Chimpanzees learned to make and use stone tools on their own, rather than copying humans, new evidence suggests.
This also means that chimps and humans likely inherited some of their sophisticated stone tool-use behaviors from a common ancestor, a report on the evidence claims.
The handheld hammers were found at a chimpanzee settlement in the Ivory Coast and date back 4,300 years.
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Chimpanzees have been observed using similar tools for the past few centuries, but scientists assumed the intelligent apes were simply copying local people cutting open fruit nearby.
[The earliest reports of stone-tool use by chimpanzees in West Africa date to the writings of Portuguese explorers in the 1600s.]
"The thinking until now was that if modern-day chimpanzees use hammers, it was only because they're imitating neighboring farmers," said Julio Mercader, archaeologist at the University of Calgary and co-author of the study. "But what we've found predates farming in the area."
[The study was published Monday in the online edition of Proceedings of the National Academy of Sciences.]
Since the ancient chimpanzees likely didn't learn the behavior from contemporary men, humans and chimps may have "inherited" the ability from a common ancestor, researchers speculate.
First Case of Prehistoric Chimp Tools
Though there were no chimpanzee remains at the settlement, testing by archaeologists revealed the tool-laden camp was most likely used by the great apes.
The stones were much bigger than anything a human could use comfortably [about the size of cantaloupes] and bore the residue of nuts that modern chimpanzees like to snack on.
"This is the only case of any prehistoric, non-human great ape tool use ever discovered," Mercader told LiveScience
Chimpanzees in the wild today are often seen using hammer tools to crack nuts, much as our ancient ancestors did a few million years ago.
The technology is transmitted socially — or taught, rather than instinctive from birth — and can take up to seven years for a young chimp to master, many scientists have found.
"What makes our find different is that we can demonstrate a prehistoric context for this, and that opens many doors," Mercader said. "Social transmission was the only way for this to happen."
It suggests that there is a cultural link between chimps today and their ancient ancestors, one that could go back even further than a few thousand years, he added.
Since human stone tool use was transmitted the same way, it's possible that both lines were taught by a single source, perhaps even millions of years ago.
["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," Mercader said in a statement reported by the Associated Press.]
[The tools may predate farming in the area but not necessarily human contact, anthropologist Stanley H. Ambrose of the University of Illinois at Urbana-Champaign told the AP. There were early human hunter-gatherers in the region at the time, he said.
If chimps and early humans shared this technology with a common ancestor between 5 million and 7 million years ago, there should be sites with chimp debris going back 5 million years and the earliest human stone tool sites should show the kinds of debris found at the chimp sites, Ambrose said: "They absolutely do not."
Some of the hammers also had starch residue on them, mostly from types of nuts that are still eaten by chimpanzees, but not humans. Some of the starch was also associated with tubers but the researchers interpreted that as "background noise" probably picked up in the ground.
Skeptical of the starch findings was anthropologist Jeanne Sept, dean of faculties at Indiana University.
"Their interpretations of the starch grains recovered from the specimens are incomplete, and somewhat circular," she said. "For example, they do not describe which surfaces of the rock fragments the starch grains were obtained from, which makes it difficult to judge whether the grains were left on the tools as a result of tool-use, or if the grains merely naturally stuck to the stones after they became buried in the soil."
"They assert that starch grains from nuts were behaviorally significant, while they decide that starch grains identified as yam roots are 'background noise' but give no justification for that," she added. "They may in fact be dismissing or ignoring evidence that does not match their chimp-nut interpretation of the site."
"It may be premature to accept the range of their claims until further evidence is presented," Sept concluded.]
Technology Not a Smooth Line
The transition from millions of years ago to the chimpanzees that lived at the ancient settlement would not have been smooth, said Mercader.
Other chimps in nearby areas may not have used the nut-smashing technique at all, he said, and the find asks many questions about why and how this particular group in the Ivory Coast was able to grasp the concept.
It does dispel the notion, however, that humans were the only forest-dwellers with any brains.
"We used to think that culture and, above anything else, technology, was the exclusive domain of humans," Mercader said, "but this is not the case."
[Mercader's research was funded primarily by the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany; Canada Research Chairs program, Canada Foundation for Innovation and the University of Calgary.]
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