those for digestion. Thus in order to obtain enough energy to survive, they had to eat a diet high in fat and protein, most easily obtainable by eating animals and animal products – insects, reptiles, fish, eggs, and birds along with mammals. Catching some of those animals may have necessitated walking or running significant distances in the hot sun, which is difficult for most mammals because they only lose body heat through panting. Homo ergaster probably had the ability to cool down by sweating, a process made easier by the fact that they were relatively hairless.
This lack of body hair facilitated cooling (and thus hunting), but it also meant that infants could not cling as easily to their mothers as could those of other primate species. How homo ergaster mothers handled this problem is not evident in the fossil record. Perhaps they did not hunt when they had small children or they left their children briefly, as sites indicate that groups sometimes had a home base to which they returned. Perhaps they devised slings made of plant or animal material to help carry their children, though like any tool made from soft materials, these have left no trace.
Another solution to the problem of a short digestive tract is to transfer some digestion outside the body, through cooking. Raw meat is hard to chew and digest, as are many raw plant products; other primates spend many hours a day chewing. Cooking allows an outside source of energy – fire – to do much of this work, breaking down complex carbohydrates and proteins to increase the energy yield of food; it also detoxifies many things that would otherwise be dangerous to eat. There are a few shreds of evidence of fire at early homo ergaster sites, and some scholars, including Richard Wrangham, argue that even without fossil evidence of actual cooking, the larger brains, smaller and less pointed teeth, and shorter guts that developed about two million years ago would only have been possible with cooked food. Other scholars see cooking as a more recent invention, perhaps as late as 400,000 years ago, when hearths become a common part of the archaeological evidence in many areas.
Wherever and whenever it occurred, cooking had enormous social and cultural consequences. Cooking causes chemical and physical reactions that produce thousands of new compounds and make cooked foods more aromatic and more complex in their flavors than raw foods. As descriptions of roasted coffee or chocolate put it, they develop “overtones” or “flavor notes” of completely different things. Because members of the genus homo were omnivores, they may have been genetically predispositioned to prefer complex flavors, so that cooked food tasted (and smelled, which is essential in taste) better. Thus cooking led to eating together in a group at a specific time and place, which increased sociability. Cooking may also have encouraged symbolic thought, as cooked foods often make us think about something else, and both cooking and eating can be highly ritualized activities – plus cooking involved fire, which itself has deep meaning in later human cultures.
The evidence for cooking among homo ergaster is thin, but the evidence for migration is unequivocal. Gradually small groups migrated out of East Africa into Central and Northern Africa, and into Asia by about 1.5 million years ago. They reached what is now Spain by at least 800,000 years ago, and then further north in Europe.
Some groups evolved into slightly different species of hominids, the most famous of which are the Neanderthals (homo Neanderthalis), named after the Neander Valley in Germany, where their remains were first discovered. Neanderthals lived throughout Europe, Western Asia, and Siberia between about 130,000 and 30,000 years ago, the era of the last ice age. They had brains as large as those of modern humans and made and used complex tools that enabled them to survive in the diverse environments and climates in which their bones have been found. They built freestanding houses, and controlled fire in hearths, where they cooked animals, including large mammals and many kinds of plants. They lived in small communities, and cared for their young, old, and injured. They sometimes buried their dead carefully, and occasionally decorated objects and themselves with red ochre, a form of colored clay.
Neanderthals most likely understood biological sex differences, but what cultural significance they gave to these and thus how they understood gender is difficult to determine. Judging by wear and tear on skeletal remains, both males and females engaged in the same type of hard physical labor, and died at similar ages, so there was little behavioral differentiation. Males and females were buried in the same way and with similar types of grave goods.
Evidence from one 50,000-year-old Neanderthal site in Spain has yielded intriguing suggestions about some aspects of gender and family relations. Here 12 individuals of various ages appear to have been killed and eaten by another group, during a period – judging by the tooth enamel of the victims – of food scarcity. DNA evidence shows that these 12 individuals were related, and that the adult males were more closely related than the females. Thus the men had most likely stayed with their birth family, while the women had come from other families, a pattern that would be replicated later among homo sapiens of many eras and places. Two of the children were offspring of the same woman, and were about three years apart in age; this birth interval, perhaps the result of long breastfeeding, is also something that would be replicated among many later foragers. Extrapolating from a single site to all of Neanderthal society is dangerous, but this provides a glimpse of Neanderthal social relationships, both hostile and caring.
What archaeologists term anatomically modern humans (AMHs or homo sapiens) spread from Africa into areas in Europe and Western Asia where Neanderthals lived, and the two groups lived side by side for millennia, hunting the same types of animals and gathering the same types of plants. Eventually Neanderthals became extinct, killed by humans or diseases they had brought in, or simply losing out in a competition for food as the climate worsened in a period of increasing glaciation that began around 40,000 years ago. Neanderthals and homo sapiens also had sex with one another, at least sometimes, for between 1.5 and 2.1 percent of the DNA in humans living today outside of sub-Saharan Africa comes from Neanderthals. Since 2010, genetic studies of Neanderthals have taken off. Scientists have found, for example, that the exchange of genes between Neanderthals and AMHs provided resistance to some viruses, but also increased the genetic risk to others, including COVID-19. They have also found sex-based differences. Neanderthal-derived DNA does not include the mitochondrial DNA passed from mother to child, which means that the children who passed on their genes came from Neanderthal males and AMH females. This does not mean that there was no sex involving Neanderthal females and AMH males, but simply that this did not produce offspring that survived. Similarly, no modern man to date has been found with a Neanderthal Y chromosome, which suggests that the male offspring of Neanderthal males and AMH females were not viable. Genetic research is also beginning to include various other recently discovered extinct members of the homo genus, such as the Denisovans, who also interbred with homo sapiens. All of this indicates that the human evolutionary path is more complex and multibranched than we used to recognize, more of a bush than a tree.
Homo Sapiens
Archaeologists distinguish anatomically modern humans (homo sapiens) from other members of the genus homo by a number of anatomical features, most notably a relatively slender build, a head with a large cranium (and forebrain) with a face tucked underneath it, small teeth and jaws, and a larynx situated lower in the throat. The earliest fossilized remains showing these features come from Ethiopia, and have been most recently dated as about 195,000 and 160,000 years old. What archaeologists term “behavioral modernity” developed after anatomical modernity, though whether this was gradual or the result of a sudden “cognitive revolution” about 50,000 years ago is hotly disputed. Behavioral modernity includes long-range planning, development of new technologies such as the bow and arrow, the wide use of symbols in burials and personal adornment, more complex speech, and broad networks of social and economic exchange.
Some scholars see the development of cognition and brain complexity as a social and cultural as well as a physical process. Some of this operated at the individual level: individuals who had better social skills were more likely to mate than those who did not – this has been observed in chimpanzees and, of course, in humans from more recent periods – and thus to pass on their genetic material, creating what biologists
