http://www.anapsid.org/hormones.html
Great article by the Neuroscientist Robert Sapolsky about the correlation between Testosterone and aggression.
tl;dr
Testosterone doesn't actually cause aggression, but exaggerates it if the tendency to be aggressive already exists.
Great article by the Neuroscientist Robert Sapolsky about the correlation between Testosterone and aggression.
tl;dr
Testosterone doesn't actually cause aggression, but exaggerates it if the tendency to be aggressive already exists.
snippet said:If you knew a great deal about the genetic makeup of a bunch of males, enough to understand how much testosterone they secreted into their bloodstream, you still couldn't predict levels of aggression among those individuals. Nevertheless, the subtraction and reinstatement data seem to indicate that, in a broad sort of way, testosterone causes aggressive behavior. But that turns out not to be true either, and the implications of this are lost on most people the first 30 times they hear about it. Those implications are important, however - so important that it's worth saying 31 times.
Round up some male monkeys. Put them in a group together and give them plenty of time to sort out where they stand with each other - grudges, affiliative friendships. Give them enough time to form a dominance hierarchy, the sort of linear ranking in which 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 numbers 1 and 2 still expect and receive from him the most obsequious brownnosing.
Hierarchy in place, it's time to do your experiment. Take that third-ranking monkey and give him some testosterone. None of this within-the-normal-range stuff. Inject a ton of it, way higher than what you normally see in rhesus monkeys, give him enough testosterone to grow antlers and beard on every neuron in his brain. And, no surprise, when you check the behavioral data, he will probably be participating in more aggressive interactions than before.
So even though small fluctuations in the levels of the hormone don't seem to matter much, testosterone still causes aggression, right? Wrong. Check out number 3 more closely. Is he raining aggressive terror on everyone in the group, frothing with 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. Testosterone isn't causing aggression, it's exaggerating the aggression that's already there.
snippet said:Another example, just to show we're serious. There's a part of your brain that probably has a lot to do with aggression, a region called the amygdala. Sitting near it is the Grand Central Station of emotion-related activity, the hypothalmus. The amygdala communicates with the hypothalmus by way of a cable of neuronal connections called the stria terminalis. (No more jargon, I promise.) The amygdala influences aggression via that pathway, sending bursts of electrical excitation that ripple down the stria terminalis to the hypothalamus and put it in a pissy mood.
Once again, do your hormone intervention: flood the area with testosterone. You can inject the hormone into the bloodstream, where it eventually makes its way to the amygdala. You can surgically microinject the stuff directly into the area. In a few years, you may even be able to construct animals with the extra copies of the genes that direct testosterone synthesis, producing extra hormones that way. The key thing is what doesn't happen next. Does testosterone make waves of electrical excitation surge down the stria terminalis? Does it turn on that pathway? Not at all. If and only if the amygdala is already sending an excited volley down the stria terminalis, testosterone increases the rate of such activity by shortening the resting time between bouts. It's not turning on the pathway, it's increasing the volume of signaling if it is already turned on. It's not causing aggression, it's exaggerating the preexisting pattern of it, exaggerating the response to environmental triggers of aggression.