannot all belong to a single species because each one is so different. Others assert that the variability of the Dmanisi fossils proves that they, along with all early Homo fossils, including H. habilis and H.rudolfensis, could all be grouped into Homo erectus (Lordkipanidze et al. 2013). Regardless of which point of view ends up dominating, the Dmanisi hominins are clearly central to the question of how to define the early members of the genus Homo.
Europe
Until recently, there was scant evidence of any Homo erectus presence in Europe, and it was assumed that hominins did not colonize Europe until much later than East Asia or Eurasia. One explanation for this was that the harsh climate of Western Europe served as a barrier to settlement. However, recent fossil finds from Spain suggest that Homo erectus could have made it into Europe over a million years ago. In 2008 a mandible from the Atapuerca region in Spain was discovered, dating to about 1.2 million years ago. A more extensive assemblage of fossils from the site of Gran Dolina in Atapuerca have been dated to about 800,000 years ago. In England in 2013 fossilized hominin footprints of adults and children dated to 950,000 years ago were found at the site of Happisburgh, Norfolk, which would make them the oldest human footprints found outside Africa (Ashton et al. 2014).
At this time, researchers aren’t in agreement as to whether the first Europeans belonged to Homo erectus proper or to a later descendent species. Some scientists refer to the early fossils from Spain by the species name Homo antecessor.
Special Topic: How We Became Hairless, Sweaty Primates
As an anthropology instructor teaching human evolution, my students often ask me about human body hair: When did our ancestors lose it and why? It is assumed that our earliest ancestors were as hairy as modern-day apes. Yet, today, we lack thick hair on most parts of our bodies except in the armpits, pubic regions, and tops of our heads. Humans actually have about the same number of hair follicles per unit of skin as chimpanzees, but, the hairs on most of our body are so thin as to be practically invisible. When did we develop this peculiar pattern of hairlessness? Which selective pressures in our ancestral environment were responsible for this unusual characteristic?
Many experts believe that the driving force behind our loss of body hair was the need to effectively cool ourselves. Along with the lack of hair, humans are also distinguished by being exceptionally sweaty: we sweat larger quantities and more efficiently than any other primate. Humans have a larger amount of eccrine sweat glands than other primates and these glands generate an enormous volume of watery sweat. Sweating produces liquid on the skin that cools the body off as it evaporates. It seems likely that hairlessness and sweating evolved together, as a recent DNA analysis has identified a shared genetic pathway between hair follicles and eccrine sweat gland production (Kamberov et al. 2015).
Which particular environmental conditions led to such adaptations? In this chapter, we learned that the climate was a driving force behind many changes seen in the hominin lineage during the Pleistocene. At that time, the climate was increasingly arid and the forest canopy in parts of Africa was being replaced with a more open grassland environment, resulting in increased sun exposure for our ancestors. Compared to the earlier australopithecines, members of the genus Homo were also developing larger bodies and brains, starting to obtain meat by hunting or scavenging carcasses, and crafting sophisticated stone tools.
According to Nina Jablonski, an expert on the evolution of human skin, the loss of body hair and increased sweating capacity are part of the package of traits characterizing the genus Homo. While larger brains and long-legged bodies made it possible for humans to cover long distances while foraging, this new body form had to cool itself effectively to handle a more active lifestyle. Preventing the brain from overheating was especially critical. The ability to keep cool may have also enabled hominins to forage during the hottest part of the day, giving them an advantage over savanna predators, like lions, that typically rest during this time (Jablonski 2010).
When did these changes occur? Although hair and soft tissue do not typically fossilize, several indirect methods have been used to explore this question. One method tracks a human skin color gene. Since chimpanzees have light skin under their hair, it is probable that early hominins also had light skin color. Apes and other mammals with thick fur coats have protection against the sun’s rays. As our ancestors lost their fur, it is likely that increased melanin pigmentation was selected for as a way to shield our ancestors from harmful ultraviolet radiation. A recent genetic analysis determined that one of the genes responsible for melanin production originated about 1.2 million years ago (Rogers et al 2004).
