Development of visual preference for closely related species by infant and juvenile macaques with restricted social experience

Japanese and rhesus monkeys aged between 9 months old and 5 yrs old pressed a lever to see a variety of pictures of seven macaque species. These monkeys had various restricted social experience: namely, either reared by humans with conspecific or heterospecific peers, or cross-fostered between these two species. Rhesus monkeys tended to prefer seeing rhesus monkeys best among the pictures of the seven species without regard to their age or social experience. Japanese monkeys having restricted experience also liked to see rhesus monkeys better than Japanese monkeys, but not the best among the seven species. In a previous study, mother-reared infants of Japanese monkeys preferred seeing pictures of their own species over those of rhesus monkeys. These results suggest a dissociation of the determinants of this basic social preference: rhesus monkeys prefer to see their own species by nature while Japanese monkeys may learn to prefer their own species.