Genetic factors in aggression

Question 1

What 3 methods do psychologists use to disentangle the influences of genetic factors from those of the environment?

Answer 1

• twin studies
• adoptions studies
• importance of MAO-A gene

Question 2

What have several twin studies suggested?

Answer 2

• that heritability accounts for about 50% of the variance in aggressive behaviour

Question 3

What did Coccaro et al find?

Answer 3

• 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

Question 4

What did Rhee and Waldman find in their meta-analysis of adoption studies?

Answer 4

• 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

Question 5

What is the MAOA gene responsible for?

Answer 5

• for controlling the production of an enzyme called MAO-A

Question 6

What does the enzyme MAO-A regulate?

Answer 6

• the neurotransmitter serotonin

Question 7

What variant results in low activity of the MAO-A enzyme?

Answer 7

• low activity variant - MAOA-L
• this has been linked to aggressive behaviour

Question 8

What did Lee and Chambers find about the MAOA-L variant?

Answer 8

• 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

Question 9

Who further cemented the link between aggression and MAOA-L?

Answer 9

• Brunner et al

Question 10

What did Brunner et al study and find on genes?

Answer 10

• 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

Question 11

Why do genes not function in isolation when looking at aggression?

Answer 11

• it appears that the MAOA-L gene activity is only related to adult aggression when combined with early traumatic experiences

Question 12

What did Frazzetto et al find about genes?

Answer 12

• 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

Question 13

What research is there to support genetic factors in aggression?

Answer 13

• 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

Question 14

What is a counterpoint to research supporting genetic factors?

Answer 14

• 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

Question 15

What is a limitation of genetic factors in aggression?

Answer 15

• 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

Question 16

What is another limitation of the genetic explanation to do with twin studies?

Answer 16

• 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