Two Genes May Explain Up to 10% of Violent Crime

What makes a criminal?

We will never have a blanket answer to that question, but according to new research out of Finland, many criminals may share a pair of genes that the researchers say is linked to higher rates of violent crime and recidivism. The paper, published this week in the journal Molecular Psychiatry, reports on the genetic analysis of approximately 900 criminal offenders. It is the first genetic study to look at such a large pool of violent criminals.

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Among criminals surveyed in Finland, those with two gene variants were more likely to be repeat offenders.

The study states that the results “imply that at least 5-10% of all severe violent crime in Finland is attributable” to the two genes. Criminals whose genome contained those variants were 13 times more likely to commit repeated violent crimes than those without. Of the 900 offenders, the 78 with the most violent profiles had the clearest connection between the two genes and their behavior, while among nonviolent offenders, the prevalence of the variants was not significant. According to the BBC, the number of the violent crimes—murders, attempted murders, manslaughters, and batteries—stood at a combined 1,154 incidences amongst the 900 offenders.

Monoamine oxidase A (MAOA) and cadherin 13 (CDH13), the two genes identified in the study, have both been linked to violent crime before. MAOA, often referred to as the “warrior gene,” is responsible for an enzyme deficiency that creates a hyperdophaminergic state, or “dopamine hyperactivity,” according to Jari Tiihonen, a professor at the Karolinska Institutet in Sweden and lead author of the paper,

Dopamine is a required neurotransmitter for processes like concentration, motivation, and retention; too much or too little has been implicated in various psychological disorders, including violent behavior. Drugs like amphetamines can exacerbate the problem.

The researchers were careful to emphasize that “the genes could not be used to screen criminals.” Simply possessing the genes is not enough to guarantee that a person will commit a violent crime, just as not carrying the genetic sequence prevents one from engaging in violence. Here’s Melissa Hogenboom, reporting for BBC News:

For now, a person’s genetic information should not have any influence on conviction outcomes in criminal courts, Prof Tiihonen added.

“There are many things which can contribute to a person’s mental capacity. The only thing that matters is the mental capacity of the individual to understand the consequences of what he or she is doing and whether or not the individual can control his or her own behavior.”

Christopher Ferguson of Stetson University in the US state of Florida agreed. He said it must be remembered that there was not “one or even two genes that by themselves code for violence or crime”.

Even if more gene variants are tied to violent behavior, genetics alone likely won’t tell us why a person is driven to criminal behavior. As always, environmental factors play an important role.

Explore the genetics behind criminal minds, the latest in lie detection, a human corpse “farm,” and more in "Can Science Stop Crime?."