1.3 The evolution of intergroup coalitionary aggression in humans

Author: Rachel Mis

Introduction: human aggression in evolutionary context

Warfare has often been interpreted as a sign of the perversion of human nature, a by-product of modern civilization, and absent from the balance of the natural world. However, it is now known that several species other than humans, including chimpanzees and even wolves, engage in coalitionary acts of aggression against other same-species groups, akin to human war (Wrangram 1999). This observation suggests that such behavior is in actuality an evolutionary adaptation , genetically passed on because it increases a perpetuator’s fitness ((Durham 1976; Van Schaik, Pandit, and Vogel 2004; etc.). An understanding of the human behavior of intergroup coalitionary aggression would therefore benefit from the application of evolutionary behavioral theory (see [link] ).

Evolutionary theories for intergroup coalitionary aggression center on the hypothesis that coalitionary aggression is an adaptive means of acquiring the resources of other groups, including territory, fresh water, food, tools, and even reproductive-age women (Buss 1997). The major perpetuators of coalitionary aggression are males, leading to the hypothesis that a major prerequisite for the occurrence of intergroup coalitionary aggression is an abundance of young males. Demographic studies indicate that males aged 15 to 29 years are most correlated with intergroup and interstate hostilities (Mesquida 1995, etc.).

This chapter will then explore the resource competition theory in humans with data from anthropological studies, as well as cross-species comparisons with chimpanzees , a close biological relative of human beings who also exhibit the behavior of intergroup coalitionary aggression (Wrangram 1999). In both cases, perpetuators may increase their fitness by co-opting resources of competing groups. Such evidence would support the hypothesis that human coalitionary aggression exists because under certain circumstances, the benefits gained by the young male perpetuators in resources and access to reproductive-aged females outweighs the potential costs suffered in the form of injuries and death, in line with the imbalance of power hypothesis. The chapter concludes with the implications of evolutionary theory and possible areas for future study.