Juvenile friends, behavior, and immune responses to separation in bonnet macaque infants.

Individual differences in the response to maternal separation in nonhuman primate infants have been attributed to (among other variables) presence or absence of processes that may model social support in humans. Alternative attachments to other members of the social group buffer the infant against a depressive response to maternal separation. This hypothesis was tested in a group of bonnet macaques by manipulating the presence or absence of alternative juvenile attachment figures (friends) during separation. Infants who retained such attachments showed fewer behavioral evidences of depression when separated from their mothers. These infants without friends also showed changes in lymphocyte activation by mitogens or natural cytotoxicity that were not evident in the infants with juvenile friends. Across all separated infants, natural cytotoxicity was positively correlated with juvenile affiliative behavior directed toward the infants during the separation. These results support the hypothesis that social support, available from alternative attachments, can modulate the response to loss, and can account for some of the individual differences seen in these responses.