Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live (4 page)

To understand how far we have come, we need to examine what life was like for the early hominins. As our ancestors moved to the savannas and woods of Africa, the climate was becoming more seasonal, with rain that was more likely to fall only at certain times of year. This seasonality meant that foods available during dry periods, like underground tubers and meat, became more important. The foods eaten, in turn, dictate the methods used to obtain them, and when it comes to humans, the big question is when and how people started hunting. Anthropologists used to think that early hominins did not eat much meat, because hunting is such a sophisticated activity (at least the way it’s practiced by people today) that our smaller-brained early ancestors were not thought to be capable of it. But over the last couple of decades, chimpanzees, which have smaller brains than
Australopithecus afarensis
, have been found to hunt regularly, preying on monkeys, antelope, and wild pigs, suggesting that you don’t have to be such a brainiac to be a predatory primate.

Such prey animals are of reasonable size—big enough, in fact, to share. And food sharing is also a significant milestone in the evolution of human social behavior. As anthropologists Rob Boyd and Joan Silk at Arizona State University note, “hunting makes sharing necessary, and sharing makes hunting feasible.”
¹⁴
What they mean is that being able to bring down a deer is about more than venison. Hunting is a chancy business, with most predators, including wolves and lions, scoring a lot more misses than hits. But if individual hunters share what they kill, and if other people in the group hand out the more steady source of food provided by vegetable matter, the risk of starving to death after a run of bad luck in hunting is reduced. So if early humans hunted, they probably had the complex social interactions that go along with dividing up the kill. Food sharing might also have been linked to divisions of labor within a group, although whether the men necessarily did all the hunting while the women stayed home and dug for roots or picked berries is not at all clear, as I will discuss in Chapter 7.

Neither hunting large game nor finding wild foods like fruits, tubers, or honey is easy, and the skills involved can take many years to master. Once such difficult ways of getting food became commonplace among early humans, a feedback loop was possible: natural selection favored distinctive traits, like large brains and a longer time spent as a juvenile, because those in turn made the foraging easier, which in turn meant selection for ever more efficient ways to get food. By 1.8 million years ago, at the beginning of the Pleistocene, more modern hominins were established in Africa, though the earliest
Homo sapiens
, our own species, did not appear until a mere 100,000 years ago.

One of these early members of our genus,
Homo ergaster
, is noteworthy because it may have marked the appearance of the first long-distance runner in our lineage. Although earlier hominins were also bipedal at least some of the time,
Homo ergaster
was tall (one skeleton with the fetching name of KNM-WT 15000 was 5 feet 4 inches tall as a young boy, projected to stand at 6 feet when he was fully grown) and had the long legs, narrow hips, and more barrel-shaped chest of modern running humans, as opposed to the long arms and stubbier legs of earlier forms that probably still spent a considerable amount of time in the trees.

The running is significant not just because it contributes to the controversy over “natural” forms of exercise that I will discuss in Chapter 6, but because some anthropologists believe it was linked to the evolution of larger brains. Running would allow ancestral humans to get to carcasses left by predators like lions before other scavengers such as hyenas, and hence gain access to high-quality protein. Such concentrated food can fuel the demands of large brains, which are physiologically expensive to maintain. To obtain and process game animals,
Homo ergaster
made more sophisticated tools than earlier humans had made, including hand axes with nifty double-faced blades and sharp, narrow points. Interestingly,
Homo ergaster
also shared a doubtless unwelcome advancement with modern humans: intestinal parasites. Recent studies of the human tapeworm, a gut inhabitant that is specialized on humans and the animals they eat, show that at least two kinds of tapeworms date back to 1.7 million years ago, long before animal domestication.
¹⁵

Homo ergaster
spread from Africa into Europe, with other species of
Homo
also appearing in various parts of Eurasia. Between 900,000 and 130,000 years ago, during the Pleistocene, the Earth became cooler, with long periods when glaciers covered large parts of the world. While the glaciers covered some areas, deserts spread over northern Africa, separating the populations of plants and animals, including humans. Anthropologists do not agree about exactly how to classify the fossil humans found from this period, but it is clear that brain size evolved substantially from that of
Homo ergaster
; and one kind of early human,
Homo heidelbergensis
, hunted and butchered large animals such as mammoths. By 300,000 years ago, humans had produced even more finely crafted stone tools, including some that were suitable for attaching to handles—a marked improvement that allows much greater force to be applied to the tool.

The Neandertals, reconstructions of whom are probably responsible for most people’s conceptions of what cavemen supposedly looked like, lived in Europe and eastern Asia from 127,000 until about 30,000 years ago. They were not human ancestors, meaning that their lineage did not lead directly to that of modern humans, but because they lived in Europe and many paleontologists found their own European homeland a more convenient place to dig for fossils than many parts of Africa and Asia, we know more about them than we do about any other early human.

The recent discovery that we humans share a small proportion of our genes with the Neandertals,
¹⁶
suggesting that early
Homo sapiens
and Neandertals mated with each other, has renewed interest in the lives of these hominins. The fossils reveal skulls with big front teeth that show heavy wear, perhaps because the Neandertals used to pull their meat through their incisors. The Neandertals also had rather stocky frames; according to Boyd and Silk, “A comparison with data on Olympic athletes suggests that Neanderthals most closely resembled the hammer, javelin, and discus throwers and shot-putters.”
¹⁷
Such a build is in keeping with a species that lives in cold climates; shorter limbs help conserve body heat.

