genetic factors

• Some psychologists believe that genes can be responsible for aggressive behaviours and can be inherited, passed from one generation to another.
• Twin and adoption studies have been used to show the impact of genetics on aggression.
• Caccaro studied aggressive behaviours in MZ twins (share 100% of genetic information) and DZ (share 50%) adult male twins. They found that concordance rates were 50% in MZ twins and 7% in DZ twins.
• McGuffin and Gottesman (1985) found an 87% concordance rate for aggressive and antisocial behaviour MZ twins compared with 72% rate in DZ twins.
• Rhee and Waldman found in their meta-analysis of adoption studies that genetic influences in direct aggression accounted for 41% in line with the twin studies
• The low activity variant of the MAOA (warrior) gene, which is responsible for the activity of the enzyme monoamine oxidase in the brain, is thought to be closely associated with aggressive behaviour.
• Stuart et al (2014) studied 97 men who had been involved with inflicting intimate partner violence (IPV) and were part of a batterer treatment programme. Findings: men with low activity MAOA gene were found to be the most violent perpetrators of IPV.

  • this study has methodological issues.
• Stuart et al's study has socially sensitive research as it deals with domestic violence so caution should be applied in publication as perpetrators may blame genetics on their actions so to say it's out of their control, which would have negative impacts on both victims and the justice system.
• A criticism of research into the role of genetic factors in aggression comes from opposing evidence suggesting that it's a combination of many genes and not specific candidate genes which causes aggression.
• Stuart et al reported that intimate partner violence in men was not just associated with low levels of MAOA but also with the serotonin transporter gene (5-HTT)
• Vassos et al believes that it is the interaction of hundreds of genes which bring about aggression, casting doubt over the action of single genes
• A limitation of twin studies is that it is difficult to separate nature and nurture because MZ twins likely grew up in the same environmental conditions
• Mertins et al (2011) who found that pps with the high-activity variant of the MAOA gene were more cooperative and made fewer aggressive moves in a money distributing game than the low-activity pps
• the MAOA gene is involved in serotonin