Lone Survivors

by Chris Stringer

  Considering its vast size and its rich finds of Homo erectus fossils from sites such as Zhoukoudian (“Peking Man”), China has surprisingly little evidence of early modern humans. This may partly be a reflection of the relatively late arrival of Homo sapiens in China, but it’s likely that the time scale for modern human evolution in China is, in fact, not much different from that of Europe, where by comparison there are dozens of Cro-Magnon skeletons and scores of rich sites representing the cultures of the Upper Paleolithic. To make matters worse, the richest collection of such material—from the Upper Cave at Zhoukoudian—was lost when it disappeared in 1941, following the Japanese occupation of Beijing.

  However, the situation improved in 2003 with the discovery of a partial human skeleton in the nearby Tianyuan Cave, which was dated by radiocarbon to about 40,000 years. The cave contains remains of mammals such as deer and porcupine, and the animal bones in the level of the skeleton show signs of processing by humans, but no artifacts have been reported so far, and it’s unclear how the well-preserved but incomplete skeleton got there: was it originally a burial, or did the individual concerned die in the cave? Thirty-four bones of the skeleton are represented, including the lower jaw, shoulder blades, various arm and leg bones, and parts of the hands and feet, and they are mostly medium-sized, making it difficult to judge the sex of the individual concerned, without a complete skull or the bones of the pelvis. However, he or she was at least middle-aged based on the high degree of tooth wear and the wear and tear on the bones preserved, including evidence of osteoarthritis.

  Research by Hong Shang, Erik Trinkaus, and their colleagues shows that the Tianyuan individual had many typically modern features such as a well-developed chin and features of the shoulder blade, arm bones, and thighbone. But it also has relatively large front teeth, and one of the finger bones has an expanded tip, which is common in Neanderthals. However, the limbs are proportioned more like those of modern humans who derive from warm climates, rather than cold climates, and in this respect they resemble the early Cro-Magnons and not the Neanderthals. That fact leads to the likelihood that these early moderns, far from their warm African evolutionary homeland, were using cultural means to cope with the cold environments in which circumstances had landed them.

  There are two well-known “rules” about the size and shape of organisms, related to their basic need to lose or conserve body heat, named after the biologists who first laid them out clearly. Allen’s rule states that warm-blooded creatures in colder climates will generally have smaller limbs (or other appendages such as ears or tails) than their equivalents in warmer climates. The reasons for this may be both genetic (inherited) or acquired (for example, by the more restricted flow of growth nutrients to the extremities in cold conditions), but the result is a reduction of heat loss in cold conditions and an enhancement of it in hot conditions (think of the large ears of African elephants, for example). Bergmann’s rule states that, in general, the body mass of organisms will increase with an increase in latitude or exposure to cold. This is related to the fact that a large animal will have a proportionately lower surface area for its weight than a small animal. Thus all other things being equal, a large animal will be better at retaining its body heat, while a smaller-bodied animal will be better at losing it. In humans, this may translate into overall build, with a more spherical shape (short and wide) performing better in cold conditions, while something more cylindrical (tall and narrow) would be favored in hot dry conditions, where heat loss is more important and increased surface area for sweating would be advantageous.

  If we look at fossil humans, these rules generally work well. African Homo erectus and heidelbergensis bones suggest that the individuals concerned were lanky and long-limbed, while Chinese erectus and European heidelbergensis were relatively more compact and heavily built. When we get to Neanderthals, the pattern is even clearer, with skeletons from the last Ice Age in Europe being particularly stocky, with shorter extremities in the arms and legs. But some thirty years ago Erik Trinkaus noted that the Cro-Magnons who lived in much the same environments as Neanderthals were more like recent African populations in body shape than the Neanderthals. And the same thing now seems to apply to the earliest modern skeleton we have from the north of Ice Age China. Of course, there may be other factors at work in body size and shape, for example, the need for power, speed, or mobility, but it seems likely that human behavior, in the form of what is called cultural buffering, is also having an effect here.

