Intraspecific killing among non-human primates

Abstract

Intraspecific killing episodes among wild non-human primates are summarized from an evolutionary viewpoint, with regard to the social structures of the species. The summary is restricted to the higher primates, the Old World monkeys and anthropoids, which have well-developed brains and more complex social structures. This phenomenon is found only in societies with other than pair-type social units; all have one-male or multi-male groups. Eight aspects of intraspecific killing among non-human primates are discussed: structure of basic social units, intolerance among males, male precourtship aggression, tendency toward incest avoidance, population density, developmental cycle of unit groups, identity of the victim and cannibalism. Episodes of intraspecific killing have been reported for 132 species in nine genera. It is notable that, for all these species, infanticide has been observed. Therefore, the episodes were classified into infanticide and killing among adults; characteristics of each category were indicated. It is apparent that pongids have a wider variety of killing than cercopithecoids. One of the characteristics of intraspecific killing among non-human primates is that there are few counteractions from a third person or from the society toward the killer. Although an integral theory to interpret this problem is not easy to formulate and we have to wait for future studies for detailed analysis, it must be emphasized that these phenomena are related to the origin of institutions and the evolution of society.