The jumble of bones and stone chips at a typical prehuman site is an uncertain guide to the past. Yet careful study sometimes turns up an informative clue.
Such is the case with scratches and grooves on animal bones at African sites from 1 million to 2 million years old. A combination of visual and microscopic analyses plus experiments using stone chips on modern bones has convinced several researchers that the marks were made by stone tools. This implies that ancient hominids -- ancestors of modern humans -- were meat- eaters and skilled at butchering animals they either caught themselves or scavenged from the kills of other predators.
Two papers recently published in Nature outline some of the evidence. One, by Henry T. Bunn of the University of California at Berkeley, deals mainly with material from Koobi Fora in Kenya and Olduvai Gorge in Kenya. The other paper, by Richard Potts of Harvard University and Pat Shipman of The Johns Hopkins University, is concerned mainly with Olduvai.
Cut marks, as distinct from tooth marks of gnawing animals, are made by slicing, chopping, or scraping with sharp chips of stone. They are well known from old Indian sites in North America. But this is the first time they have been shown on million-year- old bones. Among other things, as Bunn notes, this "constitutes the most unequivocal evidence of hominid involvement with those bones."
That is an important point. At such ancient sites, bones and stone tools are often heaped together in, say, river-bed sediments. It is always debatable whether prehumans worked on the bones or whether the stone chips and bones were merely swept together over time by river action or other natural forces.
Bunn concludes that the cut marks and hammer blows, which are also evident, show that early hominids nearly 2 million years ago were "cutting up animal carcasses and breaking open bones presumably to obtain meat and marrow." He adds , ". . . this direct evidence of early hominid diet allows us to dismiss models of human evolution which do not incorporate meat- eating as a significant components of early hominid behavior."
Potts and Shipman are more cautious. They say ". . . this evidence does not bear directly on questions about the frequency of meat-eating and hunting among early hominids." They also note that there are animal tooth marks on the bones so that the evidence can't be interpreted in terms of homonid activity alone.
Thus there still are many unanswered questions. Did you prehuman ancestors hunt or scavenge or both? Certainly it now seems clear they ate meat. But how important was this in their diet and how major an influence was it on their evolution? As C. Gamble of the University of Southampton observes in commenting on this research, "we are still mostly guessin g at what went on in the past."