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10.  Early Members of the Genus Homo

Bonnie Yoshida-Levine Ph.D., Grossmont College

Learning Objectives

Describe how early Pleistocene climate change in�uenced the evolution of the genus Homo.

Identify the characteristics that de�ne 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 classi�ed.

Describe what is known about the adaptive strategies of early members of the Homo genus, including tool tech-

nologies, diet, migration patterns, and other behavioral trends.

The boy was no older than 9 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

Kimoya Kimeu, working on the western shore of Lake Turkana, Kenya, glimpsed a dark colored piece of bone eroding in a hill-

side. This small skull fragment led to the discovery of what is arguably the world’s most complete early hominin fossil—a youth

identi�ed as a member of the species Homo erectus. Now known as Nariokotome Boy, after the nearby lake village, the skele-

ton 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.

Previous: Early Hominins

Next: Archaic Homo

                         

Figure 10.1 Skeleton of a young male Homo erectus known as “Nariokotome Boy,” along with an artist’s depiction of how he may

have looked during his life. This is the most complete hominin fossil from this time period ever found.

The previous chapter described our oldest human ancestors, primarily members of the genus Australopithecus who lived be-

tween 2 million and 4 million years ago. This chapter introduces the earliest members of the genus Homo, focusing on the

species Homo habilis and Homo erectus.

DEFINING THE GENUS HOMO

Since our discipline is fundamentally concerned with what makes us human, de�ning our own genus takes on special signi�-

cance for anthropologists. The genus is the next level up from species in the classi�cation system originally devised by Caro-

lus Linnaeus. In the 1758 publication Systema Naturae, Linnaeus assigned humans the genus name Homo, meaning “person.”

Under this classi�cation scheme, Linnaeus included several ape species, as well as wild children and mythical humans such as

cave-dwelling troglodytes. In the present-day classi�cation, the apes and monster people have long been removed, and our

species, Homo sapiens, remains as its only living representative. But ever since scientists have acknowledged the existence of

extinct species of humans, they have debated which of these display suf�cient “humanness” to merit classi�cation in our

genus.

When grouping species into a common genus, biologists will 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 speci�c fossils should be interpreted in light of the criteria.

There is general agreement that species classi�ed as Homo should share characteristics broadly similar to our species. These

include the following:

a relatively large brain size, indicating a high degree of intelligence;

a smaller and �atter face;

smaller jaws and teeth; and

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. There is

also an apparent decline in sexual dimorphism (body-size differences between males and females). While these criteria seem

relatively clear-cut, evaluating them in the fossil record has proved more dif�cult, 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, making them dif�cult to evaluate. 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 con�icting classi�cation schemes depending on which

criteria they think are most important. Previous: Early Hominins

Next: Archaic Homo

In this chapter, we will take several pathways toward examining the origin and evolution of the genus Homo. First, we will ex-

plore 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 identi�ed 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 char-

acterize 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 iso-

topes, core samples from oceans and lakes, windblown dust, analysis of geological formations and volcanoes, and fossils of an-

cient plant and animal communities. Such studies have provided valuable information about the environmental context of

early Homo.

The early hominin species covered previously, 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 Pleis-

tocene 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 ac-

tually the case. Instead, climate became much more variable, cycling abruptly between warm/wet (interglacial) and cold/dry

(glacial) cycles. The climate pattern was likely in�uenced 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 in�uence climate pattern, climate change had extreme effects on the environment in some regions but less effects on

others.

For a present-day example with which you might be familiar, consider the El Niño weather pattern. This is where warming of

the Paci�c Ocean in the equator region in�uences rainfall, hurricane frequency, and other weather activity in different parts

of the world. During El Niño years, some areas get more rainfall than average and some get less. A recent El Niño in 2017 pro-

duced catastrophic �ooding along the Peruvian coast, and one in 2015 led to drought and severe bush�res in Australia. If El

Niños, despite being a predictable and well-known occurrence, can cause so much disruption to our technologically advanced

society, imagine how vulnerable our ancestors must have been to climate change. An adaptive strategy that could buffer

against this kind of uncertainty would have been extremely valuable.

Figure 10.2 Temperature estimates during the last �ve million years, extrapolated from deep-sea core data. Note both the lower temperatures and the increased temperature oscillations starting at 2.6 million years ago, the start of the Pleistocene epoch. Glacial/interglacial cycles during the early part of the epoch are shorter, each averaging about 41,000 years.

Previous: Early Hominins

Next: Archaic Homo

Figure 10.3 A savanna grassland in East Africa. Habitats such as this were becoming increasingly common during the Pleistocene.

