Posture and reaching in tufted capuchins (Cebus apella).

This research investigated the effects of posture on lateral bias for food reaching in tufted capuchin monkeys ( Cebus apella ) by comparing hand preferences for quadrupedal and bipedal reaching. Several findings of this investigation warrant discussion. First, we found a population-level bias towards use of the right hand for bipedal reaching but not for quadrupedal reaching. Second, adults exhibited a greater right-hand preference for bipedal reaching than did immatures. Third, subjects showed a greater right-hand preference, and a greater strength of preference independent of direction, for bipedal reaching than for quadrupedal reaching. Fourth, we found a significant positive relation between the direction of hand preference for quadrupedal and bipedal reaching. We believe that capuchins provide an alternative primate model to chimpanzees for the evolution of human bipedalism and right-handedness. One implication of this model is that right-handedness emerged in hominids prior to extensive expansion of brain size and elaboration of material culture.