Laterality of limb function in wild chimpanzees of Gombe National Park: Comprehensive study of spontaneous activities

Resurgence of interest in laterality of hand function in nonhuman primates requires baseline knowledge of spontaneous hand-use in nature, in order to make sense of experimental studies in captivity. We present ethological data on 43 categories of limb movements exhibited by one community of wild chimpanzees (Pan troglodytes schweinfurthii) in the Gombe National Park, Tanzania. By focal-subject sampling, 42 individuals were observed at close-range over 4 months during their everyday activities. Laterality of hand function was largely absent, as both pooled results for the group and individual results rarely departed from 50:50 (ambilaterality). Neither age nor sex differences emerged. Nor did it matter if the subject was arboreal or terrestrial, or if the non-active hand was idle or engaged in postural support. Laterality was equally absent for unimanual and bimanual tasks. Lack of lateralization for limb movement in this natural population contrasts with findings of apparent right-handedness in captive chimpanzees. Unnatural postures and biased selection of measures in captive studies may account for these differences.