1.3 The evolution of intergroup coalitionary aggression in humans  (Page 6/7)

Lethal raiding is hypothesized to occur in chimpanzees due to extremely low fitness costs compared with potentially large fitness benefits, consistent with the imbalance-of-power hypothesis . According to researchers Manson and Wrangham, this hypothesis predicts that attacks will occur in situations where the aggressor is unlikely to be harmed due to an advantage in force. Consistent with this prediction, the researchers found that, in a number of observational studies, no male aggressors suffered physical harm. Male aggressors only attacked solitary out-group individuals, or male-female pairings if the aggressor coalition consisted of at least three males; in other words, in situations where the aggressive individuals were unlikely to suffer injury (Manson and Wrangham 1991). The imbalance-of-power theory further postulates that chimpanzees will benefit from remaining in large groups in order to avoid potential attack. In border areas between communities, chimpanzees have been observed to travel in larger groups than when in the interior of the territory. Similarly, a highly popular strategy in human warfare, both between tribes or between nations, is also to overwhelm the opposing group in strength to avoid suffering as much injury as possible (Manson and Wrangham 1991).

Additional support for the idea that coalitions of chimpanzee males compete for reproductively-essential resources derives from research into territorial defense patterns (Williams, Oehlert, Carlis, and Pusey 2004). Chimpanzee males defend a group territory, within which live females and their offspring, as well as the resources sustaining the community. Food availability correlates with territory size, supporting the hypothesis that males defend a group territory in order to maintain an adequate supply of resources, most especially food. Females residing within larger territories - which correlate with higher resource supply - reproduce at shorter intervals, reinforcing the notion that higher resource supply enhances reproductive fitness. Additionally, males are less likely to attack out-group females who are reproductively-receptive, likely because it is more adaptive for the males to directly enhance their fitness by mating with these females (Williams, Oehlert, Carlis, and Pusey)

Conclusions

Throughout human existence, coalitions of people have engaged in violence for a myriad of social, political, and economic reasons. The evolutionary analysis of human behavior in no way implies that these methodologies are irrelevant, nor that evolutionary and social scientific methodologies are mutually exclusive. Each seeks to explain the same human behavioral phenomena from a different perspective. However, as revealed by evolutionary analyses, human societies engaged in intercoalitionary aggression do appear to share intriguing commonalities that can serve to further our understanding of the causes of human warfare.