Evidence for a Social Custom in Wild Chimpanzees?

Can the concept of culture be applied validly to any of the natural behaviours exhibited by non-human primates? We compare aspects of social grooming shown by two separate populations of wild chimpanzees (Pan troglodytes) in western Tanzania. We present as an example a behaviour pattern, the grooming-hand-clasp, which occurs commonly in the chimpanzees of Kasoge but is absent in the chimpanzees of Gombe. After discussing the problems of operationally defining culture, we present eight necessary criteria of culture which are capable of empirical verification: innovation, dissemination, standardisation, durability, diffusion, tradition, non-subsistence, and natural adaptiveness. These are applied to the behaviour of wild chimpanzees andJapanese monkeys (Macacafuscata). We conclude that no single behaviour pattern yet reported satisfies all eight criteria but that the grooming-handclasp should qualify as a social custom.