Masters of the Planet

by Ian Tattersall

  Another aspect of the Boy’s anatomy also argued strongly that they didn’t possess linguistic skills. The spinal column not only supports the upper body but also conducts the spinal cord down from the brain, to control and receive information from the rest of the body via the network of nerves branching from it. The width of the canal through which the cord travels is pretty constant in most primates, including hominids; but in modern Homo sapiens (and, to be fair, in Neanderthals as well) it is unusually broad in the thoracic region, where the lungs sit. This additional breadth accommodates an increased volume of nervous tissue supplying the muscles of the thorax and abdominal wall, and it is suggested that the extra nerves are devoted to an enhanced control of breathing—a fine control that is, among other things, necessary to produce the subtle modulation of the sounds we use in speech. Interestingly, the Turkana Boy is an average primate in this regard. And it has accordingly been suggested that, regardless of the properties of his brain, he did not possess the peripheral ability to produce speech.

  It has also been controversially proposed that there may have been something pathological in the narrow space for the Boy’s spinal cord. That’s as may be; but there are plenty of independent reasons to believe that however he and his kind communicated—and they undoubtedly had a sophisticated form of communication—they did not share information using language as it is familiar to us. For a start, modern articulate language is the ultimate symbolic activity, and we find nothing in the archaeological record associated with the Homo ergaster/Homo erectus group, at any point in its long tenure, that suggests any symbolic mental manipulation of the information received from the outside world. Indeed, sketchy though it is, the archaeological record left behind by these early members of the genus Homo is remarkable for the conspicuous lack of any such evidence. Perhaps most strikingly, the Turkana Boy and his kin made stone tools that were identical in concept to those that had been made at Gona almost a million years before. On the technological level, nothing significant had changed that we can detect over that whole vast period of time. The appearance of a radically new physical type had not resulted in—or from—any kind of technological innovation; and we have little material evidence to confirm that Homo ergaster had a substantively different lifestyle from its predecessors, even though the anatomical indicators prompt us to speculate that there must have been changes.

  While it may seem counterintuitive that a new (and larger-brained) hominid should not have brought a new technology with it, this disconnect actually reflects a pattern already established among hominids: the very first toolmakers had, after all, been bipedal apes, not members of the genus Homo. This pattern set a template for future developments in that we cannot associate any later introduction of a new technology with the appearance of a new species of Homo. And this makes a lot of sense when you think about it, because ultimately a technology has to be invented by an individual—who has to belong to a pre-existing species. Innovations of all kinds must originate within species, if only because there is nowhere else for them to happen.

  SIX

  LIFE ON THE SAVANNA

  The extraordinary skeleton of the Turkana Boy gives us a remarkable insight into his species Homo ergaster: a hominid that grew up fast but physically was like nothing we know from earlier in time, and a creature that was clearly at ease away from the ancestral forest. This radically different environmental setting made enormous new demands upon the young species, but it clearly did not initially respond by making technological adjustments: as far as we can tell, the very first Homo ergaster continued making the same kinds of tools that its more anatomically archaic predecessors had made. And in the absence of substantial evidence of technological change, we have to fall back on physical and other indirect indicators if we want to understand what was new in the life of Homo ergaster. But these indicators are highly suggestive, even though we are hard put to draw specific conclusions.

  Although the Turkana Boy had a slender build, he was no weakling. In mechanical terms the shafts of the long bones of the limbs are basically hollow cylinders; and although the material of which they are made is hard and strong, it is not static. Instead, it remodels throughout life to resist the stresses placed on the limbs; and the varying thicknesses of the shaft walls reflect how high those stresses were in life, and how they were distributed. This is why fencers and tennis players have stouter bones in their dominant arms than in their passive ones, while astronauts’ bones thin out after too much time in microgravity. One major respect in which the Boy’s limb bones differed from ours is that, as in other early hominids, their shaft walls were much more robust than you see in humans today. This could indicate that in life the Boy was already immensely strong, and that he had also maintained a much higher level of activity than is typical of modern humans. Of course, our contemporary sedentary lifestyle is a very recent phenomenon; but even our ancient hunting-and-gathering Homo sapiens forerunners had relatively thin-walled long bones. Overall, since the Boy’s time the thickness of the bone in the shafts of the limb elements has plummeted, implying that bodily strength has become a significantly less important factor in the hominid way of life.

  The Boy’s environment was not an easy one, and at least to begin with he and his fellows were out there on the still tree-studded African savanna without a significantly improved toolkit. There is every reason to believe that—as relatively poor climbers—they could not and did not depend on the trees for shelter to the extent their bipedal ape predecessors had. And in the more open areas they would have favored, there roved an array of predators as fearsome as those still lurking on the forest fringes. Mainly, but far from entirely, these were big cats of a much greater variety than is found in Africa today, and they were all ready to pounce on any unwary mammal they encountered. By our standards Homo ergaster individuals were strong; but they were nonetheless relatively defenseless, lacking big jaws and slashing canine teeth. How did they respond to this hazardous new environment? And how did they exploit it? There is no shortage of ideas; and although there is little evidence to substantiate any of them, a circumstantial case can be built.

