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Biological Theories (Genetic Theory) : Twin Studies - Coggle Diagram
Biological Theories (Genetic Theory) : Twin Studies
Genetic studies such as twin studies
explains why crime runs in the family
by the fact that
family members share many of the same genes
. Genetic theorists have used studies of twins as a way of testing their theory.
Strengths
Ishikawa and Raine found evidence that crime can be explained genetically. Their research showed a
44% concordance rate of MZ twins
compared to a
21% rate for DZ twins
The results of twin studies have
helped the prevention of vulnerable disorders
Identical twins or monozygotic twins share exactly the
same genes
as they are both from the
same fertilized egg
. Therefore if one twin is criminal, the other is ought to be criminal as well
On the other hand, non- identical twins or
dizygotic twins
are from
two separate eggs
and only
share 50% of their DNA
When both twins share a characteristic such as being aggressive, there is said to be a
concordance rate
(the odds of one twin having a characteristic if the other does). Various twin studies have been taken and their is some
evidence to suggest that crime is more likely in monozygotic twins than dizygotic twins
. In other words,
genetic or nature may play a role in criminality
One of the earliest twin studies was reported by
Lange (1929)
, who found a much
higher degree of concordance in monozygotic twins
10 out of 13 MZ twins had served time in prison
2 out of 17 DZ twins had served time in prison
A later study by
Christiansen (1977)
studied
3,586 pairs of twins
from Denmark and
found evidence to support the view that crime can be explained by genetics
. This research shows the following concordance rate.
Male : Monozygotic twins (35%) and Dizygotic twins (13%
Female : Monozygotic twins (21%) and Dizygotic twins (8%)
Limitations
If genes were the cause of criminality,
identical twins would show a 100% concordance rate,
but studies show much less.
The small samples
involved in many twin studies are
unrepresentative,
and said not be typical of wider population
If twins are
brought up in the same environment
crime could be due to
nurture rather than nature
Early twin studies such as Lange were
poorly controlled
. Whether the twins were MZ or DZ were
based on appearance
rather than DNA as it did not exist at the time
Higher concordance rates among MZ tins may be due to them
sharing the same home, school etc
. Their
shared environment may cause similarities in their behavior
rather than identical genes