Genetic factors in aggression

• Genetic factors in aggression - Twin studies

  Coccaro et al: Studied adult male MZ and DZ twins

  • MZ share 100% of genes - 50% concordance rates + 30% verbal aggression
  • DZ share 50% of genes - 20% Concordance rates + 10% verbal aggression
• Genetic factors in aggression - Adoption studies

  Rhee and Waldman: Meta-analysis of adoptions studies of direct aggression and antisocial behaviour

  Findings - Genetic influences accounted for 40% of the variance in aggression
• Genetic factors in aggression - The MAOA gene

  • MAOA is an enzyme - Mop up neurotransmitters after a nerve impulse has been transmitted - Breaks down neurotransmitter (Especially serotonin)
  • MAOA gene produces the enzyme - Dysfunction leads to abnormal activity affecting serotonin levels in the brain

  Brunner et al: Studied 30 males from a family who are repeatedly involved in aggressive behaviour

  • Had abnormally low level of MAOA and gene
• Genetic factors in aggression - Gene-environment (GxE) interactions

  • Genes are not alone
  • Low MAOA gene activity is related to adult aggression when combined with early traumatic life events

  Frazzetto et al: Found an association with higher levels of antisocial aggression + Low activity MAOA gene variant

  • For those who have experiences direct trauma - First 15 year of life
• Evaluation of genetic factors in aggression - Isolating genetic factors

  • Hard to determine how influential genes are in aggressive behaviour - Hard to separate genetic and environmental factors

  Mcdermott et al:

  • Ppts with low activity MAOA gene behaved aggressively in lab based money game - Only when provoked

  Limitation: Have to highlight importance of considering both genetic and situational factors studying a aggression
• Evaluation of genetic factors in aggression - Measuring aggression

  • Methods to measure aggression vary between studies - Affecting conclusions about genetic influences

  Methods:

  • Self report
  • Parent teacher reports
  • Rhee and Waldman's Meta analysis - Genetic factors had higher influence on aggression with self-report than parent / teacher reports

  Hard to draw valid conclusion

  Limitation: Inconsistencies - Lowered reliability
• Evaluation of genetic factors in aggression - Non-human animal studies

  • Hypothesis of MAOA gene originated from mice

  Godar: Blocking serotonin with fluoxetine - Mice reverted to non-aggressive behaviour

  • Valuable insights into genetic mechanisms underlying aggression
  • Link with MAOA gene and aggressive behaviour - Controlled by serotonin levels

  HOWEVER animals and human diff

  Strength: Support validity for hypothesis - However studies themselves lack application