The first prehistoric evidence for a 'chimpanzee stone age' has been uncovered by archaeologists working in an African rainforest. Primitive stone hammers and anvils dating from 4,300 years ago were excavated from pits at three sites in the Taļ national park in Ivory Coast. The tools, used to crush and crack food, are too large for humans to have wielded with ease, and showed traces of starch from varieties of nuts that were staples of the chimp diet, but avoided by humans.
     The discovery suggests that from ancient times chimpanzees used rudimentary technology and handed the skills down to later generations. The flood plain where the stone fragments were uncovered was not widely occupied by humans at the time, leading the researchers to suspect that early tool use was not learned from humans, but may have been passed on to chimps and humans alike from a more primitive ancestor.
     "It's not clear whether we invented this kind of stone technology, or whether both humans and great apes inherited it from a common forebear," said Julio Mercader from the University of Calgary, who led the study. "There weren't any farmers living in this region 4,300 years ago, so it's unlikely the chimpanzees picked it up by imitating villagers." The study was published yesterday in the journal Proceedings of the National Academy of Sciences.
     The researchers believe the intact tools would have ranged from less than 200g to nearly 7kg (7oz to 15lb). Tests revealed the stones had most likely been used to crack open five varieties of nuts, four of which are thought to have been eaten by chimpanzees but not humans. The technique was more subtle than simply smashing the nut between two rocks, according to the researchers. Some nuts required a force of more than a tonne to crack them open, and a more complex technique was needed to do so without destroying the nut inside.
     Huw Barton, a co-author on the study at Leicester University, said the finding raised the tantalising suggestion that tool use among chimpanzees may have progressed, at least for a while, in parallel with human usage.

Source: The Guardian (13 February 2007)