Genetic Factors in Aggression

(AO1) MAOA-L 'warrior gene':

• monoamine oxidase A gene regulates enzyme monoamine oxidase A.
• breaks down neurotransmitters like serotonin and dopamine (associated with mood).
• build-up of serotonin can lead to people responding to stressful situations more aggressively.
• MAOA enzyme removes excess amounts of the neurotransmitters hence reducing aggression.

(AO2)

• Cases et al (1995) - studied genetically engineered mice which lacked MAOA. Mice had altered serotonin levels and showed enhanced aggression. (Supporting)
• Brunner (1993) - defective MAOA gene in Dutch family with a history of male violence. Acted more aggressively when fearful, angry or frustrated. Found that they had abnormal levels of serotonin from the defective MAOA gene ∴ acted with increased aggression. IDA: shared environment ∴ SLT that aggression was imitated can be brought in.
• Moffitt (1992) - 4 groups, both MAOA-L and H, and abuse/ non when children. 9x more likely to show aggressive behaviour if suffered abuse + MAOA-L. Conclude that environmental factors can influence aggression. IDA: method to measure aggression could be flawed or bias that influence the results in some way ∴ could lack internal validity.