Genetic factors in Aggression

Genetic factors in Aggression

1. Coccaro - Twin studies

   • Studied on of few studies on aggressive behaviour using adult twin pairs found that nearly 50% of the variance in direct aggressive behaviour could be attributed to genetic factors.

2. Hutchings and Mednick - Adoption studies

   • Study over 14000 adoptions in Denmark and found a significant number of adopted boys with criminal convictions had biological parents (particularly fathers) with criminal convictions.

3. Brunner - Role of MAOA

   • Study of Dutch family found that many of its males behaved in a particularly violent and aggressive manner, large proportion had been involved in serious crimes (rape, arson) These men were found to have abnormally low levels of MAOA in their body.

4. Caspi - Gene-environment interaction

   • Linked MAOAs and aggressive behaviour (500 male children). Discovered a variant of the gene associated with high levels of MAOA and a variant associated with low levels. Those with low levels of variant were more likely to grow up to exhibit antisocial behaviour, BUT ONLY IF THEY HAD BEEN MISTREATED.
     • Shows interaction between gene and environment that determines behaviour.

5. Brennan and Mednick - Genetics and Violent crime

   • Adoption studies have shown highest rates of criminal violence in adopted children is when both biological and adoptice parents have history of violent crime - CLEAR INTERACTION BETWEEN ENVIRONMENT AND GENETICS.
     • Series of adoption studies in which the criminal history of an adopted male was compared with criminal history of both his biological and his adoptive fathers, found that genetic influences were significant in cases of property crime but not violent crime.

6. Miles and Carey - A02

   • Meta analysis of 24 twin and adoption studies . Most relied on parental or ptp self report. Results suggested strong genetic influence that could account for as much as 50% of the variance in aggression.
     • Problems with samping.

7. Difficulties of determining the role of genetic factors.

8. Plomin - Problems with assessing aggression A02

   • Found no difference in correlations between Mz and Dz twin pairs, suggesting that individual differences in aggression weren't a product of environmental influences than genetic influences.

9. Walters A02

   • Meta analysis of studies in this area found only a low to moderate correlation between heredity and crime, with better designed and more recently published studies providing less support for the gene-crime hypothesis than more poorly designed and earlier published studies.

10. Young IDA Value of Animal research

    • Claim to have identified a genetic mutation that causes violent behaviour in mice.