Data on ancient geography and climate help us understand how our ancestors moved and migrated to different parts of the

world, and 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 known as 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.

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. Since our early an-

cestors were also part of this animal community, it is informative to consider how climate change caused changes in the home

ranges and migration patterns of animals. 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

animal species moved back and forth between Africa and Eurasia during the Pliocene and Pleistocene epochs. 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 when drier conditions extended out from Africa into the Middle East (Belmaker 2010).

This changing environment was undoubtedly challenging for our ancestors, but it offered

new opportunities for hominins 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. As dis-

cussed in the previous chapter, the robust australopithecines probably developed their

large molar teeth with thick enamel in order to exploit this particular dietary niche. Chemi-

cal analyses of robust australopith teeth show an isotopic signature of a diet where grasses

and sedges are prominent, such as papyrus.

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 so-

lutions such as crafting stone tools that opened up new foraging opportunities. This strat-

egy of behavioral �exibility 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 classi�ed as Homo habilis, including whether they

come from a single or multiple species, or even whether they should be part of the genus Homo at all.

Compared to the australopithecines in the previous chapter, Homo habilis has a somewhat larger brain size–an average of 650

cubic centimeters (cc) compared to less than 500 cc for Australopithecus. 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 identi�ed 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 identi�ed as belonging

to the genus Homo (Villmoare et al. 2015). If this classi�cation holds up, it would push the origins of our genus back even

further.

Previous: Early Hominins

Next: Archaic Homo

Figure 10.4 Map showing major sites where Homo habilis fossils have been found.

Discovery and Naming

The �rst 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 (Fig. 10.4). The

Leakey family had been conducting �eldwork in the area since the 1930s and had discov-

ered other hominin fossils at the site, such as the robust Australopithecus 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 �nger bones. Potassium-argon dating of the rock

layers showed that the fossil dated to about 1.75 million years. In 1964, the team published

their �ndings in the scienti�c journal Nature (Leakey et al. 1964). As described in the publi-

cation, the new fossils had smaller molar teeth that were less “bulgy” than australop-

ithecine 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 australop-

ithecines such as A. africanus. The hand bones were similar to humans’ in that they were capable of a precision grip. This in-

creased the likelihood that stone tools found earlier at Olduvai Gorge were made by this group of hominins. Based on these

�ndings, the authors inferred that it was a new species that should be classi�ed in the genus Homo. They gave it the name

Homo habilis, meaning “handy” or “skilled.”

                 

Figure 10.5 Homo habilis fossil specimens. From left to right they are: OH-24 ( found at Olduvai Gorge), KNM-ER-1813 ( from Koobi

Fora, Kenya), and the jaw of OH-7, which was the type specimen found in 1960 at Olduvai Gorge, Tanzania.

Previous: Early Hominins

Next: Archaic Homo

Loca-

tion of

Fossils

Dates Description

Ledi-

Gararu,

Ethiopia

2.8

mya

Partial lower jaw with evidence of

both Australopithecus and Homo

traits; tentatively considered old-

est Early Homo fossil evidence.

Olduvai

Gorge,

Tanza-

nia

1.7

mya

to 1.8

mya

Several different specimens clas-

si�ed 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.

Sterk-

fontein

and

other

possible

South

African

cave

sites

about

1.7

mya

South African caves have yielded

fragmentary remains identi�ed

as Homo habilis, but secure dates

and speci�cs about the fossils are

lacking.

Figure 10.6 Key Homo habilis fossil locations and the corresponding fossils and dates.

Controversies over Classi�cation of Homo habilis

How Many Species of Homo habilis?

Since this initial discovery, more fossils classi�ed as Homo habilis were discovered in sites in East and South Africa in 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 �rst 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 reminiscent of a robust australopithecine. The diversity of the Homo habilis fos-

sils prompted some scientists to question whether they displayed too much variation to all remain as part of the same species.

They proposed splitting the fossils into at least two groups. The �rst 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 ha-

bilis 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 in�uenced by variations in climates and nutri-

tional circumstances. Previous: Early Hominins

Next: Archaic Homo

Given the incomplete and fragmentary fossil record from this time period, it is not surprising that classi�cation has proved

contentious. As a scholarly consensus has not yet emerged on the classi�cation status of early Homo, this text will make use of

the single (inclusive) Homo habilis species designation.

Homo habilis: Homo or Australopithecus?

