You’re looking a guy square in the eye—quick, how do you know if he’s pissing you off? Trick question—unless you have some kind of testosterone deficiency, you’re already predisposed to being a little pissed off.
Researchers publishing in Biological Psychiatry have found that, not only does testosterone in healthy men contribute to aggressive behaviour, it also helps men recognize aggressive behaviour.
Researchers had sixteen healthy young men complete two days of testing. On both days, they received drugs suppressing their testosterone so that they’d all have similar levels. Then, half received supplementary testosterone (returning it to a normal range), and half received placebos. Subjects then completed a face-matching test while undergoing a function magnetic resonance imaging scan (fMRI).
Subjects with normal testosterone levels had increased activity in the amygdala, hypothalamus, and periaqueductal grey—all regions of the brain related to mediating threat processing and regulating aggressive behaviour—when viewing angry faces.
Of course, this doesn’t help you in any practical sense, unless you happen to be taking testosterone supplements. That said, it does help explain why our fight or flight response kicks in so quickly—and why it skews towards fight.