1.3 The evolution of intergroup coalitionary aggression in humans  (Page 5/7)

Are other forms of aggression evolutionarily favored?

Evolutionary theory may also be applied to additional forms of human aggression. Buss and Shackelford propose seven situations in which aggression may have evolved as a possible situation, two of which – acquiring resources and preventing loss of resources – lead directly to intergroup coalitionary aggression. Other situations include:

• Reduce fitness of same-sex rivals: Members of the same sex often compete for access to the same resources as well as mates. By inflicting a cost on a same-sex opponent, an individual’s relative fitness may increase. For example, both men and women engage in verbal derogation of the same sex in order to increase their own attractiveness to potential mates (Buss and Dedden 1990).
• Increase social status within a group: In some social contexts, men who expose themselves to greater physical danger in battle enjoy an increase in social status, which can translate into greater fitness (Geary and Bjorklund 2000). For example, among the Yanomamo of Venezuela, men who have killed other men are more likely to have more wives and children than men who have not killed (Chagnon 1988).
• Discourage future aggression: By promoting a reputation of aggressiveness, potential same-sex rivals may be discouraged from confronting an individual.
• Discourage mates from cheating: Jealousy by husbands or boyfriends is thought to be a leading cause of abuse by men against women. Men who are lower in relative mate value than their wives are more likely to commit aggression against their wives, in an attempt to prevent the woman from leaving (Buss and Shackelford 1997).
• Prevent resource expenditure on unrelated offspring: Parents are more likely to abuse step-children, who potentially may deprive one’s own biological children of valuable resources (Buss and Shackelford 1997).

This evidence suggests that aggression is not a “monolithic” or “unitary” phenomenon; but instead is dependent upon context (Buss and Shackelford 1997).

Imbalance of power theory and chimpanzees: when do males engage in coalitionary aggression?

Although controversial, many scientists believe that an understanding of human behavior may be augmented by the comparison of human behavior with that of other primates, particularly chimpanzees ( Pan troglodytes ). Humans and chimpanzees share many genetic similarities, and thus are believed to share a common evolutionary history (Manson and Wrangram 1991). While human intergroup coalitionary aggression was once considered unique in that humans will intentionally target and kill another human being, chimpanzees are now also known to target conspecifics . Termed lethal male raiding , groups of male chimpanzees sometimes invade neighboring territory belonging to a rival community and violently attack out-group chimpanzees, leading to serious injury or even death of the victim (Fukuyama 1998). This pattern of aggression is similar to that exhibited by small-scale human societies in raids, one of the most popular forms of coalitionary aggression (Manson and Wrangham 1991).