More men inevitably means more testosterone-fuelled violence, right? Wrong, according to a comprehensive analysis exploring how a surplus of men or women affect crime rates across the US.
In areas where men outnumber women, there were lower rates of murders and assaults as well as fewer sex-related crimes, such as rapes, sex offences and prostitution. Conversely, higher rates of these crimes occurred in areas where there were more women than men.
Ryan Schacht of the University of Utah in Salt Lake City and his colleagues analysed sex ratio data from all 3082 US counties, provided by the US Census Bureau in 2010. They compared this with crime data for the same year, issued by the US Federal Bureau of Investigation. They only included information about women and men of reproductive age.
For all five types of offence analysed, rising proportions of men in a county correlated with fewer crimes– even when accounting for other potential contributing factors such as poverty. The results suggest that current policies aimed at defusing violence and crime by reducing the amount of men in male-dominated areas may backfire. According to Schacht, when women are in short supply, men must be more dutiful to win and retain a partner. With an abundance of women, men are spoilt for choice and adopt more promiscuous behaviour that brings them into conflict with other men, and more likely to commit sex-related offences. Work in China, where men dramatically outnumber women – especially in rural villages -–because of the government’s old one-child-per-family rule, reveals a slightly different pattern, says Therese Hesketh at University College London. “In China, we didn’t find a relationship between excess males and violence,” she says. “Instead, many single rural men were depressed and introverted. Although they scored slightly higher on measures of aggression, there was no evidence of increased crime or fearfulness among women.”
“Recent work in animals also shows quite similar findings to ours, that when females are abundant and males rare, males are more violently competitive, more promiscuous and less likely to invest in offspring,” says Schacht.

source: newscientist.com