Do those with more testosterone coursing through their bodies make riskier, more aggressive decisions? To test the popular idea, researchers from Switzerland and the U.K. gave 121 women either 0.5 milligram of the hormone or a placebo and had them play an ultimatum bargaining game in pairs. With real money on the line, one player of the pair had to propose how to split the funds. The other player could reject the offer if she thought it unfair—and if the game ended in a stalemate, no money was distributed.

Given the common wisdom about testosterone, the players who had gotten the testosterone boost should be more likely to take a riskier, more antisocial approach and make a lowball offer in an effort to keep more of the pot. The behavior of the test subjects, however, did not confirm the stereotypes, according to results published online December 8 by Nature (Scientific American is part of Nature Publishing Group). Those who had received testosterone actually made higher offers than those who had gotten the placebo.

Evidently, the testosterone-fueled proposals reduced bargaining conflicts and facilitated the exchange. Those with more of the hormone may have been acting out of a desire to maintain their images by avoiding rejection. The results do not necessarily mean that testosterone has no role in complicating social negotiations, but such a contribution is likely to be more complex than previously thought.