  Neanderthals are often considered to be a cold-adapted species, but in fact they ranged widely in time and space (for example, they are found alongside hippos and warm Mediterranean forests near Rome 120,000 years ago, and also with woolly mammoths in a bleak and seemingly treeless landscape in Norfolk about 60,000 years later). Archaeological data suggest that they actually shunned the coldest locations in Europe, especially those with the lowest winter temperatures and the highest wind chills, and this may be because, despite their physical adaptations, they lacked well-tailored clothing and well-insulated dwellings. These “luxuries” are actually essentials for survival in the cold, and we should remember that it’s not just adult survival that is important here. Human babies are notoriously susceptible to low temperatures, because with their smaller body size they are less good at retaining heat (Bergmann’s rule again), and their body’s ability to stabilize temperature is still only developing. Apparently without sewing and weaving, the Neanderthals probably made fur wraps and ponchos, and fixed animal skins together with thongs or sinews, but we know from bone needles, impressions of weaving in clay, remains of huts and tents, sculptures, and the complex arrangements of beads and fastenings left from clothing in their burials that the Cro-Magnons were able to provide much better insulation for their adults and children. Even the foot bones of the Cro-Magnons provide clues about another of their innovations: shoes.

  Erik Trinkaus’s anatomical study of the foot bones of modern people who regularly do or do not wear shoes showed that the difference is reflected in the robustness of their toe bones, since wearing shoes deflects some of the pressure otherwise applied to the middle of the foot during walking; hence some of the toe bones are less strongly built when shoes are worn. The distribution of accessories in Cro-Magnon graves suggests the original presence of clothing, and at Sungir in Russia, two adults and two children were buried with elaborate grave goods about 28,000 years ago. The burials were covered in hundreds of tiny mammoth ivory beads that must have been sewn on clothing which has since rotted away, and these are also abundant around the ankles and feet, suggesting the presence of decorated shoes or boots. Moreover, the foot bones of the otherwise very robust Sungir man show the telltale signs of gracility that indicate the wearing of shoes in people today. Such signs are not known in the toes of Neanderthals, nor in the much earlier modern humans who lived in Israel about 110,000 years ago. But they are there in the Tianyuan foot bones, which are over 10,000 years older than those from Sungir. Thus the earliest known modern skeleton from China seemingly had the benefit of shoes, which would have eased travel across difficult terrain and, if waterproof, could also have provided protection from the cold, wet, and snow. Although we don’t know much about the way of life or culture of the isolated mystery Homo sapiens from Tianyuan Cave (but see chapter 3), the body of this man or woman tells us that increased protection from the Ice Age environment had arrived in northern China at least 40,000 years ago.

  Let’s now return to the ultimate ancestors of the early modern people we have been discussing from Europe and China, to fossils from Ethiopia. I explained in chapter 1 how the Omo Kibish fossils found by Richard Leakey’s team in Ethiopia in 1967 were important to me in my formulation of a Recent African Origin model. Also, the dating of the fossils was not very secure at that time, and the specimens themselves were subject to interpretations very different from my own. In chapter 9 we will see how discoveries in the last decade have put these southern Ethiopian finds back in the spotlight, bu
t now I want to focus on an arid region in the northern part of Ethiopia. Inland from the Horn of Africa, the triangular Afar depression is sinking as Africa splits apart along its great eastern rift, and the resultant basin has accumulated rich sediments through more than 5 million years of geological and early human history. The area has yielded finds of several australopithecine species including the 3-million-year-old remains of “Lucy,” and younger fossils of Homo erectus and heidelbergensis. In 2003, the village of Herto became famous with the announcement of a rich site dating from about 160,000 years ago. The first clues came with the discovery of a hippo skull, evidence that this dry area once had fertile lakes and rivers, and, just as important, the skull showed butchery marks made by early humans. Systematic excavations by the paleoanthropologist Tim White and his colleagues uncovered other animal fossils, stone tools, and the remains of seven humans. Of these, one had a nearly complete adult skull, another was the braincase of a child of about six years at death, and a third represented part of another adult skull. All were very large in size. Bill Howells, mentioned in the first chapter, had spent half his life meticulously gathering data on modern human skulls to map the variation of our species, but the most complete Herto skull exceeded in major dimensions all 5,000 of those he had measured from around the world! Perhaps such size was necessary 160,000 years ago if hunting hippos was on the agenda. Even today these temperamental beasts are reputed to be the highest cause of human deaths among all of Africa’s mammal fauna.

