Ok, Liz, I'll spare you, as I haven't investigated in detail the precise ratio of club-wielders to flower-sniffers. It is just as well I don't take offence easily, as I might otherwise think that your comment was aimed partly at my son, which would not be a very pleasant way to conduct a debate.
I think I might once have read a good article in the Guardian, but if I did, it escapes me now.
My own experience shows only that my Mummy-friends with sons have more problems with aggression than my Mummy-friends with daughters. I have also noticed that, if my son goes for a four-mile bike ride followed by a couple of hours playing tig and hide-and-seek in the garden with the children next door, he is less likely to be physically aggressive than if he has been cooped up all day in the rain!
My daughter, for her part, goes in for being verbally annoying when cooped up (nag, nag, whinge, whinge, I'm-going-to-wind-my-brother-up-so-he-kicks-me-and-gets-into-trouble-tee-hee).