Victorious gamers enjoy a surge of testosterone – but only if their vanquished enemy is a stranger. When male gamers beat friends in a shoot-em-up video game, levels of the potent sex hormone plummet.
This suggests that multiplayer video games tap into the same mechanisms as warfare, where testosterone's effect on aggression is advantageous.
Against a group of strangers – be it an opposing football team or an opposing army – there is little reason to hold back, so testosterone's effects on aggression offer an advantage.
"In a serious out-group competition you can kill all your rivals and you're better for it," says David Geary, an evolutionary psychologist at the University of Missouri in Columbia, who led the study.
However, when competing against friends or relatives to establish social hierarchy, annihilation doesn't make sense. "You can't alienate your in-group partners, because you need them," he says.
It's his hormones
Measuring these effects, however, hasn't been easy. Victors in sporting events are known to experience a burst in testosterone – particularly if they contributed to the win. But physical exertion also boosts testosterone, so it is hard to be sure just what causes an athlete's hormonal surge.
In search of a less strenuous competition that could pit people against friends and strangers, Geary and his colleague Jonathan Oxford turned to a video game called Unreal Tournament 2004. In the game, players armed with machine guns, rocket launchers and other weapons roam a post-apocalyptic world.
Unreal Tournament has a network-based multiplayer version called Onslaught where two bands of three players face each other in a "capture the flag"-type mission. In another – Death Match – players battle each other to the death.
The researchers divided 42 male university students into 14 groups of three. None of the students knew any other beforehand. To create a bond between team members, the teams spent 6 hours practising together over the course of a week.
"I ran into some of these groups, and they were pretty excited about the whole thing – they named their teams," Geary says.
Let battle commence
After this practice, half the teams faced off in 30-minute Onslaught matches. The teams played in different rooms, but they could hear each other. A week later, individual team members played one another in the death match. Geary and Oxford switched the order of these competitions for the other teams.
As an added incentive, the researchers gave winning teams $45 and losing teams just $15. Similarly, the team member who won the death matches earned $45, the other two players $15.
After the Onslaught matches, Geary and Oxford found that testosterone levels of the winning team members spiked immediately after the tournament, particularly among players who had contributed most to their team's victory. Yet when team members played one another, the highest-ranking males tended to produce less testosterone than their defeated teammates.
John Wagner, an anthropologist at the University of New Mexico in Albuquerque, says the results tally with a study of competitive domino players on the Caribbean island of Dominica that he conducted. When men played against people in their own village, the winners' testosterone levels took a dive and stayed low, whereas losers' testosterone levels fell then rebounded. Yet after these men played people from other villages, their testosterone levels tended to rise.
Journal reference: Evolution and Human Behavior, DOI: 10.1016/j.evolhumbehav.2009.07.002