It has not yet been determined why chimpanzees, genetically the closest relative of man, under some conditions live peacefully and at other times practice murderous genocidal and cannibalistic "warfare". Chimpanzees do engage in predation of other species, and it is therefore an open question how far this kind of violence is related to their intra-specific violence; particularly since they often eat the other chimpanzees that they kill. The exact interplay of innate violent predispositions, ecology, resource competition, mate competition, predation and territoriality are not yet understood.
Although fighting occurs widely throughout animals species, only a few cases of destructive intra-species fighting between organized groups of have ever been reported among naturally living species, and none of these involve the use of tools designed to be weapons. Normal predatory feeding upon other species cannot be equated with intra-species violence. Warfare is a peculiarly human phenomenon and does not occur in other animals.