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Outline and evaluate genetic factors in aggression
The use of twin studies helps explain how there could be genetic factors in aggressive behavior.
There are two types of Twin, monozygotic (identical) and Dizygotic (nonidentical). If both
types are studied in terms of aggression and the MZ twins are more similar in aggressive
behaviour it would suggest there is a genetic influence on aggression. Coccaro et al found that
when comparing MZ and DZ twins, over 50 % of variance in aggressive behaviours between
MZ twins could be attributed to genetic factors.
Additionally the use of adoption studies can contribute to our understanding of genetic factors in
aggression. If a positive correlation can be seen between adopted children and their biological
parents ( where no environmental influenced has occurred) in aggressive behaviour then it would
suggest a genetic influence. However if a positive correlation is found between adopted children
and their foster parents, it shows there must be an environmental effect , a study of 14000
adoptions in Denmark show that a significant number of boys with criminal convictions had
biological parents with criminal convictions. This provides evidence for the influence genetic
factors has in aggression.
A gene called MAOA is associated with aggressive behaviour, it regulated the metabolism of
serotonin, and additionally low levels of serotonin are associated with aggressive and impulsive
behaviour. A study from a Dutch family with a history of violence including rape and arson
found low levels of MAOA in their blood. It showed that the men had a defect in their MAOA.
This study shows that the gene MAOA is associated with aggression, this means that some
genes can influence the susceptibility to aggressive behaviour, however it is not certain that one
gene can determine aggressive behaviour, however it is likely that many genes can contribute to
human behaviour rather than one single gene.
A more integrated explanation is provided by Caspi et al who suggests that a gene environment
interaction. Genes do have an effect on behaviour but the environmental situation dictates how
major the effects are. For example, people low levels of MAOA grow up to exhibit antisocial
behaviour, but this is only if they have been maltreated as children. However children with high
levels of MAOA who were maltreated and those with low levels who were not maltreated did
not display antisocial behaviour. This shows it is an interaction between genes and the
environment which determines aggressive behaviour.
However there are difficulties in determining the role of genetics as more than one gene may
contribute to any behaviour, there are also environmental influences to so therefore genetics may
influence environmental factors and vice versa so the role of genetics primarily is difficult to
There are also problems in assessing aggression, research has relied on parental or self reports
of aggressive behaviour. Whereas other studies use observational techniques which can be
problematic as behaviour could be misinterpreted due to cultural differences in society.
Additionally parental self reports which is used to show how genetic factors explain a large
proportion of variance found in aggressive behaviours, but observational ratings showed
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example, in the replication of Bandura's Bobo doll study, twin pairs were encouraged to act
aggressively towards after being exposed to by an adult model. Researcher found no difference
in correlation between MZ and DZ pairs suggesting that individual differences in aggression
were more a product of environmental influences that genetic influences.
There are also problems in sampling when doing research on genetic factors in aggressive
behaviour. It is highly focused on individuals who have been convicted of violent crimes.…read more