Same Impulse, Different Weapon

Male and female aggression differ in method, not magnitude. The biology explains the pattern

There is a finding that has been replicated in every society anyone has ever studied, and across every historical period where we have data good enough to check.

Males commit the overwhelming majority of violent crime. That is true now and it has been true for as long as we have been keeping records.

The exact numbers move around depending on which jurisdiction you are looking at. The pattern itself does not budge.

In the United States, about 90 percent of homicides are committed by males. In the UK that number is closer to 95 percent. Japan, also about 95. Sweden, which people love to bring up as a gender equality success story, still sits at about 90 percent.

If violent aggression were entirely a product of how boys are socialized, you would expect at least one culture somewhere to have reversed the pattern. Women committing more violence than men. Researchers have been looking for a long time. Nobody has found that society yet.

When it starts

The sex difference in physical aggression shows up before anything that could reasonably be called cultural programming.

Boys are more physically aggressive than girls starting at around 17 months. That is before preschool. Before organized socialization of any kind. Before anyone has sat a toddler down and explained what gender roles are supposed to be. Physical aggression in boys peaks between ages 2 and 4. Hitting, biting, kicking, shoving. The gap is large and it is consistent.

Richard Tremblay, who has spent decades studying how aggression develops in children, makes a point that goes against the popular framing. His argument, based on longitudinal data from Canadian cohorts, is that children do not learn aggression. They come in with it. What they learn is how to hold it back (Tremblay, 2000). Physical aggression peaks in toddlerhood and then declines through childhood as the prefrontal cortex comes online and children pick up social regulation. Socialization is not installing the aggression. Socialization, along with brain maturation, is suppressing an innate tendency. And boys start out with more of that tendency to suppress.

By the time you get to adolescence, the gap between the sexes has gotten wider still. Testosterone surges during male puberty amplify what was already there. The age-crime curve, which is one of the most reliable findings in all of criminology, tracks testosterone levels in a way that is hard to look at and then dismiss as coincidence. Violent offending in males rises sharply around 14, peaks in the late teens to early twenties, and then falls off. Every country that keeps records shows the same curve. It maps onto the rise and fall of testosterone and the slow finishing of prefrontal cortex development with an almost uncomfortable degree of precision.