The strongest genetic predictor for violence and aggression is . . . having a Y chromosome. Four times more males than females suffer from antisocial personality disorder, which is characterized by impulsive aggression, and a glance at any police blotter shows which sex commits more violent crimes. While the way we raise boys has something to do with that, there is good reason to believe that testosterone is not exactly an innocent by-stander. Men average several times the amount of testosterone that women do, for one thing, and a pile of studies implicate testosterone in aggression. Call it the original cause of ‘roid rage.
Trouble is, scientists have not nailed down exactly how testosterone increases the likelihood that a man will punch his fist through a wall (or someone’s face). A new study provides the first evidence of how testosterone’s effects on the brain might do that. Elevated levels of this steroid hormone, scientists in the Netherlands find in a study to be published in the August issue of Psychological Science, seem to mess up the brain’s ability to notice and understand angry facial expressions.
Earlier studies had found that testosterone decreases emotional responses to fearful faces but increases responses to angry ones; if you are less fearful and more attuned to anger, you are more likely to react aggressively to angry expressions. In fact, people with antisocial personality disorder have trouble recognizing anger, as a 2002 study found. If you are sensitive to others’ fear, on the other hand, you are more likely to feel empathy and less likely to attack (this works in dogs and other animals, too, where demonstrating fear sends a “don’t attack me, I am pitiful and helpless” signal).
For the new study, the researchers gave 16 female volunteers either enough testosterone to bring them up to men’s average levels, or else an inert solution. The women then looked at faces on a computer screen which morphed among threatening expressions (disgust, fear and anger) and non-threatening ones (surprise, sadness and happiness). The roid-enhanced women did much worse at recognizing angry expressions. How does this square with the earlier finding that testosterone increases emotional response to angry faces? That effect seems to be unconscious; if you react more emotionally to an angry face but are not consciously aware that what you are seeing is anger in someone’s visage, you’re more likely to explode.
The connection between a diminished ability to consciously perceive fear in someone’s face and a tendency to aggression fits with the common observation that women are better than men at consciously recognizing facial expressions, and threatening ones. Testosterone, Jack van Honk and Dennis J.L.G. Schutter of Utrecht University conclude, “may promote social aggression” by impairing the ability to consciously recognize angry facial expressions.