Archeologists Find Evidence of Chimp Tool Use


March 07, 2007

Archaeologists Find Signs Of Early Chimps' Tool Use


Published: February 13, 2007

In the rain forest of the Ivory Coast 4,300 years ago, chimpanzees gathered in groups and cracked nuts the best they could, the Stone Age way. Place the nut on a hard, flat rock. Take a heavy hammer rock, and pound the nut. The chimps must have feasted well and often there under the trees by a black-water river.

Archaeologists digging in Tai National Park in Ivory Coast reported yesterday the discovery of several sites where such nut-cracking chimps long ago left broken and discarded stones that were used as natural tools. Starch residues from nuts were lodged in crevices of the stones.

This was the earliest strong evidence of chimpanzee tool use, researchers say in the current issue of the Proceedings of the National Academy of Sciences. The discovery team included scientists from Canada, Britain, Germany and the United States.

Chimps in the wild were first observed using stone tools in the early 19th century, and earlier remains of their material culture are scant. No artifacts have come to light showing that chimps have ever deliberately made stone tools by chipping, flaking and other methods, as prehuman species were doing as early as 2.6 million years ago.

The archaeologists, led by Julio Mercader of the University of Calgary in Canada, said the findings in Ivory Coast, in West Africa, indicated that these chimps developed the nut-cracking behavior without human influence. The stones are unlike any food-processing implements used by humans in the region today, and they have use and wear patterns consistent with what is seen in modern chimp sites. The sizes and shapes of the stones appear to be more suited to the large, strong hands of chimps than to human hands.

The remains at the sites, moreover, are virtually identical to what today's tool-using chimps leave behind. The material was buried as much as three feet deep and mixed with charcoal from natural forest fires. Radiocarbon analysis of the charcoal determined the age of the site.

So if chimps 4,300 years ago were not mimicking humans, the research group suggested that their capacity for tool use could have been inherited from the last ancestor that the chimp and human lineages have in common. In interviews, Dr. Mercader and John W. K. Harris of Rutgers University, another team member, contended that the new findings gave substance to that hypothesis.

Other experts in early stone tool technology said the analysis of the chimpanzee tool-use sites appeared to be sound, but they had reservations about the interpretations linking the behavior to common ancestors.

Dr. Mercader said extreme care was taken to separate pieces of stone that had been modified through use as a nutcracker from those that are naturally fractured stones often found in streams. He said independent experts, including Dr. Harris, were called in for blind tests, and they scored about 95 percent correct in recognizing the stones the chimps had used as tools.

In any case, other archaeologists agreed with the research team's concluding observation: ''That nut-cracking behavior in the Tai forest has been transmitted over the course of more than 200 generations, and that chimpanzee material culture has a long history whose deep roots are only beginning to be uncovered.''

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