Abstract
The hand preference of chimpanzees based on observation of their tool behavior was studied in the Mahale Mountains National Park, Tanzania. Observations and recording of ant fishing were conducted to study their tool behavior. The research was conducted during a period of 7 months from August 1992 to February 1993. Handedness in the use of fishing probes was examined for 49 individuals. Chimpanzees are basically two-handed in the use of probes, though a minority has a one-hand preference. For this reason, the relationship between the location of the nest-entrance and the position in which a chimpanzee can preserve its balance in the tree strictly determines which of the hands can be used. Chimpanzees are two-handed, and can fish for ants with either hand. The skill of ant-fishing does not always favour the evolution of one-hand preference. Thus, chimpanzees are variable in the use of hands, from almost one-handed to almost two-handed individuals. The use of fishing probes for ants does not necessitate the exclusive specialization of one-handedness in the manual dexterrity.
