Sex differences in the formation of coalitions among chimpanzees

Abstract

Observations were made of spontaneous coalition formation during aggressive encounters among chimpanzees in a large, semicaptive colony. The analysis of several thousand instances, collected over a period of 5 years, revealed striking differences between adult males and females. Male coalitions changed over time and showed little connection with social bonds, as measured by associative behaviors. Females, in contrast, showed stable coalitions, which strongly overlapped with their social bonds. Also, coalition formation with males and females differed. Females were treated on the basis of their coalitions and bonds with others in the group; males were not.

A single difference in proximate social goals is proposed as an explanation for these and other differences. Male coalitions seem to serve status competition. Males may form flexible coalitions in order to rise in rank, and may adopt the role of group protector in order to maintain a high rank. Female coalitions seem to serve the protection of particular individuals, namely, friends and kin. A similar sex difference has been reported for human coalition formation in experimental game situations.