genetic factors in aggression

• inherited 


  aggressive behaviour must be inherited through family lines - used twin studies, adoption studies and family studies
• twin studies

  comparing MZ and DZ twins where 1 twin shows aggressive behaviour to see how often other twin also shows aggressive behaviour - establish concordance rate - if aggression genetic concordance rate should be higher in MZ than DZ twins.
• MAOA gene

  responsible for producing protein MAOA regulates metabolism of serotonin - if defective = low levels of serotonin - serotonin has widespread inhibitory effect, low serotonin = difficult to inhibit emotional responses by amygdala = increase in impulsive and aggressive behaviour
• MAOA EVALUATION - Brunner 


  found defective MAOA gene in a Dutch family with a history of male violence (rape and arson) - suggests defective MAOA gene associated with increased risk of aggressive behaviour
• MAOA EVALUATION - Cases

  disabled MAOA gene in mice, influenced serotonin levels and males became highly aggressive - females remained unaffected - restoring gene returned male mice back to normal - MAOA gene can increase aggression when not functioning normally
• MAOA EVALUATION - focused on animals

  not representative of humans - rats physiologically different to humans and so genes may have different effect on aggression - findings can't be extrapolated
• MAOA EVALUATION - ignores evidence of learning through environment

  Bandura - children more likely to be aggressive to Bobo doll when having observed an adult being aggressive towards it - learned to imitate them - suggests not valid to suggest aggression is only biological
• MAOA EVALUATION - biological determinism

  research argues we are somehow pre programmed to be aggressive and have no free will over aggressive behaviour - may be seen as wrong for legal system to find people responsible for aggressive behaviour