Masters of the Planet (21 page)

The chimpanzee results may, of course, reflect cognitive limitations that are not directly related to sociality; but no matter exactly what those limitations might be, it seems highly likely that the vulnerable
Homo ergaster
had in some way transcended them. Almost certainly, in its simultaneously hazardous and productive new habitat,
Homo ergaster
could not have got by without some of the cognitive and social qualities that are so much a hallmark of its descendants. Sadly, we are unable to say much more than this with any confidence; but there are certain other kinds of inference we can draw about the lives those savanna pioneers led, and about the sorts of groups in which they may have lived.

We saw earlier that the australopiths, vulnerable small-bodied creatures hovering about the forest fringes, may well have lived in very large groups dictated by their high vulnerability to predation. But for the Turkana Boy and his kind the calculation was probably quite different. If, as likely, these hominids had indeed acquired cultural ways of controlling the threat of predation in their new environment, then the pressures for maintaining large group sizes would have been lessened. And with greater reliance on animal products in the diet, the constraints that apply to any professional predator would have begun to assume more importance in determining how the hominids lived. In any ecosystem prey individuals vastly outnumber their predators, for too many predators
would
eliminate the prey in short order, to everyone's disadvantage. If
Homo ergaster
was in the early stages of committing to an at least partially predatory lifestyle, then the advantage would have lain in reducing population density, and by extension group sizes, for the very good reason that the number of individuals who can be supported is determined by the sustainable availability of resources within the area that can be patrolled by a single group.

Range size would have been yet further limited by the mobility of females, who gave birth to helpless babies that demanded intense care for prolonged periods. Among primates in general, newly born offspring cling to their mothers' fur, and although the physiological demands of lactation are high, carrying clinging infants around is not a technical problem so long as there is only one, or perhaps two of them, at a time. But
Homo ergaster
mothers probably had no fur for babies to hold on to, and transporting slowly maturing infants around would have been a considerable chore. As far as offspring were concerned, more would not necessarily have been better. Indeed, among documented recent hunter-gatherer groups living in environments comparable to those of
Homo ergaster,
population control has been a much greater concern than fertility. San women living in the Kalahari of southern Africa typically breastfed their infants for up to four years, thereby maintaining high levels of the hormone prolactin that inhibits ovulation. There's little doubt that high levels of infant and juvenile mortality due to predation and other causes would have favored the maximum number of offspring an individual
Homo ergaster
mother could cope with, but this limitation in itself would have assured modest group sizes. Within those small groups, it is plain that females burdened with infants would have benefited from bonds with males who could have helped them provide for their offspring; but whether or not lasting male-female bonds were formed within the group, has to remain purely hypothetical.

The number of individuals—a dozen? twenty?—within a typical group of
Homo ergaster
also has to remain a guess, though it's clear that group sizes would have varied from place to place depending on the productivity of the local environment. Hominid groups would certainly have roved widely over large areas, perhaps splitting up into smaller foraging parties as circumstances dictated, occasionally encountering
others
of their kind, and availing themselves consistently of plant foods while obtaining animals when they could. Cut-marks made by ancient stone tools on butchered bones sometimes overlie carnivore bite-marks, which suggests that carcasses were sometimes scavenged—perhaps by power-scavenging. But in other cases butchered carcasses are entirely free of bite marks, indicating probable or at least possible hunting by hominids.

That groups of early
Homo
at least occasionally circulated around a central home base to which they frequently returned is also very much on the cards. At Olduvai Gorge, for example, evidence has been found for the processing of multiple carcasses in one spot within a single season. And at a Kenyan site called Kanjera it seems that, by some two million years ago, hominids were already regularly processing animal parts using tools made from stones derived from a variety of sources as much as 12 to 13 kilometers away. These findings have several intriguing implications, perhaps the most important among them being that, even before we have definitive fossil evidence that
Homo ergaster
was on the scene, hominids were already showing some key elements of later human behavior. But while the transport distances involved also suggest that by two million years ago hominids were already living highly energetic lives of the kind that analysis of the Turkana Boy's skeleton reveals, we can't be entirely sure exactly who those hominids were. With luck this issue will be clarified as that tantalizing assemblage of hominid fossils in the 2.5- to 2.0-million-year time frame is augmented and sorted out. Meanwhile, we can be confident that by the time the Boy himself came along some 1.6 million years ago, hominids were already living complex existences that anticipated major developments to come.

In any event, for all the sophistication of its immediate predecessors, it is clear that we cannot dismiss
Homo ergaster
as merely an advanced bipedal ape in a new kind of body. But at the same time, we can be fairly sure that this hominid's way of life exhibited a considerable degree of behavioral continuity with the past. This is hardly surprising in the larger context of hominid prehistory. For one thing, the knowledge that the first members of
Homo ergaster
wielded stone tools basically identical to those their predecessors had already been using many hundreds of thousand years before, gives us our first glimpse of yet another enduring
hominid behavioral pattern: namely, the tendency to respond to fluctuating climatic and environmental circumstances by using existing toolkits in new ways, rather than by inventing new technologies. This is totally consistent with the fact that, from the beginning, hominids have always been ecological generalists. We have typically avoided the dangers of specialization by remaining unfailingly flexible in our responses to changing external conditions, in a sometimes dramatically fluctuating world. Hominids typically haven't so much
adapted
to change, as they have
accommodated
to it.

