Genetic factors in aggression

Question 1

what are genetic factors?

Answer 1

genes consist of DNA strands. DNA produces ‘instructions’ for general physical features (eye colour, height) of an organism and also specific physical features (neurotransmitter levels, size of brain structures). these may impact on psychological features (such as intelligence and mental disorders. genes are transmitted from parents to offspring (inherited)

Question 2

what have twin studies suggested?

Answer 2

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

Question 3

what was Coccaro’s twin study?

Answer 3

he studied adult male monozygotic and dizygotic twins
•they found concordance rates of 50% for MZ twins and only 19% for DZ twins
•for verbal aggression, 28% for MZ and 7% for DZ twins

Question 4

what was Rhee and Waldman’s adoption study?

Answer 4

•they carried out a meta-analysis of adoption studies of direct aggression and antisocial behaviour
•they found that genetic influences accounted for 41% of the variance in aggression, consistent with the findings from twin studies

Question 5

what is the MAOA gene?

Answer 5

the gene responsible for the activity of the enzyme monoamine oxidase in the brain. the low-activity variant of the gene is closely associated with aggressive behaviour

Question 6

what does the MAOA enzyme do?

Answer 6

it ‘mops up’ neurotransmitters in the brain (including serotonin) after a nerve impulse has been transmitted
•it breaks the neurotransmitters down into chemicals to be recycled

Question 7

what could dysfunction in the MAOA gene cause?

Answer 7

a dysfunction in the MAOA gene may lead to abnormal activity of the MAOA enzyme which impacts serotonin levels in the brain (may cause low serotonin levels)

Question 8

what is the low MAOA gene nicknamed?

Answer 8

the warrior gene

Question 9

what did Brunner find while researching the MAOA gene?

Answer 9

•he studied 28 male members of a large dutch family who were repeatedly involved in impulsive, violent criminal behaviours such as rape
•they found that these men had abnormally low levels of MAOA gene in their brains caused by low MAOA gene (the warrior gene)

Question 10

what did stuart find while researching the MAOA gene?

Answer 10

he found evidence of low MAOA gene in men who were perpetrators of the worse cases of intimate partner violence

Question 11

how does the low MAOA gene interact with the environment?

Answer 11

•genes have a crucial influence on aggressive behaviour but do not function in isolation
•low MAOA gene activity is only related to adult aggression when combined with early traumatic life events

Question 12

what were Frazzetto’s findings?

Answer 12

•they found an association between higher levels of antisocial aggression and the low-activity MAOA gene in adult males
•but this was only the case in those who had experienced significant trauma (such as sexual/ physical abuse) during the first 15 years of life
•those without trauma were not aggressive as adults even if they possessed the low activity MAOA variant

Question 13

L-MAOA + trauma (under age 15) = aggression

Answer 13

diathesis stress

Question 14

why are men more aggressive than women? (Niehoff)

Answer 14

•the MAOA gene is carried on the X chromosome
•males only have one X chromosome- therefore if they have a dysfunctional MAOA gene (low MAOA) it will be expressed
•females have two X chromosomes and two MAOA genes, a normal MAOA gene would ‘cancel out’ a dysfunctional version of the gene
•this accounts for gender differences in aggression

Question 15

what did Mertins study?

Answer 15

•she studied participants with low-activity and high- activity variants of the MAOA gene in a money distributing game
•participants had to make decisions about whether to contribute money for the good of the group
•the researchers found that males with the high-activity variant were more cooperative and made fewer aggressive moves than the low-activity participants

Question 16

limitation: isolating genetic factors

Answer 16

•it is difficult for researchers to separate genetic and environmental factors
•an individual may possess a gene associated with aggression, but that behaviour is only expressed if environmental conditions are favourable
•eg McDermott found that participants with a low-activity MAOA gene behaved aggressively in a laboratory based money-allocation game, but only when provoked
•when not provoked they were no more or less aggressive than other participants
•means saying aggressive behaviour is due to genes is reductionist and deterministic

Question 17

limitation: multiple generic influences

Answer 17

•a study by Stuart et al. found that intimate partner violence from men was associated not just with the L-MAOA gene but also with the serotonin transporter gene. it was the combination of these that likely caused the violence
•Vassos’ metal analysis could find no evidence of an association between any single gene and aggression
•they calculated that hundreds of thousands of genes interacted in complex ways to determine aggressive behaviour, casting doubt over any search for single candidate genes
•shows that aggression cannot be linked to a single gene and that the genetic explanations cannot be used to identify potentially aggressive individuals

Question 18

limitation: measuring aggression

Answer 18

•methods of measuring aggression differ significantly between studies
•in Rhee and Waldman’s meta-analysis of 51 twin and adoption 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 draw valid conclusions about the role of genetic factors

Question 19

strength: research for the MAOA gene

Answer 19

•Mertins study
•found that males with the high-activity variant were more co-operative and made fewer aggressive moves than the low-activity participants