Aggression: Genetic Factors

Aggression: Genetic Factors

1. Twins • Identical twins share all genes. » Non-identical twins share 50% of genes. • Researchers compare concordance rate for aggression between sets of twins. » If identical twins are more alike in terms of aggressive behaviour it should be due to genes as identical twins are more genetically alike. • Coccaro et al – nearly 50% of variance in direct aggressive behaviours in adult twin pairs could be attributed to genetic factors.

   • AO2: Supported by Miles and Carey • Meta-analysis of 24 twin studies – made up of observations and use of parental and self-reports. » Genetic factors explained up to 50% of variance in aggression.
     • AO3: • Methodological issues. • Self-report techniques can make studies less valid as may be demand characteristics. » Ppts conform to experimenter’s expectations. • Social desirability bias could also be a problem. » Ppts will try to look better and be more desirable. • One way of dealing with this is deception, although this can be considered unethical.

2. Adoption • If positive correlation found between aggressive behaviour in adoptive children and their biological parents – genetic effect implied. • If positive correlation found between aggressive behaviour in adoptee and rearing family – environmental effect implied.

   • AO2: Supported by review of over 14000 adoptions in Denmark. • Significant positive correlation between number of criminal violence convictions among biological parents and their adoptive sons. • Suggests a genetic link to violence.
     • AO3: • Cultural Issues • Set in a western, individualistic society so cannot be generalised to non-western, collectivist cultures. • Different religions and different sub cultures have different values. » Non-western cultures may be more accepting of certain behaviours.

3. Genetic Link • Gene responsible for producing Monoamine Oxidase A (MAOA) had been associated with aggressive behaviour. » MAOA regulates metabolism of serotonin which inhibits neural firing. » Low levels of serotonin are associated with impulsive and aggressive behaviours.

   • AO2: Supported by Brunner et al (1993). • Dutch family in 1980s – many male members behaved particularly aggressively. » Large proportion involved in serious crimes e.g. rape and arson. • Found to have abnormally low levels of MAOA – a defect in the gene was later identified.
     • AO3: • Real world application. • Questions arise about treatment of aggressive behaviours if people are predisposed towards these behaviours and violent crimes.

4. Gene-Environment • Caspi et al – link MAOA to aggressive behaviour. • 500 male children with variants of the gene associated with high or low levels of MAOA. » Low levels of MAOA and maltreated as children = significantly more likely to exhibit anti-social behaviours. » High levels and maltreated and low levels and not maltreated did not display anti-social behaviours. • Suggests interaction between genes and environment.

   • AO2: Research that questions the link between genes and aggressive behaviours – Walters (1992) meta-analysis. • Found low to moderate correlation between heredity and crime. » Other factors could have an influence on crime like age and education level.
     • AO3: • Theory is deterministic. » Suggests that levels of MAOA determine if you will be aggressive and display impulsive behaviours or not. • Does not consider free will of those who choose to be aggressive even with high levels of MAOA or situational aggression, regardless of gene-environment interaction.