None of this means that gradually cumulative modifications couldn't have been made over the bipedal apes' long tenure. The lifeways of the australopiths had probably become more complex, and their exploitation of resources greatly refined, over the several million years of this ancient group's existence. Any such changes, though, were achieved in ways that are only indirectly reflected in the material record we have to hand so far. This is a pity, because it seems clear that the radically new
Homo ergaster
must have originated in some behaviorally sophisticated australopith isolate. And the chances are that, far from being propelled by circumstances, this new body build just happened to open up hugely advantageous new possibilities for its possessors in a new and expanding environmental setting. In keeping with this established pattern, the next technological leap most probably occurred, after a certain delay, within a population of
Homo ergaster
itself.

SEVEN

OUT OF AFRICA. . . AND BACK

The human family was born in Africa, and many millions of years passed before we have any evidence that hominids had managed to escape the continent's confines. For a long time it was believed that the first hominid movement into Eurasia must have been facilitated by some dramatic acquisition such as an enlarged brain, or the acquisition of an improved technology. Now, though, things are looking a lot more murky; for the initial dispersal out of Africa appears to have occurred as early as 1.8 million years ago, or possibly more, and in a very archaic archaeological context.

The ruined medieval town of Dmanisi, lying in the Republic of Georgia between the Black and Caspian Seas, is the last place anyone would ever have thought of looking for early hominid fossils. Far from the layer-cake sediments and bare, sun-baked exposures of the Rift Valley, Dmanisi sits high atop a black basaltic bluff in a verdant landscape, dominating the confluence of two river valleys along which important ancient trade routes converged. Its setting alone makes it among the most spectacularly sited fossil localities anywhere. After a long and tumultuous history that ended in its comprehensive sacking by invading Turkoman forces in the fifteenth century, the formerly bustling town fell into decay. Unaltered for hundreds of years except by neglect, Dmanisi
thus
offered a wonderful opportunity to twentieth-century archaeologists seeking to understand more about life along a major branch of the great medieval Silk Road. Excavations in what remained of the dwellings revealed that the ancient townsfolk had dug circular grain-storage pits beneath their homes; and in 1983, entirely unexpectedly, fossil mammal remains were found in the walls of one of these. The town, it turned out, had been constructed on a thin veneer of sediments that blanketed the basalts below; and the first fossil to be found in these soft rocks, the tooth of a rhinoceros, turned out to belong to a species that was characteristic of the early Pleistocene. Suddenly, the earth below it had become even more interesting than the town itself.

Crude stone tools were found not long thereafter, and in 1991 the first Dmanisi hominid turned up: part of a lower jaw, with a beautifully preserved set of teeth. When it was announced in 1995 this specimen elicited broad comparison with
Homo erectus,
and it was felt to be most closely comparable with specimens from eastern Africa, with which the associated mammal fossils suggested it was roughly contemporaneous. This was later confirmed by dating of the underlying basalts to some 1.8 million years ago, in concert with geological analyses revealing that the uneroded basaltic surface had been covered and protected by the fossil-bearing sediments not long after its extrusion over the landscape. Shortly before the early age of Dmanisi was verified in 2000 and 2002, dates had been published from Java that hinted at the very early (1.8- to 1.6-million-year) presence of
Homo erectus
in eastern Asia; and together, these observations placed beyond dispute that the hominid exodus from Africa had begun almost immediately following the appearance there of the new hominid body form—vastly earlier than anyone had previously suspected.

By 2004 four hominid crania and three mandibles, including one very large one, had been recovered from the Dmanisi deposits. They make up a varied assortment—particularly if you include the big mandible, of which the counterpart cranium has reportedly since been discovered—but the fact that they were found pretty close together in the sediments has been taken by most observers to enhance the probability that all represent the same species. The large mandible received the name
Homo georgicus
in 2002, but the Dmanisi team has since returned to the
notion
that all the fossils belong to
Homo erectus,
effectively postponing any definitive decision on their taxonomic assignment.

Heterogeneous as they are, the Dmanisi fossils are actually quite distinctive; and one thing they all have in common is small brains. Cranial volumes vary between 600 cc and 775 cc (they mostly cluster around the low end of this range), making all of them significantly smaller-brained than the Turkana Boy. And they are smaller-bodied, too: two partial skeletons, including that of an adolescent associated with one of the skulls, indicate that these hominids were diminutive compared to their Kenyan relative—so, relatively speaking, their brains may not have been quite so small. Estimates of stature based on individual long bone lengths came in at a rather short four feet ten inches to five feet two inches, but the shape of the bones themselves is said to be strongly suggestive of modern body form, with major elements showing much greater anatomical resemblance to the Boy than to any australopith.

The stone tools found alongside the Dmanisi hominid fossils resembled those used by contemporary
Homo ergaster
in east Africa: simple knobbly rock cores with sharp flakes knocked off them, barely distinguishable from the very first stone tools ever made. This was evidently a useful, adaptable, and durable technology—primitive tools like these continued to be made for a million years into the future—and the Dmanisi finds confirmed that it was not an improved toolkit that had permitted hominids to move out of Africa for the first time. Nor, if one may take the evidence of brain volumes at face value, were the hominids who made the tools any smarter than their African progenitors. So evidently, with the elimination of technology and expanded brains as potential enabling factors, it was the radical shift in hominid body form that had made the difference. Environmental change may also have been involved, the general drying-out of the climate spurring an expansion of the kind of habitat that was congenial to the new hominids: the dispersal of several other mammal species into Eurasia from Africa at around the same time indicates that environmental changes were afoot in southwestern Asia, as well as in the parent continent. Nonetheless, it's evident that the new hominids were significantly adaptable. For example, to judge from the kinds of mammals that were living there the Levant, the area at the eastern end of the Mediterranean that connects
northeastern
Africa to Eurasia via the Sinai Peninsula, was covered at this time primarily by Mediterranean woodlands. This environment was sufficiently different from that offered by tropical Africa to suggest that the emerging hominids must have been able to cope with a wide environmental range.