Genetic factors in aggression

Question 1

What have twin studies suggested about aggression?

Answer 1

• twin studies suggest that genetic factors account for about 50% of the variance in aggressive behaviour
• Emil Coccaro studied men who were either monozygotic or dizygotic twins. If genetic factors played a part in aggression, we would expect the most similiarities in MZ twins. The researchers found concordance rates of 50% for MZ twins and 19% for DZ twins. For verbal aggression it was 28% for MZ and 7% for DZ

Question 2

What have adoption studies said about genetic factors

Answer 2

• Similarities between adopted children and biological parents suggest that genetic influences are at play whereas similarities between adopted children and adoptive parents suggest that environmental influences are operating
• Rhee and Waldam (2002) carried out a meta - analysis of adoptive studies of direct aggression and antisocial behaviour. They found that genetic influences accounted for 41% of the variance in aggression, similar to the twin studies

Question 3

What is the MAOA gene?

Answer 3

• The MAOA gene controls the production of the enzyme called monoamine oxidase A
  The gene is MAOA and the enzyme is MAO-A.
• MAO-A regulates the neurotransmitter serotonin
• Genes come in different variants(high and low)
• The low activity variant of the gene (MAOA-L) and results in low activity of the MAO-A enzyme and therefore lower regulation of serotonin, this has been linked to high levels of aggression

Question 4

What is the research into the MAOA gene

Answer 4

• MAOA gene has been nicknamed the warrior gene due to Rod Lea and Geoff Chambers who showed that the MAOA - L variant was possessed by 56% of New Zealand Maori men compared to 34% of caucasians. Historically, the Maori people have a reputation of being ferocious warriors
• The link between the MAOA -L and aggression has further cemented by Han Brunner et al who studied 28 men from a large Dutch family who were involved in impulsively aggressive violent behaviour such as rape, murder and assault. These men had abnormally low levels of the enzyme MAO-A enzyme and the MAOA-L gene variant which is sometimes referred to as Brunners syndrome

Question 5

What are gene -environment (GxE) interactions

Answer 5

• It become evident that the MAOA - L gene is only related to adult aggression when combined with early traumatic life expierences
• Giovanni Frazzetto found an association between higher levels of antisocial aggression and the MAOA-L gene in men. But this was only the case with those who had expierenced significant trauma during the first 15 years of life. This is strong evidence of a gene - environment interaction

Question 6

What is a strength of genetic aggression

Answer 6

• One strength is that there is research support for the role of the MAOA gene in aggression
• Mertins et al found that the converse was also true. Men with high activity and low activity variants of the MAOA gene took part in an money distributing game. Men with the high activity variant (MAOA-H) were move co - operative and made fewer aggressive moves

Counterpoint: The study by Mertins et al also showed that non genetic factors were also crucial. They found that even participants with low activity variant behaved co-operatively rather than aggressively when they were made aware that others were behaving cooperatively and giving away money. This shows that environmental influences such as social norms play a part in aggressive behaviour

Question 7

What is a limitation of genetic factors of aggression (L)

Answer 7

• One limitation of the MAOA - serotonin - aggression link is that the precise mechanism is unclear
• The researcher Virkkunen linked aggression with low levels of serotonin with aggression, however having the MAOA-L gene and low activity of MAOA means that there is low regulation of serotonin and more serotonin for synaptic transmission
• This shows there is not a clear link between MAOA - serotonin - aggression and the relationship is not understood

Question 8

What is another limitation of genetic explanations (T)

Answer 8

• Another limitation of genetic explanations is that twin studies may lack validity
• In every pair of twins, they share the same environment. however, DZ twins may not as they do not look identical
• This shows that the equal environmental assumption may be wrong and therefore concordance rates are inflated and may not be accurate