Differences in Play Development of Young Chimpanzees Reared in Family Groups and in Peer Groups

Abstract

Rhesus and chimpanzee infants reared in family conditions showed higher levels of dominance and activity behaviours than infants reared only with their mother or with peers only. These results suggest that the greater the variety of social partners in a rearing condition, the more the individuals are able to develop social skills that will be advantageous to them in group life. We investigated how living in groups with peers only (n = 65) influenced behaviour development in chimpanzees aged from zero to ten years. Comparisons were made with the development of chimpanzees in the same age range in a semi-natural zoo group (n = 25). We expected that young chimpanzees reared in a family group, which offers more variation in social partners than a pcer group, would show more frequent and diverse social behaviour; i.e. more social play, more triadic interactions (in play) and more sex differentiation in play, than young chimpanzees reared in peer groups. We were surprised to find that the peer group situation had little effect on social behaviour. The differences in the amount of gymnastics performed by peer groups and zoo groups can be interpreted as direct effects of the environmental conditions. The lower level of triadic play in the pccr groups may have been caused by the greater opportunity for diadic play; this effect was found only in young infants. The lower level of social play in individuals aged from three to six years in the peer groups was due to the presence of one group of carly-separated females and, hence, was not an overall and long-term effect of peer group rearing conditions. The absence of a sex difference in the amount of adolescent social play in peer groups and the presence of such a sex difference in the zoo shows that the social rearing condition has indeed some effect on the development of social behaviour. The fact that separation age and peer-only rearing conditions had no more marked effects on the development of social behaviour, obviously docs not imply that separating young infants from their mother is to be recommended, for many of the possible effects of separation and peer group rearing were not studied. However, since both the number of animals studied and the number of observation periods were large, the existence of only one difference is meaningful: young chimpanzees reared in an all family group show only slightly more diversity in the development of social behaviours than do young chimpanzccs reared in peer groups.