  One coherent scenario involves the notion that, with its modestly increased brain size, Homo ergaster needed a higher-quality diet than the varied but still plant-based one on which its predecessors had subsisted. This is because, although the benefits of a bigger brain seem self-evident to us Homo sapiens, the costs are at least equally evident. As I’ve already briefly noted, in metabolic terms the brain is among the most “expensive” tissues of the body. For, while the mass between our ears only accounts for some two percent of our body weight, it actually consumes something between 20 and 25 percent of all the energy we take in. This has major implications for the body’s overall economy, including that of the digestive system. The broad abdomens of the Turkana Boy’s australopith ancestors had almost certainly contained huge digestive systems, a feature that stands in stark contrast to modern humans. One of our most striking characteristics—almost as striking as our large brains—is that we have remarkably small internal organs for our body size. This was also true for the relatively narrow-hipped Homo ergaster, and it has important implications for the diet of the Turkana Boy and his fellows. For the internal organs are almost as “expensive” in energetic terms as the brain; and it has been powerfully argued that gut reduction in human evolution has not only been a necessary trade-off for brain expansion, but that at the same time it also exacerbated the need for a high-quality diet. Thus, although at the time of Homo ergaster hominids were only at the very beginning of their period of dizzying brain expansion, their reduced guts alone may have mandated dependence on high-yield foods.

  Diorama in the American Museum of Natural History, showing two Homo ergaster in northern Kenya, some 1.8 million years ago. It is left to the viewer to decide whether the hominids had scavenged or hunted the impala they are shown butchering. Figures by John Holmes. Photo: Denis Finnin.

  So where did the extra energy come
from in the big-bodied and modestly brained Homo ergaster? One obvious answer is that these early hominids had turned their attention to the highest-quality diet available to them: animal proteins and fats. This resource was, after all, roaming the African savannas in enormous quantities: mammals of all sizes abounded in the newly adopted environment. At the same time, though, these tasty beasts also attracted a hugely diverse fauna of specialized carnivores, far more numerous than their counterparts occupying the continent today. In going after savanna grazers the hominids would have had not only to compete for their food with these professional predators, but they would also have had to protect themselves from them.

  Perhaps less dangerous would have been fishing, and there are reasons for thinking that this activity may have been more important for Homo ergaster (and its successors) than the material evidence indicates. Aquatic animals are an important source of nutrients, such as omega–3 fatty acids, that are important for normal brain function. Limited quantities of these—enough, for example, to sustain a small ape brain—can be synthesized by the body. But the greater amounts demanded by an enlarged brain can only be supplied by the diet, and it has been suggested that ingestion of fish and other aquatic creatures may have been one precondition for the increase in hominid brain sizes over the past two million years or so. Many primates—particularly macaques—have been observed to obtain and eat aquatic invertebrates, and in one place orangutans have been observed fishing by hand. It would not have been difficult for early Homo to obtain fish in shrinking ponds and streams during the dry season, so it seems likely that they augmented their diet with such resources.

  Whatever their origin, not only are animal products rather indigestible without treatment of some kind, but meat is also intrinsically pretty tough to get hold of. Potential prey animals are difficult to acquire because they hate to be eaten—they don’t wait around like tubers or fruits to be dug up or picked by savvy foragers. They get out of the way, fast. This propensity would have posed a problem for any savanna newcomer bent on exploiting even small-bodied animals as a primary resource. Still, some researchers believe that, with a few behavioral innovations of the kind we wouldn’t necessarily expect to find reflected in the material record, hominids could have effectively hunted larger mammals using the physical advantages offered by the new anatomy alone. They point to the fact that, although Homo ergaster would hardly have been fast compared to four-legged predators, its new slender hips and long legs would have made members of the species exemplary distance runners. In the heat of the day, the human ability to simply keep going would have allowed these lanky bipeds to single out, say, an antelope, and to keep chasing it until it fell from heat prostration.

  Such a strategy would not only have been metabolically expensive, but it would also have necessitated the mental concentration to visually follow an animal to the horizon and, should it disappear from visual range, to track the quarry using spoor, broken branches, and other indirect signs. This mode of pursuit is used by African hunter-gatherers today (who wisely tend to walk or trot, rather than run, as running on soft surfaces has turned out to be as hazardous as running on hard ones), and it is made possible not only by sophisticated cognition of the hunters but by the physiological differences between them and their prey. Though faster than humans, most mammals do not have the capacity to shed the heat load acquired and generated during sustained activity in the tropic sun, except by pausing in the shade while it slowly dissipates, largely through panting. Hairless humans, on the other hand, constantly shed heat by sweating and radiation, allowing them to keep going when other animals drop from heatstroke.

