Homicide rates, too, may be something we can affect, said Martin Daly and Margo Wilson, professors at Canada's McMaster University.

Income inequality — not low income itself but the perception that other people have more — and low life expectancy are the biggest predictors of homicides of men against men, they said. In other words, it's a question of "nothing left to lose."

Being unemployed and being unmarried are also risk factors for violence among men, they said. (Even widowers are more likely than married men to commit murders, according to their data.)

Some social scientists argue that it is America's "culture of violence" — its TV shows and its guns — that lead to a homicide rate of 94 per million, compared to, say, 4 per million in Iceland. But Daly and Wilson put the blame on "a culture that institutionalizes inequality."

E-MAIL: jarvik@desnews.com