Effects of upright posture on hand preference for reaching vs. the use of probing tools by tufted capuchins (Cebus apella).

This research examined the effects of task (reaching vs. tool use) and posture (quadrupedal vs. bipedal) on hand preference in tufted capuchins (Cebus apella). Regarding direction of hand preference, we found a significant main effect of posture, as the bipedal stance elicited greater use of the right hand than did the quadrupedal stance, and a significant posture x task interaction, as bipedal reaching elicited greater use of the right hand than did other postural and task conditions. Further, we found a significant main effect of task on strength of hand preference, as tool use elicited more consistent use of one hand over the other than did reaching. Our findings indicate that bipedal reaching facilitates a mild right-hand bias in intensely manipulative primates. We speculate that this moderate bias may have been pushed in the direction of nearly exclusive right-hand preference in most humans with the development of complex tool use.