“There’s been an increasing interest in how hormones influence moral judgments in a fundamental way by regulating brain activity,” said Bertram Gawronski, a psychology professor at The University of Texas at Austin (UT Austin).

“To the extent that moral reasoning is at least partly rooted in deep-seated biological factors, some moral conflicts might be difficult to resolve with arguments.”

The team used a system similar to the trolley problem in philosophy — a runaway trolley will kill five people unless someone chooses to pull a lever, redirecting the trolley to another track, where it will kill one person instead — and adapted it to test how far testosterone can influence our moral judgments.

The researchers created 24 dilemmas associated with real-life events to simulate situations that put utilitarian decisions, those that focus on the greater good, such as saving the largest number of people, against deontological decisions which focus on moral norms, such as avoiding an action that would harm someone. Prior research suggested that higher levels of testosterone are associated with stronger utilitarian preferences.

To put that to the test, the team ran a double-blind study in which 100 participants received a placebo and 100 participants received testosterone supplements.

“The study was designed to test whether testosterone directly influences moral judgments and how,” said Skylar Brannon, a psychology graduate student at UT Austin.

“Our design also allowed us to examine three independent aspects of moral judgment, including sensitivity to consequences, sensitivity to moral norms and general preference for action or inaction.”

The researchers created 24 dilemmas associated with real-life events to simulate situations that put utilitarian decisions, those that focus on the greater good, such as saving the largest number of people, against deontological decisions which focus on moral norms, such as avoiding an action that would harm someone. Prior research suggested that higher levels of testosterone are associated with stronger utilitarian preferences.

The team says this likely comes down to people with particular personality traits tending to have different levels of naturally-occurring testosterone. For example, people with high levels of psychopathy tend to have high levels of testosterone and exhibit lower sensitivity to moral norms. This doesn’t mean that testosterone is the cause of psychopaths’ insensitivity to moral norms, however. If anything, the findings suggest that testosterone  has the opposite effect, increasing people’s sensitivity to moral norms.

“The current work challenges some dominant hypotheses about the effects of testosterone on moral judgments,” Gawronski said.

Our findings echo the importance of distinguishing between causation and correlation in research on neuroendocrine determinants of human behavior, showing that the effects of testosterone supplements on moral judgments can be opposite to association between naturally occurring testosterone and moral judgments.

The study helps flesh-out our understanding of the link between testosterone and behavior, but it definitely raises more questions than it answers. For now, it’s safe to say that the dynamic between the two is more complicated than we assumed — but more research is needed to shed light on the details.

The paper “Exogenous testosterone increases sensitivity to moral norms in moral dilemma judgements” has been published in the journal Nature Human Behaviour.