genetic factors in aggression

Question 1

Twin studies show that genetic factors account for 50% of the variance in aggressive behaviour- who investigated this?

Answer 1

Coccaro et al

Question 2

who did Coccaro et al study?

Answer 2

adult male MZ and DZ twins

Question 3

why did Coccaro et al investigate MZ and DZ twins?

Answer 3

• MZ twins share 100% of their genes but DZ only around 50% on average, so we would expect greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors
• this is because both MZ and DZ twins are raised together in the same environment, but MZ twins have a greater degree of genetic similarity than DZs

Question 4

what did Coccaro et al find?

Answer 4

• for direct physical aggression, the researchers found concordance rates of 50% for MZ twins and less than 20% for DZ twins
• for verbal aggression the figures were 28% (MZs) and 7% (DZs)

Question 5

who carried out a meta-analysis of adoption studies and found that genetic influences accounted for 41% of the variance in aggression (in line with findings from twin studies)

Answer 5

Rhee and Waldman

Question 6

what gene is linked to low serotonin?

Answer 6

MAOA

Question 7

explain how the gene for MAOA is linked to low serotonin

Answer 7

• MAOA is an enzyme linked to ‘mopping’ up transmitters in the brain after an impulse has been transmitted from one neurone to another
• it does this by breaking down neurotransmitters, especially serotonin, into constituent chemicals to be recycled or excreted- catabolism
• the synthesis of this enzyme is determined by the MAOA gene
• a dysfunction such as a mutation in the base sequences of this gene may lead to abnormal activity of the MAOA, which will in turn affect the levels of serotonin in the brain, and low levels of serotonin are linked to aggression

Question 8

one variant of the MAOA gene is nicknamed

Answer 8

the warrior gene

Question 9

what does the warrior gene lead to?

Answer 9

low MAOA activity in areas of the brain, and has been associated with various forms of aggressive behvaipur

Question 10

who found that the most violent domestic abusers were found to have the low-activity MAOA gene?

Answer 10

Stuart et al

Question 11

what did Stuart et al do?

Answer 11

• studied approx 100 men who were part of a treatment programme for domestic abusers who had been involved in inflicting a form of aggression called intimate partner violence (IPV)

Question 12

what did Stuart et al find?

Answer 12

• men with the low-activity MAOA gene were found to be the most violent perpetrators of IPV
• they engaged in the highest levels of physical and psychological aggression and inflicted the worst injuries on their partners

Question 13

who found that low MAOA gene activity only related to aggression when combined with early-life events (diathesis-stress)?

Answer 13

Frazzetto et al

Question 14

what did Frazzetto et al discover?

Answer 14

• found an association between higher levels of antisocial aggression and the low-activity MAOA gene variant in adult males- BUT only in those who had experienced significant trauma including sexual or physical abuse during the first 15 years of life
• those who had not experienced childhood trauma did not have particularly high levels of aggression as adults , even if they possessed the low-activity MAOA gene variant
  = STRONG EVIDENCE of gene-environment interaction i.e. diathesis-stress

Question 15

what are the evaluation points for genetic factors in aggression?

Answer 15

• androcentric research
• supporting research e.g. Stuart et al
• one limitation of the MAOA gene explanation is that there are multiple genetic influences on aggression
• findings depend on how aggression is measured

Question 16

explain how one limitation of the MAOA gene explanation is that there are multiple genetic influences on aggression

Answer 16

• the sizes of genetic effects are statistically significant but nevertheless they are actually quite small= probably other genes involved in aggression
• Stuart et al found that IPV in men was associated with not just the low-activity form of the MAOA gene but also with the serotonin transporter gene (5-HTT)- another gene that influences serotonin activity in the brain
• so it was the combination of the the two genes that was most likely linked with IPV
• hundreds of thousands of genes interact in complex ways, casting doubt over any search for single candidate genes= very little predictive value

Question 17

explain how findings depend on how aggression is measured

Answer 17

• methods of measuring aggression differ significantly between studies, and include self-reports, parents and teacher reports and direct observations
• in Rhee and Waldman’s meta-analysis of twin and adoptee studies, genetic factors had a greater influence on aggression in studies using self-reports rather than parent or teacher reports
• if research findings vary depending upon how aggression is measured, then it becomes very difficult to ‘pin down’ the real causes of this behaviour and draw valid conclusions about the role of genetic factors