There is a human gene that could be linked to the programmed predisposition of violent behavior. In 1993, the German scientist Hans Georg Brunner conducted a study of a Dutch family that had 14 male members involved in different types of crimes. Brunner discovered that it is a genetic disease that produces a mild intellectual disability and generates violent and impulsive behavior in the individual from an early age. Men would be the most vulnerable to inherit this condition because it is related to the X chromosome, responsible for producing the enzyme Monoamine Oxidase (MAO) that serves to degrade neurotransmitters such as dopamine, noradrenaline, adrenaline, and serotonin.
When the level of Monoamine Oxidase is low, the brain is saturated with neurochemicals that can alter emotions and inhibitions of behavior, increasing the aggressiveness and impulsivity of the individual. Men possess a single X chromosome and inherit it from the mother. In contrast, women have 2 X chromosomes so it becomes more difficult for the Murder Gene to manifest. The environment where the individual develops also influences the activation of the Warrior Gen, especially if during childhood, or adolescence, has been a victim or witness of violent events.