1) Describe two biological theories of criminality (9 marks)
Biological theories of crimes attempt to find a link between criminality and our biological
characteristics. Genetic theories of crime look at whether there is a criminal gene that results in
criminality being inherited, thus meaning people can be born criminals while physiological theories
investigate whether people’s appearances influence their criminality.
One biological theory of crime is the XYY theory which was proposed by Jacob et al in 1965. XYY
syndrome, also known as Jacob’s syndrome, was found to occur in 1 in 1,000 male children of the
general population. Humans normally have 23 pairs of chromosomes (46 in total), and the 23 rd pair is
what determines our sex. XX is the female gene pair and XY is the male gene pair. Jacobs syndrome is
where boys are born with an extra Y chromosome (meaning they have XYY). There are other genetic
disorders which result in an extra gene, but the presence of an extra Y chromosome is characterised
by the production of higher levels of testosterone which often leads to more aggressive or violent
behaviour. Men with this extra Y chromosome have been found to be more aggressive than men who
have only one Y chromosome. Jacob also found that these men are overrepresented in prison
populations, with 15 in 1,000 male prisoners having the condition. A well-known example of a
criminal with this genetic disorder is John Wayne Gacy. He sexually assaulted, tortured, and
murdered what is thought to be at least 33 men in the USA, and he was later believed to have Jacob’s
syndrome.
The second biological theory of crime I will be discussing is twin studies, specifically Christiansen’s. In
1977, Christiansen began a large-scale study in which he examined 3,586 pairs of twins in Denmark.
The aim of his investigation was to find whether criminal behaviour can be inherited and attempted
to answer this question by using concordance rates. Concordance rates are used in twin studies to
show the percentage of the probability of both twins sharing the same trait/ characteristic/
behaviour. Christiansen’s study found concordance rates for criminality of 35% in male monozygotic
twins (identical twins) and 13% in male dizygotic twins (non-identical twins). For female twins. He
found concordance rates of criminality to be 21% in monozygotic twins and 8% in dizygotic twins.
These results indicate to some degree, criminal behaviour is a trait that can be inherited. However,
the differences between those found in male and female twins raises the question of the role of
gender in criminality.
(Rest on next page)
Biological theories of crimes attempt to find a link between criminality and our biological
characteristics. Genetic theories of crime look at whether there is a criminal gene that results in
criminality being inherited, thus meaning people can be born criminals while physiological theories
investigate whether people’s appearances influence their criminality.
One biological theory of crime is the XYY theory which was proposed by Jacob et al in 1965. XYY
syndrome, also known as Jacob’s syndrome, was found to occur in 1 in 1,000 male children of the
general population. Humans normally have 23 pairs of chromosomes (46 in total), and the 23 rd pair is
what determines our sex. XX is the female gene pair and XY is the male gene pair. Jacobs syndrome is
where boys are born with an extra Y chromosome (meaning they have XYY). There are other genetic
disorders which result in an extra gene, but the presence of an extra Y chromosome is characterised
by the production of higher levels of testosterone which often leads to more aggressive or violent
behaviour. Men with this extra Y chromosome have been found to be more aggressive than men who
have only one Y chromosome. Jacob also found that these men are overrepresented in prison
populations, with 15 in 1,000 male prisoners having the condition. A well-known example of a
criminal with this genetic disorder is John Wayne Gacy. He sexually assaulted, tortured, and
murdered what is thought to be at least 33 men in the USA, and he was later believed to have Jacob’s
syndrome.
The second biological theory of crime I will be discussing is twin studies, specifically Christiansen’s. In
1977, Christiansen began a large-scale study in which he examined 3,586 pairs of twins in Denmark.
The aim of his investigation was to find whether criminal behaviour can be inherited and attempted
to answer this question by using concordance rates. Concordance rates are used in twin studies to
show the percentage of the probability of both twins sharing the same trait/ characteristic/
behaviour. Christiansen’s study found concordance rates for criminality of 35% in male monozygotic
twins (identical twins) and 13% in male dizygotic twins (non-identical twins). For female twins. He
found concordance rates of criminality to be 21% in monozygotic twins and 8% in dizygotic twins.
These results indicate to some degree, criminal behaviour is a trait that can be inherited. However,
the differences between those found in male and female twins raises the question of the role of
gender in criminality.
(Rest on next page)
