Genetic factors in aggression

  • Genetic factors in aggression:
  • AO1:
  • Twin studies show genetic factors account for about 50% of variance in aggressive behaviour. 
  • Coccaro et al studied adult male monozygotic (MZ) and dizygotic (DZ) twins. he found that, for direct physical aggression, concordance rates of 50% for MZ twins and 19% for DZ's. For verbal aggression the figures were 28% for MZ and 7% DZ twins. 
  • Adoption studies show genetic factors account for about 41% of variance in aggressive behaviour:
  • Similarities in aggressive behaviour between an adoptedd child and biological parents suggest genetic influences are operating; but similarities with adopted parents suggest environmental factors. Rhee and Waldman's meta-analysis of adoption studies found that genetic influences accounted for 41% of the variance in aggression. 
  • MAOA is linked to low serotonin:
  • Monoamine Oxidise A (MAOA) is an enzyme - it 'mops up' neurotransmitters after a nerve impulse has been transmitted between neurons. It breaks down the neurotransmitter (eg. serotonin) into constituent chemicals to be recycled or excreted (Catabolism). Productions 9of this enzyme is determined by the MAOA gene - a dysfunction in the operation of this may klead to abnormal activity of the MAOA enzyme, which affects levels if serotonin (low levels are linked to aggression).
  • The 'warrior gene' is a variant of the MAOA gene that leads to low MOAO activity in the brain and is associated with aggressive behaviour. Brunner et al studied 28 male members of a Dutch family repeatedly involved in impulsively aggressive violent criminal behaviours (eg. ****, attempted murder, assault). These men had both abnormally low levels of MAOA in thier brains and the low-activity version of the MAOA gene. 
  • The most violent domestic abusers had the low-activity MAOA gene:
  • Stuart et al studied 97 men from a treatments progremma for domestic abusers, who had inflicted a form of aggression called intimate


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