Hand Preferences in New World Primates

Studies of hand preference s in the platyrrhine species are reviewed. Hand preferences of the New World species have been recorded during feeding activities, visuospatial reaching, haptic discrimination, tool use and in a variety of routine tasks using the hands. Of the New World species tested so far, the common marmoset (Callithrix jacchiis) and squirrel monkeys {Saimiri sciureus), appear to be the only species that do not display handedness in feeding activities: at the population level both species display a symmetrical distribution of hand preferences. It appears that only one New World primate species, the spider monkey (Ateles geoffroyi), displays left handedness during feeding while the other species are right handed or have no handedness. Thus,tlie findings for hand use in feeding do not support the Postural Origins hypothesis of MacNeilage et al. (1987) as it predicts left handedness rather than right in the arboreal platyrrhine species. Overall, tlie reports of handedness for tasks requiring complex visuospatial or tactile processing in the New World primates concur with those reported for humans, who have left handedness in haptic discrimination and complex visuospatial tasks and right handedness for manipulative tasks. Squirrel monkeys are left handed when reaching for moving objects and capuchins display left handedness in haptic discrimination tasks, and right handedness during sponging tasks. There is strong evidence of an effect of posture on the strength of hand preferences, and some affects of age and gender on hand use have also been reported. However, these variables do not influence hand preferences consistently across species or across tasks conducted with the same species.&nbsp