  The brow ridge of the most complete skull is strong and projecting, above a broad and flat face, while the braincase is high, rounded, and modern-looking overall. The child’s skull is too young to bear a brow ridge yet is equally modern-looking. But the rear portions of the two adult fossils are very strongly built, and reminiscent of the same regions in the Broken Hill skull from Zambia, which I classify in the species that was probably ancestral to H. sapiens in Africa: H. heidelbergensis. Two of the three Herto braincases also display evidence of human modification, including cut marks; could this be evidence of cannibalism? The scientists who described the material considered it was more likely that the skulls were kept as trophies or revered objects, because the child’s skull was highly polished with extensive evidence of wear and scraping, as though it had been regularly handled, and thus it might have been linked with postmortem ritual behavior, perhaps even as a drinking cup—but this must remain speculation for now. It was hard to know how the Herto fossils should be classified. The authors of the Nature article of 2003 assigned them to a new form of H. sapiens called “H. sapiens idaltu” (idaltu means “elder” in the Afar language), because of their large size and robustness. I argued at the time—and still do—that the specimens are not so remarkable when compared with some other early moderns, such as those who lived in Australia near the end of the last Ice Age, so the distinct idaltu subspecies name is probably unnecessary. Crucially, however, the deposits containing the Herto fossils were sandwiched between volcanic layers dated by the argon-40/argon-39 method (see chapter 2) to 154,000 years old and 160,000 years old; therefore, along with the Omo Kibish 1 skeleton from southern Ethiopia, these may be the oldest definite traces of humans like us anywhere in the world.

  In this chapter we have seen how recent discoveries opened up completely new windows on the evolution of Homo sapiens. They illuminated our African origins more than 150,000 years ago, they helped us map the dispersal of early moderns out of Africa and into Asia and Europe, and they told us much more about our cousins and possible competitors the Neanderthals. Fossils are vital to our story, of course, but so is the record of human behavior. However, it too requires careful extrapolation from the evidence left behind, as we shall see in the next two chapters.

  5

  Behaving in a Modern Way: Mind Reading and Symbols

  I used to believe that humans half a million years ago were very different from us in their behavior. Even though they were making beautifully shaped handaxe tools, they were probably much closer to apes than they were to us, living a very basic life and getting what meat they could by scavenging from the kills of far better predators. But as I followed the progress of excavations at Boxgrove in Sussex in the 1990s, I started to realize that things were not so clear-cut, and I began to develop much greater respect for the abilities and achievements of those early Britons, living at the edge of the inhabited world 500,000 years ago. I well remember a conversation with Mark Roberts, the director of the Boxgrove excavations, where we speculated about how the Boxgrove people got their meat. They were using almond-shaped handaxes, skillfully made from flint, to skin, disarticulate, and butcher carcasses of horse, deer, and even formidable animals like rhinos. We know this because the animal bones, covered in impact and cut marks, are scattered across an ancient preserved landscape. So were the Boxgrove humans actively hunting game, even as large as rhinos, or were they scavenging already dead animals? Well, they were certainly spending a considerable amount of time on the butchery, seemingly getting at every bit of nutrition available, in a potentially dangerous open landscape. This indicates that they were organized enough to secure the carcasses from competing animals, such as lions, hyenas, and wolves, which we know were also at Boxgrove.

  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 phys
ical 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.