Twin Studies

• What are Monozygotic Twins?


  Identical Twins (100% identical DNA)
• What are Dizygotic Twins?


  Non-Identical Twins (50% identical DNA)
• What does Concordance mean?


  In agreement or harmony
• What do Twin Studies suggest?

  Support connection that a heritable trait e.g. XYY gene may increase the chance of criminal behaviour.

  When both twins share a characteristic there is a concordance rate. This is where the nature vs nurture debate comes into play.
• What did Lange (1929) do in his twin study?


  One - He studied 30 pairs of twins who were of the same sex.

  Two - 17 of these pairs were DZ twins, and 13 of these pairs were MZ twins. Atleast one of each pair were known to have committed a crime.

  Three - Lange found that both twins in 10 of the 13 MZ twin pairs were known criminals, compared with both twins in only 2 of the 17 DZ pairs.
• What did Christiansen (1977) do in his twin study?


  One - Evaluated criminal behaviour of over 3000 twin pairs born in Denmark between 1881-1910.

  Two - He found that the chance of one twin engaging in criminal behaviour when the other twin was criminal was 50% among the MZ twin pairs but only 20% among the DZ twin pairs.

  Three - The correlation between the genetic closeness of the biological relationship and crime was especially true for serious violent crime and for more lengthy criminal careers.
• What are 2 Strengths of Twin Studies?

  One Strength - The result of twin studies have aided the prevention of vulnerable disorders (such as eating disorders,

  schizophrenia etc).

  One Strength - Twin studies are natural experiments, as the biological relationship between the twins is a naturally occurring variable.
• What are 2 Limitations of Twin Studies?

  One Limitation - The sample involved in twin studies may not be representative of the general population.

  One Limitation - If twins are brought up in the same environment, criminality could just as easily be related to nurture as to genetics.