Discuss the influence of genetic factors in aggression
Christiansen carried out a study, where there was an analysis of criminality in pairs of twins in
Denmark to discover a concordance rate. 926 people from this study were registered by the police for
criminal activity. Identical and non- identical twins were compared on the rate registered. Identical
male twins showed 35% concordance rate whereas non-identical twins showed a 12% concordance
rate for criminality. Identical female twins showed a 21% concordance rate whereas non-identical
twins showed 8% concordance rate for criminality. These results suggest that genes are linked to
aggression i.e If they share the same genes (MZ/identical twins) there is a higher chance that if one
becomes a criminal the other will too. The fact that females were less likely to be criminals overall,
suggests that there may be a genetic link to criminality and aggression.
However, as concordance rates were not 100% it suggests that genetics is not the only factor in
aggression. As it was a twin study and it was in a specific region of Denmark the results may not
generalise to the wider population. As monozygotic twins look the same they are more likely to share
the same experiences as one another and are more likely to behave in the same way. In addition, not
all convicted criminals have committed aggressive/violent acts so criminality may not be a good
predictor of aggression.
The MAOA gene affects an enzyme involved in processing neurotransmitters, including serotonin.
Serotonin plays a role in aggression as it is a natural mood stabiliser, therefore lower levels of
serotonin have been linked to aggressive and impulsive behaviour.
E.g. Brunner et al studied an extended family in the Netherlands where multiple male family members
showed impulsive aggression E.g. violent crime. A flaw was identified in the MAOA Gene i.e. the
participants who displayed impulsive aggression which was not found in other male family members
were deficient in the MAOA gene.
Animal studies also support the role of the MAOA gene in the development of aggressive behaviour
e.g. Cases et al studied mice, and discovered a similar correlation between aggression and the
MAOA Gene. They found that the male mice who were missing the MAOA producing gene were more
aggressive.
The MAOA gene cannot account for all the cases of aggression as it does not take into account
environmental factors that could also influence aggression e.g.upbringing.
This explanation for the MAOA gene is limited as the results do not generalise to women because the
MAOA gene is not found within women.
Strengths of the theory:
Most of the studies conducted showed there was a genetic element involved in aggression.
On the other hand, Caspi et al established that men with low MAOA activity genes were not more
likely to engage in antisocial behaviour. However, there was a significant effect in men who had been
maltreated as children.This suggests that genetics go hand in hand with environmental factors to
influence aggression levels.
Limitations of the theory:
It can be challenging to identify the role of genetic factors in aggression because more than one gene
contributes to a certain behaviour.
The genetic explanation for aggression is also quite deterministic because it suggests that some
people may not have control over their behaviour, and it may also be used as an excuse
for aggressive behaviour.
Much of the research has been carried out on animals making it less reliable and therefore it may not
extrapolate to humans because animals act more on instinct and have less conscious control than
humans.
Christiansen carried out a study, where there was an analysis of criminality in pairs of twins in
Denmark to discover a concordance rate. 926 people from this study were registered by the police for
criminal activity. Identical and non- identical twins were compared on the rate registered. Identical
male twins showed 35% concordance rate whereas non-identical twins showed a 12% concordance
rate for criminality. Identical female twins showed a 21% concordance rate whereas non-identical
twins showed 8% concordance rate for criminality. These results suggest that genes are linked to
aggression i.e If they share the same genes (MZ/identical twins) there is a higher chance that if one
becomes a criminal the other will too. The fact that females were less likely to be criminals overall,
suggests that there may be a genetic link to criminality and aggression.
However, as concordance rates were not 100% it suggests that genetics is not the only factor in
aggression. As it was a twin study and it was in a specific region of Denmark the results may not
generalise to the wider population. As monozygotic twins look the same they are more likely to share
the same experiences as one another and are more likely to behave in the same way. In addition, not
all convicted criminals have committed aggressive/violent acts so criminality may not be a good
predictor of aggression.
The MAOA gene affects an enzyme involved in processing neurotransmitters, including serotonin.
Serotonin plays a role in aggression as it is a natural mood stabiliser, therefore lower levels of
serotonin have been linked to aggressive and impulsive behaviour.
E.g. Brunner et al studied an extended family in the Netherlands where multiple male family members
showed impulsive aggression E.g. violent crime. A flaw was identified in the MAOA Gene i.e. the
participants who displayed impulsive aggression which was not found in other male family members
were deficient in the MAOA gene.
Animal studies also support the role of the MAOA gene in the development of aggressive behaviour
e.g. Cases et al studied mice, and discovered a similar correlation between aggression and the
MAOA Gene. They found that the male mice who were missing the MAOA producing gene were more
aggressive.
The MAOA gene cannot account for all the cases of aggression as it does not take into account
environmental factors that could also influence aggression e.g.upbringing.
This explanation for the MAOA gene is limited as the results do not generalise to women because the
MAOA gene is not found within women.
Strengths of the theory:
Most of the studies conducted showed there was a genetic element involved in aggression.
On the other hand, Caspi et al established that men with low MAOA activity genes were not more
likely to engage in antisocial behaviour. However, there was a significant effect in men who had been
maltreated as children.This suggests that genetics go hand in hand with environmental factors to
influence aggression levels.
Limitations of the theory:
It can be challenging to identify the role of genetic factors in aggression because more than one gene
contributes to a certain behaviour.
The genetic explanation for aggression is also quite deterministic because it suggests that some
people may not have control over their behaviour, and it may also be used as an excuse
for aggressive behaviour.
Much of the research has been carried out on animals making it less reliable and therefore it may not
extrapolate to humans because animals act more on instinct and have less conscious control than
humans.
