London, United Kingdom. Women understand how testosterone affects behavior but the lack of hard scientific data relegates female insights to the social margins, a situation subject to change as scientific interest has ramped up in recent years.

Recent research shows how testosterone can make an individual overvalue their own opinions at the expense of cooperation, leading affected individuals to dominate group decisions.


Research from the Wellcome Trust Centre for Neuroimaging at University College London (UCL) focused on how group problem solving can provide benefits over individual decisions, since it involves the sharing of information and expertise. However, cooperation and self-oriented behavior are in tension. While groups may benefit from a collective intelligence, collaborating too closely can easily lead to an uncritical groupthink ending in decisions that are bad for all.

Attempts to understand the biological mechanisms behind group decision making generally have focused on factors that promote cooperation. Research has shown that people given a boost of the hormone oxytocin tend to be cooperative.

Now researchers have shown that the hormone testosterone has the opposite effect: it makes people act less cooperatively and more egocentrically. Their findings appear in the Proceedings of the Royal Society B: Biological Sciences.

Testosterone is naturally secreted in men and women; the levels correlate with important behaviors in both men and women (e.g., antisocial behavior). However, when men and women are exposed to identical additional doses in an experimental setting, the effects will differ.

• In women, this markedly increases their testosterone from its low baseline level.
  
  
• In men, it is more complicated: males already have high baseline levels of testosterone, so giving such additional doses will decrease their own production of testosterone, a feedback effect that will act to offset the increase caused by the treatment itself.

Dr Nick Wright and colleagues therefore used female subjects because giving standard experimental doses causes a straightforward and well characterised increase in testosterone levels.

• The researchers carried out a series of tests using seventeen pairs of female volunteers who had previously never met.
  
  
• The test took place over two days, spaced a week apart.
  
  
• On one of the days, both volunteers in each pair were given a testosterone supplement.
  
  
• On the other day, they were given a placebo.

During the experiment, both women sat in the same room and viewed their own screen.

• Both individuals saw exactly the same thing.
  
  
• They were shown two images in each trial, one of which contained a high contrast target — and the job of the participants was to decide individually which image contained the target.
  
  
• If their individual choices agreed, they received feedback and moved on to the next trial.
  
  
• However, if they disagreed then they were asked to collaborate and discuss with their partner to reach a joint decision.
  
  
• One of the pair then input this joint decision.

The researchers found that, as expected, cooperation enabled the group to perform much better than the individuals alone when individuals had received only the placebo. But, when given a testosterone supplement, the benefit of cooperation was markedly reduced. In fact, higher levels of testosterone were associated with individuals behaving egocentrically and deciding in favor of their own selection over their partner's.

"When we are making decisions in groups, we tread a fine line between cooperation and self-interest: too much cooperation and we may never get our way, but if we are too self-orientated, we are likely to ignore people who have real insight," explains Dr Wright.

"Our behavior seems to be moderated by our hormones — we already know that oxytocin can make us more cooperative, but if this were the only hormone acting on our decision-making in groups, this would make our decisions very skewed. We have shown that in fact testosterone also affects our decisions, by making us more egotistical."

The authors note that most of the time, this allows us to seek the best solution to a problem, but sometimes, too much testosterone can help blind us to other people's views. This can be very significant when we are talking about a dominant individual trying to assert his or her opinion in, say, a jury.

Testosterone is implicated in a variety of social behaviors. For example, in chimpanzees, levels of testosterone rise ahead of a confrontation or a fight. In female prisoners, studies have found that higher levels of testosterone correlate with increased anti-social behavior and higher aggression. Researchers believe that such findings reflect a more general role for testosterone in increasing a motivation to dominate others and increase egocentricity.

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