Abstract
In many social-living primates, encounters between neighboring groups are characterized by aggressive interactions, involving agonistic threats, chases, and physical attacks. Because of the potential benefits of cooperation among group members, these contests between groups have featured prominently as a selective pressure in theoretical models of the evolution of primate social behavior. Intense intergroup aggression has been suggested to favor female philopatry, permanent male–female associations, tolerant intragroup dominance relations, and reproductive concessions. Until recently, however, systematic study of these interactions was limited due to the relative rarity of intergroup encounters and the logistical difficulties of studying multiple social groups simultaneously.