genetic explanations of aggression

• Genes influence aggressive behaviour by influencing processes in the brain
• Aggression is a complex behaviour so is controlled by many genes.
• Genes influence our level of aggression and different gene alleles make people behave more or less aggressively.
• The MAOA gene controls aggression. There are two alleles of the MAOA gene, a long one, and a short one. The MAOA gene produces a chemical that controls the levels of neurotransmitters available at the synapse.
• The short MAOA gene tends to make people more aggressive and is worse at breaking down neurotransmitters like serotonin. The long MAOA allele tends to make people less aggressive.
• Support for genetic explanation. Christiansen 1977 investigated concordance rates for criminal behaviour in a sample of MZ and DZ twins and found concordance rates of 55% for MZ twins and 22% for DZ twins. This is positive as it suggests that genetics play a role in influencing the likelihood of aggressive behaviour. However, since the concordance rate for MZ twins was not 100% it can be concluded criminal behaviour is a combination of biological and environmental factors.
• Support for genetic explanation. Hutchings & Mednick 1975 conducted an adoption study comparing adopted children who displayed criminal behaviour to a control group who didn’t display criminal behaviour and found those who displayed criminal behaviour were significantly more likely to have biological parents who also displayed criminal behaviour. This is positive as it suggests that genetics play a role in influencing the likelihood of aggressive behaviour. However, adoption studies assume biological parents can pass on genes but can’t influence the child’s environment.
• Support for the role of the MAOA gene. Brunner et al 1993 conducted DNA analysis on 5 men from the same family and found all of the men had a mutation of the MAOA gene. This is positive as it suggests that the MAOA gene has a role in producing aggressive behaviour.
• Genetic explanation ignores environmental factors which may contribute to aggression. Caspi et al observed 500 male children from birth to adulthood and found children with the short MAOA allele were more likely to become hyper-aggressive but this depended on the child’s environment; only those who were maltreated by their family became aggressive. This is problematic because the genetic explanation is not a comprehensive explanation for aggression.