There is also disagreement on whether Homo habilis legitimately belongs in the genus Homo. Most of the fossils �rst classi�ed

as Homo habilis consisted mainly of skulls and teeth. When arm, leg, and foot bones were later found, making it possible to es-

timate body size, they 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 question whether Homo habilis behaved more like an aus-

tralopithecine—with a shorter gait and the ability to move around in the trees (Wood and Collard 1999). They also questioned

whether the brain size of Homo habilis was really that much larger than that of Australopithecus. They have proposed reclassi-

fying some or all of the Homo habilis fossils into the genus Australopithecus, or even placing them into a newly created genus

(Wood 2014).

Figure 10.7 Cast of the Homo habilis cranium KNM-ER-1470. This cranium has a wide, �at face, larger brain size, and larger teeth than other Homo habilis fossils, leading some scientists to give it a separate species name, Homo rudolfensis.

Other scholars have interpreted the fossil evidence differently. A recent reanalysis of Homo habilis/rudolfensis fossils con-

cluded that they sort into the genus Homo rather than Australopithecus (Figure 10.8). In particular, statistical analysis per-

formed indicates that the Homo habilis fossils differ signi�cantly 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 signi�cant as brain- and tooth-size differences (Anton et al. 2014).

Previous: Early Hominins

Next: Archaic Homo

Hominin Homo habilis

Dates 2.5 million years ago to 1.7 million

years ago

Region(s) East and South Africa

Famous

Discov-

eries

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; par-

abolic dental arcade shape

Cranial

Features

Rounder cranium and less facial

prognathism than Australopithecus

Postcra-

nial

Features

Small stature; similar body plan to

Australopithecus

Culture Oldowan tools

Figure 10.8 Summary features of Homo habilis.

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. Based on what we know from nonhuman-

primate tool use, it is assumed that all hominins used tools of some sort. For example, australopithecines could have used dig-

ging sticks to extract the roots and tubers that were part of some species’ diets (though tools made from perishable material

would leave no trace). As discussed in the previous chapter, stone tools almost certainly predated Homo habilis (possibly by

Australopithecus garhi or the species responsible for the tools from Kenya dating to 3.7 million years ago). However, stone

tools become more frequent at sites dating to about 2 million years ago, the time of Homo habilis (Roche, Blumenschine, and

Shea 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. Studying the form of the tools, the raw ma-

terials selected, and how they were made and used can provide insight into the thought processes of early humans and how

they modi�ed their environment in order to survive. Paleoanthropologists have traditionally classi�ed collections of stone

tools into industries, based on their form and mode of manufacture. There is not an exact correspondence between a tool in-

dustry and a hominin species; however, some general associations can be made between tool industries and particular ho-

minins, locations, and time periods. The names for the four primary tool industries in human evolution (from oldest to most

recent) are the Oldowan, Acheulean, Mousterian, and Upper Paleolithic.

The oldest stone tool industry is the Oldowan, named after the site of Olduvai Gorge where the tools were �rst discovered.

The time period of the Oldowan is generally considered to last from about 2.5 mya to 1.6 mya. The tools of this industry are Previous: Early Hominins

Next: Archaic Homo

described as “�ake and chopper” tools—the choppers consisting of stone cobbles with a few �akes 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 hammer-

stone at just the right angle so that one or more �at �akes are removed. This requires selecting rocks that will fracture pre-

dictably instead of chunking, as well as the ability to plan ahead and envision the steps needed to create the �nished product.

The process leaves both the core and the �akes with sharp cutting edges that can be used for a variety of purposes.

Figure 10.9 Drawing of an Oldowan-style tool. This drawing shows a chopper; the �akes removed from the cores functioned as cutting tools.

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. Animal bones with

cutmarks start appearing at sites with Oldowan tools. Studies of animal bones at the site show leg bones are often cracked

open, suggesting that they were extracting the marrow from the bone cavities. It is interesting to consider whether the ho-

minins 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 dif�cult 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 evaluated the scavenging

hypothesis by directly observing the behavior of present-day animal carnivores and scavengers on the African savanna. From

this, he inferred that there were scavenging opportunities for Plio-pleistocene hominins. When lions abandon a kill after eat-

ing their �ll, scavenging animals arrive almost immediately to pick apart the carcass. By the time the slow-footed hominins ar-

rived 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 1987).

Reconstructing activities that happened millions of years ago is obviously a dif�cult undertaking, and there is an active debate

among anthropologists about whether scavenging or hunting was more commonly practiced during this time. Regardless of

how they were acquiring the meat, all these activities suggest an important dietary shift from the way that the australop-

ithecines 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 process-

ing 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, Blumenschine,

and Shea 2009).

Overall, increasing use of stone tools allowed hominins to expand their ecological niche and exert more control over their en-

vironment. As we’ll see shortly, this pattern continued and became more pronounced with Homo erectus.

