Genetic theories of crime try to understand whether certain inherited factors can influence the risk of aggressive or norm-breaking behavior. The topic has long been debated, not least because it is easy to misunderstand as meaning that genes determine a person's future.

Sex chromosomes and early research

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

Some older studies suggested that people with unusual chromosome sets appeared somewhat more often in crime statistics, but research has not shown any simple relationship with violent crime. Instead, the findings point to a far more complex link between chromosomes, aggression, and criminality.

MAOA, CDH13, and violent crime

Research has also examined whether specific genes matter for violent behavior. An international research team led from 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 convicted of different types of crime. The results showed a relationship between repeated violent offenses and MAOA, a gene that affects the breakdown of dopamine in the brain. Among people who had committed repeated violent acts, researchers also identified CDH13, which earlier research has linked to behavioral disorders and difficulties with impulse control.

What the results do not mean

Even if research can connect certain genes to increased vulnerability for violent behavior, the results cannot be used to predict whether a particular person will commit crime. Genes are only one part of the explanation.

Instead, the research suggests that genetic factors interact with the environment, life experiences, and factors such as substance use. It is in that interaction that the risk of aggressive or violent behavior may increase.

Genetics may contribute to an understanding of risk, but it never tells the whole story of an individual.

Sources: Howitt, D. (2002). Forensic & Criminal Psychology. Pearson Education. Karolinska Institutet News, Genes linked to repeated violent crime.