Genetic

• Twin studies and criminality - Lange (1930)

  13 MZ twins, 17 DZ twins

  One of the twins in each pair had spent some time in prison

  10 of the MZ twins but only 2 DZ twins had a twin in prison
• Twin studies and criminality- Raine (1933)

  Reviewed research on delinquent behaviour of twins

  found 52% concordance rate for MZ twins and 21% for DZ twins
• Bruner et al (1933) A study of violence in a family of genetic abnormality - Method

  28 males in the same family who were affected by a syndrome of borderline mental retardation and abnormal violent behaviour

  Took urine samples over a 24hr period
• Bruner et al (1933) A study of violence in a family of genetic abnormality - Results

  • Urine Samples showed disturbed monoamine metabolism associated with a deficit of the enzyme monoamine oxidase A (MAOA)
  • A mutation was found in the X chromosome of the gene responsible for producing MAOA
• Bruner et al (1933) A study of violence in a family of genetic abnormality - Conclusion

  As MAOA is involved in serotonin metabolism, the defect in the gene could be the cause of the mental retardation seen in this family; which in turn could lead to violent behaviour
• Study supporting Candidate Genes for criminality

  Tiihonen et al. (2015)

  • genetic analysis of approx 900 (Finnish) offenders
  • Abnormalities on 2 genes that may be associated with violent crimes: MAOA & CDH13
  • Those with these abnormalities were 13x more likely to have a history of violent behaviour
• What is the MAOA gene responsible for

  controls dopamine and serotonin in the brain and is linked to aggression
• What is the CDH13 gene linked to

  substance abuse and attention deficit disorder
• study supporting the diathesis-stress model in criminality

  Caspi et al (2002)

  • longitudinal study
  • New Zealand
  • 1000 people from when they were babies in 1970s
  • assessed anti-social behaviour at age 26 and found that 12% of those men with low MAOA genes have experienced maltreatment when they were babies but were responsible for 44% of violent convictions
• Why do some people who were maltreated develop anti-social behaviour and some don‘t

  Caspi- Dunedin Study

  • a functional polymorphism of the MAOA gene was found to moderate the effect of maltreatment
  • maltreated children with a genotype conferring high levels of MAOA expression were less likely to develop anti-social problems
• Key parts of the biological approach to offending

  • Twin studies
  • Candidate genes
  • Diathesis-stress
• Twin Studies Limitations

  Higher concordance rates in MZ twins may be due to being treated more similarly than DZ twins, questioning the assumption of equal environments
• Strength of diathesis-stress model

  Mednick et al’s adoption study supports genetic and environmental roles in crime. When neither biological nor adoptive parents had convictions, adoptee offending was 13.5% rising to 24.5% when both sets of parents had convictions