HOMO ERECTUS: BIOLOGICAL AND CULTURAL INNOVATIONS Previous: Early Hominins Next: Archaic Homo

After 2 million years ago, a new hominin appeared on the scene. Known as Homo erectus, the prevailing scienti�c view was

that this species was much more like us. These hominins were equipped with bigger brains and large bodies with limb propor-

tions similar to our own. Perhaps most importantly, their way of life is now one that is recognizably human, with more ad-

vanced tools, hunting, use of �re, 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 �rst summarize the anatomical characteristics that de�ne 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 dis-

played key differences from later hominin species including our own.

Although the head of Homo erectus was less ape-like in appearance than the australopithecines, neither did it resemble mod-

ern humans (Figure 10.10). Compared to Homo habilis, Homo erectus had a larger brain size (average of about 900 cc compared

to 650 cc to 750 cc). Instead of having a rounded shape like our skulls have, 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 appear-

ance. 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.

Figure 10.10 Replica of Homo erectus from Java, Indonesia. This cranium (known as Sangiran 17) dates to approximately 1.3 million to 1 million years ago. Note the large brow ridges and the occipital torus that gives the back of the skull a squared-off appearance.

Apart from these distinctive features, signi�cant variation is present between Homo erectus fossils from different regions. Sci-

entists 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 dis-

tinctive characteristics. As with Homo habilis, this diversity has prompted a classi�cation 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 �rst. This text will use the

species name Homo erectus for both variants. Previous: Early Hominins

Next: Archaic Homo

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 ef�ciently. 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 ef�cient 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).

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’s. Even the Nariokotome skeleton itself has been reassessed to be quite a bit shorter (predicted to

be closer to 5 feet 4 inches when fully grown, rather than over 6 feet), although there is still disagreement about which mea-

surement is more accurate. One explanation for the range of body sizes could be adaptation to a range of different local envi-

ronments, just as humans today show reduced body size in poor nutritional environments (Anton and Snodgrass 2012).

Homo erectus also shows some evidence of a reduction in sexual dimorphism in body size compared to the earlier australop-

ithecines. In other words, Homo erectus males were only slightly larger in body size than females. The degree of sexual dimor-

phism among early hominin species is a contentious issue. It is a dif�cult characteristic to measure and assess in the fossil

record, since fossils have to be complete enough to determine both body size and sex. However, if Homo erectus was less sex-

ually dimorphic, it may signify changes in social organization within the species. If you recall from the chapter on primates,

highly dimorphic species are those where males compete intensely for mating access to females. Decreased sexual dimor-

phism suggests that the lifestyle of Homo erectus may have been different from that of earlier hominins.

SPECIAL TOPICS: HOW WE BECAME HAIRLESS, SWEATY PRIMATES

As an anthropology instructor, one question about human evolution that students often ask me concerns human

body hair—when did our ancestors lose it and why? It is assumed that our earliest ancestors were as hairy as mod-

ern-day apes. Today, though, we lack thick hair on most parts of our bodies except in the armpit and pubic regions

and on the 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 ef�ciently than any other primate. Humans have a larger amount of eccrine sweat glands than other pri-

mates and these glands generate an enormous volume of watery sweat. Sweating produces liquid on the skin that

cools you off as it evaporates. It seems likely that hairlessness and sweating evolved together, as a recent DNA

analysis has identi�ed a shared genetic pathway between hair follicles and eccrine sweat gland production (Kam-

berov 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 cli-

mate 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.

Previous: Early Hominins

Next: Archaic Homo

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 bod-

ies made it possible for humans to cover long distances while foraging, this new body form had to cool itself effec-

tively 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.

When did these changes occur? Although hair and soft tissue do not typically fossilize, there are several indirect

methods that have been used to explore this question. One method tracks a human skin color gene. Since chim-

panzees 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 to shield our ancestors from harmful ultraviolet radiation. A re-

cent genetic analysis determined that one of the genes responsible for melanin production originated about 1.2

million years ago (Jablonski 2012).

Another line of evidence tracks the coevolution of a rather unpleasant human companion—the louse. A genetic

study identi�ed 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, Kayser, and Stoneking 2003). Because human body lice can only

spread through clothing, this may have been about the time when humans started to regularly wear clothing. How-

ever, the split between human head and pubic lice is estimated to have occurred much earlier, about three million

years ago (Reed et al. 2007). When humans lost much of their body hair, lice that used to roam freely around the

body were now con�ned to two areas: the head and pubic region. As a result of this “geographic” separation, the

lice population split into two distinct groups.

