Natural born killers? Low heart rates associated with violent crime

At some point you’re going to disagree with the following statements – how far along will not only demonstrate how authoritarian you are, but also how you welcome the simplistic conclusions of a new study:

• Crime is bad.

• It would be great if we could end all crime.

• A brilliant way of ending crime is to stop it before it happens.

• It would be great if we could identify criminals before they break the law.

• If we can spot likely criminals before they offend, we should pre-emptively strike.

• It is our duty to lock up all future criminals before they strike to protect law-abiding citizens.

I could go on, but if you’re still nodding to yourself at this point, I’m not sure you and I can be friends. You probably thought Minority Report was a bit too liberal. In any case, a new study from Sweden has made a concerning link between a low resting heart rate, and a predisposition for violent crime.

This isn’t the first time such conclusions have been drawn, but previous studies have been from small samples. That’s not a problem with this one, which draws upon the records of 710,264 young men. How? Most Swedish men are required to take a “conscription assessment” for the army when they turn 18. By tracking these subjects over the years that followed, researchers were able to draw some interesting conclusions.

First things first, 94% of the men assessed had never been convicted of a violent crime, so the link is far from absolute. Still, while accounting for other factors including BMI, blood pressure, fitness, IQ, socio-economic status and psychiatric health, they found that men with a heart rate of between 35 and 60 beats per minute were 39% more likely to be convicted of violent crime than those with faster tickers. They were also 25% more likely to be convicted of non-violent crimes, such as drug or driving offences.  

Why would this be? It’s possible that those with a lower heart rate don’t feel fear in the same way as those with high heart rates. When people get scared, their heart rates go up – meaning, from a lower base, fear probably just doesn’t feel as, well, scary. If you’re not frightened of getting your face rearranged, or of the prison sentence that follows rearranging someone else’s face, then there’s less stopping you settling your differences with fists, rather than words.

Another linked theory is that those with lower heart rates find the experience uncomfortable, and are therefore more likely to resort to violence to raise it to levels the rest of the population enjoys by default – a kind of boredom of rest.

Additionally, the difference between the men with the fastest and slowest heart rates was just 0.8% – enough to be statistically significant, but not a clear-cut recipe for killers, by any means.

There are some biological and socio-economic signs that make someone more likely to commit a crime – high levels of testosterone is one, and CDH13 and monoamine oxidase A genes are two others – but nothing that cleanly guarantees a criminal. The idea that you can spot a criminal based on their skull shape (phrenology) came and went before the dawn of the 20th century, and to date there have been no clear-cut genetically visible traits that have filled the gap. People are, it seems, not just born bad.

That doesn’t make things easy, but does avoid opening a fresh can of worms. If science found a sure-fire marker of guaranteed criminal behaviour, we’d find ourselves in a real moral pickle, to put it mildly. We could, as a species, take the executive decision to “remove the problem”. If that euphemism doesn’t sound troubling to you, then re-read it. You could either lock up or kill everyone likely to commit a crime, or modify their genes to just edit the problem away. How ever you deal with the issue, it feels uncomfortably close to eugenics.

Alternatively, we could choose to keep an eye on those with criminal warning signs, but that in itself is problematic. If you treat someone like a potential criminal, at what point does it cease to be their fault when they go out and commit the crime that society has been anticipating and planning for?

Worse, this would do troubling things to our whole criminal justice system, which is not only based on the idea that everyone is innocent until proven guilty, but also that they’re equal – and that those choosing to break the law must face the consequences. If some are genetically more predisposed to commit crimes, then free will falls apart, and it is completely unjust to judge people on the same terms. Two people can commit the same crime, but if one has the socio-economic and biological markers that make it statistically inevitable, then should they be punished as harshly as someone who’s “just bad”? Solicitors would have a field day with that question.

So all in all, it’s perhaps just as well that there’s no known criminal gene. Identifying one could well reduce crime, but the only mechanisms for doing so should leave us feeling distinctly queasy. I, for one, would prefer to keep the lid on this particular can of worms.

Images: Michael Coghlan and Double M used under Creative Commons