A recent study helps explain why vanquishing rivals is more satisfying than winning games against one's bros. Testosterone levels increase when men defeat others in competitions, but not nearly as much when they compete against friends. Low testosterone reactivity helps maintain male friendships.

While the hormone spikes frequently and dramatically in the world of Game of Thrones, it's unlikely to increase much during spats in Judd Apatow-style bromances.

Increased testosterone has long been linked to success in competitions. Circulating levels of the aggression-promoting hormone are boosted in both men and women after winning in team sports, and even fans watching from the sidelines experience testosterone boosts after their favorite team achieves victory.

Anthropologist Mark Flinn of the University of Missouri led a team of researchers in examining how post-competition testosterone levels might be affected by the social relationships among men in Bwa Mawego, a rural community on the island of Dominica.

Testosterone Increases In Competition With Rivals

Researchers collected saliva samples from 27 adult participants before and after they competed in a dominos tournament, and from 37 teenage boys who competed in a cricket match. They also collected data on "coalition strength," or friendship, among the participants, indicated by how strongly they would support each other in a fight.

Results revealed that when the participants competed against their friends, circulating testosterone levels during and after the game did not change much from the baseline whether they won or lost.

When they competed against strangers or rivals from outside their community, however, testosterone spiked if they won and dropped if they lost.

The findings highlight how sensitive the body's endocrine mechanisms are to social context, and how hormones influence our relationships to each other.

"One interesting thing about humans is that we are the only animal that competes in teams," said Flinn in a news release. "Our hormonal reactions while competing are part of how we evolved as a cooperative species."

Lower Testosterone Reactivity Promotes Cooperation

The researchers write in the study that fluctuating testosterone levels help explain warfare throughout human history, and how social relationships can strengthen or break based on competitive stakes.

Testosterone is part of the reason why people cooperatively band together in groups that are unfailingly kind and loyal to other group members, even while they commit horrible acts of aggression against outsiders.

Feelings of dominance over defeated enemies are strengthened by increasing testosterone, but friends remain on good terms after competitions because levels of the aggression-promoting hormone remain low.

That hypothesis may be supported by another recent study on the tight-knit indigenous Tsimane people in Bolivia, who are vigorously active and experience testosterone increases during competitions, but actually have lower circulating testosterone levels than American men.

The Tsimane men of Bolivia maintain strong social bonds to each other, and probably not incidentally, have relatively low baseline testosterone levels despite their active lifestyles. [Michael Gurven]

Interestingly, Flinn's study also found that while testosterone levels usually spike when a man interacts with a sexually attractive woman, the circulating hormone actually decreases when he interacts with a friend's wife or long-term partner. If men truly respect their good friends, the results imply, their testosterone reactivity will adjust to avoid friction in the bromance, making them less likely to take competition too far or act on attractions to each other's wives.

"Our findings suggest that men's minds have evolved to foster a situation where the stable pair bonds of friends are respected," said Flinn.

Source: Mark V. Flinn, Davide Ponzi, Michael P. Muehlenbein. Hormonal Mechanisms for Regulation of Aggression in Human Coalitions. Human Nature, 2012.