We’ve known for a while that testosterone is associated with aggressive behavior. But a fascinating new experiment reveals that these hormones are a two-way street: Simply acting aggressive can also raise levels of testosterone, in both women and men.

You may know testosterone as the “male hormone,” because it produces facial hair and deeper voices in boys going through puberty. For decades, scientists didn’t question its status as a male hormone because they found higher levels of testosterone in adult men, too. But recent studies reveal that the situation is more complicated. Testosterone is present in adult women, and it seems to be crucial for women’s sense of well-being and sexual health. So if testosterone is important for adult men and women, why do we see more of it in men?

It seems like an obvious question, but nobody had actually thought to ask it until a group of researchers at the University of Michigan at Ann Arbor came up with an incredible experiment to find out. Psychologist Sari van Anders, who led the study, has spent a number of years researching how social factors can affect our hormones. She and her colleagues wondered whether social pressure to behave “like a man” or “in a ladylike way” could be affecting hormone levels.

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Could people’s gendered behavior account for the testosterone gap? To answer that, researchers needed to find out whether merely acting aggressive could change the chemicals in your brain.

That’s why Van Anders brought in theater director Jeffrey Steiger to work with a group of actors who would participate in the experiment. As van Anders and her colleagues write in Proceedings of the National Academy of Science, the actors would need to behave competitively and wield power over another person. Both types of behavior are associated with testosterone. Working with Steiger, they came up with the ultimate power-grab scenario: Firing a person from a job.

But this wasn’t just your ordinary firing. The monologue that Steiger wrote for the experiment is the stuff of nightmares. Actors were encouraged to embody an unfair boss whose goal seems to be to undermine and bully his or her underling before telling them to walk in the cruelest possible way.

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In the script, our evil boss is ripping into somebody who keeps trying unsuccessfully to reply. It’s worth reading this long excerpt here before finding out what came next:

So, a month or so ago, we discussed my concerns regarding your job performance and I gave you some specific feedback on ways that I felt you could improve. Do you remember this meeting?

(beat)

... I recall asking you to keep clearer track of the tasks that you needed to complete. I asked you to –

Hold on. I’d really like to finish what I have to say.

I asked you to be more proactive. To think about what needed to get done before I had to ask you to get it done. I asked you to –

Please let me finish speaking before you respond, okay? It’s hard to feel like you’re listening to me if you don’t let me finish saying what I’m trying to say.

I asked you to be more communicative about what you needed from me ...

(pause)

I’m just - I’m struggling, Pat. I’m struggling with what to do here...

What am I supposed to do with this attitude? What am I supposed to do with you? Would you like to tell me what you think I should do from here? Because at this point, I’m all ears. But that’s all I really have left. Ears.

(pause)

So, it sounds like there isn’t much more to say. It sounds like we’re done. This is done. I’m done. You’re done. You’re fired. I have to fire you. You made me fire you. Pack your things and go. Goodbye forever.

For anyone who has ever worked a bad job, just reading that script might make your blood pressure rise. So what happened to actors who actually performed it with feeling?

Before and after reading this monologue, each actor was given a saliva test, wetting a swab in their mouths that could be analyzed for testosterone levels. When the tests came back, it turned out that all the actors–male and female–had elevated levels of testosterone after taking power away from that poor sod who was told “you made me fire you.”

The actors were also directed to read the script while acting like stereotypical men and women, to see whether testosterone levels would be affected by acting “manly” or not. The difference was negligible. The main thing that affected testosterone was what the researchers simply called “wielding power.”

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These results suggest that if people act aggressive, their testosterone levels will stay higher, and may make them feel more aggressive generally. So acting aggressive begets true feelings of aggression. As an aside, it’s also pretty amazing to consider that a piece of theater could change your brain chemistry (and might help explain actor meltdowns).

So what does this tell us about why adult men have higher levels of testosterone than women? Van Anders and her colleagues suggest that adult men may have more testosterone because they live in cultures that encourage men to be competitive and take power over others. If a boy is told to “act like a man” and be aggressive or competitive, over time his behavior will jack up that testosterone in his brain. When girls are told to avoid conflict and be nurturing, that may be lowering their levels of testosterone.

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This study isn’t just about gender roles, though. Van Anders and her colleagues picked testosterone partly because it’s a highly-studied chemical, and partly because it’s easy to measure it with simple saliva tests. However, this study design could also open the gates to explore other ways that our behavior affects our hormones–and, by extension, our moods.

Van Anders explained via email:

With this paper, we were specifically interested in gender/sex. However, others could use this paradigm to investigate other hormones and neurotransmitters ... So, my main interest in this paper and method is the conceptual contribution and the gateway to other investigations of how gender modulates hormones and gets into the body.

Still, it might be a while before we can test other neurotransmitters quite so easily as we did testosterone. Van Anders points out that you can’t test levels of dopamine–key for modulating our feelings of happiness and self-worth, among many other things–with a blood or saliva test.

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But now, at least, van Anders and her colleagues have provided more evidence that we are not doomed to have certain kinds of feelings and urges. In some cases, just acting differently can make us feel different in the long term.

Knowing this might change our social expectations, too. As I mentioned earlier, scientists believed for a long time that male testosterone levels were the result of an innate difference between the sexes. This supposed fact about testosterone has been used to justify the idea that men are naturally more competitive than women, and more prone to taking on powerful roles in society.

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Now a new picture is emerging. When people are pushed to take powerful positions, that may inspire the release of testosterone. It’s not a male thing; it’s a human thing. For better and for worse.

Read the full scientific paper at PNAS.

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Illustration by Jim Cooke


Contact the author at annalee@gizmodo.com or follow her on Twitter.