Genetics and Crime

One genetic difference often discussed is the sex chromosomes X and Y. The XX combination usually leads to female sex, while XY leads to male sex. Because masculinity is sometimes linked to higher levels of aggression, researchers have examined whether people with an extra Y chromosome, that is, Klinefelter syndrome (XXY), may be more aggressive than others.

People with this chromosome pattern are relatively few in the population, but some studies have shown that they appear slightly more often than average in crime statistics. However, research has not been able to show that they are overrepresented in violent crime, but rather in non-violent crime. This suggests that the relationship between chromosomes, aggression, and criminality is more complex than was once believed.

Genes and violent crime

Research has also examined whether specific genes may matter for violent behavior. An international research team led by researchers at Karolinska Institutet identified two genes, MAOA and CDH13, that may be linked to an increased tendency to commit repeated violent crimes.

The study analyzed the genomes of 895 people in Finland who had been convicted of different types of crime. The crimes ranged from less serious offenses, such as theft and drunk driving, to aggravated assault and lethal violence. The results showed a relationship between repeated violent crime and the gene MAOA. This gene affects the breakdown of the neurotransmitter dopamine in the brain, which may matter for how impulses and aggression are regulated. The gene is sometimes called the warrior gene because of its connection to aggressive behavior.

Among people who had committed repeated violent acts, the researchers also identified the gene CDH13. Earlier research has also linked this gene to behavioral disorders and difficulties with impulse control.

Even if studies can link individual genes to violent behavior, genetic factors are only one part of the explanation. The results cannot be used to predict whether a particular person will commit crime or not. The research suggests that genes interact with factors such as the environment, life experiences, and substance use in the development of aggressive and violent behavior.