How does testosterone affect your body?

By Kate Kelland

London - Testosterone makes people behave badly, but only because of our own prejudices about its effect, not its true biological action, scientists said on Tuesday.

A Swiss and British study found evidence that debunks the myth that testosterone causes aggressive, egocentric behaviour, suggesting instead that the sex hormone can encourage fair play - particularly if it improves a person's status.

"We wanted to verify how the hormone affects social behaviour," said Christoph Eisenegger, a neuroscientist at the University of Zurich who worked on the study. "We were interested in the question: what is truth, and what is myth?"

The study, published in the journal Nature, analysed around 120 women who were asked to distribute a real amount of money.

Participants were given either a testosterone pill or a placebo, or dummy pill, and allowed to make both fair and unfair offers which their negotiating partners could accept or reject.

"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," Eisenegger said in a commentary.

But the results contradicted that view. Those who had been given testosterone generally made better, fairer offers than those who got placebos, reducing the risk of rejection.

The scientists said their findings suggest testosterone increases sensitivity about personal status. In animals, that may come out as aggression, they said, but in humans it may require a more subtle and less combative approach.

"In the socially complex human environment, pro-social behaviour secures status, and not aggression," said Michael Naef from Royal Holloway University London.

US researchers published a study in August which found that women with higher testosterone levels were far more likely to choose risky jobs like financial trading.

Naef and colleagues said popular scientific literature, art, media have long linked testosterone - often referred to as a "male" sex hormone although both males and females produce it - to aggressive behaviour, and this appeared to be confirmed in experiments where castrating male rodents reduced combativeness.

But Naef said his study suggested this popular belief was so deeply entrenched that it might change behaviour on its own.

The test participants who thought they had received the hormone, not the placebo "stood out with their conspicuously unfair offers", the researchers wrote.

"It appears that it is not testosterone itself that induces aggressiveness, but... the myth," Naef said. "In a society where qualities and manners of behaviour are increasingly traced to biological causes... this should make us sit up and take notice." - Reuters


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