Testosterone! Aggression!

Could low testosterone be what made us modern humans?!

The hormone, associated with both biologically male characteristics and aggression, makes skulls grow those heavy brows we associate with our evolutionary ancestors…The key, the researchers claim, could be found in the feminized skulls that became more prevalent around that time. A rounder face in humans isassociated with less testosterone, and less testosterone can mean better cooperation between individuals. Less head clubbing and more community building, basically.

The paper is pretty heavy on speculation – human skulls have gotten less masculinized over time, though obviously that could be for reasons beyond changing levels of testosterone; something downstream or different altogether could be the cause. But I think this is a good time to review some things about testosterone. From Sapolsky’s The Trouble With Testosterone:

Okay, suppose you note a correlation between levels of aggression and levels of testosterone among these normal males. This could be because (a) testosterone elevates aggression; (b) aggression elevates testosterone secretion; (c) neither causes the other. There’s a huge bias to assume option a, while b is the answer. Study after study has shown that when you examine testosterone levels when males are first placed together in the social group, testosterone levels predict nothing about who is going to be aggressive. The subsequent behavioral differences drive the hormonal changes, rather than the other way around…

Yes, it’s going to be on the final, and it’s one of the more subtle points in endocrinology—what is referred to as a hormone having a “permissive effect.” Remove someone’s testes and, as noted, the frequency of aggressive behavior is likely to plummet. Reinstate precastration levels of testosterone by injecting that hormone, and precastration levels of aggression typically return. Fair enough. Now this time, castrate an individual and restore testosterone levels to only 20 percent of normal and . . . amazingly, normal precastration levels of aggression come back. Castrate and now generate twice the testosterone levels from before castration—and the same level of aggressive behavior returns. You need some testosterone around for normal aggressive behavior—zero levels after castration, and down it usually goes; quadruple it (the sort of range generated in weight lifters abusing anabolic steroids), and aggression typically increases. But anywhere from roughly 20 percent of normal to twice normal and it’s all the same; the brain can’t distinguish among this wide range of basically normal values…

Round up some male monkeys…number 3, for example, can pass his day throwing around his weight with numbers 4 and 5, ripping off their monkey chow, forcing them to relinquish the best spots to sit in, but, at the same time, remembering to deal with numbers 1 and 2 with shit-eating obsequiousness…Take that third monkey and inject him with testosterone.  Inject a ton of it in him…And no surprise, when you check the behavioral data, it turns out that he will probably be participating in more aggressive actions than before…Is he now raining aggressive terror on any and all in the group, frothing in an androgenic glaze of indiscriminate violence?  Not at all.  He’s still judiciously kowtowing to numbers 1 and 2 but has become a total bastard to numbers 4 and 5. This is critical: testosterone isn’t causing aggression, it’s exaggerating the aggression that’s already there.

And don’t forget that the “effect of testosterone” can be culturally contingent:

However, subjects who believed that they received testosterone—regardless of whether they actually received it or not—behaved much more unfairly than those who believed that they were treated with placebo. Thus, the folk hypothesis seems to generate a strong negative association between subjects’ beliefs and the fairness of their offers, even though testosterone administration actually causes a substantial increase in the frequency of fair bargaining offers in our experiment.

And, revisiting this somewhat-embarrassing early post of mine about the role of testosterone in social domination (and physical displays associated with it):

However, if you go ahead and stick a needle in the other birds – the ones that didn’t get the testosterone injection – they also had an increase in testosterone level.  In fact, they had the same level of testosterone in their bloodstream as those with the injection.  But these birds had smaller combs [dominance displays]! …So testosterone levels per se don’t mediate dominance.  It’s also not at all clear whether testosterone is needed for aggression…Dark-eyed juncos will defend their territory by squawking at unwanted intruders…But at least for [some] behaviors, testosterone surges aren’t associated with aggressive social behavior.

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One thought on “Testosterone! Aggression!

  1. Pingback: News | SignsOfLowT.netSignsOfLowT.net

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