Brian Switek in Laelaps:
The ability of our species to make and use tools clearly separated us from all other organisms, at least until it was discovered that chimpanzees, too, made and used tools. More than that, studies since the 1960's have confirmed that different populations of chimpanzees have distinctive tool cultures affected by the contingencies of their surroundings, and a recent study published two years ago in PNAS illustrates that these cultures of tool use among non-human primates stretch back at least 4,300 years.
Since September of 1979 primatologists have studied the wild chimpanzees of the Tai National Park in the western African nation of Côte d'Ivoire, and in this particular location the chimpanzees use a variety of tools. Among the most common tools are twigs used to get at different kinds of food (be it honey in a tree or the brains of a monkey they have killed), but the Tai chimps also frequently use stone hammers and anvils to crack open nuts. Naturally this process modifies the stones used in the process, and this made some researchers wonder whether chimpanzees might have an archaeological record all their own.
To find out, scientists Julio Mercader, Huw Barton, Jason Gillespie, Jack Harris, Steven Kuhn, Robert Tyler, and Christophe Boesch looked for signs of ancient chimpanzee sites within the Tai forest. They found three, all of which were within about 200 meters of each other in an area of the park still inhabited by chimpanzees and dated to a span of time between 4,300 years ago and 2,200 years ago. From these sites the researchers gathered a large collection of modified stones, most of which (206 pieces) came from a single site, but the question was whether they were truly looking at a chimpanzee-made assemblage or one that had been artificially made by flowing water.