Masters of the Planet

by Ian Tattersall

  It was dangerous out there in the woodlands and savannas for small, slowmoving hominids. This artist’s reconstruction of a leopard dragging off a juvenile Paranthropus is based on a braincase fragment from the South African site of Swartkrans which is pierced with holes that exactly match the size and spacing of a leopard’s canine teeth. Illustration by Diana Salles after a sketch by Douglas Goode.

  WHAT CAN CHIMPANZEES TELL US?

  The evidence of tool use, and yet more of tool-making, tells us that the bipedal apes had graduated—perhaps as much as 3.4 million years ago, and at least before 2.6 million years ago—to a cognitive state that lay well beyond anything we can infer for the apes as we know them today. Not only were the early stone tool makers spontaneously indulging in an activity that required an insight into how stone fractures that Kanzi the bonobo simply hasn’t demonstrated, but they also showed a degree of foresight that is not reflected in the activities of hunting chimpanzees today. Still, these are evidently not cognitive skills that were possessed by the first hominids to quit the forest; indeed, quite probably at that early stage our forebears didn’t even have the biological wherewithal to possess them. Let’s also keep this in perspective and remember that chimpanzees are actually very complex beings, as we saw in the opening paragraphs of this book. No human being looking at a chimpanzee will fail to see a lot of him- or herself there, although what the usually caged individual is feeling or experiencing always remains veiled.

  On the technological front, the similarities between humans and chimpanzees (and other apes) are keenly reflected in the fact that hardly a month seems to pass in which these primates are not documented to indulge in yet another sophisticated behavior we’d thought only we possessed. The most recently discovered of these behaviors is the spearing on sharp sticks of sleeping bushbabies, though this remarkable practice may well have been superseded as the revelation du jour by the time this book goes to press.

  The wide variety of simple technologies that chimpanzees exhibit— and which are passed along through the generations in a form of imitative “cultural” transmission—is at least in part attributable to the range of environments they inhabit. Chimpanzees live in a remarkably wide variety of central and western African habitats ranging from dense rain forests to wooded grasslands. This environmental spectrum resembles that of the early hominids—though a big difference is that, even in drier and more open areas, the chimpanzees tend to select foods—mostly fruits—that resemble the resources available to them in the forests. Tubers and other tough, gritty, open-country foods of the type that the early hominids evidently enjoyed are of little interest to them. Nonetheless, the chimpanzees are highly conscious of the potential resources around them.

  At a place called Fongoli, in Senegal, where the environment is a mosaic of trees interspersed with grassland, chimpanzees live alongside a population of bushbabies, small defenseless nocturnal primates that spend their days hidden, often deep inside holes within trees. Evidently the Fongoli chimpanzees regard the bushbabies as tasty snacks, because researchers at the site saw many instances of chimpanzees fashioning wooden “spears” and thrusting them into tree holes, apparently in the hope of impaling a bushbaby. I was relieved to learn that only one such attempt out of 22 recorded was successful, but what is most interesting here—in addition to the unusual fact that not just adult males but also females and juveniles engaged in this kind of hunting—is that the chimpanzees always followed the same, evidently well-established, procedure.

  First, a branch was broken from a tree. Then it was stripped of smaller branches and twigs, in much the same manner used by other chimpanzees to prepare the slenderer tools used in “fishing” for termites in their mounds. Often the bark was removed from the proto-spear, and further trimming was done; and on some occasions the spearmaker used his or her incisor teeth to sharpen the spear’s working end. Once the 18-inch- to 3-foot-long implement had been completed, it was jabbed forcefully into a tree hole, then withdrawn, inspected, and sniffed. In the single case observed where the hunt was successful, the bushbaby was not withdrawn from its branch cavity impaled on the spear. Rather, after apparently detecting the prey’s scent or tissues on the spear point, the adolescent female hunter broke the branch by jumping up and down on it, and then retrieved the inert bushbaby by hand. After this she withdrew and ate the carcass alone. In two other cases, Fongoli chimpanzees were seen eating bushbabies, though it’s not known by what method they acquired them. These individuals were also basically alone, though one may have shared her prey with her juvenile daughter.

  The use of spears in hunting by chimpanzees is a technological eye-opener, on a par with the amazing recent report that these primates use stone anvils to help in cracking hard-shelled nuts, and the even more astonishing revelation that this behavior has a 4,300-year-old archaeological record in the form of ancient stone scatters. It is also a reminder of the incredible flexibility of chimpanzee behavior, since the Fongoli way of hunting differs hugely from what is seen among chimpanzees in other locales. In more closely forested habitats in both western and eastern Africa, chimpanzees do sometimes hunt alone; but they normally hunt cooperatively, and this behavior is more common than was once thought. Where they live in the same African forests as the widespread red colobus monkey, for example, chimpanzees hunt these primates between four and ten times each month, and their success rates hover above 50 percent. Often hunts are opportunistic, apparently initiated purely by chance encounters between predators and prey; but at other times male chimpanzees seem to actively patrol the forest in search of the colobus. Hunting is largely a male pursuit, and the larger the number of males cooperating in a hunt, the higher the success rate tends to be. The process is something to behold. The tree-living colobus themselves live in large groups that spend their lives in the forest canopy. A hunting party of chimpanzees will surround an entire group, with some of the hunters stationed on the ground and others up in neighboring trees. Some of the chimpanzees actively chase the monkeys, dashing after potential victims with enormous vigor, while others apparently just observe; but all are in a state of high excitement. The chimpanzees have greatest success when they are able to corral one or more fleeing monkeys in a spot where the forest canopy is broken, and they can isolate their victims in a single tree. Once the victim is caught, it is eagerly torn to pieces and shared among those in attendance, each anxious to receive a share.

