A03

• What are the strengths of genetic factors in aggression?

  1. Research support for role of MAOA gene
• What are the limitations of genetic factors in aggression?

  1. Difficult to isolate genetic factors
  2. Problems with measuring aggression
  3. Problems with twin studies
• Strength = research support for role of MAOA gene

  • Brunner et al. (1993) showed that the low-activity variant of the MAOA gene is associated with aggression
  • Mertins et al. (2011) found the converse to be true and that the high-activity variant is associated with less aggressive behaviour
  • They studied participants with the low-activity and high-activity variants in a money-distributing game
  • Found that males with the high-activity variant were more co-operative and made fewer aggressive moves than the low-activity participants
• Limitation = difficult to isolate genetic factors

  • Diathesis-stress model offers a more comprehensive explanation for role of genes in aggression
  • Individuals may possess a gene associated with aggression but behaviour is only expressed if the environmental conditions are favorable
  • Caspi et al. (2002) studied 500 male children and found those with the MAOA-L variant were more likely to grow up to exhibit anti-social behaviour only if they had been maltreated as children
  • Those with the MAOA-H variant who were maltreated and those with the MAO—L variant didn’t display anti-social behaviour
• Limitation = problems with measuring aggression

  • Studies investigating aggression differ massively in terms of the method they use to measure aggression
  • Rhee and Waldman (2002) carried out a meta-analysis of adoption studies investigating the genetic influences of aggression
  • Genetic factors had a greater influence on aggression in studies using self-reports rather than parent or teacher reports
  • Becomes difficult to draw valid conclusions about the role of genetic factors
• Limitation = problems with twin studies

  • Twin studies may lack validity
  • In every pair of twins we assume both individuals share the same environment as each other = equal environments assumption
  • However, DZ twins may not share the same environment to the same extent as MZ twins
  • This assumption may be wrong as one aspect of the environment is the way twins are treated by others - MZ twins are treated very similarly whereas DZ twins are treated in less similar ways
  • This means concordance rates are inflated