Are Killers Born or Made? Both

James Fallon and Adrian Raine, both law-abiding college professors, also have the biological signs of born killers.

Fallon, a neuroscientist, describes one day when he saw a brain scan that looked like it belonged to a psychopath—it showed low activity in areas tied to self-control, empathy, and ethics—and then learned that it was his own.

At first he thought this must be a mistake. But Fallon underwent a series of genetic tests and discovered a number of variants associated with violence and low empathy. As the news sunk in, it began to make sense: He counts seven alleged murderers on his family tree. Although he hasn’t confessed any crimes, he admits that he’s “aggressive” and “obnoxiously competitive.”

One of the variants that put Fallon at a higher risk of becoming a killer also can lead people to be more substantially affected by their upbringing. He believes that he turned into a “pro-social psychopath”—someone who behaves within social norms but isn’t empathic—because his parents were devoted to him. Had he been abused or neglected as a child, it seems very likely that this aggressive competitive scientist would instead have become a killer.

In The Anatomy of Violence, University of Pennsylvania criminologist Adrian Raine lines up several biological markers for potential criminality: being male, certain gene variants, a low resting heart rate, brain damage, and a mother who smoked and drank while carrying the baby. Raine’s research backs up Fallon’s observation about devoted parenting: when children are separated from parents before the age of three, or their mothers are cold and their fathers disengaged, they are more likely to show signs of a psychopathic personality at the age of 28.

The signs of a criminal future show up before the teens, he argues. In another study, he and his team had about 200 11-year-olds on the tropical island Mauritius take a test measuring their impulsivity—they saw the numbers 1-9 on a screen and had to press a button when they saw 5. The game produced a measure of their “P3 amplitudes” (the larger the P3, the greater the control they had in their nervous system). Their parents also filled out questionnaires about their behavior. As predicted, children with low P3 amplitudes also were more likely to act up—swearing, getting into fights, or making threats. When the children had grown to age 23, the researchers checked who had been convicted of a crime. As expected, significantly more of the low P3 kids were offenders.

In his book, Raine reports that he had a difficult birth and suffered from a vitamin deficiency as a child, two circumstances that can lead to poor self-control. As a young man, he had a low resting heart rate. Worst of all, his brain scans look like those of serial killers.

It’s good to know that people carrying the seeds of criminality may choose to study it instead. But you might think twice before you date a criminologist.

A version of this piece appeared on YourCare Everywhere.