  Some chimpanzee communities may consume hundreds of pounds of monkey meat in a year; but nonetheless, while the monkeys might hence seem to be a valuable dietary resource, more often than not when the two species encounter each other the colobus are ignored rather than pursued, even by chimpanzees out foraging for food. Moreover, if challenged a chimpanzee holding a juicy colobus carcass will more readily give it up than he would a branch full of ripe fruit. What this suggests is that, despite its frequency, hunting is not an essential economic activity for chimpanzees. Indeed, a recent appraisal of chimpanzee hunting in a forest in Uganda found that hunting was consistent seasonally, and was thus not done to make up dietary shortfalls when preferred kinds of food were scarce. Meat may have made a nice dietary supplement, but it did not seem to be critical to the nutritional needs of the chimpanzees. So why go to all the trouble? One possibility was that the sharing of meat by successful male hunters gave them preferential access to females, and therefore a reproductive advantage. Here the evidence is equivocal, and observations from different localities have varied. Generally, sexually receptive females are successful in obtaining a share of hunted meat only about a third of the time, doing no better than anyone else. And when they do get a share, it is as likely to be after as before copulation. On the other hand, one study in West Africa showed that, over the longer term, males got more sex from females with whom they had shared meat. Still, a consensus does seem to be developing among chimpanzee researchers that chimpanzees hunt colobus at least principally in pursuit of a larger social goal: to obtain meat to be shared, mostly w
ith other males, in ongoing alliance-building exercises. This makes considerable sense, for chimpanzee societies are fluidly hierarchical, each male’s position in society (and, of course, his reproductive advantage) at a given moment being determined not solely by his strength or his temperament, but by the state of his coalitions with others.

  SPECIALIZED BIPEDAL APE BEHAVIORS

  Hunting is one thing, and tool-making is another. Animal carcasses were butchered early on in hominid history, but this says nothing about how the carcasses themselves were obtained. Certainly, the very earliest stone tools don’t look at all like the kinds of implements that would have been used in killing large animals. If the early hominids did have a substantial meat component in their diet, it seems overwhelmingly likely that many of the animals providing the meat were small enough to be captured by chasing and cornering. Those hyraxes, for example, or small vertebrates like lizards. The only plausible alternative to this (apart from that sneaky leopard-kill stealing) is that significant protein came from the larger prey of full-time predators that were temporarily driven away from their kills through some form of hominid aggression. Given that the early hominids were small bodied, slow moving, and not fearsome in the least, and that non-fresh carcasses may be deadly, there is only one obvious possibility in the latter event: that hominids had already learned to accurately throw heavy objects.

  Throwing seems like a natural thing to us today, and indeed such sports as baseball depend on it; but in reality it’s another of our unusual qualities. Today we are the only precision thrower out there. A camel may be able to spit in your eye, but for all the strength in their arms, chimpanzees can’t throw a rock very far or hope to hit anything much smaller than a barn door with it. They may have a fearsome feces-flinging reputation among zoo-goers; but they don’t have the projectile abilities you’d want to depend on in a life-and-death situation. And this of course is just what you’d be in, if you were trying to chase carnivores off a kill by hurling rocks at them in the process known to paleoanthropologists as “power scavenging.” Throwing accurately involves exquisite harmonization between the hand and the eye, and the ability to string together a whole sequence of actions based on an instinctive assessment of what is needed. This is no small feat of neuromuscular coordination; and we have no direct evidence that any hominids could manage it before they began to make stone tools of the kind that were evidently hafted as the tips of missiles.

  In this imaginative reconstruction we see a group of early tool-using hominids out on the African savanna in the period before two million years ago. We do not know exactly how hominids like these obtained the mammal carcasses they butchered, but the figures in the left middle-ground hurling rocks at a pack of hunting dogs suggest the very hazardous process of power scavenging: driving the primary predators temporarily from their kills, while limbs and organs are removed for consumption at safer spots. Such refuge might have been provided by the forest in the background. Meanwhile, in the right middle-ground two of the hominids are seen using a stick to dig up tubers, also a resource for the earliest hominids that ventured out into the expanding grasslands. © ’95 J. H. Matternes.

