if violence is in your genes, ta loco...,

theverge | In 2009, an Italian court reduced a murderer's sentence by one year because doctors had identified a gene in the defendant's DNA, called MAOA, that had been linked to violent behavior. The ruling was controversial and some scientists objected to the sentence reduction. "MAOA findings have been generally used in murder trials, sometimes to suggest diminished capacity of the defendant to premeditate his criminal behavior," but most often to reduce a sentence, writes Paul Appelbaum, a psychiatrist at Columbia University, in an essay published today in Neuron. In the essay, Appelbaum explains that genetic evidence demonstrating a defendant's predisposition for antisocial behavior or mental illness is showing up in courtrooms at an ever-quickening pace. And that pace, he warns, might be outrunning the legal system's ability to interpret it.

"Premature introduction of genetic evidence in court carries a number of risks," said Appelbaum in an email to The Verge. "The most obvious is that the purported associations [between genetics and behavior] are not real and will be disproved over time." But even the most replicated and widely accepted findings, he said, can be misinterpreted by judges and jurors.

In the case of the Italian court, the gene that was used has indeed been associated with impulsiveness and criminal behavior among men in a number of studies. Moreover, childhood maltreatment has been linked to lower MAOA activity — providing a great example of how a genetic predisposition can be triggered by environmental factors. Most experts agree, however, that even evidence as strong as that surrounding MAOA shouldn't be used to absolve someone of responsibility for their actions. "The major mistake the people make is to think that if you've identified a cause, it must mean that people are excused or mitigated," says Stephen Morse, a professor of law at the University of Pennsylvania who has written on the subject. But that isn't how the law works. Only a limited number of impairments — such as failing to appreciate the wrongfulness of one's acts — are considered exculpatory. So "if someone is a rational agent," Morse says, "I don't care if they have bad genetics."

Jorim Tielbeek, a neuroscientist and criminologist at VU Medical Center Amsterdam who has studied the effects of genetics on antisocial behavior, agrees with Morse, stating in an email to The Verge that a "higher genetic liability towards committing a crime doesn't necessarily mean a lessened responsibility." Although scientists have made links between certain genes and antisocial behavior, Tielbeek says, there is "no clear predictive relationship between a single gene and a criminal act — especially since hundreds of genes are involved in criminal behavior, and that each have a very small effect."