Genetic factors in aggression Flashcards
What 3 methods do psychologists use to disentangle the influences of genetic factors from those of the environment?
- twin studies
- adoptions studies
- importance of MAO-A gene
What have several twin studies suggested?
- that heritability accounts for about 50% of the variance in aggressive behaviour
What would we expect the find from twin studies?
- MZ twins share 100% of their genes but DZs only share 50%
- we would expect to find greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors
What did Coccaro et al study and find?
- studied men who were monozygotic (MZ) and dizygotic twins (DZ)
- aggressive behaviour (defined as direct assault)
researchers found concordances rates of 50% for MZ twins and 19% for DZ - genetic factors account for 50% of variance in aggression
Why do researchers carry out adoption studies to see influence of genetic factors in aggression?
- similarities in aggressive behaviour between an adopted child & their biological parents suggest that genetic influences are operating
- similarities between an adopted child and their adoptive parents suggest that environmental influences are operating
What did Rhee and Waldman find in their meta-analysis of adoption studies?
- meta-analysis of direct aggression & anti-social behaviour
- found that genetic influences accounted for 41% of the variance in aggression
What is the MAOA gene responsible for?
- for controlling the production of an enzyme called MAO-A
What does the enzyme MAO-A regulate?
- the neurotransmitter serotonin
What variant results in low activity of the MAO-A enzyme?
- low activity variant - MAOA-L
- this has been linked to aggressive behaviour
What did Lee and Chambers find about the MAOA-L variant?
- nicknamed MAOA the ‘warrior gene’
- because they found that that MAOA-L variant was possessed by 56% of New Zealand Māori men compared to 34% of Caucasians
Who further cemented the link between aggression and MAOA-L?
- Brunner et al
What did Brunner et al study and find on genes?
- studied 28 men from a large Dutch family who where repeatedly involved in impulsive aggressive violent criminal behaviours e.g. rape, physical assault etc
- found that these men had abnormally low levels of the enzyme MAO-A as well as the MAOA-L variant > sometimes referred to as Brunner syndrome
Why do genes not function in isolation when looking at aggression?
- it appears that the MAOA-L gene activity is only related to adult aggression when combined with early traumatic experiences
What did Frazzetto et al find about genes?
- an association between higher levels of antisocial aggression & the MAOA-L gene variant in men
- this was only the case in those who had experienced significant trauma during the first 15 years of their life e.g. sexual or physical abuse
- those who had not experienced such trauma did not have high levels of aggression even if they possessed the MAOA-L variant
What research is there to support genetic factors in aggression?
- support for the role of the MAOA gene in aggression
- research shows that the MAOA-L gene is associated with greater aggression
- Mertins et al> men with low-activity & high-activity variants of the MAOA genes took part in money distributing game
- men with high activity variant were more co-operative & made fewer aggressive moves than low-activity p’s
-support relationships between MAOA-L gene activity & aggression
