The next time your girlfriend, wife, or mother complains about all the time you spend playing PS3 or online games, you can tell her that your attraction to video games may actually be a by-product of evolution. Scientists at the University of Missouri have found that hormonal surges in men playing violent multiplayer videogames are very similar to hormonal responses males of other species experience during reproductive and territorial challenges. These responses may be evolutionarily hard-wired to help males succeed in coalitionary combat against competitors.

For the study, 42 undergraduate subjects were randomly assigned to three-person teams and each played in two different rounds: the “outgroup” competition between their team and an opposing team, and the “ingroup” competition, in which each player was pitted against their own teammates. Unreal Tournament 2004, in which multiple armed players compete in an arena, was the game of choice. In the outgroup competition, teams played in the Onslaught mode, in which each team competes to destroy the opposing team’s power core, located at their home base. During the ingroup competition, subjects used the Death Match mode, a free-for-all in which players compete to inflict the most damage on their competitors.

The researchers gave each team 6 hours to practice together before the actual competition began. This practice time also gave each team the opportunity to bond and build a group identity, as social animals do when forming coalitions to compete against other groups of males. During the actual tournament, opposing teams were separated by a partition, allowing members of the same team to see, hear, and interact with each other. All tournaments occurred in the early afternoon, were 30 minutes long, and ended with a clear winner. To test hormone activity, each player’s saliva was collected at regular intervals both before and after the competitions.

Directly following the outgroup competition, men on winning teams had much higher testosterone levels than the members of the losing teams. This effect was especially strong for the players who had contributed the most to the team’s victory. In animals, a similar hormonal pattern occurs: testosterone levels increase in all competitors to increase aggression and enhance competitive ability, but the most successful males often experience strong post-contest testosterone surges.

Interestingly, when playing against their own teammates in the ingroup part of the tournament, all players showed a decrease in testosterone, with the best males actually having the lowest levels. This muted testosterone response may be an evolved mechanism to blunt the intensity of ingroup competition. It’s not particularly adaptive for males of any species to engage in intense competition with their allies, since they run the risk of damaging group cohesion and decreasing their success in later competitions with opposing groups.

These hormone results show that men seem to react to video games in a similar physiological way to male animals that are competing for mates or defending territory. Multiplayer videogames such as Unreal Tournament 2004 may simulate situations in which men are naturally predisposed to work with other group members to form strategies, engage in combat, and eliminate a social threat. Just remember, guys: it’s only a game.

Evolution and Human Behavior, 2010. DOI: 10.1016/j.evolhumbehav.2009.07.002 (About DOIs).