for National Geographic News
Humans might not be as pioneering as we're cracked up to be.
That's one possible explanation for new evidence that West African chimpanzees learned to use stone tools on their own to crack nuts at least 4,300 years ago.
The research pushes back chimpanzee tool use thousands of years. It casts into doubt the long-standing theory that direct human ancestors were the only animals to independently develop tools—and that chimps learned to use stone tools by watching humans.
(Follow a time line of human evolution.)
Instead both humans and chimps could have inherited the ability to crack nuts with rocks from a common ancestor, Julio Mercader of the University of Calgary in Canada and co-authors report in today's issue of the Proceedings of the National Academy of Sciences.
Or chimps may have developed the behavior on their own. In either case, it's no longer likely that chimps learned to use stones as tools only by imitating humans.
At 4,300 years old, the chimps' tools correspond to the late Stone Age of human history—before the advent of agriculture in West Africa.
"Until recently people used to say that among modern-day chimpanzees the behavior came from imitation of farmers," Mercader said. "That assumption is no longer valid. What we present predates the presence of farming."
Mercader and colleagues found subtly altered rocks in Côte d'Ivoire (Ivory Coast) in Africa at a research site that houses the only known prehistoric chimpanzee settlement.
(Related news: "Chimp Nut-Cracking Site Offers Clues to Early Tool Use" [May 23, 2002].)
The excavated stones resemble those used by ancient humans and modern chimpanzees to smash nuts—showing evidence of flakes, chips, and worn edges.
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