Aggression Revision Notes

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  • Created on: 08-04-13 15:52
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Genetic Factors
Twin and Adoption Studies
Twin studies: monozygotic twins share all genes; dizygotic twins share max of 50%. If MZ twins have
a higher concordance rate than DZ twins in terms of aggressive behaviour strong genetic influence
Adoption studies: if +ve correlation found between adopted child's aggressive behaviour and that
of a biological parent, this implies a genetic effect. If correlation is stronger between adopted child
and their adoptive family, this suggests environmental influences stronger
Hutchings and Mednick ­ 14, 000 adoptions in Denmark, significant no. of adopted boys with
criminal convictions had biological parents with criminal convictions evidence for genetic effect
Support: Miles and Carey ­ meta-analysis of 24 twin + adoption studies found evidence of strong
genetic influence. In younger individuals, both genetic + environmental influences contributed to
aggression. In older individuals, genetic influences more important in determining aggressive
o Rhee and Waldman ­ meta-analysis of 51 twin + adoption studies. Concluded that
aggressive and antisocial behaviour was largely the product of genetic contributions
However: in both studies, several variables contributed to the strength of the genetic influence on
aggression, including age of ppt, method used to assess aggression genetic factors are important
in development of aggression, but other factors determine expression of aggressive behaviour
o A03
Problems assessing aggression ­ most studies rely on parental/self-reports of
aggressive behaviour. Those that found strong genetic influence on aggressive had
used parental/self-reports ­ those that used observational techniques found
significantly less genetic influence
method used to assess aggression has significant influence on findings
Gene for Aggression
MAOA: protein, regulates metabolism of serotonin in brain - low serotonin = high aggression
Brunner et al ­ study of Dutch family, known for its male members to be violent, found many of the
men had abnormally low levels of MAOA and also a defective gene for production of MAOA
Gene-Environment interactions: Caspi et al ­ 500 male children, discovered 2 variants of gene for
MAOA. One associated with high levels of MAOA and one with low levels. Those with low levels
were significantly more likely to display aggressive behaviour, but only if maltreated as children
suggests interaction between genes and environment determines aggression, not genes alone
o Nature/nurture debate - McGue et al - study on twins, found higher correlation in MZ twins
than in DZ twins suggests that genes (nature) play bigger role in aggression as MZ twins
(who share 100% genes) had higher similarity in levels of aggression than DZ twins
o However - reason MZ twins are more similar may be due to environmental factors
MZ twins more likely to be treated same in home environment as result of their
similar appearance therefore, their high concordance rate may be due to
aggression being treated the same (nurture)
o The effect of genes on behaviour could involve both nature and nurture, having the genes
gives us a vulnerability to be triggered by certain experiences to cause true aggression.
Difficulties determining role of genetic factors ­ more than one gene contributes to a given
Problems of sampling ­ most studies focus on individuals convicted of violent crime. These
individuals represent very small minority of those who regularly engage in aggressive behaviour, a
person who's imprisoned for single violent offence (e.g. murder) isn't necessarily a consistently
violent individual questions validity of conclusions drawn from these studies
Value of animal research ­ studies of rodents (e.g. Young) have advantage of allowing researchers
to eliminate a single gene from experimental group to see its effect
o Researchers can identify genetic mutation that causes aggressive behaviour in mice

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Evolutionary Explanations of Human Aggression
Men may experience parental uncertainty, therefore they are at risk of cuckoldry (reproductive cost
that might be inflicted on a man as a result of his partner's infidelity
o Consequence of cuckoldry ­ the man might unwittingly invest his resources in offspring that
are not his own
Men have evolved to reduce risk of cuckoldry by using various strategies
o Direct guarding ­ restricting their partner's autonomy
o Negative inducements ­ in form of violence/threats of violence…read more

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Neural and Hormonal Mechanisms
Neural Mechanisms
A01 ­ Serotonin
Low levels = high aggression.…read more

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Institutional Aggression
Institutional Aggression
`collective violence' e.g. prisons (within institutions), religious groups (between different collectives)
Different forms.…read more

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Evolutionary Explanations of Group Display
Sports & Xenophobia
A01: Xenophobia ­ a fear and hatred of strangers or foreigners
Wilson ­ xenophobia has been seen in virtually every group of animals displaying higher forms of
social organisation natural selection favours genes in humans to be altruistic to members of
own group + hostile to outsiders minimising risk of attack
Shaw & Wong ­ explain adaptive advantages of xenophobia argue mechanisms prompting
suspicion towards strangers favoured by natural selection enabling ancestors avoid
attack/protect offspring
Podaliri…read more

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are responsible for group displays of aggression social identity theory states that when identifying
with groups, individual's self-esteem increases leads to hostility to out group
Social Psychological Theories of Aggression
Social Learning Theory
Developed from learning theory by behaviourists behaviours learnt through observation of
Models can be family, friends and/or mass media through observing actions of others and
consequences of those actions, people model their behaviour vicarious reinforcement
Imitator only likely to reproduce behaviour at an appropriate time in the future
o…read more

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Support: Zimbardo ­ people who were deindividuated (KKK-like outfits of lab coats+hoods) gave
more electric shocks (measure of aggression) than those who were not
o Lacks ecological validity: unlikely to deliver shocks in a group situation as sign of
o Demand characteristics: Johnson and Downing ­ nurses/KKK outfits nurses gave less
shocks because nurses associated as being less aggressive despite being deindividuated…read more



This is really helpful, thank you so much! :)

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