The Origin of Humankind (9 page)

In this view of early human prehistory, our ancestors become much less humanlike, not just in their mode of subsistence but also in other elements of behavior: for instance, language, morality, and consciousness would be absent. Binford concluded: “Our species had arrived—not as a result of gradual, progressive processes but explosively in a relatively short period of time.” This was the philosophical core of the debate. If early
Homo
displayed aspects of a humanlike way of life, then we have to accept the emergence of the essence of humanity as a gradual process—one that links us to the deep past. If, however, truly humanlike behavior emerged rapidly and recently, then we stand in splendid isolation, disconnected from the deep past and the rest of nature.

Although Isaac shared Binford’s concerns about past overinterpretation of the prehistoric record, he took a different approach to rectifying it. Where Binford worked largely with other people’s data, Isaac decided he would excavate an archeological site, looking at the evidence with new eyes. Although the distinction between hunting and scavenging was not crucial to Isaac’s food-sharing hypothesis, it became important in reexamining the archeological record. Hunter or scavenger? This was the crux of the debate.

In principle, hunting should imprint itself in a different way on the archeological record from scavenging. The record of the difference should be evident in the body parts left behind by the hunter and the scavenger. For instance, when a hunter secures a kill, he has the option of carrying the entire carcass, or any part of it, back to camp. A scavenger, by contrast, has available only whatever he might find at an abandoned kill site: the choice of body parts he can take back to camp will be more limited. The variety of bones found at the camp of a hominid hunter should therefore be wider—including, at times, an entire skeleton—than that at the camp of a hominid scavenger.

There are, however, many factors that can confound this neat picture. As Potts has observed: “If a scavenger finds the carcass of an animal that has just died of natural causes, then all the body parts are available to the scavenger, and the bone pattern that results will look just like hunting. And if a scavenger manages to drive a predator off its kill very early, the pattern will again look like hunting. What are you to do?” The Chicago anthropologist Richard Klein, who has analyzed many bone assemblages in southern Africa and Europe, believes the task of distinguishing between the two subsistence methods may be impossible: “There are so many ways that bones can get to a site, and so many things that can happen to them, that the hunter-versus-scavenger question may never be resolved for hominids.”

The excavation Isaac embarked upon to test the new thinking was known as site 50, which is located near the Karari Escarpment about 15 miles east of Lake Turkana, in northern Kenya. During a period of three years, beginning in 1977, he and a team of archeologists and geologists exposed an ancient land surface, the sandy bank of a small stream. Carefully, they unearthed 1405 pieces of stone artifacts and 2100 fragments of bone, some large, most small, which had been buried some 1.5 million years ago when a seasonal stream had flooded early in a rainy season. Today, the region is arid, with bush and scrub interspersed among badlands carved by eons of erosion. The goal Isaac and his team set themselves was to discover what had occurred 1.5 million years ago, when stone artifacts and many animal bones came to rest in the same place.

In his earlier critiques, Binford had suggested that many co-occurrences of bone and stone were the result of water action. That is, a fast-running stream can carry pieces of bone and stone along and then dump them at a point of low energy, such as where the stream widens or at the inside bank of a bend. In this case, the accumulation of bone and stone in the same location would be the result of chance, not hominid activity. The “archeological site” would be no more than a hydraulic jumble. Such an explanation seemed unlikely for site 50, because the ancient land surface had been on the bank of a stream, not in it, and because clues from geology showed that the site had been buried very gently. Nevertheless, a direct association between bone and stone had to be demonstrated, not assumed. That demonstration came in a most unexpected way and formed one of the landmark discoveries in archeology in recent times.

When an animal is dismembered or a bone is defleshed with a knife, either of metal or of stone, the butcher inevitably slices into the bone occasionally, leaving long grooves or cut marks. During dismemberment, the cut marks would be concentrated around the joints, while in defleshing they would be inflicted elsewhere, too. When the University of Wisconsin archeologist Henry Bunn was examining some of the bone fragments from site 50, he noticed such grooves. Under the microscope, they could be seen to be V-shape in cross section. Was this a cut mark, made 1.5 million years ago by a hominid forager? Experiments with modern bone and stone flakes confirmed it, proving conclusively a causal relationship between the bone and the stone at the site: hominids had brought them there and processed them for a meal. This discovery was the first direct demonstration of a behavioral link between bones and stones at an early archeological site. It was the smoking gun in the mystery of ancient sites.

It often happens in science that important discoveries are made independently at about the same time. So it was with cut marks. Working with bones from archeological sites around Lake Turkana and at Olduvai Gorge, Richard Potts and the Johns Hopkins archeologist Pat Shipman also found cut marks. Their methods of study were slightly different from Bunn’s, but the answer was the same: hominids close to 2 million years ago were using stone flakes to dismember carcasses and deflesh bones (see
figure 4.1
). In retrospect, it is surprising that cut marks had not been discovered earlier, because the bones examined by Potts and Shipman had been studied many times by many people. A moment’s reflection would have convinced the alert mind that, if the prevailing archeological theory was correct, signs of butchery must be present on some fossil bones. But no one had looked assiduously, because the answer was assumed. Once the unspoken assumptions of prevailing theory were questioned, however, the time was right to look for and find them.