Another line of evidence tracks the coevolution of a rather unpleasant human companion—the louse. A genetic study identified human body louse as the youngest of the three varieties of lice that infest humans, splitting off as a distinct variety around 70,000 years ago (Kittler et al. 2003). Because human body lice can only spread through clothing, this may have been about the time when humans started to regularly wear clothing. However, the split between human head and pubic lice is estimated to have occurred much earlier, about three million years ago (Bower 2003; Reed et al. 2007). When humans lost much of their body hair, lice that used to roam freely around the body were now confined to two areas: the head and pubic region. As a result of this separation, the lice population split into two distinct groups.
Other explanations have been suggested for the loss of human body hair. For example, being hairless makes it more difficult for skin parasites like lice, fleas, and ticks to live on us. Additionally, after bipedality evolved, hairless bodies would also make reproductive organs and female breasts more visible, suggesting that sexual selection may have played a role.
Homo erectus Lifeways
Now, our examination of Homo erectus will turn to its lifeways—how the species utilized its environment in order to survive. This includes making inferences about diet, technology, life history, environments occupied, and perhaps even social organization. As will be apparent, Homo erectus shows significant cultural innovations in these areas, some that you will probably recognize as more “human-like” than any of the hominins previously covered.
Tool Technology: Acheulean Tool Industry

In early African sites associated with Homo erectus, stone tools such as flakes and choppers identified to the Oldowan Industry dominate. Starting at about 1.5 million years ago, some Homo erectus populations began making different forms of tools. These tools—classified together as constituting the Acheulean tool industry—are more complex in form and more consistent in their manufacture. Unlike the Oldowan tools, which were cobbles modified by striking off a few flakes, Acheulean toolmakers carefully shaped both sides of the tool. This type of technique, known as bifacial flaking, requires more planning and skill on the part of the toolmaker; he or she would need to be aware of principles of symmetry when crafting the tool. One of the most common tool forms, the handaxe, is shown in Figure 10.13. As with the tool illustrated below, handaxes tend to be thicker at the base and then come to a rounded point at the tip. Besides handaxes, forms such as scrapers, cleavers, and flake tools are present at Homo erectus sites.
One striking aspect of Acheulean tools is their uniformity. They are more standardized in form and mode of manufacture than the earlier Oldowan tools. For example, the aforementioned handaxes vary in size, but they are remarkably consistent in regard to their shape and proportions. They were also an incredibly stable tool form over time—lasting well over a million years with little change.
Curiously, the Acheulean tools so prominent at African sites are mostly absent in Homo erectus sites in East Asia. Instead, Oldowan-type choppers and scrapers are found at those sites. If this technology seemed to be so important to African Homo erectus, why didn’t East Asian Homo erectus also use the tools? One reason could be environmental differences between the two regions. It has been suggested that Asian Homo erectus populations used perishable material such as bamboo to make tools. Another possibility is that Homo erectus (or even an earlier hominin) migrated to East Asia before the Acheulean technology developed in Africa. The recent discovery of the 2.1-million-year-old tools in China gives credence to this last explanation.
What (if anything) do the Acheulean tools tell us about the mind of Homo erectus? Clearly, they took a fair amount of skill to manufacture. Apart from the actual shaping of the tool, other decisions made by toolmakers can reveal their use of foresight and planning. Did they just pick the most convenient rocks to make their tools, or did they search out a particular raw material that would be ideal for a particular tool? Analysis of Acheulean stone tools suggest that at some sites, the toolmakers selected their raw materials carefully—traveling to particular rock outcrops to quarry stones and perhaps even removing large slabs of rock at the quarries to get at the most desirable material. Such complex activities would require advanced planning and communication with other individuals. However, other Homo erectus sites lack evidence of such selectivity; instead of traveling even a short distance for better raw material, the hominins tended to use what was available in their immediate area (Shipton et al. 2018).
In contrast to Homo erectus tools, the tools of early modern Homo sapiens during the Upper Paleolithic display tremendous diversity across regions and time periods. Additionally, Upper Paleolithic tools and artifacts communicate information such as status and group membership. Such innovation and social signaling seem to have been absent in Homo erectus, suggesting that they had a different relationship with their tools than did Homo sapiens (Coolidge and Wynn 2017). Some scientists assert that these contrasts in tool form and manufacture may signify key cognitive differences between the species, such as the ability to use a complex language.
