Lone Survivors (18 page)

Wherever bones had both cut marks and signs of carnivore chewing, the cut marks were always made first—so these humans had primary access. And more direct evidence of hunting may come from an apparent spear-point hole in the shoulder blade of a horse. Although no spears are preserved in the conditions of the sediments at Boxgrove, wooden spears of yew and spruce have been discovered at Clacton in Essex and Schöningen in Germany, dating from 300,000 to 400,000 years ago. The Clacton “spear” is only a broken tip, but the German spears are some two meters long and beautifully made, and their use in hunting seems established by the fact that they were found among twenty or so horse skeletons. Archaeologists are still debating whether such spears were for throwing or thrusting but, in either case, these ancient people were clearly capable of tackling large and dangerous wild animals for their next meal.

How might relatively puny humans, albeit ones who were almost certainly stronger, fitter, and more muscular than the average person today, have coped with such dangerous predators and prey? Rocks, sharp stones, and wooden spears must have been part of the answer for a creature that was not equipped with speed, great strength, or sharp teeth or claws, but cooperation and cunning were probably even more important. Mark Roberts told me of a conversation he had had with an expert on wild rhinos in Africa, when he asked how, armed only with wooden spears, a man could kill a rhino. Well, the expert said, he would never be so foolish as to attempt such a thing, but when Mark pressed him further he said if he
really
had to do it, he and some friends would wait to find a solitary rhino asleep in the shade of a tree. Then, spears at the ready, they would creep up on the rhino, stab it quickly in its exposed belly as it slept, and hurriedly climb the tree. They would then hope the rhino bled to death; otherwise they could be stuck up the tree for a long time!

But at least
four
rhinos were butchered at Boxgrove, over an unknown period of time, suggesting this was not an exceptional event. Instead of a one-off foolhardy or lucky enterprise, it looks far more likely that this was part of the normal repertoire of
Homo heidelbergensis
. No doubt the ability to outthink and outwit the opposition, to “predict” its likely behavior, and the behavior of your fellow hunters, would have been crucial. This mind-reading ability, first developed in our primate ancestors, is now a significant part of the characteristics that have made humans, and particularly modern humans, so special. For some experts, this led to a heightened ability to control thoughts, emotions, and actions; to plan far into the future; and to evolve self-consciousness. Through growing social complexity we also developed greater powers of imitation, social learning, imagination and creativity, cooperation and altruism, enhanced memory, and complex language.

So far in this consideration of modern human origins I have focused largely on the physical evidence of what it is to be a modern human—for example, features in the skull, jaws, and body that survive in fossils—and what they tell us about how we may have evolved. But of course so much of what we think of as human lies in our behavior, many aspects of which are accentuated versions of what we can find in our closest living relatives, the great apes—things like tool manufacture and use, a long period of infant dependency, and social complexity. Other aspects seem to be quite unique to us among the primates—things like composite tools, art and symbolism, elaborate rituals and religious beliefs, and complex language. The gap between us and the great apes may seem more like a vast chasm, but we are the only surviving representative of what were extensive evolutionary experiments in becoming human, and so many of the features we think of as unique to us were shared, to a greater or lesser extent, with now-extinct species like
Homo erectus
and the Neanderthals.

There are certainly hints in our biology of odd quirks that, if we understood them better, could give us clues to how humans came to be so different, or at least so much more complex socially, than our primate relatives. For example, in most of the primates—and probably our ancient African ancestors—the outer covering of the eyeball, the sclera, is dark brown. This means that the pupil and iris in the center of the eye, which move to focus the gaze, are difficult to differentiate from the surrounding tissue, especially where they are dark. But humans have an enlarged, unpigmented, and therefore white sclera, which means we can detect where other people are looking; equally, they can detect where we are looking. This must have evolved as part of the development of our social signaling, enabling us to “mind-read” each other. (This idea even has a name: the Cooperative Eye Hypothesis!) Similarly, many domestic dogs have an accentuated white sclera compared with their wild wolf ancestors, which perhaps evolved to augment the close social relationship between dogs and humans.

Another remarkable feature in humans is the large size of the penis, of which much was made when Desmond Morris's book
The Naked Ape
was published in 1967. In fact, the human penis, when erect, is no longer than that of chimpanzees and bonobos, although all of these are about double the length of the penis in much larger orang and gorilla males. But the human penis is considerably thicker than any of the others and has a much more bulbous end. Explaining how and why these differences evolved has led to much speculation, ranging from the enhancement of pleasure to displacing the sperm of competing males, to providing a very obvious sexual display as a signal to either females or other males. The other obvious external part of the male reproductive organs—the testicles, containing the sperm-bearing testes—is less distinct in humans, intermediate in size between that of chimps (very large) and orangs (small) and gorillas (tiny). It is believed that this is related to both frequency of mating (high in chimps, low in gorillas) and competition between males for impregnation of fertile females (again high in chimps, low in gorillas). Humans thus fall between the extremes, suggesting that we mate (or, more appropriately, our ancestors mated) fairly often, but with only moderate levels of promiscuity compared with chimps.

Darwin had to make extensive use of analogies with other animals, because the fossil and archaeological evidence that he would have valued so much took many more years to blossom. However, accepting our close kinship with the great apes, he recognized similarities between their behavior and intelligence and ours. In 1871 he wrote:

As man possesses the same senses with the lower animals, his fundamental intuitions must be the same … But man, perhaps, has somewhat fewer instincts than those possessed by the animals which come next to him in the series. The orang in the Eastern islands, and the chimpanzee in Africa, build platforms on which they sleep; and, as both species follow the same habit, it might be argued that this was due to instinct, but we cannot feel sure that it is not the result of both animals having similar wants and possessing similar powers of reasoning. These apes, as we may assume, avoid the many poisonous fruits of the tropics, and … we cannot feel sure that the apes do not learn from their own experience or from that of their parents what fruits to select.

