Masters of the Planet (20 page)

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.

At the other end of the timescale, it is actively argued that habitual fire use was a late acquisition in hominid history. But there can nonetheless be no doubt that fire control would have been a revolutionary innovation in hominid life; and it certainly seems odd that once it had been invented it would not have been widely adopted, in which case there should be more and better evidence of it. There are numerous sites at which you would expect to find hearths if there had been any—and don't. And several hundred thousand years passed after the well-documented Israeli occurrence before we begin to pick up further evidence of controlled fire in hearths, quite plausibly at first in opportunistic rather than habitual contexts.

While it is impossible to ignore the fact that the evidence for fire use by
Homo ergaster
is almost entirely circumstantial, the case for believing that food was cooked by these early relatives remains mildly compelling. Further, it is bolstered by other considerations, albeit also indirect. There can be no doubt whatever that the use of fire would have made life a great deal easier for
Homo ergaster
groups out there on the savanna, and it's been argued that fire control was the only thing that could have rendered this new lifestyle possible at all. For the very resource—the grazing animals—that may have lured
Homo ergaster
out on to the savanna in the first place also made it a dangerous place for the hominids, who certainly did not fit tidily into a dichotomy between predators and prey.
While
they may have been predators, at least to some degree, they were slow and vulnerable targets as well. Indeed, one
Homo ergaster
frontal bone, from a site in Kenya, shows carnivore tooth-marks above one orbit that suggest a violent demise at the claws of a predator.

Early hominids at this stage were essentially amateur hunters, just breaking into the business and low on the learning curve. Indeed, for all the vaunted technological prowess that has made us today's top predator, we have not entirely put the vulnerabilities of our remote past behind us. Any jogger mauled by a mountain lion, or bow hunter chased up a tree by a bear, will assure you of that. Fire would have been an excellent way for
Homo ergaster
to discourage predators, especially to make up for the limited throwing abilities of that forwardly rotated arm joint. And if you are prepared to pile on a few more assumptions, the implications of fire use go well beyond this: some authorities have even gone so far as to suggest that many of the behavioral hallmarks of
Homo,
including its high degree of sociality and cooperativeness, stem from the closeness among group members that huddling for warmth and protection around a fire would have involved, in those early times as much as at present.

THE SOCIAL SETTING

There is no denying that fire has a unique symbolic as well as practical meaning to human beings today, and it's important to resist the resulting temptation to anthropomorphize. Still, while it may be reading a bit too much into what is already an elaborate succession of assumptions to suggest that the domestication of fire is directly responsible for our uniquely intense form of sociality, it is certainly true that modern humans are strikingly cooperative compared to other primates. Beyond simple cooperation, though, they also share an elaborate kind of sociality—known as “prosociality”—that seems to be unique. To put this at its most elementary, humans care at least to some extent about each other's welfare; and chimpanzees—as well as probably all of our other primate relatives—do not. Of course, mother-offspring bonds among chimpanzees can last a lifetime; and hunting and similarly complex activities sometimes involve extensive coordination among group members. What's more, chimpanzees have been observed to console victims of aggression, suggesting that
they
have some form of individual empathy. But such manifestations are different from the general concern for others that underwrites prosociality; and, in a large body of experimental studies, chimpanzees have come across—even to chimpophile researchers—as creatures that show a striking lack of regard for their fellows.

Researchers have tested this in captive settings. In one series of experiments, carried out on a number of different captive groups in different locations, chimpanzees were in various ways given the option of obtaining a food reward both for themselves and a neighbor, or just for themselves. For the chooser, the reward was the same in either case; but invariably the chimpanzees chose more or less randomly among the two options. On the basis of these tests, at least, the individual chimpanzee subjects seemed pretty consistently indifferent to the interests of others; and this stands in striking contrast to humans, who in psychological tests seem to be remarkably willing even to incur costs to help strangers.