Genetic Factors in Aggression

Genetic Factors in Aggression

1. 2. MAOA gene

   • This gene controls MAOA, which regulates the metabolism of serotonin. The MAOA-I variant decreases serotonin, thereby increasing aggression.
     • Brunner et al - case study of Dutch family in which many of the male members had been involved in aggressive behaviour and crime. These males had the MAOA-I variant.
       • Family shared the same environment so environmental factors cannot be ignored.
       • Very small sample size, not generalisable.

2. 1. Twin studies

   • Researchers compare the degree of similarity for a particular trait between MZ and DZ twins. MZ twins share 100% of their genetic material so if MZ twins are more alike in terms of aggression, it is likely that it is due to genetics rather than environmental factors.
     • Caccaro et al - found concordance rate for aggression was nearly50% higher in MZ adult twins that adult DZ twins.
       • If genes were the only causal factor, results should be 100% so other factors must be involved.

3. 3. Combination of genetic and environmental factors

   • If genes were the only causal factor, then concordance rates between MZ twins should be 100%. Therefore other factors must also be in play.
     • Caspi et al - studied MAOA and aggression levels in 539 boys. Low levels of MAOA = more likely to grow up aggressive, but only if they had been maltreated as a child.
       • Gene-environment interaction = plausible explanation, free will plays a part.