Aggression

Genetic - twin and adoption studies - AO1

aggression is heritable by about 50%
Coccaro - physical assault: 50% MZ, 19% DZ. verbal: 28% MZ, 7% DZ
similar in adoption studies: meta analysis by Rhee and Waldman: 41% genetic influence

Genetic - Genes - AO1

MAOA gene produces enzyme called MAO-A. Breaks down serotonin at end of day. Nicknamed warrior gene.
low activity means not enough cleaning of serotonin: high serotonin. Make’s a person more receptive to stress: will respond with fight during fight or flight

Brunner - Genetics

28 men from a large Dutch family who had been involved in various aggressive criminal acts such as rape, attempted murder, physical assault. They had abnormally low levels of enzyme MAO-A

Frazzetto - Genetics

diathesis stress: those who had low MAOA activity would only be aggressive if they had had severe trauma in first 15 years of life - 1/3 of men have this gene, so not purely genetic - nomothetic vs idiographic

AO3 - Genetics - Research

knockout mice where MAOA was knocked out showed higher serotonin and more aggressive behaviour, but when Fluoxetine (serotonin inhibitor) was administered, returned to original behaviour

AO3 - Genetics - General

Twin studies: equal environments assumption
Nature versus Nurture: genes are not a direct cause
Neural: low serotonin can cause aggression as unable to inhibit aggressive impulses from amygdala at orbitofrontal cortex - at odds with each other

AO1 - Neural - limbic system

hypothalamus, amygdala, parts of hippocampus
reactivity of amygdala is a predictor of aggressive behaviour.
orbitofrontal cortex controls behaviour to prevent amygdala impulse

AO1 - Neural - Orbitofrontal Cortex and Serotonin

serotonin has an inhibitory effect → slows/calms neuronal activity. Greater behavioural self-control when normal levels of serotonin in orbitofrontal cortex. More impulsive when deficiency of serotonin.

AO1 - Hormonal - Testosterone

Increased testosterone is associated with aggression
mice research implicates aromatase, an enzyme which metabolizes testosterone: deficiency of the enzyme → testosterone increases reactivity of aggression
testosterone reduces orbitofrontal cortex activity allowing amygdala to have more response
testosterone reduces serotonergic activity.

AO1 - Hormonal - Progesterone

aggression in women. vary during ovulation cycle, lowest during/after menstruation. negative correlation between progesterone levels and self reported aggression

AO3 - Hormonal - Testosterone

castration of animals removing testes reduces aggression in males of many species. injecting testosterone restores aggression - CP: human aggression based on many factors vs animals (humans multifaceted) ~ caution should be taken when extrapolating

Dolan - positive correlation between testosterone levels and aggressive behaviours in 60 male offenders in UK max security hospitals. they had personality disorders and histories of impulsive violent behaviour

AO3 - research - neural

Wong - MRI scans of 19 violent male criminals in one hospital, compared with 20 controls, found they had significantly smaller amygdalas
|CP: androcentric → beta bias, small sample size, correlational
Raine - PET scans showed murderers who had pleaded not guilty had reduced activity in orbitofrontal cortex
Ferrari - everyday encouraged rats to fight at a time, on 11th were not allowed to, dopamine up by 65%, serotonin decreased by 35%
contradicting evidence → genetic explanation suggests high serotonin results in aggression
Virkkunen - compared 5-HIAA in cerebrospinal fluid of violent impulsive/non-impulsive offenders. Much lower in impulsive offenders

AO3 - Neural - General

free will vs biological determinism → socially sensitive and takes away from guilt
reductionist → ignores sociocultural factors