Subsistence and Diet
In reconstructing the diet of Homo erectus, researchers can draw from multiple lines of evidence. These include stone tools used by Homo erectus, animal bones and occasionally plant remains from Homo erectus sites, and the bones and teeth of the fossils themselves. These data sources suggest that compared to the australopithecines, Homo erectus consumed more animal protein. Coinciding with the appearance of Homo erectus fossils in Africa are archaeological sites with much more abundant stone tools and larger concentrations of butchered animal bones.

It makes sense that a larger body and brain would be correlated with a dietary shift to more calorically dense foods. This is because the brain is a very energetically greedy organ. Indeed, our own human brains require more than 20% of one’s calorie total intake to maintain. When biologists consider the evolution of intelligence in any animal species, it is often framed as a cost/benefit analysis: For large brains to evolve, there has to be a compelling benefit to having them and a way to generate enough energy to fuel them.
One solution that would allow for an increase in human brain size would be a corresponding reduction in the size of the digestive tract (gut). According to the “expensive tissue hypothesis,” initially formulated by Leslie Aiello and Peter Wheeler (1995), a smaller gut would allow for a larger brain without the need for a corresponding increase in the organism’s metabolic rate. More meat in the diet could also fuel the larger brain and body size seen in the genus Homo. Some researchers also believe that body fat percentages increased in hominins (particularly females) around this time, which would have allowed them to be better buffered against environmental disruption such as food shortages (Anton and Snodgrass 2012).
As indicated above, evidence from archaeology and the inferences about Homo erectus body size suggest increased meat eating. How much hunting did Homo erectus engage in compared to the earlier Oldowan toolmakers? Although experts continue to debate the relative importance of hunting versus scavenging, there seems to be stronger evidence of hunting for these hominins. For example, at sites such as Olorgesailie in Kenya (Figure 10.14), there are numerous associations of Acheulean tools with butchered remains of large animals.
However, Homo erectus certainly ate more than just meat. Studies of the tooth surfaces and microscopic wear patterns on hominin teeth indicate that these hominins ate a variety of foods, including some hard, brittle plant foods (Unger and Scott 2009). This would make sense, considering the environment was changing to be more dominated by grasslands in some areas. Roots, bulbs, and tubers (known as underground storage organs) of open savanna plants may have been a primary food source. Indeed, hunter-gatherer groups such as the Hadza of Tanzania rely heavily on such foods, especially during periods when game is scarce. In the unstable environment of the early Pleistocene, dietary versatility would be a definite advantage.
Tool Use, Cooking, and Fire
One key characteristic of the genus Homo is smaller teeth compared to Australopithecus. Why would teeth get smaller? In addition to new types of foods, changes in how food was prepared and consumed likely led to a decrease in tooth size. Think about how you would eat if you didn’t have access to cutting tools. What you couldn’t rip apart with your hands would have to be bitten off with your teeth—actions that would require bigger, more powerful teeth and jaws. As stone tools became increasingly important, hominins began to cut up, tenderize, and process meat and plants, such that they did not have to use their teeth so vigorously.
Cooking food could also have contributed to the reduction in tooth and jaw size. In fact, anthropologist Richard Wrangham (2009) asserts that cooking played a crucial role in human evolution. Cooking provides a head start in the digestive process because of how heat begins to break down food before food even enters the body, and it can help the body extract more nutrients out of meat and plant foods such as starchy tubers.
Obviously cooking requires fire, and the earliest use of fire is a fascinating topic in the study of human evolution. Fire is not only produced by humans; it occurs naturally as a result of lightning strikes. Like other wild animals, early hominins must have been terrified of wildfires, but at some point in time they learned to control fire and put it to good use. Documenting the earliest evidence of fire has been a contentious issue in archaeology because of the difficulty in distinguishing between human-controlled fire and natural burning at hominin sites. Burned areas and ash deposits must have direct associations with human activity to make a case for deliberate fire use. Unfortunately, such evidence is rare at ancient hominin sites, which have been profoundly altered by humans, animals, and geological forces over millions of years. Recently, newer methods—including microscopic analysis of burned rock and bone—have revealed clear evidence of fire use at Koobi Fora, Kenya, dating to 1.5 million years ago (Hlubik et al. 2017).
