genetic factors

Question 1

what are genetic factors in aggression?

Answer 1

genetic explanations of aggression assume that aggressive behaviour is the result of inherited characteristics

Question 2

3 genetic factors in aggression:

Answer 2

• MAOA gene
• adoption studies
• twin studies

Question 3

what is the MAOA gene?

Answer 3

responsible for activity of enzyme in the brain, lower the enzyme the higher the aggressive behaviour

Question 4

what is the role of the MAOA gene in aggression?

Answer 4

• humans with the MAOA-L gene have a lack of MAOA enzyme
• without this enzyme; serotonin, noradrenaline and dopamine may be affected
• if adrenaline isn’t metabolised, we end up with too much, which leads to overreaction to external stimulus and perceived threats, that don’t exist
• lower enzyme = increased aggression

Question 5

who did research into the Dutch family MAOA?

Answer 5

Brunner

Question 6

outline Brunner’s Dutch family research

Answer 6

• Brunner provided evidence for the link between decreased MAOA levels and aggression
• his study of a Dutch family found that many of its male members behaved violent and aggressively, and a large portion had been involved in serious crimes of violence (arson, rape)
• these men were found to have abnormally low levels of MAOA gene in their nervous system, and a defect in this gene was later identified

Question 7

who researched MAOA in mice?

Answer 7

Godar

Question 8

outline Godar’s findings

Answer 8

• MAOA removal in mice showed increased aggression and lower levels of serotonin
• they were given fluoxetine to raise serotonin levels, and behaviour returned to normal

Question 9

who researched interaction of MAOA gene and abusive childhood?

Answer 9

Caspi

Question 10

outline Caspi’s findings

Answer 10

• found that if boys with the MAOA gene suffered abuse in their childhood, they were 3x more likely to be aggressive when they reached adulthood
• boys with MAOA gene are more aggressive

Question 11

what do adoption studies show?

Answer 11

similarity between adopted child and biological parents shows nature
similarity between adopted child and adopted parents shows environmental influencing genes

Question 12

who conducted a meta-analysis of adoption studies and aggression

Answer 12

Rhee and Waldman

Question 13

outline Rhee and Waldman’s findings

Answer 13

meta analysis of twin and adoption studies showed that genetic factors account for 41% of variance in aggression

Question 14

who researched Denmark adoptions?

Answer 14

Hutchins et al.

Question 15

outline Hutchin’s research

Answer 15

• conducted a study of over 14,000 adoptions in Denmark
• found that a significant number of adopted boys with criminal convictions had biological parents (particularly fathers) with criminal convictions
• shows a link between genetics influencing aggression

Question 16

what do twin studies show?

Answer 16

concordance rates of genetic basis’ of aggression

Question 17

who conducted the main research on twin studies in aggression?

Answer 17

Coccaro

Question 18

outline Coccaro’s research

Answer 18

• compared MZ twins to DZ twins
• twins were examined for the concordance of criminal behaviour for both twin pairs
• MZ twins (100% genes) = 50% concordance rate
• DZ twins (50% genes) = 19% concordance rate

Question 19

what does Coccaro’s research show?

Answer 19

• strongly suggests a strong genetic basis for aggression
• however, MZ twin concordance rate wasn’t 100%, suggesting other factors play a role in aggression

Question 20

who researched Danish twins?

Answer 20

Christiansen

Question 21

outline Christiansen’s research

Answer 21

• used old Danish police records
• found that levels of criminality showed a stronger correlation between MZ twins than between DZ twins

Question 22

evaluation: strong link between MAOA activity levels and concentrations of serotonin

Answer 22

ID: there is also evidence supporting the strong link between MAOA activity levels and concentrations of serotonin
Q: this has been based upon animal studies where researchers are able to prevent the expression of the gene coding for the MAOA enzyme, thus
allowing the researchers to study its effects in isolation.
EV: for example, Godar found that by removing the MAOA gene in mice, they showed increased aggression and also lower levels of serotonin, demonstrating the relationship between genes and neurotransmitters. when the mice were given fluoxetine to raise their serotonin levels, their behaviour returned to normal.
AN: therefore, this suggests that the link between MAOA and aggression is valid because correlations in both directions (increasing and decreasing MAOA levels) are supported by research evidence.

Question 23

evaluation MAOA: difficulties determining the role of genetic factors

Answer 23

ID: difficulties determining the role of genetic factors
Q: the connection between one gene and aggression is not straightforward, especially when looking at a behaviour as complex as aggression
EV: for example, more than one gene contributes to a given behaviour. New et al. found that acts of impulsive aggression, such as domestic violence, have a genetic link to the serotonergic system, suggesting that many genes may be involved in aggression
as well as genetic, there are several non genetic factors and it is difficult to isolate to genetics alone.
AN: therefore, we cannot establish a valid cause and effect relationship as It is unlikely that the MAOA gene is solely responsible for aggression and, in fact, research trying to establish which other genes may be involved in aggression is ongoing

Question 24

evaluation: twin studies may lack validity

Answer 24

ID: twin studies may lack internal validity
Q: if genetic factors alone were responsible for aggression then concordance for MZ twins should always show a 100% concordance rate which has never been the case
EV: for example, in Coccaro’s twin study about criminal behaviour, he found that MZ twins had a 50% concordance rate and DZ twins had a 19% concordance rate.
AN: although this provides a genetic basis for aggression, it cannot be based entirely on genetics as MZ twins didn’t have a 100% concordance rate, suggesting there are other factors involved in aggression
ELAB: furthermore, several studies, such as Caspi’s childhood abuse study, demonstrate that environmental factors interact with the MAOA gene to increase the likelihood of aggression, supporting the argument that aggression isn’t entirely genetic