Other explanations have also been suggested for the loss of human body hair. For example, being hairless has other

advantages such as making it more dif�cult for skin parasites like lice, �eas, and ticks to live on us. Additionally, af-

ter bipedality evolved, hairless bodies would also make reproductive organs and female breasts more visible, sug-

gesting that sexual selection may have played a role.

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 identi�ed 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 �nds are a female pelvis from

the site of Gona, Ethiopia (Simpson et al 2008), and a cranium from Olduvai Gorge known as Olduvai 9, thought to be about 1.4

million years old with massive brow ridges.

Homo erectus’ presence in South Africa is not well documented, though fossils thought to belong to the species have also been

uncovered from the famed South African Swartkrans cave site along with stone tools and burned animal bones.

Regional Discoveries Outside Africa

It is generally agreed that Homo erectus was the �rst hominin to migrate out of Africa and colonize Asia and later Europe (al-

though recent discoveries in Asia may challenge this view). Key locations and discoveries of Homo erectus fossils, along with

the fossils’ estimated age are summarized below, and in Figure 10.12. Previous: Early Hominins

Next: Archaic Homo

Figure 10.11 Map showing the locations of Homo erectus fossils around Africa and Eurasia.

Indonesia

The �rst 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 some other bone fragments on a riverbank. While the femur

looked human, the top of the skull was smaller and thicker than a modern person’s. 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.

Homo erectus has a long history in Indonesia; further discoveries of fossils from Java were dated by argon dating to about 1.6

million to 1.8 million years. A cache of H. erectus fossils from the site of Ngandong in Java has yielded very recent dates of

43,000 years, although a more recent study with different dating methods concluded that they were much older—between

140,000 and 500,000 years old. Still, the possible existence of isolated, yet-to-be-discovered hominin populations in the re-

gion is of great interest to paleoanthropologists, especially given the discovery of the tiny Homo �oresiensis fossils discovered

on the nearby island of Flores, Indonesia, and the very recent announcement of possible tiny hominin fossils from the island of

Luzon in the Philippines.

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, in-

cluding six nearly complete skulls, were excavated from the 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. What exactly happened to them is

murky—there are several con�icting accounts. Fortunately, an anatomist named Frans Weidenreich who had previously stud-

ied the bones had made casts and measurements of the skulls, so this valuable information was not lost. More recent excava-

tions, 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.

Previous: Early Hominins

Next: Archaic Homo

Despite this lengthy history of scienti�c 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 no-

table �nds at sites like Nariokotome and Olorgesaille took center stage during the 1970s and 80’s, as scientists focused on elu-

cidating the species’ anatomy and adaptations in its African homeland. In contrast, fewer research projects were focused on

East Asian sites (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

stone tools from China dated to 2.1 million years caught everyone’s attention. Dated by paleomagnetic techniques that date

the associated soils and windblown dust, these tools indicate that hominins in Asia predated those at 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 earlier than

Homo erectus could have migrated out of Africa. These exciting 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 �rst hominin fossils were discovered in the early 1990s, and since that time, at least �ve rela-

tively 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 re-

duced 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 in-

creases 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 (Lordikipanidze et al. 2013). Regardless of which point of view ends up dominating, the Dmanisi hominins

are clearly central to the question of how to de�ne 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 ice age climate of

Western Europe served as a barrier to living there. However, recent fossil �nds 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, dat-

ing 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).

Previous: Early Hominins

Next: Archaic Homo

At this time, researchers aren’t in agreement as to whether the �rst 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.

Re-

gion Sites Dates Signi�cance of Fossils

East

Africa

East and West Lake

Turkana, Kenya;

Olduvai Gorge,

Tanzania

1.8 to 1.4

mya

Earliest evidence of H. erec-

tus; signi�cant variation in

skull and facial features.

West-

ern

Eura-

sia

Dmanisi, Republic of

Georgia 1.75 mya

Smaller brains and bodies

than H. erectus from other

regions.

West-

ern

Eu-

rope

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.

In-

done-

sia

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 sug-

gests great antiquity of Homo

in East Asia.

Figure 10.12 Regional comparisons of Homo erectus fossils.

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 organi-

zation. As will be apparent, Homo erectus shows signi�cant 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 �akes and choppers identi�ed 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–classi�ed 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 modi�ed by striking off a few �akes, Acheulean toolmakers care-

fully shaped both sides of the tool. This type of technique, known as bifacial �aking, requires more planning and skill on the

Previous: Early Hominins

Next: Archaic Homo

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 �ake tools are

present at Homo erectus sites.

Figure 10.13 Drawing of an Acheulean handaxe. This specimen is from Spain. When drawing a stone tool, artists typically show front and back faces, as well as top and side pro�les.