Migration out of Africa
Homo erectus is generally thought to be the first hominin species to have left Africa. It is hypothesized that they settled in places in Eurasia, such as the Republic of Georgia, Indonesia, and northern China, where fossil evidence of Homo erectus exists. But why would this species have traveled such vast distances to these far-flung regions? To answer this question, we have to consider what we have learned about the biology, culture, and environmental circumstances of Homo erectus. The larger brain and body size of Homo erectus were fueled by a diet consisting of more meat, and their longer, more powerful legs made it possible to walk and run longer distances to acquire food. Since they were eating higher on the food chain, it was necessary for them to extend their home range to find sufficient game. Cultural developments—including better stone tools and new technology such as fire—gave them greater flexibility in adapting to different environments. Finally, the major Pleistocene climate shift discussed earlier in the chapter certainly played a role. Changes in air temperature, precipitation, access to water sources, and other habitat alteration had far-reaching effects on animal and plant communities; this included Homo erectus. If hominins were relying more on hunting, the migration patterns of their prey could have led them to traverse increasingly long distances.
Life History
The life history of a species refers to its overall pattern of growth, development, and reproduction during its lifetime, with the assumption that these characteristics have been shaped by natural selection. The field of human behavioral ecology, explored in more detail in Appendix C, examines the roots of human behavior and life history. Our species, Homo sapiens, is characterized by a unique life history pattern of slow development, an extended period of juvenile dependence, and a long lifespan. Whereas the offspring of great apes achieve self-sufficiency early, human children are dependent on their parents long after weaning. Additionally, human fathers and grandparents (particularly postmenopausal grandmothers) devote substantial time and energy to caring for their children.

Human behavioral ecologists who study modern hunter-gatherer societies have observed that foraging is no easy business (Figure 10.15). Members of these groups engage in complex foraging techniques that take many years to master. An extended juvenile period gives children the time to acquire these skills. It also allows time for large human brains to grow and mature. On the back end, a longer developmental period results in skilled, successful adults, capable of living a long time (Hill and Kaplan 1999). Despite the time and energy demands, females could have offspring at more closely spaced intervals if they could depend on help from fathers and grandmothers (Hawkes et al. 1998).
What can the study of Homo erectus reveal about its life history pattern? Well-preserved fossils such as the Nariokotome boy can provide some insights. We know that apes such as chimpanzees reach maturity more quickly than humans, and there is some evidence that the australopithecines had a growth rate more akin to that of chimpanzees. Scientists have conducted extensive studies of the Nariokotome skeleton’s bones and teeth to assess growth and development. On the one hand, examination of the long bone ends (epiphyses) of the skeleton suggested that he was an early adolescent with a relatively large body mass, though growth had not yet been completed. On the other hand, study of the dentition, including measurement of microscopic layers of tooth enamel called perikymata, revealed a much younger age of 8 or 9. According to Christopher Dean and Holly Smith (2009), the best explanation for this discrepancy between the dental and skeletal age is that Homo erectus had its own distinct growth pattern—reaching maturity more slowly than chimpanzees but faster than Homo sapiens. This suggests that the human life history pattern of slow maturation and lengthy dependency was a more recent development. More work remains on refining this pattern for early Homo, but it is an important topic that sheds light on how and when we developed our unique life history characteristics.
The Big Picture of Early Homo
We are discovering that the evolution of the genus Homo is more complex than what was previously thought. The earlier view of a simple progression from Australopithecus to Homo habilis to Homo erectus as clearly delineated stages in human evolution just doesn’t hold up anymore.
