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This lesson examines the evidence for a genetic basis of aggression and evaluates evolutionary explanations that view aggression as an adaptive behaviour shaped by natural selection. We consider twin studies, the role of the MAOA gene, gene-environment interactions, and evolutionary theories of aggression related to sexual jealousy and mate retention.
Key Definition: Evolutionary explanations propose that aggression evolved because it conferred survival and reproductive advantages on our ancestors. Genes associated with aggression were passed on because aggressive individuals were more successful at competing for resources and mates.
Twin studies compare concordance rates for aggression between monozygotic (MZ) twins (who share 100% of their DNA) and dizygotic (DZ) twins (who share approximately 50%). If aggression has a genetic component, MZ twins should show higher concordance rates than DZ twins.
Miles and Carey (1997) conducted a meta-analysis of 24 twin and adoption studies examining genetic and environmental contributions to aggression. Their key findings were:
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