Lethal aggression in wild chimpanzees and bonobos is better explained by adaptive strategies than human impacts.

An international team of researchers from the Max Planck Institute for Evolutionary Anthropology, the University of Minnesota, Harvard University and other contributors has now analyzed the reasons why our closest relatives, chimpanzees and bonobos, sometimes kill conspecifics in a fight. To this aim they compared information they had collected from 18 chimpanzee and four bonobo communities over five decades. The researchers found that bonobos rarely kill conspecifics while chimpanzees do so more frequently. The aggression is directed mainly from males to non-kin males and killings are often committed by a group of males that outnumbers its victims. Surprisingly, the human impact on the habitats of chimpanzees and bonobos did not result in an increase of these killings. The researchers thus conclude that killing conspecifics improves the attacker’s fitness through increased access to territory, food and mates.