Genetic explanations for Aggression

Genetic explanations for Aggression

1. Family studies

   • Inheritance. Often hard to separate genes from environment. Twin Studies - Coccaro et al. (1997) - physical assault- 50% MZ vs. 19% DZ, verbal aggression- 28% MZ vs. 7% DZ. Adoption Studies - Rhee & Waldman (2002) - meta-analysis of adoption studies - are children more like biological family (genes) or adopted family (environment)? For direct aggression & antisocial behaviour- 41% of aggression is accounted for by genes

2. Evaluation

   • Unlikely to be one gene (MAOA). In Stuart et al., 5-HTT also linked. It is a complex issue. Vassos et al. (2014) suggests 100s or 1000s of genes could interact - pointless to look at single genes. Measuring (operationalising) aggression- meta-analysis - self report, teacher/parent obs, direct obs. Rhee & Waldman - self report found higher influence. Validity questioned.
   • Further support for MAOA gene - Merton et al. (2011) - those with overactive MAOA showed more pro-social behaviour in a money giving game. Gender bias - a lot of the research is on a male only population (Brunner, Stuart, Frazzetto)

3. Genes

   • Gene-environment interaction - genes alone is a too simplistic (deterministic) explanation. Low MAOA activity only linked to aggression when linked with traumatic childhood. Frazzetto et al. (2007) - low MAOA activity + trauma before 15yo (sexual/physical abuse) = Aggression. Low MAOA + no trauma = little aggression Diathesis-stress model
   • MAOA (warrior) gene - monoamine oxidase A - linked to neurotransmitter (esp. Serotonin) breakdown and production. Affects serotonin levels. Brunner et al. (1993) - Dutch family - 28 males involved in impulsive aggressive behaviour (assault, rape, attempted murder). All found to have abnormally low levels of MAOA and low activity in MAOA gene. Stuart et al. (2014) - 97 men - intimate partner violence (IPV) - most violence and highest levels of physical & psychological aggression, worst injuries = lowest MAOA activity.