Genetic Factors in Aggression

Question 1

what percent of heritability accounts for the variance in aggressive behaviour

Answer 1

50% according to twin studies

Question 2

what was Coccaro et al (1997) study

Answer 2

• studied the concordance rates of aggressive behaviour in monozygotic or dizygotic twins
• found concordance rates for physical assault of 50% for MZ and 19% for DZ
• verbal assault were 28% MZ and 7% DZ

Question 3

what do adoption studies show

Answer 3

• similarities between the adopted child and biological parents suggest that environmental influences are operating
• similarities between the adopted child that their adoptive parent suggest that environmental influences are operating

Question 4

what did Waldman (2002) meta- analysis of adoptions show

Answer 4

• genetic influences account for 41% of variance in aggression
• in line with findings from twin studies

Question 5

what does the MAOA gene do

Answer 5

• controls the production of the enzyme MAO-A

Question 6

what does the enzyme MAO-A do

Answer 6

regulates the neurotransmitter serotonin

Question 7

link between MAOA gene and aggression

Answer 7

• MAOA-L results in low activity of the MAO-A enzyme (MAO-A deficiency) which is linked to high levels of aggressive behaviour

Question 8

studies suggesting the link between MAOA and aggression

Answer 8

1. lea and Chambers (2007)
   - warrior gene
   - 56% of new Zealand Maori men have the MAOA-L gene compared to 34% of Caucasian men
   - Maori men are ferocious warriors
2. Brunner et al (1993)
   - Brunner sydrome
   - 28 men for a dutch family with involvement in impulsive aggressive violent crimes
   - had low levels of MAO-A and MAOA-L

Question 9

what is the gene- environment interaction

Answer 9

• MAOA-L gene is only related to adult aggression when combined with early childhood trauma
• Frazzetto et al (2007) found an association between high levels of aggression and MAOA-L gene in men but only in those who had experienced significant trauma in their for 15 years of life

Question 10

strengths of genetic

Answer 10

1. research support
   - Mertins et al (2011)
   - men with high active variant (MAOA-H) were more co-operative and made fewer aggressive moves

Question 11

limitation of genetic factors of aggression

Answer 11

1. complex link
   - disruptions in serotonin levels
2. problems with twin studies
   - lack validity
   - DZ twins do not share the same environment but we assume they do (equal environment assumptions )