Testosterone doesn't cause people to become aggressive or risky as many people believe but actually encourages fairness, European researchers say.

Researchers at the University of Zurich and Royal Holloway, University of London conducted a study of 120 women and found that testosterone promoted fairness in a bargaining game.

The women took part in a game to determine the distribution of real money, where both fair and unfair offers were allowed. The partner in this negotiation could either accept the offer or decline it, but if no agreement was reached, neither person would receive any money.

Before the game, the women were given either a dose of testosterone or a placebo. (Women were chosen for the experiment because the physiological effects of artificial testosterone are better understood in women than in men.)

"If one were to believe the common opinion, we would expect subjects who received testosterone to adopt aggressive, egocentric and risky strategies regardless of the possibly negative consequences on the negotiation process," said Christoph Eisenegger of the University of Zurich in a statement.

Instead, the study, published this week in Nature, found that women who received the testosterone behaved more fairly and had fewer conflicts in their negotiations.

However, the women who thought they had received the hormone, whether they did or not, behaved more aggressively and unfairly than those who believed they had received the placebo.

"It appears that it is not testosterone itself that induces aggressiveness but rather the myth surrounding the hormone," said economist Michael Naef of Royal Holloway.

Eisenegger said the experiment suggests that testosterone increases a person's sensitivity to status. In animals with simple social systems, aggressiveness can lead to higher social status, so testosterone leads to aggression.

"In the socially complex human environment, pro-social behavior secures status and not aggression," said Naef.

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