Ancient Chimpanzee Tool Use	Volume 61 Number 1, January/February 2008
by Zach Zorich

Ancient Chimpanzee Nutcrackers • Taï forest, Ivory Coast


(Courtesy Paco Bertolani)

Archaeologists led by Julio Mercader of the University of Calgary have uncovered the first known ancient chimpanzee archaeological site, a grouping of stone hammers that were used by apes 4,300 years ago to smash open nuts. By analyzing pollen grains embedded in the stones, the team was able to identify five species of nuts the tools were used to open, four of which are not eaten by humans. The discovery shows that stone tool use is not a behavior that chimpanzees learned recently by watching the farmers who live in the area, as some skeptics believe. Mercader thinks that humans and chimpanzees may have inherited stone tool use from an ancestral species of ape that lived as long as 14 million years ago.

Although using a big rock to smash open a nut may seem like a simple task, Mercader sees the stones as clues to much more complex behavior. "There is clear evidence that chimpanzees understand what raw materials they need," he says, pointing out that the apes prefer specific, durable types of stone, such as quartzite or granite. Knowing where to find the stones also requires planning and a good memory in a thick jungle where visibility is only about 40 feet.

The number of behaviors that are uniquely human has been steadily dwindling as scientists learn more about our primate cousins, but producing cutting tools still seems to be beyond the abilities of chimpanzees living in the wild.

"If you go to a nut-cracking site today, you would find there are flakes that come off of the hammers," Mercader says. "What we haven't seen is a chimp picking up any of those by-products and using them."

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