  Still, a good degree of hand-eye coordination is an essential component of stone tool making; and this suggests that despite their archaic body proportions the early stone tool makers might have been able to cultivate throwing skills good enough to help them obtain meat at least occasionally. Carnivore kills, though, are hardly the kind of food source any hominid would want to depend on. You’d certainly have to be very highly motivated to make a living this way; and if chimpanzees are anything to go by, it’s not at all a sure bet that our ancestors went after meat initially because they were starving—though once they had started scavenging fresh kills with any regularity, it’s fairly easy to see how they might have become dependent on this practice. But if they did take this hazardous dietary route—and we need to bear in mind that from the beginning they were butchering large animals—it would be a powerful indication that they lived in large aggregations, since a small group of tiny hominids tossing rocks at lions, or sabertooths, or giant hyenas, would have got pretty short shrift. And there are other reasons, which we’ll look at shortly, to suggest that early hominids lived in large groups.

  Meanwhile, those butchered carcasses also suggest much about both the early tool-wielding hominids themselves and the cognitive level they had achieved. Rock suitable for making tools does not occur everywhere on the Rift Valley landscape over which the early hominids roamed. And when they needed to butcher a large animal carcass, the evidence is clear that they assured the availability of good tool-making materials by carrying appropriate rocks around with them. Especially after we pass the two-million-year point, it becomes reasonably common to find the fossilized remains of cut-marked butchered carcasses with ancient stone tools scattered around and even within them. Characteristically, the tools themselves were not made from stone naturally available in the immediate area; sometimes the nearest natural source was often several miles away. In such cases the fine-grained rocks needed for tool-making must have been carried in from at least that far afield. What’s more, they were not brought in as slimmed-down finished tools. We know this because the tool-making process didn’t just produce one sharp tool after another. A single cobble might have produced two or even several cutting flakes, but in the process a lot of “debitage”—unusable fragments of stone—also resulted. And archaeologists have repeatedly pieced together entire cobbles from both useful and useless fragments found at a single butchery site. Not only has this laborious process of reconstruction told them a lot about how the stone tools were made, but it also provides clear evidence that the heavy cobble had originally been carried in complete—evidently in anticipation of being needed for tool production. And it hardly seems likely that hominids would have lugged weighty chunks of rocks around for miles, if they were rarely going to use them.

  This kind of anticipation and foresight is different from anything we see in chimpanzees. Certainly, they hunt. But they usually do it on a situational basis, according to opportunities that present themselves. And if they need an implement to perform an activity with, they fashion it from available materials on the spot. The early stone tool makers, on the other hand, seemingly set out knowing precisely what they were going to do—whether hunting, or power scavenging, or whatever—and what they would need to do it with. They also understood the properties of materials, and how to work them, in a way that chimpanzees don’t. This is already enough to tell us that the early hominids had taken a cognitive leap of some kind compared not only to their Pliocene relatives, but to modern apes as well. Clearly, in their time the tool-wielding australopiths, and plausibly also their immediate non-technological ancestors, were by a substantial margin the smartest creatures around.

  Sadly, at present there is much less to say about these ancient precursors than we’d like, although it’s a good bet that they were very cooperative creatures. But if you crammed four hundred chimpanzees into the back of an airplane and flew them from New York to Tokyo, there’s little doubt that on arrival you’d find that the chimps had all massacred each other. Chimpanzees are highly social beings by any standard, but they do not have the special kind of sociality that it takes to live in a world as packed with people as ours is today. We certainly didn’t acquire this particular form of sociality in response to modern crowded conditions, for our population explosion is recent; indeed, hominids have typically been very thin on the ground, at least over the past two million years or so. Perhaps, then, we should seek earlier in our evolutionary history for the biological underpinnings of our peculiar social propensities. And one suggestion is that we should look to the biological role and environmental preferences of the early bipeds.

  EARLY SOCIETIES

  So far we have discussed much about chimpanzees and hunting, and this is certainly a reasonable thing to do if we want to place our ancient ancestors in the context of our (and their) closest living r
elatives—creatures that we can actually watch going about their business in the natural world. It is also true that an emphasis on hunting is deeply embedded in paleoanthropological tradition. Indeed, in the 1950s Raymond Dart, who described the very first australopith fossil (actually, the infant victim of a predatory eagle) back in 1925, was dramatically proclaiming that “the blood-bespattered, slaughter-gutted archives of human history” were a direct reflection of “this common bloodlust differentiator, this predaceous habit” of mankind’s earliest ancestors.

  However, while we are undoubtedly the world’s top predator today, my colleagues Donna Hart and Bob Sussman have recently emphasized just how misplaced this focus on hunting in our early evolution is. They point out that we are not simply super-chimpanzees; and that for all their evolutionary nearness to us, chimps retain all the instincts of forest animals, even where they spend a lot of their time in thinly wooded settings, as at Fongoli. According to Hart and Sussman, what most fundamentally differentiated our very ancient ancestors from chimpanzees is that, unlike the living apes, they adjusted their entire way of life to the exploitation of forest-edge and woodland settings. We see this in their bipedality, in their teeth, in their geochemistry, and in a host of other features. The ecological move to these more open environments brought with it new opportunities for hominids, as well as extraordinary future possibilities; but it also came at a huge immediate cost. This penalty was, of course, vulnerability to woodland predators. It is impossible to overstate the significance of this new factor: no new force could have had anything close to the impact on small-bodied bipeds, venturing away from their ancestral habitat, that the ubiquity of predators must have had.