As is apparent from the information presented here, there is tremendous variability during this time. While fossils classified as Homo habilis show many of the characteristics of the genus Homo, such as brain expansion and smaller tooth size, the small body size and long arms are more akin to australopithecines. There is also tremendous variability within the fossils assigned to Homo habilis, so there is little consensus on whether it is one or multiple species of Homo, a member of the genus Australopithecus, or even a yet-to-be-defined new genus. Similarly, there are considerable differences in skull morphology and body size and form of Homo erectus, of which some specimens show more similarity to Homo habilis than previously thought.
What does this diversity mean for how we should view early Homo? First, there isn’t an abrupt break between Australopithecus and Homo habilis or even between Homo habilis and Homo erectus. Characteristics we define as Homo don’t appear as a unified package; they appear in the fossil record at different times. This is known as mosaic evolution. Indeed, fossil species such as Australopithecus sediba, as well as Homo naledi and Homo floresiensis (who will be introduced in Chapter 11), have displayed unexpected combinations of primitive and derived traits.
We can consider several explanations for the diversity we see within early Homo from about 2.5 million to 1.5 million years ago. One possibility is the existence of multiple contemporaneous species of early Homo during this period. In light of the pattern of environmental instability discussed earlier, it shouldn’t be surprising to see fossils from different parts of Africa and Eurasia display tremendous variability. Multiple hominin forms could also evolve in the same region, as they diversified in order to occupy different ecological niches. However, even the presence of multiple species of hominin does not preclude their interacting and interbreeding with one another. As you’ll see in Appendix D, sequencing of ancient hominin genomes has led to deeper understanding of genetic relationships between extinct species such as the Neanderthals and Denisovans.
Diversity of brain and body sizes could also reflect developmental plasticity—short-term adaptations within a lifetime (Anton et al. 2014). These have the advantage of being more flexible than genetic natural selection, which could only occur over many generations. For example, among human populations today, different body sizes are thought to be adaptations to different climate or nutritional environments. Under Pleistocene conditions of intense variability, a more flexible strategy of adaptation would be valuable.
New discoveries are also questioning old assumptions about the behavior of Homo habilis and Homo erectus. Just as the fossil evidence doesn’t neatly separate Australopithecus and Homo, evidence of the lifeways of early Homo show similar diversity. For example, one of the traditional dividing lines between Homo and Australopithecus was thought to be stone tools: Homo made them; Australopithecus didn’t. However, the recent discovery of stone tools from Kenya dating to 3.3 million years ago challenges this point of view. Similarly, the belief that Homo erectus was the first species to settle outside Africa may now come into question with the report of 2.1-million-year-old stone tools from China. If this find is supported by additional evidence, it may cause a reevaluation of Homo erectus being the first to leave Africa. Instead, there could have been multiple earlier migrations of hominins such as Homo habilis or even Australopithecus species.
These various lines of evidence about the genus Homo point out the need for a more nuanced view of this period of human evolution. Rather than obvious demarcations between species and their corresponding behavioral advancements, it now looks like many behaviors were shared among species. Earlier hominins that we previously didn’t think had the capability could have been doing things like expanding out of Africa or using stone tools. Meanwhile, some other hominins that we had considered more advanced didn’t actually have the full suite of “human” characteristics previously expected.
From a student’s perspective, all this complexity probably seems frustrating. It would be ideal if the human story were a straightforward, sequential narrative. Unfortunately, it seems that human evolution was not a nice, neat trajectory of increasingly humanlike traits and behaviors; rather, it is emblematic of the untidy but exciting nature of the study of human evolution.
Despite some haziness dominating the early Homo narrative, we can identify some overall trends for the million-year period associated with early Homo. These trends include brain expansion, a reduction in facial prognathism, smaller jaw and tooth size, larger body size, and evidence of full terrestrial bipedalism. These traits are associated with a key behavioral shift that emphasizes culture as a flexible strategy to adapt to unpredictable environmental circumstances. Included in this repertoire are the creation and use of stone tools to process meat obtained by scavenging and later hunting, a utilization of fire and cooking, and the roots of the human life history pattern of prolonged childhood, cooperation in child raising, and the practice of skilled foraging techniques. In fact, it’s apparent that the cultural innovations are driving the biological changes, and vice versa, fueling a feedback loop that continues during the later stages of human evolution.
