By Ann Gibbons
Paleoanthropologists once considered making tools to be one of the defining characteristics of being human--along with a big brain, language, and upright walking. But they had to rethink the concept of "man the toolmaker" in recent decades as they spotted wild chimpanzees pounding nuts open with stone hammers, fishing for termites and ants with sticks, and extracting honey with brushes made of sticks. Skeptics countered that tool-wielding chimpanzees were just imitating humans living in the same forests.
A new study bolsters the idea that chimps came up with the tools themselves. Researchers working in Africa's Côte D'Ivoire (Ivory Coast) have discovered stone hammers made 4300 years ago that appear to be the handiwork of chimpanzees, not humans. The ancient age of the tools shows that they were made by chimpanzees because "we know this was happening when no farmers were around--it predates farming in the area by 2000 years," says lead author Julio Mercader, a Paleolithic archaeologist at the University of Calgary in Canada.
In excavations in the Taï rainforest, researchers have uncovered a trail of stone tools that are the first prehistoric evidence of a chimpanzee tool-kit, according to a report published online this week in the Proceedings of the National Academy of Sciences. Earlier, Mercader and primatologist Christophe Boesch of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, had documented how chimpanzees had systematically transported specific types of stone to use as hammers to smash open nuts in the Taï forest. They also had proposed that chimpanzees might have an archaeological record similar to the Oldowan stone tools made by early human ancestors (Science, 24 May 2002, p. 1452). Last year, they systematically dug test trenches at ancient chimpanzee sites in the forest, leading to the discovery of stone tools from three areas.
Next, they had to prove that the stone hammers were actually tools and that they were chimp-made, not man-made. They found that the stones were too large for humans to use (but just right for chimpanzees); had starchy residue from nuts that chimpanzees eat, but living humans don't; were made from granitoid stone that chimpanzees use for tools today, but humans don't; and were unlikely to be the result of natural erosion.
The antiquity of the tools suggests that chimpanzee tool-making has been passed from chimpanzee to chimpanzee for more than 200 generations, the authors write. It raises the specter that some of the simple stone tools attributed to modern human ancestors at archaeological sites in Africa might also be the handiwork of chimpanzees, says Mercader. And it prompts questions about how early--and how often--stone tool-making arose in the human and chimpanzee lineages. "We now have evidence ... that there is a chimpanzee archaeological record--a Chimpanzee Stone Age," says primatologist William McGrew of the University of Cambridge in the United Kingdom.