The Male Warrior Hypothesis
Tribalism is a classic human behavior: We're nice to people in our groups, and suspicious if not downright hostile to strangers. The tendency is so ingrained and historically ubiquitous as to seem natural. But exactly why this state of mind prevailed during human evolution is unknown.
According to evolutionary psychologist Melissa McDonald of Michigan State University, it's an indirect consequence of reproductive biology. Female reproduction is limited by physiology, while male reproduction is -- generally speaking -- limited by access to partners. As a result, males compete fiercely within their groups for mates. Alliance-building shifts the focus of competition to groups of other males, and their females are the reward. Over evolutionary time, what McDonald calls "the warrior male" emerges.
"If men's psychology is designed in ways that facilitate success in intergroup conflicts, evidence for the workings of the mechanisms should be apparent in the thoughts, emotions, motivations and behaviours relevant to intergroup conflict among men in modern societies," she writes, and indeed it is. Men tend to be more xenophobic, more reliant on stereotype, and endure greater sacrifice to ensure the punishment of others -- so long as those others are men.
Image: James Whatley/FlickrCitation: "Evolution and the psychology of intergroup conflict: the male warrior hypothesis." By Melissa M. McDonald, Carlos David Navarrete and Mark Van Vugt. Philosophical Transactions of the Royal Society B, Vol. 367 No. 1589, March 5, 2012.