In 1993, a group of researchers from the Netherlands and the USA described a genetic defect discovered in one large Dutch family that caused impulsive, violent and hostile behaviour in the males. To these men afflicted, the most seemingly mild stressful situations were met with overly aggressive outbursts which involved shouting, cursing or assaulting an individual they deemed as a threat. In addition, these men have attempted rape, committed arson and exposed themselves in public. The abnormal behaviours exhibited by these men are linked to the gene responsible for the productions of monoamine oxidase-a, an enzyme which destroys neurotransmitters in the brain. This particular family study does seem to suggest that genetics play an important role in antisocial or criminal behaviour highlighted by the violence and aggression portrayed by the individuals.
Further research has been conducted to expand on the impulsive and aggressive behaviour displayed by criminals to determine whether there is a biological or chemical explanation. Serotonin is a chemical in the brain that plays an important role in the personality traits of depression, anxiety, and bipolar disorder. It has also been shown to be involved with brain development. A lack of Serotonin has been found to be associated with impulsive behaviour and emotional aggression in individuals. Dopamine, a transmitter in the brain that is