Genetic Factors are those that we inherit through our parents, they are used to explain why aggression runs through families. Genetic factors play a role in aggressive behaviour and lies within an individual’s genetic make-up. Psychologists, look at twin studies to try and find evidence on a genetic basis to compare the degree of similarity of aggression between sets of monozygotic (MZ) twins and dizygotic (DZ) twins. A lot of the time, it is found that aggressive behaviour is more highly correlated in MZ twins than DZ twins. An example of this would be when McGuffin and Gottesman found a concordance rate of 87% for aggressive behaviour in MZ twins, compared with 72% for DZ twin pairs. However we cannot just rely on evidence from twin studies because they can be problematic as it is hard to disentangle nature and nurture. Many have suggested that MZ twins are treated more alike and share more similar environments than DZ twins because they act more like 'one' person rather than two separate people. This may affect how alike they are and how likely they are to express aggression.
Researchers have also identified a number of genes that can potentially cause aggression. Although no individual gene for aggression has been identified in humans, a gene responsible for the production of the protein MAOA has been associated with aggressive behaviour. MAOA regulates the metabolism of serotonin in the brain. Low levels of serotonin have been associated with aggression. In 1993, a study of a Dutch family found that many of its male members behaved in a particularly violent manner and most had convicted serious violent crimes. These men were found to have significantly low levels of the MAOA gene and a defect in this gene was later identified by Brunner. However, the role of environmental factors may have affected the findings as the behaviour may have been due to shared