According to a New Scientist study, you"ll be hit with a surge of testosterone if you win at your favourite game, but only if the opponents you defeat are strangers. If you happen to beat your friends the opposite occurs, your testosterone levels fall.
Head of the study, David Geary is an evolutionary psychologist at the University of Missouri. His explanation for these phenomena traces back to our primordial origins, and the impact that testosterone has on our levels of aggression. "In a serious out-group [group of strangers] you can kill all your rivals and you"re better for it." This applies whether you"re battling an army or the rival football team.
In contrast, it doesn"t make sense to kill friends or relatives to establish social hierarchy. Geary states, "You can"t alienate your in-group [friends] partners, because you need them."
To undertake this study, Geary and colleague Jonathan Oxford, used the game Unreal Tournament 2004 to pit players against friends and strangers. The researchers divided their subjects (all male) into 14 groups of three to play Onslaught (a capture the flag style game) after practising together for a week to create a bond with one another. A week later the groups were broken apart and each player took part in a death match against all other subjects, including ex-teammates.
Following the tournament it was found that testosterone levels of winning team members spiked immediately after battle. Yet, when team members played against one another, the highest-ranking players produced less testosterone than the players they defeated.
The full study can be read via the Journal of Evolution & Human Behaviour.