A generation ago, for every one girl arrested for assault, there were 10 boys arrested for assault. Now it's more like four boys for every one girl.

You play lacrosse, you hit with a stick. You play hockey, you push a stick around. Soccer, you're tackling people. Some of the research shows that if you get involved in competitive sports, it raises your testosterone level, whether you're a boy or a girl.

The more you play competitive sports, whether you're a girl or a boy, it tends to raise testosterone levels. It used to be girls got the message: 'Girls don't hit.' But now, even if you say that to girls, it's patently not true.

Boys are beyond the range of anybody's sure understanding, at least when they are between the ages of 18 months and 90 years.

Boys are beyond the range of anybody's sure understanding, at least when they are between the ages of 18 months and 90 years.

This is a point of major social transition. The data are now coming out and roiling the idea that boys are the hunters and young girls are the prey. It absolutely defies the stereotype.