Development of preference for conspecific faces in human infants

Previous studies have proposed that humans may be born with mechanisms that attend to conspecifics. However, as previous studies have relied on stimuli featuring human adults, it remains unclear whether infants attend only to adult humans or to the entire human species. We found that 1-month-old infants (n = 23) were able to differentiate between human and monkey infants' faces; however, they exhibited no preference for human infants' faces over monkey infants' faces (n = 24) and discriminated individual differences only within the category of human infants' faces (n = 30). We successfully replicated previous findings that 1-month-old infants (n = 42) preferred adult humans, even adults of other races, to adult monkeys. Further, by 3 months of age, infants (n = 55) preferred human faces to monkey faces with both infant and adult stimuli. Human infants' spontaneous preference for conspecific faces appears to be initially limited to conspecific adults and afterward extended to conspecific infants. Future research should attempt to determine whether preference for human adults results from some innate tendency to attend to conspecific adults or from the impact of early experiences with adults.