To watch parents vie for parking spaces at the school gates, you might not think it, but a new study in Aggressive Behavior claims that becoming a parent reduces both men’s and women’s aggressive tendencies, although the caveat with men is that they need to be living with a partner too.

Lynda Boothroyd and Catharine Cross analysed all the sentences handed down for robbery or larceny by US federal courts between 1994 and 1999. They focused on these two crimes because both involve theft, but robbery includes the use of force – such as bank robbery or carjacking – whereas larceny – including crimes like theft from benefit plans or receiving stolen goods – does not. The records also included information on whether the 22,344 sentenced criminals had any dependents and the researchers used this as a proxy for parenthood.

Men were seven times more likely than women to be sentenced for robbery rather than nonviolent larceny, and violent theft was also more common among younger age groups, as you’d expect. But the novel revelation is that overall, non-parents were 1.6 times more likely to commit robbery than parents.

Note that sex trumps parental status: fathers were more violent than even childless women. Also, the data for one year (1999) included information on marital and habitation status, and this showed that parental status made no difference to the violent tendencies of single men, but was only associated with reduced violence among partnered men.

The study didn’t follow people over time, so it’s possible that less violent people are more likely to become parents, rather than that parenthood reduces violent tendencies. However, the researchers argue that their results match other research suggesting that parenthood leads to reduced testosterone levels, which favours the idea that parenthood really does cause reduced violence.

Also, the researchers say the notion that parenthood is associated with less aggression fits explanations for violence grounded in evolutionary psychology, whereby men are more violent than women because they have more to gain and less to lose. “Parents – of either sex – have more to lose from aggressive competition than non-parents, and very little to gain,” they said. Personally I can’t help wondering if most parents are simply too exhausted to get involved in any crime that involves physical exertion.

—The impact of parenthood on physical aggression: Evidence from criminal data

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Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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