— Chimpanzee stone tools excavated in TaÃ¯ National Park, CÃ´te de Ivoire (Image: Gerald Newlands)
Over 4000 years ago, prehistoric chimpanzees were using stone tools to smash nuts in the west African rainforest, a new study suggests.
The discovery represents the earliest known use of technology by chimps, and could indicate we share a common tool-wielding ancestor with them.
When Julio Mercader of the University of Calgary in Canada, and colleagues, excavated a 4300-year-old floodplain site in Tai National Park, Ivory Coast, they found a variety of fashioned stone fragments. A few are clearly of human origin, as they show systematic efforts to flake rock to form edges. However, most of the fragments resulted from the kind of cruder bashing action that chimps and humans use to crack nuts.
When Mercader and two colleagues reconstructed the original stone tools from which the fragments came, they found that most were relatively large, weighing an average of 710 grams. This is larger than tools used by Stone Age humans, but a similar size to the hammer stones used by modern-day chimps.
Moreover, from the shape and size of the grains in plant residues lodged in crevices in the stones, Mercader concludes that most came from nuts rather than tubers or legumes. Many of these nut species, he says, are eaten by modern chimps, but not ancient human hunter-gatherers. Putting the two lines of evidence together, he reckons the site represents an ancient feeding area where chimpanzees used stone tools
âThe simplest, most parsimonious explanation to having two lineages using bashing technologies is that they both inherited that, rather than inventing it separately,â Mercader says.
Not everyone agrees. There may have been prehistoric cultures we have yet to discover that used heavier hammer stones and ate a wider range of nut, notes Sally McBrearty, a paleaoanthropologist at the University of Connecticut in Storrs, US. By piling inference upon inference as Mercader does, she says, âyou just get on shakier and shakier ground, because of the uncertainty with each one of the stepsâ.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0607909104)