The role of genetic factors in aggression

The role of genetic factors in aggressionAGGRESSION: Year 13

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 dont work in isolation, but amongst environmental factors as well2Sapolsky (1997)Genes are the hand behind the scenes... directing testosterones actions...

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.3Genes 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.

XYYEarly research focussed on chromosomal abnormalities specifically the XYY genotype, as being correlated with aggression.Males with an extra Y (male) chromosomeOver represented in prisonsXYY also linked with low intelligenceBUT a definitive link has not been provedHeritability studiesSelectively bred animalsTurner (2007) aggressiveness in pigsSuggests that pig farmers may try to selectively breed non-aggressive pigs and aggressiveness should fall by 5% per year during the early years of selectionEvaluation?

Usually done on animalsAggressiveness in pigs is a moderately heritable trait and aggressive characteristics in pigs can be passed down from parent to offspringWill fall if selection pressure in placed on aggressiveness6Monoamine 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 didnt have the gene had unusually high levels of neurotransmitters such as serotonin, noradrenaline, dopamine

Scientists became interested in the gene when it was discovered that angry mice lack it..Neurotransmitters are the brains chemical messengers High levels of neurotransmitters such as serotonin, noradrenaline, dopamine.7Monoamine oxidase A (MAOA)On its own the MAOA gene variant has no effectBUTIf 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.Monoamine oxidase A (MAOA)Functional outcome depends on social context!

Reverse geneticsScientists have managed to clone genetic DNAMutant mice have been produced that lack a gene for the serotonin receptorThese mice have normal behaviour generally, but are twice as aggressive as normal miceBock & Goode, 1996

Also, male mice who are reared alone are more likely to attack other male mice than those reared with others. It is suggested that this shows that aggression is a natural biological tendency since they could not have learned the behaviour, having been reared in isolation. The other mice, reared with their parents, had been shown when it was necessary to be aggressive and when it wasnt (Bock & Goode, 1996)10Monoamine 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 miceEvaluation?

Female mice with the defective gene behaved normallyA resident intruder test is when a new mouse is introduced into a cage11Monoamine oxidase A (MAOA)This gene has been implicated in human aggression (Cases et al., 1995)

Members of a Dutch family whose men suffered from excessive bouts of aggression carried a rare MAOA gene mutation12Moffitt et al (1992)Participants: 1037 children (442 boys, 595 girls) all born in 1972 in Dunedin, New ZealandLength of study: 26 years from birthWhat 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.

How did they measure the antisocial behaviour? FindingsWhat 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 adultsWhat did the find out about men who didnt 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 groups convictions for violent crime.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 its thought that it doesnt 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.

Brunner et al. (1993)Dutch family all males have mutant MAOA gene.All borderline retardationReacted aggressively when angry, fearful or frustrated.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 HTR1BAdoption StudiesMednick et al (1984)14,000 male adoptees

Mednick et al (1984)Evaluation?ReductionistEthicsExtrapolation animal studiesResearch supportMethodological issuesSampleOperationalisation etc

Essay structureCritically consider the role of genetic factors in aggressive behaviour.Hand behind the scenesXXYInheritabilityMAOATwin studiesAdoption studies

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