BIOLOGY AND HUMAN NATURE

Does Testosterone Actually Promote Aggression and Violence in Men?

The challenge hypothesis and the role of testosterone in driving status seeking

Testosterone is a potent hormone with a chequered past. It’s probably most famous for its role as an anabolic steroid in professional sport and bodybuilding, and has been closely associated with aggression and violence (e.g., the infamous ‘roid rage’).

This seems to make intuitive sense. After all, men have vastly more testosterone than women, men are far more violent and aggressive than women, and going through puberty with male levels of testosterone confers much greater physical strength.

Everything seems to check out, and the notion that testosterone causes aggression and violence satisfies our intuitions. But as you’ve likely guessed, there’s more to the story.

What is testosterone? A brief overview

Before we discuss aggression, violence, and competition, we’ll quickly cover the basics about what testosterone is and where it comes from. If you’re not interested in these details, feel free to skip to the next section.

Testosterone is a type of hormone known as an anabolic steroid, but what does that actually mean? A hormone is a chemical that’s released in one organ of the body (e.g., reproductive organs or adrenal glands) in order to act on other organs of the body (e.g., the brain).

Steroids are naturally-occurring chemicals that can act as hormones. Steroid hormones belong to two main categories, depending on where in the body they’re synthesised.

Testosterone is primarily synthesised in the gonads, meaning testes in men and ovaries in women. Smaller amounts are also released by the adrenal glands that sit atop our kidneys, and by fat cells.

The other type of steroid is synthesised in part of the adrenal glands known as the adrenal cortex. Because they’re synthesised in the adrenal cortex, these steroid hormones are known as corticosteroids. This class of hormones includes glucocorticoids, better known as stress hormones. (Stay tuned for more about glucocorticoids and stress in a future article.)

Although it’s found in men and women, testosterone levels are much higher in men, and testosterone plays a key role in ‘masculinisation’ (e.g., deeper voice, greater hair growth, changes in muscle tone). As such, testosterone is known as a male sex hormone (i.e., an androgen). By contrast, female sex hormones are known as estrogens, as they’re found in females and males, but occur at much higher levels in females.

Confusingly, people often refer to estrogen as if it’s a specific hormone, rather than a category of hormone. However, as a type of hormone, estrogens come in various forms that are more important at different stages of life, such as estradiol (reproductive years), estrone (post-menopause), and estriol (pregnancy).

Finally, the term ‘anabolic’ refers to the fact that testosterone tells our cells to use energy in order to build new tissue (i.e., anabolism), including muscle tissue. The opposite also occurs, as tissue deemed unnecessary is deconstructed to release energy for use elsewhere in the body (i.e., catabolism).

For instance, catabolism occurs when we’re deprived of food and literally ‘eat’ ourselves in order to survive. But that’s a very dramatic example, as catabolism is also a regular bodily process that occurs outside of starvation, and is crucial for ordinary housekeeping in the body.

Testosterone, aggression, violence, and competition

After it was discovered in 1935, testosterone soon became associated with male aggression, violence, and competition. As we already noted, this was partly because males have much higher levels of testosterone than women, and males perpetrate the lion’s share of aggression and violence.

Another observation is that testosterone peaks in adolescence, when males are most aggressive and violent. Further, in many species, testosterone also peaks during mating season, coinciding with upticks in male-male competition over breeding grounds and females.

Some experimental evidence also paints a similar picture. For instance, levels of aggression and violence decline in castrated males, and increase when castrated males are given testosterone supplements. This is true in humans and many of our mammalian cousins.

Given these findings, it’s easy to see how testosterone got its reputation. So, where is this narrative wrong?

For starters, loss of testosterone reduces aggression and violence without eliminating it. A good example is eunuchs, who were fairly common throughout history (and Game of Thrones), and could be just as ruthless and competitive as uncastrated males.

Violent sex offenders are another grim case in point. It was thought that they could be prevented from reoffending by using court-enforced ‘chemical castration’ (i.e., drugs that suppress androgens, including testosterone).

But benefits are weaker and more inconsistent than we’d expect if androgens like testosterone were the whole story. The reason seems to be that, once people have experience with aggression and violence, the role of testosterone in future offences actually becomes less important. This is especially true when the crimes have to do with anger and power.

Another key finding is that testosterone doesn’t seem to create aggression and violence, but amplifies tendencies toward them. Such tendencies can be gained via life experiences, and initially reinforced by testosterone, before it then becomes increasingly superfluous as these behaviours continue.

Emerging from all this, it’s now known that an individual’s levels of testosterone don’t predict aggressive/violent behaviour. This is true among birds, fish, mammals, and primates, including humans.

Things differ when people heavily supplement with testosterone. The classic example is ‘roid rage’, seen in many professional athletes and bodybuilders who abuse testosterone. But these levels of testosterone are far beyond the normal range, and aren’t relevant to the regular goings on of our everyday biology.

Studies also find that when testosterone does increase aggression and violence, the results aren’t as indiscriminate as our intuitions predict. Instead, artificially jack up a male’s testosterone, and he selectively lashes out at individuals that he sees as lower than him in the social hierarchy.

As one example, this was demonstrated in a study involving talapoin monkeys. A middle-ranking male was administered testosterone, and he became more aggressive and violent towards lower-ranking monkeys, but not towards higher-ranking monkeys.

The challenge hypothesis

Clearly, testosterone has an association with aggression and violence, but not the simplistic one we originally imagined. Fortunately, some clever researchers put forward an alternative idea that ties together many of these findings: the challenge hypothesis.

The challenge hypothesis argues that the release and effects of testosterone are closely linked to how we think events affect our social status. This idea helps to explain some curious subtleties about how testosterone seems to function.

Take sporting events. Winning (or watching your team win) typically elevates testosterone, while losing (or watching your team lose) does the opposite. But this also depends on what counts as ‘winning’.

If you lose, but do better than expected, your levels of testosterone may still rise as if you won. The flip side is also true, as barely beating an opponent you were expected to demolish will likely result in a decline in testosterone. It’s not just about the outcome, it’s about what that outcome means for your perceived status.

The challenge hypothesis also suggests that testosterone motivates us to defend our social status when we feel that it’s under threat. In this view, testosterone doesn’t increase aggression and violence per se, it’s just that aggression and violence are common means by which individuals gain and maintain social status.

Studies tested this idea by manipulating the rules for gaining status to see if that changes the effects of testosterone. For example, one study had people play a game where social status was determined by how generously people make offers.

What happened when some people were given extra testosterone before playing the generosity game? Consistent with the challenge hypothesis, they made more generous offers.

The take-home message

Where does this leave us? On the one hand, it’s good that testosterone doesn’t seem to inevitably make us aggressive and violent. On the other hand, these findings suggests that we tend to reward aggression and violence with higher social status. This is both bleak and hopeful.

It’s depressing that we often reward people (or at least males) for aggression and violence. But since we make our own social rules, we don’t have to be bound to the mistakes of the past. And if we want to reduce aggression and violence, a good strategy would be to stop rewarding them with status.

To be sure, that’s easier said than done, as systems of social reward have been baked into our culture over many millennia. But at the very least, understanding the problem and the solution is a good start.