A* Model answer for genetics in aggression

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Genetics play a major role in all behaviour. The more genetically similar you are to someone, the
higher the likelihood of you displaying the same behaviour, for example aggression. Some argue that
the inheritance of a maladaptive gene (s) is an absolute explanation for aggression, where as other
researchers suggest it is from a biological predisposition (genes) which is encouraged by an
environmental trigger, for example the Social Learning Theory.
Research from Sandberg (1961) identified a genetic difference in males named the XYY Karyotype.
Most individuals have 46 chromosomes (23 from each parent), and it is possible for a male to have an
extra Y chromosome making then XYY. This extra chromosome is strongly linked to aggression.
Research to support the link between XYY Karyotype and aggression come from Court-Brown who
studied a sample of 314 participants. They found that those with the XYY Karyotype were linked to
aggression. Therefore, this supports the influence of genetic factors in particular chromosomes on
aggressive behaviour. Further research to support comes from Cairns who studied mice as a method
of 'selective breeding' to create aggressive males and females in mice. Therefore, this shows
support that aggression can be genetically inherited. Both of these studies increase the reliability of
the theories as consistent result are being achieved between genetics and aggression.
To evaluate this research, it carries animal bias. It is difficult to extrapolate results from animals to
humans due to differences in genetic make-up. Also, animals are driven by instinct where as humans
can face legal consequences and therefore use their free will and choose whether to be aggressive
or not. However, others argue that we share enough of the basic physiology and therefore the
research can still be used to support the role of genetics and aggression.
Furthermore, another weakness is that Thailgaard (1984) stated that we cannot conclude that the
XYY Karyotype alone causes increased aggression as the XYY has been linked to other characteristics
such as intelligence. Some researchers have suggested that this genetic defect instead affect
intelligence. A lack of intelligence may result in an individual being more likely to conform, commit
and be convicted of a crime. Therefore, the studies of the XYY and aggression using criminal
populations are misleading and decrease the validity of the genetic explanation to aggression.
A gene responsible for producing a protein called MAOA has been associated with aggressive
behaviour. MAOA regulates serotonin in the brain, and low levels of serotonin are associated with
impulsive and aggressive behaviour. Brunner carried out a study on a Dutch family in which many of
the male members are particularly violent and aggressive, and a large population had been involved
in serious crimes such as arson and rape. These men were found to have abnormally low levels of
MAOA in their bodies, and a defect in this gene was later identified. This led to their aggressive
To evaluate Brunners research, a weakness is that it carries a high gender bias. All participants were
male, therefore they cannot generalise to explain a females response to a MAOA defect as females
may react differently (More verbally aggressive than physically) and this would cause beta bias.
Therefore, this research can only offer partial support for the genetic explanation of aggression.
Furthermore, another weakness is that it could be that the unusual aggressive behaviour is now an
expectation of the Dutch family through Social Learning Theory or the self-fulfilling prophecy

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This suggests that members of the family
may just be living up to the expectation of the aggressive label rather than just acting aggressively
due to genetic causes.
Adoption studies have also investigated the role of genetics in aggression. A study by Hutchings et al
with over 14,000 adoptions in Denmark found that a significant number of adopted boys with
criminal convictions had biological parents (mainly the father) who also had a criminal conviction,
showing a genetic link to aggression.…read more


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