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 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 have several twin studies suggested?
- that heritability accounts for about 50% of the variance in aggressive behaviour
What did Coccaro et al find?
- studied men who were either monozygotic (MZ) and dizygotic twins (DZ)
- researchers found concordances rates of 50% for MZ twins and 19% for DZ in terms of physical acts of aggression
- genetic factors basis for 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
- similar to twin studies they 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 men from 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
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?
- takes an interactionist approach
- found that low MAOA-L levels only resulted in increased aggression when accompanied by significant traumatic events 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
> supports diathesis stress model
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> found that men with high activity variant were more co-operative & made fewer aggressive moves in a money distributing game than low-activity p’s
- support positive correlation between MAOA gene activity & aggression
What is a counterpoint to research supporting genetic factors?
- study by Mertins et al also showed that non-genetic factors are crucial
- found that even p’s with the low-activity MAOA variant behaved cooperatively rather than aggressively when they were made aware that others in study were behaving cooperatively
- knowledge of social norm partly determined how aggressive or cooperative MAOA-L p’s were > genes influence by environmental factors
What is a limitation of genetic factors in aggression?
- precise mechanism of MAOA-serotonin-aggression link is unclear
- previously, research linked aggression with low levels of serotonin e.g. Berman
- But the MAOA-L gene causes low-activity of the MAO-A enzyme which in turn should lead to higher serotonin
- thus it may be more accurate to say that people with the MAOA-L variant > their serotonin levels are disrupted
- relationship not fully understood
What is another limitation of the genetic explanation to do with twin studies?
- twin studies may lack validity
- In every pair of twins, both individuals share the same environment as eachother
- however, DZ twins may not share their environment to the same extent that MZ twins share theirs> researchers assume they do & this is called equal environments assumption
- the assumption may be wrong because twins may be treated differently e.g. parents praise MZ twins equally for being aggressive > DZ treated in less similar ways
= concordance rates inflated