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 re-

gard 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. Perhaps the rocks available in Asia weren’t of the material suitable for making the Acheulean handaxes. It has

been suggested that Asian Homo erectus populations used perishable material such as bamboo to make tools. Another possi-

bility 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.

Tool Use and Cognitive Abilities of Homo erectus

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. They also

likely required cooperation and communication with other individuals, as such actions would be dif�cult to carry out solo.

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.

Previous: Early Hominins

Next: Archaic Homo

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.

Meat Eating and Increased Brain Size

It makes sense that a larger body and brain would be correlated with a dietary shift to more calorically dense foods. This is be-

cause the brain is a very energetically greedy organ. Indeed, our own human brains require more than 20% of one’s calorie to-

tal intake to maintain. When biologists consider the evolution of intelligence in any animal species, it is often framed as a

cost/bene�t analysis: In order for large brains to evolve, there has to be a compelling bene�t 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 di-

gestive 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. Judging from their skeleton, australopithecines have a wider rib cage and trunk region more similar to apes than humans.

It is thought that the australopithecines had large gut sizes similar to today’s great apes because they were eating mainly plant

foods, which require more gut bacteria to digest. More meat in the diet would allow for a smaller gut and could also fuel the

larger brain and body size seen in the genus Homo. Some researchers also believe that body fat percentages increased in ho-

minins (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).

Evidence for Die�ary Versatility in Homo erectus

As indicated above, evidence from archaeology and the inferences about Homo erectus body size suggest increased meat eat-

ing. 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 ho-

minins. 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. Modern-day hunter-gatherer societies have been used as models

for considering the behavior patterns and environmental constraints of our early ancestors. Plant foods make up the bulk of

calories for most modern-day hunter-gatherer societies, since they are a much more reliable food source. It would make

sense that we would see similar patterns among early hominins.

Studies of the tooth surfaces and microscopic wear patterns on hominin teeth indicate that Homo erectus 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 or-

gans) of open savanna plants may have been a primary food source. Indeed, hunter-gatherer groups such as the Hadza of Tan-

zania 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 de�nite advantage.

Tool Use, Cooking, and Fire Previous: Early Hominins

Next: Archaic Homo

Figure 10.14 Excavations at the site of Olorgesailie, Kenya. Dated from between 1.2 million years ago and 490,000 years ago, Olorgesailie has some of the most abundant and well-preserved evidence of Homo erectus activity in the world. Fossils of large mammals, such as elephants, along with thousands of Acheulean tools, have been uncovered over the decades.

One key characteristic of the genus Homo is smaller teeth compared to Australopithecus. Why would

teeth get smaller? Besides the change in the type of foods eaten, there may have also been changes

in how food was prepared and consumed. 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. During this time, stone tools

were becoming increasingly important. If hominins were using these tools to cut up, tenderize, and

process meat and plants, they wouldn’t have to use their teeth so vigorously.

Cooking food could also have contributed to the reduction in tooth and jaw size. In fact, anthropolo-

gist Richard Wrangham (2009) asserts that cooking played a crucial role in human evolution. Cook-

ing 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. According to Wrangham’s model, this improved diet had a num-

ber of far-reaching consequences for human evolution. Most importantly, it allowed for the larger

brain and body size (and smaller gut size) seen in Homo erectus.

Obviously cooking requires �re, and the earliest use of �re is a fascinating topic in the study of hu-

man evolution. Fire, of course is not limited to humans; it occurs naturally as a result of lightning

strikes. Like other wild animals, early hominins must have been terri�ed of wild�res, but at some

point in time learned to control �re and put it to good use. Cooking, warmth, and scaring off wild

animals are just some of the bene�ts of �re. Consider the potential social bene�ts of having a light

source after dark. Rather than just going to sleep, members of the group could repair tools, plan the

next day’s activities, or socialize—just as you might do sitting around a camp�re with family or

friends. Isn’t it intriguing to think about how such activities might have encouraged the development

of language?

Documenting the earliest evidence of �re has been a contentious issue in archaeology because of the dif�culty in distinguish-

ing between human-controlled �re and natural burning at hominin sites. Burned areas and ash deposits must have direct as-

sociations with human activity to make a case for deliberate �re use. Examples might include the presence of wood ash in

caves where trees don’t naturally grow, deep ash deposits in hearths lined with stones, or burned pieces of stone tools and

butchered animal bones (Gao 2017). 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 �re 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 �rst hominin species to leave the continent of Africa and settle in Eurasia in places

such as the Republic of Georgia, Indonesia, and northern China. We previously discussed the timing and fossil evidence for the

appearance of Homo erectus at those sites; now we can address why the species traveled such vast distances to these far-�ung

regions. To do this, 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 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 �nd suf�cient game. Cultural developments including better

stone tools and new technology such as �re gave them greater �exibility in adapting to different environments. Finally, the

major Pleistocene climate shift discussed earlier in the chapter certainly played a role. Changes in air temperature, precipita-

tion, access to water sources, and other habitat alteration had far-reaching effects on animal and plant communities; this in-

cluded Homo erectus. If hominins were relying more on hunting, the migration patterns of their prey could have led them in-

creasingly long distances.

