genetic explanations

• Twin studies:

  Christiansen 1977 3500 Danish between 1880 and 1910 twin pairs 35% MZ 13% DZ. This data indicates its not just the behaviour it may be underlying predisposing traits.
• Adoption studies:

  Crowe 1972 found that adopted children whose mother had a criminal record had a 50% of becoming a criminal compared to the 5% risk of mothers who did not have a criminal record.
• Candidate genes:

  Genetic analysis 800 Finnish offender Tiihonen 2015. MAOA gene regulates serotonin and has been linked to aggressive behaviour. CDH13 gene linked to substance abuse and ADHD. 5-10% of Finnish offenders have the gene.
• Diathesis-stress model:

  Biological gene which can be triggered by an environmental, or psychological trigger.
• Presumed that adoption studies such as Mednick are a good way of separating nature from nurture. If crime has a genetic component then an adopted child should still feel the influence of the biological parent despite not living with them. But many adoptions take place when the children are older and have lived with their biological parents for several years and when the child has been adopted they are encouraged to keep in contact with their biological family so biological parents exert an environmental influence.
• Strength support for diathesis stress for offending. Mednick 1984 conducted 13000 Danish adoptees when neither adoptive or biological mother had a criminal record 13.5% when either had a criminal record it was 20% but when  both had a criminal record it was 24.5%. Shows that genetic inheritance plays an important role in offending but environmental factors also have a clear role in offending.
• Limitation using twin studies as it assumes that they have an equal environment which is more likely to happen with MZ rather than DZ due to them looking the same so they are more likely to be treated similarly which affects their behaviour. Therefore higher concordance rates occur in MZ due to them being treated similarly.