Twin Studies

• If monozygotic twins are separated and raised differently, their environment is different, and they have different experiences, they will have different personalities. However, genetics would suggest that if one mz twin ends up being criminal the other will too.
• Christiansen examined over 3,500 twin pairs in Denmark and identifies concordance rate of

  male mz twins as 35%

  male dz twins as 13%

  female mz twins as 21%

  female dz twins as 8%
• Twin studies support the idea that a heritable trait may increase risk for criminal behaviour. Twins share a genetic make-up but may differ in their wider social experience. Identical twins (monozygotic twins), are genetically identical because they are the product of a single egg and a single sperm that have split into two. Their genes are 100% similar. Non-identical twins (dizygotic twins) are the product of two eggs that are fertilised at the same time by two different sperm and so are as genetically alike as brothers and sisters born at different times. Their genes are 50% similar.