Aggression: Genetic factors Flashcards
Twin studies
Lots of twin studies have suggested that heritability (genetic factors) accounts for about ½ of the variance in aggressive behaviour.
Coccaro et al - adult male monozigotic + dizygotic twins. As MZ twins share 100% of their genes but DZ twins share only 50% (on avg), would expect to find greater similarities in aggressive behaviour between MZ if aggression is mostly influenced by genetic factors. This is because both MZ + DZ twins are raised together in the same environment, but MZ have a greater level of genetic similarity than DZs. For aggressive behaviour defined as direct physical assault, researchers found concordance rates of 50% fro MZ + 19% for DZ. Corresponding figures for verbal aggression: MZ - 28% + DZ - 7%.
Adoption studies
Similarities between an adopted child + their bio parents suggest that genetic influences are operating. Similarities with adopted parents suggest that environmental influences are operating.
Rhee + Waldman - meta-analysis of adoption studies of direct agg. + antisocial behaviour (prominent feature is aggressive behaviour). Found - genetic influences accounted for 41% of the variance in aggression, similar to findings found from twin studies.
MAOA gene
Monoamine oxidase A - an enzyme, role to ‘mop up’ neurotransmitters in brain after nerve impulse has been transmitted from one neuron to another. It does this by breaking down the neurotransmitter (serotonin) into constituent chemicals to be recycled/excreted (catabolism). The production of enzyme - determined by MAOA gene.
A dysfunction in the gene may lead to abnormal activity of the MAOA enzyme which then affects levels of serotonin.
One variant of the gene leads to low MAOA activity in areas of brain + has been associated with various forms of aggressive behaviour.
Brunner er al - 28 male members of a Dutch family who were repeatedly involved in impulsively violent aggressive criminal behaviours (rape, attempted murder, physical assault). Men - abnormally low MAOA levels + low activity version of MAOA gene.
Stuart et al - 97 men who had been involved in inflicting intimate partner violence in a batterer treatment programme. Men with low activity MAOA gene - most violent perpetrators of IPV + engaged in highest levels of physical/psychological aggression + inflicted the worst injuries on their partners.
Gene-environment (GxE) interactions
Genes - crucial influences on aggression but don’t function in isolation. It was found that low MAOA gene activity is only related to adult aggression when combined with early traumatic life events.
Frazzetto et al - link between higher levels of antisocial aggression + low activity MAOA gene variant in adult males - only if they had exp. significant trauma (sexual/physical abuse) in the first 15 years of their life. Those who hadn’t didn’t have particularly high levels of aggression as adults, even if they had the low activity MAOA variant.
Strong evidence of a gene-environment interaction (sometimes described as diathesis-stress).
AO3 - Isolating genetic factors
Limitation - Isolating genetic factors - been challenging to establish how influential genes are in aggression.
One reason is difficulty researchers have in separating genetic + environmental factors. A person may have a gene associated with aggression but the behaviour is only expressed if the environmental conditions are favourable.
McDermott et al - participants with low-activity MAOA gene behaved aggressively in a lab-based money-allocation game but only when they were provoked. Otherwise - no more/less aggressive than other participants.
AO3 - Multiple genetic influences
Limitation - Multiple genetic influences - sizes of genetic effects are statistically sig. but are small - means other genes involved in aggression.
Stuart et al - IPV in men was associated with low-activity MAOA gene but also the serotonin transporter gene (5-HTT) which influences serotonin activity. Comb. of genes that was linked to IPV.
Vassos et al - meta-analysis - found no association between any single gene + aggression. Even several genes can’t explain a behaviour as multifaceted as aggression. Hundreds/thousands of genes interact in complex ways to determine aggression casting doubt for any research on singular candidate genes.
AO3 - Measuring aggression
Limitation - Measuring aggression - Methods differ sig. between studies + include self-reports, parent + teacher reports + direct observations.
Rhee + Waldman - genetic factors had a greater influence on aggression in studies using self-reports rather than parent or teacher reports.
If research findings vary depending on how aggression is measured, then it becomes difficult to draw valid conclusions about the role of genetic factors.