Neandertals had large brains—larger in an absolute sense, not necessarily relative to body size, than those of modern humans—and made complex stone tools that were probably used to hunt elk, deer, bison, and other large game animals. I say “probably” because, as with all conclusions drawn about early humans, this one is indirect. We find stone tools, and we find the bones of animals with marks on them from those tools. Did the Neandertals kill the animals, or could they have scavenged them from other predators? The consensus is that they were indeed killing the prey, but the data are not conclusive. Hunting or scavenging aside, the Neandertal life was not an idyllic one. Most Neandertals died before the age of fifty, and many of the adult skeletons show signs of diseases such as arthritis, gum disease, and deformed limbs.

Anatomically modern humans, which first appeared on the scene about 100,000 years ago, not only looked different from the Neandertals; they had a more complex social life, using materials that came from far away to make their tools, which suggests that they traded with distant people. Unlike the Neandertals, they built shelters, and they created art and buried their dead. They certainly hunted game, but how much they relied on meat as opposed to plant foods is unclear, and almost certainly it varied depending on what part of the world they lived in—humans migrated from Africa throughout much of the rest of the world during the Paleolithic—and what time period is being considered. Bones and tools preserve much better than stems, seeds, or pits, but that does not mean that early humans relied more on meat than on other food sources.

About 50,000 years ago, the fossil tools and other cultural accoutrements found in Europe underwent a marked change. Although people had looked like, well, people, for a long time, humans began to make more elaborate tools, clothing, and shelters, and at some point they began to use the symbolic communication that we call language. When and how language arose is, again, a hotly debated topic. Linguists are pessimistic that we will ever be able to trace the origin of modern language back further than 5,000 or at most 10,000 years, though it’s very likely that humans were using some form of symbolic spoken communication well before then.

Indeed, the recent discovery of a gene called
FOXP2
, which is present in virtually identical form in all humans, has led scientists to believe they may have uncovered an essential component in the evolution of language.
FOXP2
occurs in many animals, including mice, and chimpanzees and gorillas possess identical forms of the gene. Defects in human
FOXP2
are associated with an inability to use words correctly. Biologist Svante Pääbo and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, examined the small differences within the gene in chimps and gorillas, as well as in humans from several parts of the world, and discovered that
FOXP2
changed rapidly after humans and chimpanzees split off from our common ancestor, perhaps because strong selection made the ability to use language advantageous. Pääbo then calculated that the current version of the gene appeared in the human lineage within the last 200,000 years.
¹⁸

Although other species of
Homo
were living in Europe and Asia over 100,000 years ago, modern humans,
Homo sapiens
, moved out of Africa to populate the rest of the world only about 60,000 years ago. All of the people on Earth today are descended from a rather small number of Africans. This limited population of origin is probably why humans are much less variable genetically than are many other species, including our close relatives the chimpanzees. We tend to think we are terribly different from each other while every chimp in the zoo looks alike, but our genes tell a different story. Pluck any two people at random, even from a relatively large population like that of southern Europe, and sequence their DNA, and you will find that their genes differ less than the genes of two chimpanzees from central Africa.

Bushmen, bones, and “chimpiness”

The next big step in human evolution after the great expansion from Africa was the beginning of agriculture, which facilitated larger populations and the eventual establishment of towns, social classes, and other modern accoutrements. But the time before that transition, from perhaps 60,000 to 10,000 years ago, when humans were living as hunters and foragers, is what inspires our paleofantasies. This is the time that some evolutionary psychologists call the Environment of Evolutionary Adaptedness, or EEA, when humans became what we are today.
¹⁹
In Chapter 2 I will examine the idea of such an environment, and how it may or may not be reflected in our modern behavior. Now I want to consider a more basic question: What do we know about what human life was like during this period, and how do we know it?

Scientists have traditionally relied on three sources of information about early humans: (1) the fossils of those people and their associated artifacts, like tools and paintings; (2) the lives of modern-day hunter-gatherers—for example, the Kalahari bushmen, also called San—living what is thought to be a lifestyle closer to that of our ancestors; and (3) modern apes, particularly chimpanzees and their close relatives the bonobos, with which we share a common ancestor more recently than any other living animals. In recent years the scientist’s kit has been expanded to include a new and potentially extremely powerful tool: the examination of our own genes, which bear the marks of past natural selection in ways we are only starting to appreciate. Each of these sources has advantages and drawbacks, and each feeds into our paleofantasies.

First let’s look at the lives of what we now call modern hunter-gatherer or forager societies, or what used to be referred to as savages. Living in exotic and nearly inaccessible corners of the world, the Kalahari bushmen, the Hadza nomads of Tanzania, or the Aché of South America have sometimes been seen as a window into life before civilization. Early anthropologists classified human societies around the world according to their supposed evolutionary advancement, with hunter-gatherers in a state of arrested evolutionary development. Therefore, the reasoning went, studying those peoples would allow us to understand life before the advent of agriculture.

This classification, in addition to being objectionable from a sociopolitical viewpoint, is incorrect; all human groups have been evolving for the same period of time. But even after the idea that native South American Indians or other such human societies were in an earlier, and somehow more innocent or pure, state of nature was rejected, the notion that we can use them as models of what life was like for much of humanity’s past has lingered.

If these people are hunter-gatherers and we know our ancestors were hunter-gatherers, why can’t we look at these contemporary societies and draw inferences about our earlier way of life? The answer is that we can, but to a much more limited extent than many people would like. First, contemporary hunter-gatherers are variable in what they eat, how they divide labor between men and women, the way they raise their children, and a whole host of other features of daily life. Were our ancestors more like the Aché of tropical South America, who hunt small game but also eat a variety of plant foods; or the Inuit of the Arctic, who rely on large animals like seals for much of their food? They were probably like both, at different times and in different places, but it is impossible to tell at this stage which lifestyle was more common or which features were truly universal.