Genetic Explanation

• What are Genetic Factors?

  • Genes consist of DNA which decides things such as hair colour, height, size of brain structures etc
  • Genes are inherited from parents to offspring and may impact upon behaviour
• What is MAOA?

  • It is a gene responsible for the activity of the enzyme Monoamine Oxidase in the brain which is an enzyme that breaks down neurotransmitters such as serotonin
  • Low activity variant of gene is closely associated to aggressive behaviour
• What is a concordance rate?

  • A measure of similarity
  • Expressed as a % between two individuals on a given trait
• Twin Studies: Coccaro et al

  • Studied adult male monozygotic and dizygotic twins
  • For direct physical aggression he found a concordance rate of 50% for MZ and 19% for DZ
  • For verbal aggression a concordance rate of 28% for MZ and 7% for DZ
• Adoption Studies: Rhee and Irwin Waldman

  • Similarities in aggressive behaviour between an adopted child and biological parents suggest that genetic influences are operating
  • Similarities between adopted parents means that environmental influences are operating
  • Carried out a meta analysis and found that genetic influences accounted for 41% of variance in aggression
• Warrior Gene:

  • Variant of MAOA gene -> leads to low MAOA activity in the brain and is associated with aggressive behaviour
• Brunner et al:

  • Studied 28 male Dutch members of a family involved in impulsively aggressive and violent criminal behaviours
  • These men had abnormally low levels of MAOA in brain and the low activity variant of MAOA gene
• Limitation - Genetic factors are hard to isolate:

  • Difficult to separate genetic and environmental factors
  • Someone aggressive may only behave that way if the conditions are suitable
  • McDermott et al - Ps with low activity gene behaved aggressively in lab based work but only when provoked
• Limitation - Difficult to have a standardised measurement:

  • The way in which we measure aggression differs significantly between studies and include self report, parent and teacher report, and direct observations
  • In Waldman's meta analysis self reports had higher results compared to parent teacher reports
• Strength - MAOA explanation is support for prosocial behaviour research:

  • Low activity variant - associated with greater aggression so must mean the opposite is also true
  • Mertins et al - found males with high activity variant were more cooperative in lab based tasks
• Strength - Support from animal studies:

  • Genetic deletion techniques allow researchers to remove single genes in mice
  • Godar et al showed MAOA removal makes mice hyper aggressive due to more serotonin
  • When given fluoxetine they revert to non aggressive