Does target animacy influence manual laterality of monkeys? First answer from northern pig-tailed macaques (Macaca leonina).

The evolutionary origin of human right-handedness remains unclear. Many factors such as emotion and tool use have been implicated in primate handedness evolution. With regard to emotional lateralization, most related research focuses on facial asymmetry and behavioral laterality under the non-social context, whereas few studies investigate social laterality. This study, for the first time, investigates the effect of target animacy on hand preference in Old World monkeys, compares our findings with previous related studies in great apes and humans, and aids in filling the knowledge gap on primate handedness evolution. Nine captive northern pig-tailed macaques (Macaca leonina) were chosen as focal subjects in this study. There was no group-level handedness for both animate and inanimate targets. No significant interaction was found between lateral hand use and target animacy. Left-hand use was more frequent than right-hand use for animate targets, whereas right-hand use was more frequent than left-hand use for inanimate targets, both of which demonstrate no significant level. On the whole, northern pig-tailed macaques showed a similar tendency as that in great apes and humans. Regarding handedness linked with emotive stimuli, it is likely that Old World monkeys, great apes and humans evolved from a common ancestor.