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21.12.2008


Testosterone makes dominant men aggressive, but not the nice guys

If you're a dominant man who likes to boss others around, your testosterone probably makes you aggressive. If you are so relaxed that you don't feel the need to order others about, then testosterone has no effect on your mood, psychologists at Brock University in Canada have discovered.

The researchers did experiments with forty male first-year-students. They started by doing a test to determine whether the men had a dominant personality, and then got them to play a computer game. The men had to score points, but someone else who the test subjects couldn't see could take points away from them. The subjects had a choice in the game: defend themselves against having their points stolen, or take points away from the other. They could choose therefore between an aggressive or defensive game strategy.

Before and after the games sessions, the researchers measured the testosterone concentration in the men's saliva.

The researchers discovered to start with that the men who had a naturally high testosterone level often - but not always - had a dominant character. The graph below shows the relation between character and testosterone level.


Testosterone makes dominant men aggressive, but not the nice guys


Aggression was linked to testosterone. The more testosterone the men produced while playing their computer game, the more aggressive they were.


Testosterone makes dominant men aggressive, but not the nice guys


Nothing new so far. Dominance is known to be linked with aggression, and it is also known that testosterone is linked to aggression. But what about the interaction between the different factors? This is illustrated in the figure below.


Testosterone makes dominant men aggressive, but not the nice guys


The men whose testosterone level rose and who had a dominant character were aggressive. The non-dominant men whose testosterone level rose were not. In fact, in these men it was a decrease in testosterone level that made them aggressive.

This study describes the effect of an endogenous rise in the testosterone level. But the research does show that testosterone doesn't make all men aggressive.

The Canadians also did tests with women. The results were fairly similar but the relationships were much weaker. The researchers suspect that the method they used to measure the testosterone concentration didn't work as well in the women.

Sources:
Psychoneuroendocrinology. 2008 Dec 1. [Epub ahead of print].