Women Given Testosterone Become More Distrustful

It seems something of a sexist cliché that women are generally more social than men, and more likely to trust people they have just met; men are usually perceived as being more aloof and watchful when encountering strangers. An article by Rachael Rettner, reporting on a study appearing in this week’s Proceedings of the National Academy of Sciences, outlines what may be a biological underpinning to these generalized sex differences.

Trusting Females Get Testosterone

The study was conducted by Peter A. Bos and David Terburg of Utrecht University in the Netherlands, and Jack van Honk of the University of Cape Town, South Africa. They chose 24 female subjects with an average age of twenty. The subjects first received a placebo and were asked to rate a series of 150 photographs of faces for the trustworthiness of the people pictured. A scale of -100 (least trustworthy) to 100 (most trustworthy) was used. Based on this test, the subjects were then divided into “high trusting” and “low trusting” groups. Both groups participated in sessions over three days, receiving testosterone or placebo in a standard series of double-blind trials.

Testosterone Group Becomes Less Trusting

The subjects who had been classified as “high trusting” had their trust significantly lowered by the administration of testosterone. In fact, these women rated the strangers’ photographs ten points lower, on average, than their previously established baseline for trustworthiness. Care was taken to control for the subjects’ natural levels of testosterone, as well as their mood on the day of the test. These did not appear to alter the outcome. More interestingly, women who were naturally less trusting did not appear to be affected by the testosterone to any significant degree.

Testosterone, Oxytocin, and Vasopressin

Oxytocin is known as the “feel-good” hormone for its role in social bonding and love feelings, both in humans and other animals. The researchers speculate that testosterone could serve to counterbalance the presence of oxytocin in more trusting people, making them more suspicious. They also theorize that the testosterone could be increasing the production of vasopressin, another hormone that has been linked with increased aggression in other animals.

Trust and Social Relationships

In the abstract for their paper, the scientists point out that trust is one of the main components of social relationships, but that trusting strangers also leaves one open to the possibility of deception or even violence. And while they acknowledge that testosterone, which male bodies possess in about ten times the quantity of females’, acts to inhibit sociality and trust, thereby encouraging conflict rather than cooperation, it can also offset an abundance of oxytocin which may cause some people to trust too easily.