The hormone makes people more egocentric and dramatically reduces cooperation between people, according to a new study of females.


A study testing the effect of testosterone has found that it dramatically lowers cooperation between individuals, making people more egocentric. In this study, people performed their task more poorly under the influence of testosterone. It didn't affect their individual performance, but the lack of cooperation it caused resulted in partners making the wrong choice more frequently than they did when not under the influence of testosterone. Oh, and by the way, all the subjects were women.

Self-centered, unwilling to listen, and overly sure of yourself. This is your life on testosterone, even if you are female.

The study was of 17 pairs of women who had never met before. Each pair participated in two sessions held three to seven days apart. In one session, both women were given an oral testosterone supplement (80 mg of testosterone undecanoate) six to seven hours before the session. For the other session, neither woman received testosterone.

Each session consisted of 192 trials. In each trial, the women sat at separate computer screens and were shown the same two sets of images. Each set contained six images of a grating. In one set, one image was sharper (higher contrast) than all the others. The women had to decide which set of images contained the sharper image. If they disagreed, they were asked to collaborate and discuss their decision with their partner. One partner was randomly selected as the ultimate decision maker in each trial.

The clarity of the sharper image was modified in each trial. In some trials, the difference was obvious. In others, it wasn't and took high visual sensitivity to pick out.

In trials where the participants disagreed, collaboration allowed them to perform better, picking the right image set more often than each woman did individually. But under the influence of testosterone, the benefits of collaboration were greatly reduced. The decision maker was much more inclined to go with her own selection than her partner's, an inclination which led to more incorrect picks than occurred without testosterone.

Testosterone didn't affect each woman's visual sensitivity and ability to pick the right image, but it did reduce their ability to cooperate, to accept that their partner was right and that they were wrong. And in this task, that led to more errors.

The best real life decisions often require a proper balance between individual judgment and group consensus. Cooperation has many benefits, but it isn't always the best approach: committees can take months or years to arrive at a decision that an individual could make in minutes. Sometimes individual initiative is the way to go.

Hormones play a key role in how people decide to balance the needs of group and self in their everyday life. Much recent research has focused on oxytocin, a hormone so good at increasing cooperation that it's sometimes called the love hormone. Testosterone appears to send people in the opposite direction, a direction where the self takes precedence.

An article on the study was published online by Proceedings of the Royal Society B.

This article originally appeared on, an Atlantic partner site.