Intergroup Violence: Chimpanzees and Lions
Some mammals live in permanent social groups that occupy and aggressively defend the same area for generations. Like many mammals, female lions generally remain for life in their natal pride. Males leave their pride before breeding and attempt to take over another pride by fighting and evicting the resident males, evicting subadults, and killing cubs. Infanticide hastens the resident females’ return to sexual receptivity, allowing the new males to sire their own cubs more quickly. Once resident, males assist females in defending the territory, even against females from neighboring prides. In chimpanzees, as in many human societies, males remain for life in their natal community while most females transfer to other communities before breeding. Males actively patrol the group territory, engaging in aggressive contests with neighbors and sometimes killing infants, males, and even adult females. In both lions and chimpanzees, males cooperate in inter-group conflict with group-mates who are often relatives and with whom they maintain close, life-long social bonds. Evidence is mounting that successful intergroup aggression and killing results in better resources for group members in both species.