Genetic Factors
Cards (7)
- Twin StudiesCoccaro et al studied adult male twins:
- For direct physical assault - 50% MZ, 19% DZ
- For verbal aggression - 28% MZ, 7% DZ
- Adoption StudiesHutchings and Mednick
- Studied over 14,000 adopted males in Denmark
- Found biological parents (mostly father) had a greater influence on criminality
- The MAOA GeneA gene responsible for producing an enzyme that has been associated with aggressive behaviour. It regulates the metabolism of serotonin in the brain and low levels are linked with high aggression
- Brunner et al - studied 28 males of aggressive criminal Dutch family and found they had abnormally low levels of MAOA
- Lea and Chambers - MAOA-L is much more frequent in populations with a history of warfare
- Gene-Environment InteractionsResearchers discovered a variant of the gene associated with high levels of MAOA (MAOA-H) and a variant associated with low levels (MAOA-L)
- Caspi et al - found boys with the MAOA-L variant were more likely to exhibit anti-social behaviour only if they were mistreated as children.
- Boys with MAOA-H who were maltreated and boys with MAOA-L who weren't maltreated did not display anti-social behaviour
- Eval : StrengthMiles and Carey conducted a meta-analysis combining results of 24 twin and adoption studies, finding that aggressive anti-social behaviour was largely a product of genetic contributions. This provides the genetic explanation of aggression with high reliability.
- Eval : WeaknessThe genetic explanation suffers from biological reductionism as it says aggression is down to genetic influences alone, but Coccaro et al's study shows this is not the case as concordance rated form MZ twins were only 50%, not 100%.
- Eval : WeaknessThe genetic explanation minimises the role of nurture, like in Caspi et al's research where boys were only aggressive if they had the MAOA-L gene and were maltreated, suggesting that a more interactionist approach may be appropriate to consider both nature and nurture.