The Human Beast

Questions on polygyny and the changing marriage market

Violence might be due to a shortage of single women who haven't got a child by another man. (all other things being equal)

I'm sorry, but none of this analysis holds together. What you're really talking about here are the effects of marriage and aging on testosterone levels, not "extramarital sex," as you claim.

The most dangerous element in any society is young men who are not under some sort of control, be it domestic (family responsibilities) or work, or military. Trying to tie it to sex, as you do, just clouds the issue. Ask yourself whether levels of violence would go up or down if these guys weren't having any sex. Clearly, if you add sexual frustration to the mix, things get worse.

Your analysis ignores plentiful evidence of the opposite. Why, for example, are violent crime rates so much lower in countries like Sweden or Denmark with very low marriage rates? Alternatively, why so much violence in places where extramarital sex is prohibited, like Pakistan or Morocco?

In my opinion, you're trying too hard to come up with a simple answer to a situation with complex causes. You simply cannot ignore history, economics, religion, and politics and think you're going to answer a broad question about two continents.