Male-Male Relationships and the Transition to Adulthood in Chimpanzees

Abstract

Strong social bonds play an important role in primate behavior. These bonds feature prominently in the lives of adult male chimpanzees (Pan troglodytes). Male chimpanzee friends form coalitions, share food, join each other on territorial border patrols, and help each other as they attempt to rise in the dominance hierarchy. Despite the importance of friendship and dominance rank in adulthood, scant information exists regarding how they develop. Do social bonds with other males form early in life? Do males start to jockey for position in the dominance hierarchy before they reach adulthood? For one year, I observed male chimpanzees transitioning to adulthood at Ngogo in the Kibale National Park, Uganda. In contrast to adults, adolescent male chimpanzees do not compete for status with their peers. Instead, they prioritize affiliative relationships. Adolescent and young adult males form social bonds with maternal brothers, as do older adult males. Unlike middle-aged adult males, however, adolescent and young adult males forge some of their strongest bonds with old males rather than with their peers. Unexpectedly, some of the strongest grooming relationships were between adolescent and young adult males and their fathers. Because chimpanzees mate promiscuously, there is no reason to suspect that male chimpanzees can recognize their fathers or that fathers can recognize their sons. These unsuspected grooming bonds appear to emerge, in part, due to past relationships formed when adolescent and young adults were infants and juveniles. Adolescent and young adult males joined subgroups with older males who occupied similar parts of the territory as their mothers in the past. They also groomed formerly high-ranking males. Thus, as males transition to adulthood they form bonds with old, formerly high-ranking males with whom they are familiar. These findings raise the intriguing possibility that fatherhood may have evolved from an ape-like social system.