Previous: Early Hominins

Next: Archaic Homo

Figure 10.15 Hadza men practice bowing. Native to Tanzania, the Hadza have retained many traditional foraging practices. Although most do not subsist entirely upon wild foods today, their way of life may shed light on how humans lived for most of their evolutionary history.

Life History

The life history of a species refers to its overall pattern of growth, development, and reproduction during its lifetime, with

the assumption being that these characteristics have been shaped by natural selection. Our species, Homo sapiens, is charac-

terized by a unique life history pattern of slow development, a long period of juvenile dependence, and a long lifespan. Unlike

the great apes whose offspring achieve early self-suf�ciency, human children are dependent on their parents long after wean-

ing. Additionally, human fathers and grandparents (particularly post-menopausal 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 are dif�cult and take many years to mas-

ter. 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 inter-

vals 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. Scien-

tists 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 hu-

man life history pattern of slow maturation and lengthy dependency was a more recent

development. More work remains on re�ning this pattern for early Homo, but it is an im-

portant question, as it sheds light on how and when we developed our unique life history

characteristics (Figure 10.16).

Previous: Early Hominins

Next: Archaic Homo

Hominin Homo erectus

Dates 1.8 million years ago to about 200,000 years ago

Region(s) East and South Africa; West Eurasia; China and Southeast Asia

Famous

Discoveries

Lake Turkana, Olorgesailie, Kenya; 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 �re; migration out of Africa

Figure 10.16 Summary features of Homo erectus.

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 pre-

vailing view of a simple progression from Australopithecus to Homo habilis to Homo erectus as clearly delineated stages in hu-

man evolution just doesn’t hold up anymore.

Variability in the Fossil Record of Early Homo

As is apparent from the information presented here, there is tremendous variability during this time. While fossils classi�ed 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 no consensus on whether it is a single or multiple species of Homo, a member of the genus Australop-

ithecus, or even a yet-to-be-de�ned 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 de�ne as Homo don’t appear as a uni�ed

package; they appear in the fossil record at different times. This is known as mosaic evolution. Indeed, fossil �nds such as

Australopithecus sediba, and Homo naledi and Homo �oresiensis discussed in the next chapter, 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 diversi�ed in order to oc-

cupy different ecological niches. However, even the presence of multiple species of hominin does not preclude their interact-

ing and interbreeding with one another. As you’ll see in the next chapter, sequencing of ancient hominin genomes has led to

deeper understanding of genetic relationships between extinct species such as the Neanderthals and Denisovans.

Previous: Early Hominins

Next: Archaic Homo

Diversity of brain and body sizes could also re�ect developmental plasticity—short-term adaptations within a lifetime (Anton,

Potts, and Aiello 2014). These have the advantage of being more �exible 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. Keeping in mind that the climate was intensely variable, wouldn’t a more �exible

strategy of adaptation be valuable under these conditions?

Trends in the Behavior of Early Homo

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 chal-

lenges this point of view. Similarly, the belief that Homo erectus was the �rst 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 �nd is supported by additional evidence, it

may cause a reevaluation of Homo erectus being �rst to leave. Instead, there could have been multiple earlier migrations of ho-

minins 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 increas-

ingly humanlike traits and behaviors; rather, it is emblematic of the untidy but exciting nature of the study of human

evolution.

Despite the haziness dominating the early Homo narrative, we can identify some overall trends for the million-year period as-

sociated 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 empha-

sizes culture as a �exible 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 �re and cooking, and

the roots of the human life history pattern of prolonged childhood, cooperation in child raising, and the practice of skilled for-

aging techniques. In fact, it’s apparent that the cultural innovations are driving the biological changes, and vice versa, fueling a

feedback loop that will continue during the later stages of human evolution.

Review �uestions

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 de�ne the genus Homo.

Why has classi�cation of early Homo fossils proved dif�cult? What are some explanations for the variability

seen in these fossils?

Compare and contrast the Oldowan and Acheulean tool industries.

Name some speci�c behaviors associated with Homo erectus in the areas of tool use, subsistence practices,

migration patterns, and other cultural innovations. Previous: Early Hominins

Next: Archaic Homo

Bonnie Yoshida- Levine

Key Terms

Acheulean: Tool industry characterized by teardrop-shaped stone handaxes �aked on both sides.

