The first prehistoric evidence for a "chimpanzee stone age" has beenuncovered 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 Tai national park in Ivory Coast.
The tools, used to crush and crack food, are too large for humans tohave wielded with ease, and showed traces of starch from varieties of nutsthat were staples of the chimp diet, but avoided by humans.
The discovery suggests that from ancient times chimpanzees usedrudimentary technology and handed the skills down to later generations.
The flood plain where the stone fragments were uncovered was not widelyoccupied by humans at the time, leading the researchers to suspect thatearly tool use was not learned from humans, but may have been passed on tochimps and humans alike from a more primitive ancestor.
"It's not clear whether we invented this kind of stone technology, orwhether 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'sunlikely the chimpanzees picked it up by imitating villagers."
The study was published yesterday in the journal Proceedings of the National Academy of Sciences. He added: "We used to think that culture and, above anything else,technology was the exclusive domain of humans, but this is not the case."
The researchers believe the intact tools would have ranged from less than200g to nearly 7kg (7oz to 15lb). Tests revealed the stones had mostlikely been used to crack open five varieties of nuts, four of which arethought to have been eaten by chimpanzees but not humans.
The technique wasmore subtle than simply smashing the nut between two rocks, according tothe researchers. Some nuts required a force of more than a tonne to crackthem open, and a more complex technique was needed to do so withoutdestroying the nut inside.
Huw Barton, a co-author on the study at Leicester University, said thefinding raised the tantalising suggestion that tool use among chimpanzees may have progressed, at least for a while, in parallel with human usage.
"At the moment, we know for chimpanzees tool use goes back at least4,300 years, but what if it goes back much further? Who knows what we'd find."