GENETIC FACTORS

• What do twin studies show in relation to aggression?

  Coccaro et al studies adult male MZ and DZ twins. Direct physical aggression the concordance rates were 50% for MZ and 19% DZ. Verbal aggression was 28% for MZ and 7% for DZ. Shows genetic factors account for 50% of variance in aggressive behaviours
• What do adoption studies show in relation to aggression?

  Rhee and Waldman conducted a meta analysis. Found genetic influences accounted for 41% of variance. There were similarities with both the biological and the adopted parents
• What is MAOA

  an enzyme that ‘mops up’ neurotransmitters after a nerve impulse has been transmitted between neuron's. Breaks down neurotransmitters into chemicals to be recycled or excreted. Production of the enzyme is determined by the MAOA gene
• how is aggression impacted by MAOA gene?

  if a dysfunction in the operation it may lead to abnormal activity of the MAOA enzyme which affects levels of serotonin, therefore aggression
• what is a variant of the MAOA gene?

  The Warrior Gene, leads to low MAOA activity in the brain, associated with aggressive behaviour
• Study of the warrior gene

  Bruner et al, studies 28 male members of a Dutch family repeatedly involved in impulsively aggressive violent criminal behaviours. They had both abnormally low levels of MAOA in their brains and the low activity version of the MAOA gene
• MAOA gene and violent abusers

  Stuart et al studied 97 men from a treatment programme for domestic abusers who had inflicted intimate partner violence. Men with low activity MAOA gene were the most violent perpetrators of IPV, they engaged in the greatest psychological and physical aggression and inflicted worse injuries on partners
• what did Frazzetto et al find?

  an association between antisocial aggression and the low activity MAOA gene variant in adult males but only in those who had experiences significant trauma (sexual or physical abuse) during the first 15 years of their life. Those who hadn't were not especially aggressive even if they had the variant gene. Diathesis Stress
• Evaluation point 1

  LIMITATION - genetic factors are difficult to isolate from the environment. Study showed participants with low activity MAOA gene behaved aggressively in a lab based task but only when provoked. Difficult to establish how influential our genes are
• Evaluation point 2

  LIMITATION measuring aggression differs between research, some include self reports or observations and aggression is operationalised differently. In Rhee and Waldman’s meta analysis, genetic factors had a greater influence when using self reports rather than parent or teacher. difficult to pin down the causes, decreased the validity
• Evaluation point 3

  STRENGTH support from animal studies. genetic deletion techniques allow researchers to knockout single genes in mice, experimental manipulation that lets them observe effects on aggression. MAOA knockout mice have increased serotonin and are hyper aggressive, when serotonin is blocked by the drug Fluoxetine the mice return to non aggression. Show MAOA must normally have some function in relation to serotonin, keeping it at a normal level
• Evaluation point 4


  LIMITATION multiple genetic influences

  the sizes of genetic effects are statistically significant but actually quite small. Stuart et al found that Intimate partner violence in men was associated with serotonin transporter gene, combination of this and MAOA was most closely linked with IPV. Hundreds thousands of genes interact in different ways, casting doubt over search for single candidate genes