Darwin has been criticized for his excessive anthropomorphism in the recognition of “human” behavior in other animals, and given his lack of reliable data on great ape behavior—much of it based on captive animals or the tales of explorers—it is not surprising that he got things wrong at times. But overall he was cautious in his extrapolations. We now know far more about our close evolutionary relationship to our primate kin, and we should not be surprised to find both shared behaviors and shared brain pathways behind them. Thus monkeys and apes can recognize the different elements and expressions that make up faces from simple drawings rather than accurate pictures. The neuroscientist Vilayanur Ramachandran stressed the potential importance of
mirror neurons
in their brains and ours, nerve cells that are triggered both when an animal performs an action and when an animal observes another animal performing that same action. Such acting out of deeds in the brain is thought to be important in human learning, social interaction, and empathy, giving primates the basic elements of “mind reading,” which, as we will see, is so important in complex societies like ours.

But we do have a major problem when we turn to reconstructing the complexities of past human behavior, since what is left behind as physical evidence in the form of stone tools and butchered bones only represents the end products of chains of thoughts and deeds that are lost to us now, and which we attempt to reconstruct at our peril. Certainly we can turn to living apes to provide models for early human behavior for such activities as simple toolmaking and primitive hunting, but how much like a chimpanzee were, say, the
Homo heidelbergensis
people of Boxgrove in England 500,000 years ago, who were already living far from their tropical African homeland, making complex tools like handaxes, and acquiring not just small mammals but potentially dangerous big game such as horse, deer, and rhino? Just as significant,
H. heidelbergensis
already had a big brain, one nearly as large as ours today. To understand the evolution of those large human brains, we need to look at what they might have been used for.

There is now evidence that chimps in the wild do have “cultures,” shared traditions of how to behave—for example, in gathering or processing food with tools—which differ from one group or regional population to another. These cultural norms are learned as the chimp grows up in its group, and female chimps seem to be prominent, both in passing on traditions to new generations and in developing new ones. Yet these cultures are still rudimentary, and chimps are seemingly a long way from the cultural repertoire of even the earliest humans in Africa 2 million years ago. We remain unique in the extent to which we modify the world we live in through the things we create. Beyond that, we create imaginary worlds that are entirely virtual, made up of thoughts and ideas—worlds that live in our minds, from stories and spiritual domains through to theories and mathematical concepts. Chimps possess basic concepts of cause and effect; for example, if they strip a grass stem and lick it, it will then be thin enough and sticky enough to be used as a probe to catch termites. But humans have the ability to imagine a much longer chain of cause and effect, to consider several different outcomes that could result from an action or an alternative action. Through the medium of language, we can communicate these complex concepts to each other, both those relating to the material world, such as how to make a fire, and those relating to imagined worlds, such as what may happen to us after we die.

Instead, should we perhaps turn to modern hunter-gatherers in places like Brazil, Australia, and Namibia to help us reconstruct how the Boxgrove people, or the Neanderthals, or our African ancestors lived? We have to use such data cautiously and always be aware of the assumptions and extrapolations we make, since much has evolved and changed in the intervening millennia. So how could such complexity of behavior, including the ability to create virtual worlds, have evolved? One possibility is that an increase in meat eating in our ancestors not only gave access to more concentrated foods, removing previous constraints on large, energetically demanding brains, but also set in motion far-reaching changes in behavior, enhancing the power of reading the minds not only of our prey but of members of our own social group.

Daily life in primate troops in the wild has been compared with the worst aspects of television soap operas or reality TV shows like
Big Brother
: bullying and domination by the strongest, fear and abuse for the weakest. Yet primate groups also demonstrate tenderness and affection, strong alliances for the greater good, and social bonds that can last throughout life. This brings us to what is called the Social Brain Hypothesis (SBH), advanced by psychologists and anthropologists such as Nicholas Humphrey, Robin Dunbar, Richard Byrne, and Andrew Whiten. By this hypothesis our large brains have evolved not just in response to human needs for things like foraging and hunting skills, toolmaking, and invention, but also because of the complex societies in which we live. All primates have large brains for their body sizes relative to the average in mammals, particularly the so-called higher primates, the monkeys and apes. Brains are very demanding of energy; in fact, in humans, the demands of the brain are second only to those of the heart. So why would, say, a lemur or bush baby need a relatively larger brain than a hedgehog or a squirrel? One argument has been that the forested environments in which primates generally live require a keener intelligence to cope with problems, while another perspective has to do with the longer growth and development found in primates both before and after birth. Yet these explanations on their own do not seem sufficient, which is why SBH has gathered an increasing number of influential supporters.

Various comparative studies have shown that the relative size of the neocortex of the primate brain is much larger than normal in mammals (and in humans it constitutes a whopping 85 percent of total brain weight). The neocortex is part of the cerebral cortex and is known from brain mapping to be responsible for higher-level cognitive functions, such as learning, memory, and complex thought. That might seem to support the idea that it is large because the environment in which primates have evolved demands a keen intelligence in finding food and escaping predators. Yet plots of neocortex size against environmental complexity seem to explain less of the primate pattern than do plots against variables that reflect social complexity, such as group size, numbers of females in a group, frequency of social alliances, and amounts of social play, manipulation, and learning. Thus while environmental hypotheses tend to assume that animals solve problems individually by trial-and-error learning, without relying on the social groups in which they live, SBH proposes that such problems are solved socially, with the need for a larger neocortex to enhance social comprehension and cohesion. No doubt, in reality, both the social and general environment play a part in generating evolutionary demands, but in the case of humans it is very difficult to argue that general environmental demands have been anywhere near as important as social ones in the development of our extraordinarily large brains.