1. The role of genetic factors in aggression
AGGRESSION: Year 13

2. There is lots of research into this..
Huge body of research evidence that suggests that all behaviour including aggression is influenced by genetic factors. They probably don’t work in isolation, but amongst environmental factors as well

3. Genetics Animals Galton
Psychological (as well as physical) characteristics are governed by heredity...
Biological inheritance is more important than learnt characteristic, intellect or talents.
Tendency to vice – (doing bad things) alcoholism and criminality all inherited.
Animals
can be selectively bred to be more or less aggressive (dogs, foxes etc.)
Young et al identified a genetic mutation that breeds fierce mice.

4. Twin Studies
Miles and Carey (1997) did a meta-analysis of 24 twin and adoption studies
They concluded that genetic influence could account for up to 50% in the variance in aggressive anti social behaviour.
You can use this evidence to support the role of genetics in aggression.
You can also use this evidence to contradict the role of genetics
MZ (Identical) Twins
DZ (Non-Identical) Twins
reared together
reared apart
0.72
0.64
0.42
0.34

5. Hutchings (1975) Adoption Studies
Studied 14,000 adoptions in Denmark, and found that a significant number of adopted boys with criminal convictions had biological parents (particularly fathers) with criminal convictions.
However, the highest rates of criminal violence occur when both biological and adoptive parents have a history of violent crime.
You can use this evidence to support the role of genetics in aggression.
You can also use this evidence to contradict the role of genetics

6. Brunner et al (1993)
Examined the role of genetics and neurotransmitters in aggressive behaviour. He specifically examined a mutation on the MAOA gene
Brunner reported on a Dutch family with a genetic abnormality, some of whose members were violent & criminal

7. Method:
Clinical examinations of affected male family members and comparison with normal family members.
Data was collected from analysis of urine samples over 24 hours!

8. Which is involved in serotonin metabolism
All 5 of the affected males had below average IQ.
Only 1 completed primary education.
(All unaffected males attended school and were employed)
There were no specific DYSMORPHIC signs.
All females, including carriers, appeared normal
DNA ANALYSIS:
All affected males showed genetic mutations in the genes producing MONOAMINE OXIDASE A (MAOA)
Which is involved in serotonin metabolism

9. there is supporting evidence
Caspi (2002) found that men with low MAOA gene activity and had been abused in childhood were 4 times more likely to be convicted of a violent crime by the time they were 26

10. After Caspi, Newman (2005) looked at monkeys...
45 unrelated male macaque monkeys raised with or without mothers
Looked at MAOA activity
Concluded that aggressiveness is influenced by MAOA activity, but might be changed by the environment the monkey is brought up in
This supports Caspi’s findings

11. Monoamine oxidase A (MAOA)
Mice that lack this gene also suffer serious anger management problems
Scientists became interested in the gene when it was discovered that angry mice lack it..
Neurotransmitters are the brain’s chemical messengers
High levels of neurotransmitters such as serotonin, noradrenaline, dopamine.

12. Monoamine oxidase A (MAOA)
MAOA-deficient male mice were quick to attack an intruder in a resident intruder test and failed to establish the usual dominant-submissive relationships, which meant that these mice were injured more when confined with other male mice
Female mice with the defective gene behaved normally
A resident intruder test is when a new mouse is introduced into a cage