It’s a question that has dogged criminologists for decades: might some people be predisposed to commit certain crimes because of genetics? Academic studies over the past decade indicate the answer is yes.
In 2014, the journal Molecular Psychiatry published a Finnish study in which researchers studied the genetic make-up of roughly 900 criminals convicted of both extremely violent (homicide, attempted homicide, manslaughter, and battery) crimes and non-violent offenses. The investigators then compared the genetic profiles of both types of offenders with the general population. Their findings showed two genes to be associated with the “extremely violent” offender group.
First, they discovered all the individuals in the violent offender group showed low activity of monoamine oxidase A, an enzyme encoded by the MAOA gene (also called the “warrior gene”). This enzyme is responsible for controlling the amount of dopamine, serotonin, and other mood-affecting neurotransmitters in the brain. Earlier studies had already shown that the MAOA enzyme’s low activity to be linked to “dopamine hyperactivity.” Such heightened amounts of dopamine can lead to aggressive behavior, hypersensitivity, and poor impulse control–particularly when coupled with alcohol or drugs such as amphetamines.
The violent offender group also had a variant of cadherin 13 (CDH13), a gene associated with substance abuse and Attention Deficient and Hyperactivity Disorder.
None of the non-violent offenders shared this genotype. Researchers speculated that, based on these results, 5-10 percent of all violent crime in Finland could be attributed to people with these genotypes. However, as reported by the BBC, the lead author of the study, Jari Tiihonen of the Karolinska Institutet in Sweden, said that most people with a “high-risk combination” of these genes would never commit a crime.
The researchers also emphasized that genes should not be used to influence criminal convictions and that environmental and social factors also play a fundamental role in whether an individual will turn to crime.
Nonetheless, a few defense attorneys have successfully used a defendant’s genetic information to reduce criminal sentences. For example, a court in Italy reduced a convicted murderer’s sentence by one year because he had low activity levels of the MAOA enzyme. A few defense attorneys in the U.S. have introduced similar genetic evidence in eleven cases, particularly at the sentencing phase. Of these cases, the court reduced the defendants’ sentence in two instances.