This is the 2007 version. Click here for the 2017 chapter 15 table of contents.

Hormones and Aggression

In general, men are more likely to be violently aggressive than women. Men are far more likely than women to commit violent crime. The male hormone, testosterone , is clearly related to aggression in all primate species including humans. Not only does more testosterone result in more aggression; successful aggression (winning a fight) results in more testosterone. A monkey that wins a fight for dominance in a monkey colony secretes more testosterone into its bloodstream, resulting in still more aggressive behavior, as well as more mating activity.

What happens in males after successful aggression?

Researchers find that testosterone levels can be altered by observing a struggle for dominance. Georgia State University psychologist James Dabbs analyzed saliva samples from men in sports bars during a World Cup soccer match between Brazil and Italy. On this occasion, Brazil trounced Italy. The Italian fans showed a mixed response, but among 11 of 12 Brazilian fans, testosterone levels rose (Holden, 1995). This may explain why violence among fans is common after important sporting contests, even if the favored team wins.

What evidence from the Yanomami suggests an evolutionary explanation of male aggression?

Among primitive humans, warriors are apparently more likely than non-warriors to mate and have children. In one interesting study, Napoleon Chagnon studied Yanomami tribesmen. He found that warriors in the tribe, despite having a higher chance of being killed on war parties, were more likely over the long run to procure wives and produce children.

A man who kills a foe during a skirmish establishes himself as a unokai, "brave warrior." But a Yanomamo who behaves in ways perceived as cowardly on raids becomes the butt of jokes; other men make sexual overtures toward his wife. A unokai is likely to have one more wife than a non-unokai; unokai average 4.5 children, compared with 1.6 for non-unokai. ("Why we fight," 1991, p.2)

How is antisocial aggression less beneficial now?

Anthropologists find this type of pattern in many cultures. This suggests that male aggression has been positively selected in the evolutionary past of the human race. However, what was adaptive in ancient times is not necessarily adaptive in the modern world, and this finding is a great example of that principle. There is no obvious evolutionary benefit for antisocial aggression among modern men. Prosocial aggression in sports and business may still be a winning strategy, but antisocial aggression is more likely to result in prison incarceration, depriving a person of the opportunity to raise a family.

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