Determined: A Science of Life without Free Will

by Robert M. Sapolsky

For starters, T rarely generates new patterns of aggression; instead, it makes preexisting patterns more likely to happen. Boost a monkey’s T levels, and he becomes more aggressive to monkeys already lower-ranking than him in the dominance hierarchy, while brown-nosing his social betters as per usual. Testosterone makes the amygdala more reactive, but only if neurons there are already being stimulated by looking at, say, the face of a stranger. Moreover, T lowers the threshold for aggression most dramatically in individuals already prone toward aggression.[11] The hormone also distorts judgment, making you more likely to interpret a neutral facial expression as threatening. Boosting your T levels makes you more likely to be overly confident in an economic game, resulting in being less cooperative—who needs anyone else when you’re convinced you’re fine on your own?[*] Moreover, T tilts you toward more risk-taking and impulsivity by strengthening the ability of the amygdala to directly activate behavior (and weakening the ability of the frontal cortex to rein it in—stay tuned for the next chapter).[*] Finally, T makes you less generous and more self-centered in, for example, economic games, as well as less empathic toward and trusting of strangers.[12]