Gamers tend to be more aggressive when they play against strangers, reveals a study.
When male gamers beat friends in a shoot-em-up video game, levels of the potent sex hormone testosterone plummeted, indicating that multiplayer video games tap into the same mechanisms as warfare, where testosterone's effect on aggression is advantageous.
However, against a group of strangers, the players do not hold back and thus 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," New Scientist quoted David Geary, an evolutionary psychologist at the University of Missouri in Columbia, who led the study, as saying.
But when competing against friends or relatives to establish social hierarchy, annihilation didn't really make sense.
"You can't alienate your in-group partners, because you need them," he said.
For the study, the researchers turned to a video game, called Unreal Tournament 2004, in which 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, who were strangers to each other, into 14 groups of three and they all were then made to spend 6 hours practising together over the course of a week.
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. The researchers switched the order of these competitions for the other teams.
After the Onslaught matches, the researchers 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.
However, when team members played one another, the highest-ranking males tended to produce less testosterone than their defeated teammates.