genetic

• twin and adoption studies suggest genes predispose offenders to crime


  - Chrisitiansen (1977) studied over 3500 twin pairs in Denmark finding a concordance for offender behaviour of 35% for MZ males and 13% for DZ males. This supports a genetic component in offending

  - Crowe (1972) found that adopted children who had a biological mother with a criminal record had a 50% risk of having a criminal record age 18. Whereas adopted children whose mother didn't have a criminal record only had a 5% risk
• candidate genes (MAOA and CDH13)

  a genetic analysis of about 800 offenders by Tiihonen et al (2015) suggested two genes may be associated with violent crime:

  - MAOA gene regulates serotonin and linked to aggressive behaviour

  - CDH13 gene linked to substance abuse and ADHD

  - the study found that 5-10% of all severe violent crime in Finland is attributable to MAOA and CDH13 genotypes
• diathesis-stress model


  - if genes have an influence on offending, this influence is likely to be at least partly moderated by environmental factors

  the diathesis-stress model suggests that a tendency to offending behaviour is due to a combination of:

  - genetic predisposition

  - a biological or psychological stressor or 'trigger
• limitation


  P - twin studies are assuming equal environments

  E - often assumed that environmental factors are the same for MZ and DZ twins because they experienced similar environments

  E - however because MZ twins look identical, people tend to treat them more similarly which affects their behaviour

  L - therefore higher concordance rates for MZs may be because they are treated more similarly than DZs suggesting conclusions lack validity
• strength


  P - support for a diathesis-stress model of offending

  E - Mednick et al (1984) studied 13,000 Danish adoptees having at least one court conviction

  E - conviction rates 13.5% (biological or adoptive parents had no convictions), 20% (one biological parent), 24.5% (both adoptive and biological parents)

  L - this data suggests that both genetic inheritance and environment influence criminality - supporting the diathesis-stress model of crime
• limitation


  P - nature vs nurture

  E - adoption studies separate nature and nurture - similarities due to biological parents can only be genetic

  E - however, many adoptions occur when children are older and many adoptees maintain contact with biological family, so still environmental influences

  L - this suggests that adoption studies cannot fully separate nature and nurture