They also become more violent, rising more readily to perceived slights and insults, and starting more fights -- often over trivial issues. These are the triggers for most man-on-man assaults and homicides.
Many factors contribute to the number of men who will never find a mate. Economic inequality, for one, leaves a great many poor young men unable to attract a wife. When a society allows powerful men to take several wives, too few women remain for many poor men to take even a single wife. But most dramatically of all, male-biased sex ratios consign the excess men to never having a family of their own.
Under each of these scenarios, large numbers of young men competing for dominance elevate local rates of violence, homicide and lawlessness. Martin Daly and Margo Wilson's studies show that local income inequality can explain variation in homicide rates on a number of scales: from Chicago neighborhoods to American States and Canadian provinces.

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