Effects of parity and age on female attraction to faces of infants and neonates in rhesus macaques.

This study investigated the effects of parity and age on female rhesus macaque attention toward infants, and assessed whether the faces of neonates are more attractive than those of older infants. Six nulliparous and six multiparous females were shown digitized images of neonates' and 5- to 6-month-old infants' faces. Attention and preferences for images were measured by gaze duration and other picture-directed behaviors, including lip smacking, approaches, and presentations. As predicted, nulliparous females displayed significantly longer gaze durations for images than did multiparous females. There were no significant differences in gaze duration for faces of neonates and those of infants, but images of infants were approached more frequently than images of neonates. This difference is tentatively explained on the basis of differences in female familiarity with neonates' and infants' faces and differences in opportunities for allomothering with neonates and infants.