genetic factors of aggression Flashcards
What are the 4 broad approaches to the study of the influence of genetics and environment on behaviour (such as aggression)
- Twin studies
- Adoption studies
- Gene for aggression
- Gene environment interaction
Explain the rationale for twin studies
MZ twins share all their genes, we assume that any differences between them must be due to their environment. Similarly if both MZ twins are highly aggressive we could assume this is due genetics. This degree of similarity on some measurable trait is called a concordance rate – the presence of the same trait in both members of a pair of twins. Usually we compare concordance rates to DZ twins as they’re only 50% related. Higher concordance rates in MZ twins suggest a heritable component to whatever’s being measured.
What did Coccaro et al. (1997) show in their twin studies
He found that MZ twins had a concordance rate of 50% and DZ twins had 19%. As the concordance rate was higher for MZ twins it demonstrates that genetics do play a good role on aggression due to the fact they have greater genetic similarity than DZ twins
How is Coccaro (1997) study different than other twin studies that have looked at the influence of genetics on aggression?
Most other twin studies have focused on criminal behavior generally and not specifically on aggression therefore its difficult to determine the validity of the study
Explain the rationale for adoption studies
If there is a positive correlation found between aggressive behavior in adopted children and aggressive behavior in their adopted parents an environmental effect is implied. If the correlation is between the adopted child and their biological parents then a genetic effect is implied.
Rhee and Waldman (2002)
a meta analysis and found direction aggression and anti-social behavior. They found genetic influences accounted for 41% of the variance in aggression – the same finding as twin studies
Hutchings and Mednick (1975)
study on 14000 adoptions in Denmark and discovered a significant number of a adopted boys had criminal convictions
Which gene has been implicated in aggression, and what is the mechanism thought to be?
MAOA which is an enzyme regulating the metabolism of monoamines (dopamine, noradrenaline, serotonin)
Low levels of serotonin are associated with high levels of aggression
Which allele of the gene has been associated with aggression?
MAOA gene controls the production of the MAO-A enzyme
Which neurotransmitters does the MAO enzyme metabolise (break down)?
Dopamine, Serotonin, Noradrenaline
Explain the relationship between a dysfunction of the gene that codes for the enzyme, and the levels of each of these transmitters and how this impacts behaviour.
MAOA-L results in low activity of the MAOA enzyme which has been linked to high levels of aggression
Why is MAOA-L referred to a the ‘warrior gene’?
The MAOA-L variant is seen a lot more frequently in populations with a history of warfare with 2/3rds of these populations having low activity versions
How did Brunner et al’s(1993) study implicate the MAOA-L gene variant in aggression?
Studied a Dutch family of which 28 males behaved very aggressively and violently these men were found to have abnormally low levels of MAO-A enzyme and the MAOA-L gene variant. This is socially sensitive because people who have this variant might not be aggressive any cant generalize this to everybody.
How did Stuart’s (2014) study suggest that the MAOA-L variant is implicated in aggression
Suart found that of 97 men convicted of intimate partner violence those with the MAOA-L variant were the most violent perpetrators and caused the worst injuries on their partners
How did Caspi et al. (2000) suggest that there may be a gene x environment interaction with MAOA-L?
Studied 500 male children and found those with the MAOA-L gene are more likely to grow up anti social but only if they were mistreated a children, children with MAOA-H who were also mistreated and those with MAOA-L who had not been mistreated didn’t show antisocial behavior
