Background Romantic love and parental love are essential to the perpetuation of species.However, previous studies focus on mothers brain responses to their own child or gender differences in brain responses to attractiveness of both genders.Little is known about the gender differences among neural mechanisms of viewing novel faces of infants, ordinary looking female adults and male adults.In this study, we used fMRI approach to address this question.Methods Sixteen female and sixteen male participants were asked to view infant, female adult and male adult faces with neutral expression, and to give attractiveness ratings for all faces during fMRI scanning.One hundred and eighty infant faces (which were divided into five levels based on cuteness), 18 male adult faces, and 18 female adult faces were used as stimuli.Results Infant faces of high cuteness levels were rated as more attractive than that of low cuteness levels.There was neither a significant main effect of gender nor a significant interaction between gender and infant cuteness level.Level 1 infant faces were not significantly different from female and male adult faces.Female participants attractiveness ratings to female faces were significantly higher than ratings to male faces while male participants ratings were not.However, imaging data showed a complex pattern.(1) Males showed greater activation in the right superior frontal gyrus and right middle frontal gyrus to female adult faces than infant faces, greater activation in the bilateral middle occipital gyrus to infant faces than male adult faces, and greater right nucleus accumbens activation to female adult faces than male adult faces.(2) Only in female participants can we find linear increase in activation with increasing attractiveness ratings for infant faces in right ventral striatum and left orbital frontal cortex.Infant faces evoked greater activation in left anterior insula and left anterior cingulated cortex while compared male participants with female participants.(3) Bilateral nucleus accumbens and bilateral anterior cingulated cortex were activated in male participants versus female participants while viewing female adult faces.Conclusion Infant faces modulated females brain reward system and female faces activated males brain reward system.The results might suggest that female and male play different evolutionary roles, that is, male give priority to female to make sure that genes have opportunity to pass from one generation to the next while female give priority to infant to make sure that genes survive.