The ontogeny of social relationships with group companions among free-ranging infant rhesus monkeys II. Differentiation and attractiveness

Infants are frequently with their mothers when troop members initiate interaction with them. To what extent are the infants' companions attracted specifically to them rather than to the mother? A simple method is presented for approaching this question and for assessing the extent to which the relationships of 11 free-ranging rhesus (Macaca mulatta) infants on Cayo Santiago have acquired qualities independent of (differentiated from) those of the mother. Companions of all ages tend to be attracted specifically to infants between 1 and 14 weeks of age and not simply to their mothers. However, this tendency is less marked for sibling companions than for more distantly related companions. No differences are found between infants of high- and low-ranking mothers. Infantile attractiveness is not necessarily sustained when infants are 17 to 30 weeks of age. The degree to which relationships with infant companions and with older female companions have, differentiated by 17 to 30 weeks is negatively related to the companion's age. Infants show early and increasingly marked tendencies to develop differentiated relationships with one another; however, they show no signs of doing so with adult female companions by 30 weeks of age.