  It is impossible to know for sure whether Homo ergaster was indeed hairless and sweaty: even today, we retain our covering of body hair, though in such a reduced form as to be invisible in most places. But advocates of the notion that Homo ergaster was naked-skinned ingeniously point to some interesting studies of human lice. Most kinds of mammal only support one louse species; but humans have the luxury of sustaining two. One of these parasites lives in the hair of the head; the other inhabits the hair of the pubic region. A bit embarrassingly, while the human head louse is distinctive, the human pubic louse is a close relative of the form that inhabits gorillas, and is thought to have been acquired from this source. The head louse seems to be a survivor of the form that roamed all over the body of the human ancestor, while the pubic louse was acquired subsequent to the loss of body hair. Using the “molecular clock” (basically, the assumption that mutations in the DNA accumulate at a more or less constant rate), parasitologists have been able to estimate that the two kinds of lice parted ways some three to four million years ago; and this date range would logically indicate that body hair loss had occurred well before the time of the Turkana Boy, and perhaps even before that of Lucy.

  While the parasite data may be a bit controversial, there is nonetheless general consensus that once modern body form had been achieved, luxuriant body hair was gone. Away from the trees, out in the tropic African sun, the physiological rules had changed; and because it is such a good bet that heat-shedding by sweating was the primary means of keeping the brain and body cool, the betting has to be that the Boy and his like were bare-skinned. What’s more, in an environment of intense solar radiation, that skin would have been very dark. As northerners who have spent too long on a tropical beach know well, light skin is highly sensitive to ultraviolet radiation, and it’s no coincidence that the highest skin cancer rates in the world today occur in Australia’s sunny Queensland, where fair-skinned folk are wont to unwisely disport themselves in minimal clothing.

  Perhaps, though, these behavioral speculations sound a little too human to add up to a convincing picture of Homo ergaster, as if our main behavioral characteristics had been established at that remote point in time, and that all that remained was for hominids to wait around another million and a half years for their brains to become bigger. What’s more, the endurance-hunting scenario begs a number of important questions. Among these is whether Homo ergaster had the technology to carry around water—because while sweating may be an efficient way to lose heat, it is also a very effective way of using up the body’s fluid supplies. Replenishing those fluids while chasing animals all over the landscape in the hot tropic sun would have required the constant availability of water, and we have no direct evidence that Homo ergaster possessed the technology to provide the containers needed to accomplish this. On the other hand, since the perishable stomachs or bladders of medium-to-large-bodied animals represented the only plausible materials to transport water, we would not expect to find evidence of their use preserved. And we can’t take absence of evidence as evidence of absence. Beyond this, it is fair to point out that there is nothing we know or can reasonably infer about Homo ergaster cognition that would rule out the possibility that these creatures used simple containers. We know for instance that, long before the genus Homo came along, the earliest australopith stone toolmakers were already exhibiting foresight and planning in the course of their daily activities. At a certain level these early hominids understood the properties of hard materials; why not of some soft ones, too? Still, it is notable that, where the necessary landscape archaeology has been done, hominid activity sites in the Turkana Boy’s time frame typically occur near places where water had been available; only later do we find evidence that hominids were venturing limitlessly across the countryside. All in all, the picture is frustratingly incomplete.

  FIRE AND COOKING

  However exactly it was that the requisite high-quality diet was acquired, hunting is still an energetically expensive activity. So, especially for a hominid with a small gut, it is imperative to get as much as possible out of the results of the hunt. As I’ve already briefly mentioned in connection with the probably carnivorous propensities of the bipedal apes, one way of doing this is by cooking the carcasses of your victims. Raw meat is pretty indigestible if you don’t, like a lion or a hyena, have a digestive tract that is specialized for the
task. Even after endless chewing, chimpanzees with their large stomachs and long intestines excrete lots of undigested bits of meat in their feces after the hunt. Primate digestive tracts just don’t do a great job of extracting energy from raw animal sources. But cooking changes the game entirely, and brings with it a long list of virtues. Judicious cooking makes foods—of all kinds, not just meat— easier to chew, and easier to extract nutrients from. It kills toxins, makes foods edible for longer, and just plain improves flavors and textures. At whatever point it was introduced, cooking clearly made a huge difference to hominid life.

  Nonetheless, whether this activity really was essential in allowing a creature like Homo ergaster to flourish still remains a speculative matter. This is not least because cooking presupposes the mastery of fire, and there is precious little direct evidence that Homo ergaster had achieved this. There are a couple of early indications that fires had burned at hominid sites in the Homo ergaster time frame, in the form of apparently singed bones some 1.8 million years old from Swartkrans in South Africa, and scorched clay balls about 1.4 million years old at the robust australopith site of Chesowanja in Kenya. But although these objects do seem to have burned at campfire temperatures, it is hard to see them as definitive evidence of controlled fire under hominid supervision. The earliest substantial evidence of fire control turns up only very much later: from an 800-thousand-year-old site in Israel, whence hearths containing thick layers of ash have been reported. You can, of course, argue that fire use is not always going to leave traces that will preserve over the long term, and that the African archaeological record we have in this period is sufficiently sketchy as to leave lots of room for doubt; and you would be right to do so.