Play and development of social skills in infant rhesus macaques

Abstract

The purpose of this study was to monitor the development of playful and socially skilled behaviours in infant rhesus monkeys (Macaca mulatta) in order to discover whether there was any relationship between them. Important factors of rhesus social organization: genetic relationship, dominance rank, and the long birth season, were investigated for their relationship to the development of playful and socially skilled behaviours. Twenty infants from one social group on Cayo Santiago, Puerto Rico, were observed using a focal animal sampling technique. The focal infants were born in the same birth season, and were all males. Observations were made on each infant from 9 to 79 weeks of age. Summaries of playful and skilful behaviours were made for three 14-week age periods: 9-22 weeks, 23-36 weeks and 66-79 weeks. Associations between playful and skilful behaviours were investigated within and between age periods. Play did not have a delayed effect on the development of the social skills measured in this study. Play was related to skills in play and skills in grooming within the same age period. Play was related to persistence in initiating play in the later age periods. Play and skills in grooming were competing for infants' time at 9-22 weeks. At 66-79 weeks high levels of play and skills in grooming occurred in the same infants. Early social skills in play were related to later play. This relationship could be accounted for by date of birth acting as a common factor. Dominance rank and genetic relationships were important in the development of play, but did not act as common factors in the development of playful and socially skilled behaviours. With increasing age, infants became more selective in their choice of play partners. Focal infants tended to play with monkeys of the same age, the same sex, of close genetic relationship, and of adjacent dominance rank, and this trend increased. In this study, knowledge of the behaviour of infants at one age was not useful to predict their behaviour at a different-age. Play appears to have a few specific associations rather than a general association with the development of social skills with age.