Better cooperation through testosterone?

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Everyone knows that testosterone makes people more aggressive, right?

Scientists have found that administering the hormone to rodents prompts a surge in aggressive behavior. In humans, prisoners with higher levels of testosterone are more likely to break the rules and get into fights. One study of 692 adult male inmates found that those serving time for crimes like rape, murder and armed robbery had more testosterone than their counterparts convicted of nonviolent offenses like theft and drug abuse.

But a group of European researchers decided to challenge this conventional wisdom. They wondered whether testosterone induced people to seek a higher social status. In prisons, this would play out by breaking rules and starting fights. But in other situations, testosterone might make actually encourage people to cooperate.

To test this theory, they recruited 60 women to play the “ultimatum bargaining game.” In this game, players A and B try to agree on a way to split a certain amount of money. Player A proposes a split to Player B, who can either accept or reject it. If she accepts, they both keep the money. If not, they both wind up empty-handed.


The researchers gave 30 women a 0.5-milligram dose of testosterone and gave the rest a placebo without telling them which was which. Then they played the game. The researchers predicted that the women who got testosterone would go to greater lengths to make sure their offers weren’t rejected; therefore, their offers would be more generous.

And they were. The total pot was 10 monetary units, and players were allowed to offer 0, 2, 3 or 5 units. Women who took testosterone offered an average of 3.9 units, compared with only 3.4 units for women who got the placebo, according to a study online today by the journal Nature. The difference was statistically significant.

If you’re surprised, you’re not alone. The researchers asked the women whether they thought they got testosterone or the placebo. In accordance with the conventional wisdom, women who believed they had ingested the hormone made lower offers than those who guessed they got a dummy pill.

-- Karen Kaplan