Extreme Male Brain Theory of Autism Overturned as Huge Study Finds No Link Between Testosterone and Lack of Empathy

Testosterone doesn't make it harder for men to empathize, according to scientists who have questioned the idea that the hormone distorts this ability in people with autism.

Autism spectrum disorder is most commonly diagnosed in men, and some people with the condition struggle with cognitive empathy, or inferring what others think and feel.

The influential Extreme Male Brain theory is considered a potential explanation for this link. It proposes that males are organized and systematic while women are more inclined towards empathy. Past studies have suggested being exposed to high levels of testosterone, including in the womb, could "masculinize" the brain and make it harder for men to empathize, rising to pathological levels in those with autism. The ratio between the length of a person's index and ring finger, thought to be an indicator of how much testosterone a fetus encounters in the womb, has also been tied to a lack of empathy. This is known as the 2D:4D digit ratio.

The authors of the new study, published in the journal Proceedings of the Royal Society B, conducted two experiments to explore this association.

The first involved 243 males aged 18 to 55 in Southern California, who had their hands scanned, provided saliva samples, and filled out demographic and mood questionnaires. Participants also applied a gel to their skin: Some unknowingly used a testosterone gel, while others used a placebo and acted as the control group.

Before and after applying the gel, participants completed the Reading the Mind in the Eyes Test. Researchers showed participants a pair of eyes and asked them to select one of four words which best described the emotional state expressed by the eyes.

In the second experiment, 400 men with an average age of 22 in Canada followed similar steps, but instead half used a spray containing testosterone, while the others used a placebo.

All of the participants in both tests were neurotypical, the term used to describe a person without autism.

Neither experiment showed a link between testosterone levels, including finger length, and cognitive empathy.

Study co-author Amos Nadler, assistant professor of finance at Ivey Business School at Western University, commented in a statement: "Several earlier studies have suggested a connection between testosterone and reduced cognitive empathy, but samples were very small, and it's very difficult to determine a direct link."

"Our results unequivocally show that there is not a linear causal relation between testosterone exposure and cognitive empathy," he said.

Nadler and co-author Gideon Nave, an assistant professor of marketing at the University of Pennsylvania Wharton School, told Newsweek the results echo a 2016 study which similarly concluded there is no relationship between prenatal testosterone exposure and autistic traits.

"The extreme male brain hypothesis is highly influential, and our work will help direct autism-related research resources towards other potentially fruitful directions," they said.

But the study doesn't rule out all possible channels through which testosterone may influence autism, they argued.

"One of the results of our study is that the 2D:4D digit ratio, which is considered by many to be a proxy for prenatal testosterone exposure, is not associated with cognitive empathy. However, this result could merely be driven by the fact that the 2D:4D is just not a good proxy," they told Newsweek.

The pair said their study reflects the fact "that autism is a complex trait which is likely influenced by a combination of many genetic factors and possibly also prenatal environment, and thus it is unrealistic to assume that there is one sole biological factor that causes it."

"We should also acknowledge that it is very difficult to study autism in humans, because we cannot experimentally manipulate genes or prenatal factors and establish a causal relation between them and real-life outcomes in humans (although this has been done in rodents)," they argued.

However, one expert not involved in the research questioned whether such a test was relevant to individuals with autism.

Dr Punit Shah, assistant professor in psychology at the University of Bath, told Newsweek: "At first blush, this seems like an exciting and important study. The general scientific method used—of conducting a randomized controlled trial—is far superior to most previous studies on testosterone, social-emotional processing, and autism.

"However, there is a critical flaw in the study which undermines the authors conclusions," he argued. "The authors used a so-called 'empathy test' that is not a test of empathy at all. The 'Reading the Mind in the Eyes Test', as used by the authors, has recently been found to be a measure of emotion processing or even just a vocabulary test as it involves knowledge of complex words. So, while it is unclear what this test measures, it was not prudent for it to be used as a measure of empathy. This is a broader problem in autism and psychological research that needs to be addressed."

Shah said he was "deeply confused" why the authors claimed the study has major implications for understanding autism as it didn't test participants with the condition, and didn't measure autistic tendencies.

"Overall, we have learnt nothing from this study about the influence of testosterone on empathy or autism, as neither empathy nor autism were measured in the study," he said.

Steven Stagg, a senior lecturer at Anglia Ruskin University who studies autism spectrum disorders but did not work on this paper, also told Newsweek the study had a fundamental flaw in relying on the Reading the Mind in the Eyes Test. Separate studies have arrived at conflicting conclusions on how useful it is. One, in 2004, showed a low score indicated high levels of empathy, while another in 2009 found the opposite.

"Studies show that people with ASD [austism spectrum disorders] are just as good as neurotypicals at identifying emotional states when it comes to the RMIET [Reading the Mind in the Eyes Test] task; therefore, the results of this study add little to our knowledge of autism," he continued.

"However, if future research manages to disassociate testosterone with behavioural features of ASD this might shift research into a more fruitful direction," he said.

This article has been updated with comment from Steven Stagg.

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A stock image of a man making different gestures. Some people with autism process other people's emotions differently to those who are neurotypical. Getty