Born to kill (or hurt)


You’re scrolling down the front page of your favourite news site, and you inevitably come across a report on some violent crime—perhaps an abuse or murder. You skim over the story and briefly wonder about the aggressor. You think, “What does it take to be that violent?”

Eventually, you conclude the aggressor must be crazy or sick. You probably don’t spend that much time thinking about the aggressor after that. You might give an explanation for their behaviour—usually that something must have happened to this person in their childhood, or maybe even their adult life, to make them behave the way they did.

But some  scientists say environment may not be the only factor in moulding an aggressive person.

In their 2009 paper “Natural born killers: The genetic origins of extreme violence”,  Christopher Ferguson and Kevin Beaver compiled a list of genes that have been associated with aggressive behaviour in various studies.

Of the genes the researchers examined, the gene monoamine axidase-A (MAO-A) was of particular interest to them. MAO-A  had already been linked to antisocial behaviour in several studies. The MAO-A gene encodes an enzyme of the same name that regulates dopamine and serotonin in the brain—two chemicals intricately involved in our mood changes. Previous studies have found that an impaired MAO-A gene correlates with increased violent tendencies.

In 1993, Discover Magazine published an article on the effect of a dysfunctional MAO-A gene in a family with five generations of men whose MAO-A gene wasn’t working as it should be. All the males in the family had exhibited some sort of violent behaviour; the least of these aggressive offences was one man’s attempt to run his boss over with a car.

The researchers determined that the males in the family had all inherited the same gene defect, or more accurately the same stop codon. During the translation of genetic information into the actual proteins, a stop codon signals the end of the translation. In itself, a stop codon doesn’t always result in a gene defect—unless it falls on the wrong spot. This particular stop codon being produced in this family’s genes appeared in the X chromosome, and since males have only one X chromosome, this meant their only copy of the gene was defective. The story of this Dutch family sparked a lot of interest in the MAO-A gene and its relation to aggression in the 1990s.

Psychologists who study aggression sometimes take these genetic factors into account, but the link between aggression and genetics is not yet completely understood. On the pragmatic scene, the “defective gene” defence has yet to hold up in legal cases. Even proponents of the genetic basis of aggression concede that carrying certain genetic variants doesn’t guarantee that individuals will commit aggressive acts.

In the end, the role of genetics in aggression is much more complicated than that. It needs to be studied further before we can understand the biological component of aggressive behaviour.