Testosterone Rises In Men Competing With Rivals, But Not Among Friends

Rivalry and aggression are common at sporting events, but a new study shows that the relationship between the players will determine the testosterone levels present in men.

The team of anthropologists report that levels of male testosterone will increase when in competition against rivals but not when competing against friends.

Using relationships to modulate testosterone levels during group competition may be related to the formation of alliances in ancient warfare, the researchers report.

"One interesting thing about humans is that we are the only animal that competes in teams," said Mark Flinn, professor of anthropology at University of Missouri.

"Our hormonal reactions while competing are part of how we evolved as a cooperative species. What we found in our study is that although male's testosterone levels increase when men are victorious against strangers or rivals, levels of the hormone tend to stay the same when competing against friends."

For the study, Flinn and colleagues studied men of various ages playing dominoes and cricket in the island of Dominica. The researchers found that when males competed against a group outside of their community, their testosterone levels rose during and after competition if they won, but diminished following a defeat. However, when males competed with their friends, their testosterone levels did not change in response to victory or defeat.

But males don't even have to be competing in order to see a rise in testosterone. Being a spectator and the bond that comes from being part of a coalition of spectators  also effect testosterone levels, Flinn said. Flinn suggests that coalitions may have had important effects on the evolution of human social psychology.

"The fascinating thing about humans is that whether we are watching or playing the sport, we have the ability to put interactions among the whole team in our heads," Flinn said. "That just shows how complex our social psychology is. For example, a hockey or basketball player can anticipate how his teammates are going to react when he passes to each one of them and predict the outcome. The ability for humans to be able to do that is pretty astonishing."

Members of Flinn's research team include Davide Ponzi, now a postdoctorate at the University of Chicago, and Michael Muehlenbein, associate professor of anthropology at Indiana University.