Chimpanzees in West Africa may have used stone tools to crack nuts 4,300 years ago, says a recent study. Archaeologists Julio Mercader and Christophe Boesch published their study in the journal Proceedings of the National Academy of Sciences (Vol 104, No 7), which claims that prehistoric chimpanzees in West Africa could have inherited their skills from a common ancestor of chimps and humans. Archaeologists found the stones at the Noulo site in the Ivory Coast, home to the only known prehistoric chimpanzee settlement. Several types of starch grains were also found on the stones which could be residues derived from cracking local nuts.