New research from University College London (UCL) has found that testosterone makes us overvalue our own opinions at the expense of cooperation. The findings, say the researchers, have implications for how group decisions are affected by dominant individuals.
When groups attempt to solve problems there is a tension between cooperation and self-oriented behavior. Attempts to understand the biological mechanisms behind group decision making have tended to focus on the factors that promote cooperation. For example, people given the hormone oxytocin tend to be cooperative. The new study shows that the hormone testosterone has the opposite effect; it makes people act less cooperatively and more egocentrically.
For the study, UCL's Nick Wright 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. First, in each trial they were shown two images, one of which contained a high contrast target - and their job 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 favour of their own selection over their partner's.
"Our behaviour 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," explained Wright. "We have shown that in fact testosterone also affects our decisions, by making us more egotistical. 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."
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Source: Wellcome Trust