Testosterone drives ego, trips cooperation
Testosterone drives egocentricism at the cost of cooperating with others, consequently affecting group decisions, a study reveals. 
Collective problem solving can provide benefits over individual decisions as we are able to share our information and experiences, said a new study from Wellcome Trust's Centre for Neuroimaging at the University College London.
Now researchers have shown that the testosterone has the opposite effect -- it makes people act less cooperative and more egocentric, the journal Proceedings of the Royal Society B reported.
Researcher Nick Wright and colleagues at the Centre for Neuroimaging carried out a series of tests using 17 pairs of female volunteers who had previously never met. The test took place over two days, spaced a week apart, a university statement said.
"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," explained Wright.
On one of the days, both volunteers in each pair were given a testosterone supplement; on the other day, they were given a placebo.
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.
