Genetic theories

Question 1

Twin studies

Answer 1

• Monozygotic twins share the same genes (if criminality is passed on genetically, twins will both be criminal).
• Christiansen’s study found that 52% of monozygotic twins both had a criminal record and dizygotic twins there was only a 22% chance.
• Not all twins both have a criminal record.

Question 2

Adoption studies

Answer 2

• To see whether criminality was genetic, adoptees were studied.
• If they had criminal parents and had a criminal record despite being adopted, criminality was proven genetic.
• If they did not have a criminal record, criminality is based on environmental factors.
• The study found that adoptees who did not have criminal birth parents, tended to not have a criminal record as to those who do.

Question 3

XXY syndrome

Answer 3

• Known as the super male syndrome.
• In prisons and psychiatric hospitals for prisoners, most inmates were found to have this abnormality.
• XXY males are more aggressive, immature and less intelligent than the average man, which can cause them to commit motiveless property crimes.

Question 4

Brain injuries and disorders

Answer 4

• Some brain injuries can cause extreme personality changes.
• Some studies showed that prisoners are more likely to have suffered head injuries than to non-prisoners.
• Some brain diseases are linked with anti-social behaviours.