The role of genetic factors in aggression

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

2. There is lots of research into this..

3. Sapolsky (1997) Genes are the ‘hand behind the scenes’... directing testosterone’s actions...

4. Genes determine how much testosterone or oestrogen is produced and how quickly it circulates around the body. Genes determine the synthesis of testosterone receptors, and how many and how sensitive such receptors are. Testosterone may affect brain function and contribute to aggression but genes regulate how much testosterone is made and how effectively it works.

5. XYY Early research focussed on chromosomal abnormalities – specifically the XYY genotype, as being correlated with aggression. Males with an extra Y (male) chromosome Over represented in prisons XYY also linked with low intelligence BUT a definitive link has not been proved

6. Heritability studies Selectively bred animals Turner (2007) – aggressiveness in pigs Suggests that pig farmers may try to selectively breed non-aggressive pigs and aggressiveness should fall by 5% per year during the early years of selection Evaluation?

7. Monoamine oxidase A (MAOA) 1995 – mice that lack this suffer serious anger management problems The enzyme made by the gene mops up the excess neurotransmitters, so mice who didn’t have the gene had unusually high levels of neurotransmitters such as serotonin, noradrenaline, dopamine

8. Monoamine oxidase A (MAOA) On its own the MAOA gene variant has no effect BUT If males who carry the MAOA gene were abused as children, there is a greatly increased chance of them committing violent crime. Sensitive to social experiences in early development.

9. Monoamine oxidase A (MAOA) Functional outcome depends on social context!

10. Reverse genetics Scientists have managed to clone genetic DNA Mutant mice have been produced that lack a gene for the serotonin receptor These mice have normal behaviour generally, but are twice as aggressive as ‘normal’ mice Bock & Goode, 1996

11. 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 Evaluation?

12. Monoamine oxidase A (MAOA) This gene has been implicated in human aggression (Cases et al., 1995)

13. Moffitt et al (1992) Participants: 1037 children (442 boys, 595 girls) all born in 1972 in Dunedin, New Zealand Length of study: 26 years from birth What did the researchers look at? Whether the participants had high or low levels of MAOA and the upbringing of the children (were they abused?) and anti social behaviour.

14. How did they measure the antisocial behaviour?

15. Findings • What did they find out about men who had the genotype for high MAOA activity? • In all four of the areas above, men who had been maltreated or abused as children were far less likely to show antisocial behaviour as adults • What did the find out about men who didn’t have the genotype for high MAOA activity? • Men who had been maltreated were more likely to show antisocial behaviour as adults. • Maltreated men without the genotype for high MAOA activity only made up about 12% of the group studies – however, they accounted for 44% of the group’s convictions for violent crime.

16. It is important to note that the MAOA gene variant had no effect on its own, but if men who carried the gene that generated low levels of MAOA activity were abused as children then they were over three times more likely to commit violent crime. A gene that generated high levels of MAOA seemed to give ‘trauma resistance’ – people who had been abused in childhood were protected against the potential negative effects.  The gene is found on the X chromosome, and it’s thought that it doesn’t have an effect on girls because the other X chromosome cancels out the effect, as it were. Boys do not have the luxury of two X chromosome so the effects are more noticeable.

17. Brunner et al. (1993) Dutch family – all males have mutant MAOA gene. All borderline retardation Reacted aggressively when angry, fearful or frustrated.

18. New et al (2003) Impulsive aggression (domestic / work based) have genetic component related to seretonergic system. Aggressive patients with personality disorders had a G-allele variant of a serotonin gene HTR1B

19. Adoption Studies • Mednick et al (1984) • 14,000 male adoptees

20. Mednick et al (1984)

21. Evaluation? • Reductionist • Ethics • Extrapolation – animal studies • Research support • Methodological issues • Sample • Operationalisation etc

22. Essay structure AO2 • Critically consider the role of genetic factors in aggressive behaviour. • Hand behind the scenes • XXY • Inheritability • MAOA • Twin studies • Adoption studies