New Scientist reports on a study that pitted male gamers against groups of friends or groups of strangers in Unreal Tournament 2004, and measured their testosterone levels, learning: "Victorious gamers enjoy a surge of testosterone – but only if their vanquished foe is a stranger. When male gamers beat friends in a shoot-em-up video game, levels of the potent sex hormone plummeted." This jibes with previous research involving dominos players, and helps them reach this conclusion: "This suggests that multiplayer video games tap into the same mechanisms as warfare, where testosterone's effect on aggression is advantageous." Thanks Mike Martinez.