Genetic explanation

• Genetic explanation

  Suggests offenders inherit a gene or combination of genes that predispose them to commit crime.
• Twin study (Christiansen)


  Studied over 3500 pairs of twins in Denmark, used police records.

  Concordance rates for offending behaviour:

  • MZ males = 35%
  • DZ males = 13%(lower for females)
• Limitation of Twin Studies

  • Assumption of equal environments for twins.
  • Shared environment may apply more for MZ twins than DZ twins as they look identical so will be treated more similarly which then affects behaviour.
  • Higher concordance rates for MZ may be due to the way they were treated.
• Adoption study (Crowe)


  Adopted children whose bio mother had criminal record had a 50% chance of a criminal record by age 18.

  Adopted children whose bio mother had no criminal record had a 5% risk.
• Candidate genes (Tilhonen et al)

  • Genetic analysis of almost 800 Finnish offenders.
  • Suggested two genes associated with violent crime.MAOA (regulates serotonin in the brain) linked with aggressive behaviour.
  • CDH13 linked to substance abuse and ADHD.
  • Found 5-10% of all crime in Finland had MAOA and CDH13 genotypes.
• Diathesis-stress model

  Offending behaviour may be due to a combination of genetic predisposition and biological/psychological triggers.
• Support: diathesis stress (Mednick et al)

  • Studied 13,000 adoptees.
  • Neither sets of parent had convictions, 13.5% of adoptees did.
  • One bio parent had convictions, 20% of adoptees did.
  • Both sets of parents had convictions, 24.5% of adoptees did.
  • Genetic inheritance plays an important role but so does environmental influence.