WASHINGTON (Reuters) - Chimpanzees may have had their own “Stone Age,” with evidence showing they were using stone tools to crack nuts 4,300 years ago, researchers reported on Monday.
They said their findings suggest that the common ancestor of chimpanzees and humans started using tools more than 7 million years ago, when the two species started to evolve separately.
“It’s not clear whether we hominins invented this kind of stone technology, or whether both humans and the great apes inherited it from a common forebear,” said archeologist Julio Mercader of the University of Calgary in Alberta, who led the study.
“There weren’t any farmers living in this region 4,300 years ago, so it is unlikely that chimpanzees picked it up by imitating villagers, like some scientists used to claim.”
The international team of researchers was working in Ivory Coast. They found rocks that clearly had been used to break up nuts, buried in 4,300-year-old deposits.
“Can we demonstrate that such stones were used by chimpanzees?” the researchers wrote in their report, published in the Proceedings of the National Academy of Sciences.
They said the rocks are bigger and look different from the type typically used by early humans, but are the same type that are used by chimps today to crack nuts. And they are still coated with the crushed remains of nuts that appear to be some of the same varieties eaten today by chimps, but not humans.
“Present-day chimpanzees crack five nut species that, except for one (Coula edulis), are not cracked by local human populations,” they wrote.
“The chimpanzee assemblages are contemporaneous with the local Later Stone Age; and thus they represent a parallel ‘Chimpanzee Stone Age,’” they added.
And there is no evidence that humans lived there.
“Typical archeological features commonly found in Later Stone Age sites from the African rainforest were not found here, such as inhabitation structures, activity areas, hearths, or charred food remains.”
Chimps have been known to use stones to crack nuts since the 19th century. They are bigger and stronger than humans and so use different types of stones than people would.
“We know that modern chimpanzee behavior regarding nut-cracking is socially transmitted and takes up to seven years to learn,” Mercader said in a statement.
“Some of the nuts require a compression force of more than a thousand kilograms (2,200 pounds) to crack. And the idea is to crack the shell but not smash it — it’s not a simple technique.”
The study adds to growing evidence that culture — passing complex social information from one generation to the next — is not unique to humans.
“We used to think that culture and, above anything else, technology was the exclusive domain of humans, but this is not the case,” Mercader said.