Why are infants so attractive to others? The form and function of infant handling in bonnet macaques.

Female macaques and baboons are intensely interested in other females' infants, but provide little direct care for them. The selective factors that shape this strong attraction to neonates may differ from those that shape alloparental care in other taxa. The attraction to neonates may have evolved because (1) it enhances young females' acquisition of maternal skills, (2) it is a form of reproductive competition among females, or (3) it is a by-product of selection for appropriate maternal care. I studied patterns of infant handling in a large group of bonnet macaques, Macaca radiata, at the California Primate Research Center at the University of California, Davis. Infant handling was generally gentle and nonintrusive, although females sometimes tugged on infants. Females were more strongly attracted to infants than were males, regardless of their age. Adult females handled infants as often as subadult females did. Male and female infants were handled at equal rates, and rates of handling towards all infants declined sharply as infants matured. Infants were handled by related females at higher rates than by unrelated females, and at higher rates by higher-ranking females than by lower-ranking females. The data provide little support for the 'learning to mother' hypothesis, because older females were as interested in infants as were subadult females. Although mothers were reluctant to allow their infants to be handled, the data do not support the reproductive competition hypothesis because patterns of infant handling did not match patterns of harassment of infants. The data provide a better fit to the by-product hypothesis. Females were most strongly attracted to infants when maternal care was most critical for infant survival and females of all ages were strongly attracted to infants. Taken together, these data suggest that a strong attraction to infants is favoured by selection because females that are highly responsive to infants make good mothers. Copyright 1999 The Association for the Study of Animal Behaviour.