Site 50 yielded further evidence of hominids’ using stone on bone as part of their daily life. Some of the long bones at the site were shattered into pieces, the result, it developed, of someone’s placing the bone on a stone, like an anvil, and then delivering a series of blows along the bone, thus giving access to the marrow inside. This scenario was reconstructed from a paleolithic jigsaw puzzle, in which the fragments were assembled to form the entire bone and analysis made of the pattern of breakage, which included characteristic signs of percussion. “Finding the fitting pieces of hammer-shattered bone shafts invites one to envisage early proto-humans in the very act of extracting and eating marrow,” Isaac and his colleagues wrote in a paper describing their findings. Of the cut marks they said: “Finding an articular end of bone, with marks apparently formed when a sharp-edged stone was used to dismember an antelope leg, cannot but conjure up very specific images of butchery in progress.”

Adding to these images of hominid activity 1.5 million years ago is a message from the stones themselves. When a stone-knapper strikes flakes from a cobble, the pieces tend to fall in a small area around him or her. This is just what the University of Wisconsin archeologist Ellen Kroll found at site 50: stone-knapping was concentrated at one end of the site. Similarly, the bone pieces—there were parts of giraffe, hippopotamus, an eland-size antelope, and a zebra-like animal, as well as catfish spines—were concentrated in the same place. “We can only speculate what made the northern end of the site a favorite place to do things, but the observed pattern could, for example, imply the existence of a shady tree there,” Isaac and his colleagues wrote. An even more remarkable aspect of the stone flakes was that, like the shattered long bone, some of these too could be reconstructed to form the original whole, a lava cobble.

FIGURE 4.1

Signs of ancient butchery. These small cut marks (indicated by arrows) in the surface of a fossilized animal bone from a 1.5-million-year-old archeological site in northern Kenya show that early humans used sharp stone implements to remove flesh from animal carcasses. (Courtesy of R. Lewin.)

I mentioned in
chapter 2
that Nicholas Toth and Lawrence Keeley had performed microscopic analysis of several stone flakes and found indications of butchery, wood whittling, and the cutting of soft plant tissue. Those flakes were from site 50, and the results of the analysis add to the image of a scene of diverse activity 1.5 million years ago. Far from the hydraulic jumble image, the activity at site 50 must have involved hominids bring parts of carcasses there, which were then processed with stone tools made at the site. The demonstration of the deliberate transport of bones and stones to a central place of food-processing activity was a major step in realigning archeological theory, after the theoretical turmoil of the late 1970s. But does this evidence imply that the hominids of site 50,
Homo erectus
, were hunters or scavengers?

Isaac and his colleagues put it this way: “The characteristics of the bone assemblage invite serious consideration of scavenging rather than active hunting as a prominent mode of meat acquisition.” Had entire carcasses been found at the site, a conclusion of hunting could be drawn. But, as I indicated earlier, the interpretation of patterns of bone assemblages is fraught with potential error. Other lines of evidence, however, have been adduced to imply scavenging as the mode of meat acquisition in early
Homo
. For instance, Shipman examined the distribution of cut marks on ancient bones and made two observations. First, only about half were indicative of dismemberment; second, many were on bones that bore little meat. Furthermore, a high proportion of cut marks crossed over marks left by carnivore teeth, implying the carnivores got to the bones before the hominids did. This, Shipman concluded, is “compelling evidence for scavenging,” an image of our ancestor she notes is “unfamiliar and unflattering.” It is certainly far from the Man the Noble Hunter image of traditional theory.

I would expect that the meat quest in early
Homo
would have involved scavenging. As Shipman observed, “Carnivores scavenge when they can and hunt when they must.” But I suspect that the recent intellectual revolution in archeology has gone too far, as often happens in science. The rejection of hunting in early
Homo
has been too assiduous. I find it significant that Shipman’s analysis of the distribution of cut marks shows so many on bones with little meat. What can be obtained here? Tendons and skin. With these materials it is very easy to make effective snares for catching quite large prey. I would be very surprised if early
Homo erectus
did not engage in this form of hunting. The humanlike physique that emerged with the evolution of the genus
Homo
is consistent with a hunting adaptation.

For Isaac the work at site 50 was salutary. Although it confirmed that hominids were transporting bone and stone to a central place, it did not necessarily demonstrate that the hominids used that location as a home base. “I now recognize that the hypotheses about early hominid behavior I have advanced in previous papers made the early hominids seem too human,” he wrote in 1983. He therefore suggested modifying his “food-sharing hypothesis,” making it the “central-place-foraging” hypothesis. I suspect he was being too cautious.

I cannot say that the results of the project at site 50 confirm the hypothesis that
Homo erectus
lived as hunter-gatherers, moving every few days from one temporary home base to another—bases to which they brought food and where they shared it. How much of the social and economic milieu of Isaac’s original food-sharing hypothesis might have been present at site 50 remains elusive. But in my judgment there is sufficient evidence from the work to dispense with the notion that early
Homo
was little advanced beyond the chimpanzee grade of social, cognitive, and technological competence. I’m not suggesting that these creatures were hunter-gatherers in miniature, but I’m sure that the humanlike grade of the primitive hunter-gatherer was beginning to be established at this time.

Although we can never know for certain what daily life was like in the earliest times of
Homo erectus
, we can use the rich archeological evidence of site 50, and our imagination, to re-create such a scene, 1.5 million years ago:

A seasonal stream courses its way gently across a broad floodplain on the east side of a giant lake. Tall acacia trees line the stream’s circuitous banks, casting welcome shade from the tropical sun. For much of the year the stream bed is dry, but recent rains in the hills to the north are working their way down to the lake, slowly swelling the stream. For a few weeks now, the floodplain itself has been ablaze with color, with flowering herbs splashing pools of yellow and purple against the orange earth and low acacia bushes looking like billowing white clouds. The rainy season is imminent
.