Developmental plasticity: The capability of an organism to modify its phenotype during development in response to environ-

mental cues.

Human behavioral ecology: 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 �akes 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.

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, [email protected]

Bonnie Yoshida-Levine is an instructor of anthropology at Grossmont College, where she teaches biological an-

thropology 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 �eld projects in Bolivia and coastal California.

 

For Further Exploration

Boaz, Noel Thomas, and Russell L. Ciochon. 2004. Dragon Bone Hill: An Ice-Age Saga of Homo erectus. New York: Oxford Universi

Press.

Human Evolution by the Smithsonian Institution: http://humanorigins.si.edu/ Produced by the Smithsonian National Museum o

Natural History, this website covers many aspects of human evolution including 3-D models of hominin fossils. Previous: Early Hominins

Next: Archaic Homo

Jablonski, Nina G. 2010. “The Naked Truth.” Scienti�c American 302 (2): 42–49.

Lewin, Roger, and Robert A. Foley. 2004. Principles of Human Evolution. Oxford, UK: Blackwell Publishing.

Stoneking, Mark. 2015. “Of Lice and Men: The Molecular Evolution of Human Lice.” Lecture, Center for Academic Research &

Training in Anthropogeny, San Diego, California, October 16, 2015. https://carta.anthropogeny.org/events/unique-features-

human-skin

Tarlach, Gemma. 2015. “The First Humans to Know Winter.” Discover, February 26.

Ungar, Peter S. 2017. Evolution’s Bite : A Story of Teeth, Diet, and Human Origins. Princeton, NJ: Princeton University Press.

Wrangham, Richard. 2009. Catching Fire: How Cooking Made Us Human. New York: Basic Books.

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Acknowledgments

The author gratefully acknowledges funding from the California Community Colleges Chancellor’s Of�ce Zero Textbook Cost

Degree Grant Program—Implementation Phase 2.

Figure Attributions

Figure 10.1a KNM-WT 15000 Turkana Boy Skeleton by Smithsonian [exhibit: Human Evolution Evidence, Human Fossils, Fos-

sils, KNM-WT 15000] is copyrighted and used for educational and non-commercial purposes as outlined by the Smithsonian.

Figure 10.1b MNP – Turkanajunge 2 by Wolfgang Sauber (photograph) and E. Daynes (sculpture) is used under a CC BY-SA 4.0

License.

Figure 10.2 Five Myr Climate Change by Dragons �ight (Robert A. Rohde), based on data from Lisiechi and Raymo (2005), is

used under a CC BY-SA 3.0 License.

Figure 10.3 Savanna grasslands of East Africa by International Livestock Research Institute (ILRI)/Elsworth is used under a CC

BY-NC-SA 2.0 License.

Figure 10.4 Homo habilis site map original to Explorations: An Open Invitation to Biological Anthropology by Chelsea Barron at

GeoPlace, California State University, Chico is under a CC BY-NC 4.0 License.

Figure 10.5a Homo habilis: OH 24 lateral right view by eFossils is copyrighted and used for non-commercial purposes as out-

lined by eFossils.

Figure 10.5b Homo habilis: KNM-ER 1813 lateral right view by eFossils is copyrighted and used for non-commercial purposes as

outlined by eFossils.

Figure 10.5c Homo habilis OH 7 Jaw by ©BoneClones is used by permission and available here under a CC BY-NC 4.0 License.

Figure 10.6 Homo habilis table original to Explorations: An Open Invitation to Biological Anthropology is under a CC BY-NC 4.0

License.

Figure 10.7 Homo rudolfensis Cranium KNM-ER 1470 by ©BoneClones is used by permission and available here under a CC BY-

NC 4.0 License.

Figure 10.8 Summary features of Homo habilis original to Explorations: An Open Invitation to Biological Anthropology is under

a CC BY-NC 4.0 License.

Figure 10.9 Chopping tool by José-Manuel Benito Álvarez is used under a CC BY-SA 2.5 License.

Figure 10.10 Homo erectus: Sangiran 17 lateral left view by eFossils is copyrighted and used for non-commercial purposes as

outlined by eFossils.

Figure 10.11 Homo erectus site map original to Explorations: An Open Invitation to Biological Anthropology by Chelsea Barron

Previous: Early Hominins

Next: Archaic Homo

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Explorations by Beth Shook, Katie Nelson, Kelsie Aguilera,

and Lara Braff, Eds. is licensed under a Creative Commons

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pology is under a CC BY-NC 4.0 License.

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