Hominin Species Summaries
Hominin |
Homo habilis |
Dates |
2.5 million years ago to 1.7 million years ago |
Region(s) |
East and South Africa |
Famous discoveries |
Olduvai Gorge, Tanzania; Koobi Fora, Kenya; Sterkfontein, South Africa |
Brain size |
650 cc average (range from 510 cc to 775 cc) |
Dentition |
Smaller teeth with thinner enamel compared to Australopithecus; parabolic dental arcade shape |
Cranial features |
Rounder cranium and less facial prognathism than Australopithecus |
Postcranial features |
Small stature; similar body plan to Australopithecus |
Culture |
Oldowan tools |
Other |
N/A |
Hominin |
Homo erectus |
Dates |
1.8 million years ago to about 110,000 years ago |
Region(s) |
East and South Africa; West Eurasia; China and Southeast Asia |
Famous discoveries |
Lake Turkana, Olorgesailie, Kenya; Java, Indonesia; Zhoukoudian, China; Dmanisi, Republic of Georgia |
Brain size |
Average 900 cc; range between 650 cc and 1,100 cc |
Dentition |
Smaller teeth than Homo habilis |
Cranial features |
Long, low skull with robust features including thick cranial vault bones and large brow ridge, sagittal keel, and occipital torus |
Postcranial features |
Larger body size compared to Homo habilis; body proportions (longer legs and shorter arms) similar to Homo sapiens |
Culture |
Acheulean tools (in Africa); evidence of increased hunting and meat-eating; use of fire; migration out of Africa |
Other |
N/A |
Review Questions
- Describe the climate during the early Pleistocene. Explain why climate is important for understanding the evolution of early Homo.
- List the key anatomical characteristics that are generally agreed to define the genus Homo.
- Why has classification of early Homo fossils proved difficult? What are some explanations for the variability seen in these fossils?
- Compare and contrast the Oldowan and Acheulean tool industries.
- Name some specific behaviors associated with Homo erectus in the areas of tool use, subsistence practices, migration patterns, and other cultural innovations.
Key Terms
Acheulean: Tool industry characterized by teardrop-shaped stone handaxes flaked on both sides.
Developmental plasticity: The capability of an organism to modify its phenotype during development in response to environmental cues.
Human behavioral ecology: The study of human behavior from an evolutionary and ecological perspective.
Life history: The broad pattern of a species’ life cycle, including development, reproduction, and longevity.
Mosaic evolution: Different characteristics evolve at different rates and appear at different stages.
Occipital torus: A ridge on the occipital bone in the back of the skull.
Oldowan: Earliest stone-tool industry consisting of simple flakes and choppers.
Perikymata: Microscopic ridges on the surface of tooth enamel that serve as markers of tooth development.
Pleistocene: Geological epoch dating from 2.6 million years ago to about 11,000 years ago.
Pliocene: Geological epoch dating from 5.3 to 2.6 million years ago.
Prognathism: Condition where the lower face and jaw protrude forward from a vertical plane.
Sagittal keel: A thickened area along the top of the skull.
About the Author
Bonnie Yoshida-Levine, Ph.D.
Grossmont College, bonnie.yoshida@gcccd.edu
Bonnie Yoshida-Levine is an instructor of anthropology at Grossmont College, where she teaches biological anthropology and archaeology. She received her bachelor’s degree in history from the University of California, Los Angeles, and her M.A. and Ph.D. degrees in anthropology from the University of California, Santa Barbara. Her dissertation research focused on the bioarchaeology of early civilizations in north coastal Peru. Bonnie has also collaborated on archaeological field projects in Bolivia and coastal California.
FOR FURTHER EXPLORATION
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Human Evolution by the Smithsonian Institution. Produced by the Smithsonian National Museum of Natural History, this website covers many aspects of human evolution including 3-D models of hominin fossils.
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Acknowledgments
The author gratefully acknowledges funding from the California Community Colleges Chancellor’s Office Zero Textbook Cost Degree Grant Program—Implementation Phase 2.
The act of searching for food.