Some studies argue that certain genes are a good predictor of future criminality.
The MAOA warrior gene was the first candidate gene to be linked to antisocial behavior, identified in 1993 in a large Dutch family that was notorious for violence. A geneticist called Rod Lea reported that the MAOA-3R mutation was more common in the violent indigenous Maori population of New Zealand than in caucasian males (56% vs 34%). Lea went on to link this gene to a whole host of undesirable traits, such as violence, aggression, risk-taking and gambling/addiction.
ref#1Beaver (2013) conducted research into MAOA-3R in America and found that it increased the likelihood of an individual joining a violent gang.
ref#2Studies have found differences in the frequency distribution of variants of the MAOA gene between ethnic groups: of the participants, 59% of Black men, 54% of Chinese men, 56% of Maori men, and 34% of Caucasian men carried the 3R allele
According to a large meta-analysis in 2014, the 3R allele had a small main effect on aggression and antisocial behavior, even in the absence of other interaction factors
if there was a mutation to the gene that is involved in the process of promoting or inhibiting MAO enzymes, it could affect a person's personality or behaviour and could therefore make them more prone to aggression.
ref#3Scientists say it's the "warrior gene," a controversial name for a genetic variation that research has shown to have an ugly side tied to violence, risk taking and aggression.Found in one-in-three western men, it is literally a shorter, less active version of a gene allele on the X chromosome known as Monoaminine oxidrase A gene.
"In many, many studies it appears implicated in behaviors that look like they're related to physical aggression or some kind of conduct disorder,"
The genetic variant is located on the X chromosome of DNA and because men only have one X chromosome the connections to violence are seen more readily in men. Studies have also linked the variant to gambling, gang membership and weapon use.