Visual discrimination of male and female faces by infant rhesus macaques.

Recent studies have revealed that human infants process female faces differently from male faces. To test whether a similar preference for female faces exists in other primates, we presented nursery-reared infant rhesus macaques with photographs of macaque faces and human faces. At <1 month old, infant macaques preferentially oriented towards female macaque faces when faces were presented upright. No preference for female human faces was found. At 9 months old, infants failed to show a visual preference for female macaque faces or female human faces, although they showed significantly more lipsmacking responses at female human faces. Compared to human infants, macaques appear to have stronger predispositions early in life but this preference may nonetheless be amendable to experience. Understanding how innate predispositions and the social rearing environment shape infants' understanding of faces remain important issues to be explored in order to understand facial processing abilities in humans and other primates.