By guest blogger Richard Stephens

I have a professional interest in the naughty. In my recent book Black Sheep The Hidden Benefits of Being Bad I explored in a light hearted fashion the psychology around the upsides of various antisocial behaviours – things like swearing, drinking, affairs and untidiness to name a few. However, this post is about physical violence, a much more serious form of bad behaviour for which I see no upside at all.

Thankfully there is some fascinating psychology into the factors that may lead people to violence, and that may yet help society to curb such negative behaviour. While it’s true that many of the factors associated with violence are situational – things like poverty, unemployment and educational attainment – there are also personal characteristics that are strongly associated with the chances that a person will behave violently. One of these is a person’s heart rate.

A recent study published in The International Journal of Epidemiology is just the latest to find a link between lower resting heart rate and more violent behaviour. Joseph Murray at the University of Cambridge and his colleagues measured resting heart rate in over 3,000 male and female children growing up in Pelotas, a relatively poor city in a relatively rich southern state of Brazil.

This was longitudinal study in the style of the British “Seven Up!” documentary series, with children born in 1993 periodically called back for interviews and testing as they grew up. The researchers were specifically interested in their participants’ resting heart rate, which is the heart’s beats per minute after 10 minutes of sitting still quietly. The researchers measured this three times – when the children were aged 11, 15 and 18.

A novel aspect of this study compared with earlier research (including in the UK in the 1950s and 1970s and more recent US and Swedish studies), is the sheer frequency of extreme violence in Pelotas: in 2011 the city had a murder rate of 18.9 per 100,000 population, almost 20 times higher than in England and Wales and Sweden. The new study also included women whereas the earlier research focused only on men.

The researchers identified criminal behaviour through a combination of asking the young people at the age of 18 if they had committed any crimes during the past year, and by checking with legal agencies to see if they had a criminal record. Crimes were flagged as violent if they involved assault, robbery, weapons, murder, kidnapping, non-consensual sex, serious personal threats and other rare violent acts.

For males there were clear links between resting heart rate at age 11, 15 and 18 and participation in violent crime. Males with a lower resting heart rate averaging around 59-65 beats per minute were between one-and-a-half-times and two-times as likely to have committed violent crimes compared with males with a higher resting heart rate averaging around 90-92 beats per minute. Women with a lower resting heart rate were twice as likely to have committed violent crimes than women with a higher resting heart rate.

I should add that the researchers did some additional work checking whether several situational contexts known to be associated with violent behaviour – things like unplanned pregnancy, the mother’s years in education and the family income – had any bearing on the results. But the findings stood even after taking these situational factors into account.

Why might resting heart rate be linked with violence? One theory is that having a low resting heart rate is very unpleasant to the extent that it drives individuals to seek stimulation, which may manifest as antisocial behaviour. A similar explanation was put forward by Hans Eysenck in the 1960s to explain the extravert personality trait.

Another theory is that low resting heart rate is a sign of fearlessness. Children lacking fear may be more likely to commit antisocial acts because they are unconcerned about the possible adverse consequences such as admonishment by a parent or teacher. The current study did not have any means of testing these competing theories but earlier US research found no effect of fearlessness when looking at resting heart rate and aggressive antisocial behaviour. On balance then, fearlessness seems less likely to be the underlying cause.

As the authors of the new research point out, it is surprising that a personal, physical characteristic like resting heart rate can have such a clear cut link with violent behaviour for both men and women, above and beyond societal influences like poverty, inequality, gangs, drug trafficking and corrupt justice systems.

I asked study author Joseph Murray, what the direct impacts of these findings might be – could we use what we know about resting heart rate to prevent violent outbreaks before they happen? Professor Murray said “While these were fascinating findings, I do not think that there are any direct implications for practice”, adding, “the level of current understanding about the mechanisms involved does not permit more than speculation.”

Still, this study provides a clear illustration that if we want to understand societal problems like crime and antisocial behaviour, we should look closely at the psychological and biological factors that are involved, as well as the social and societal contexts in which these behaviours are played out.

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Murray, J., Hallal, P., Mielke, G., Raine, A., Wehrmeister, F., Anselmi, L., & Barros, F. (2016). Low resting heart rate is associated with violence in late adolescence: a prospective birth cohort study in Brazil International Journal of Epidemiology DOI: 10.1093/ije/dyv340

Post written by Richard Stephens for the BPS Research Digest. You can read more of Richard’s work in his critically acclaimed popular science book: Black Sheep The Hidden Benefits of Being Bad.

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