genetic

• The genetic expiation from crime suggests that offenders inherit a gene or a combination of genes that predispose them to commit crime
• twin studies

  3500 pairs of twins studied in denmark, found concordance rates for offender behaviour of 35% identical twins and 13% non identical twins
• adoption studies

  Found that adopted children whose biological mother had a criminal record had a 50% risk of having a criminal record by the age of 18

  whereas those who’s biological mother didnt have a criminal record had a risk of 5%
• candidate genes

  genetic analysis of 800 Finnish offenders suggested that 2 genes may be associated with violent crime

  The MAOA gene regulates serotonin in the brain and has been linked to aggressive behaviour and the CDH13 gene has been linked to substance abuse and attention deficit hyperactivity disorder 

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

  If genetics do have some influence on offending, it seems likely that this is at least partly moderated by the effects of the environment.

  A tendency towards offending behaviour may come about through the combination of genetic predisposition and biological or psychological trigger - for example, being raised in a dysfunctional environment or having criminal role models
• A limitaion is issues with twin evidence

  It is assumed by researchers studying twins that environmental factors are held constant because twins are brought up together and therefore must experience similar environments.

  However, this 'shared environment assumption' may apply much more to MZ twins than DZ twins because MZ twins look identical and people tend to treat them more similarly which affects their behaviour.

  Therefore higher concordance rates for MZs in twin studies may simply be because they are treated much more similarly than DZ twins.
• A strength is support for diathesis-stress

  A study of 13,000 Danish adoptees was conducted When neither the biological nor adoptive parents had convictions, the percentage of adoptees that did was 13.5% (which is quite high).

  This figure rose to 20% when either of the biological parents had convictions, and 24.5% when both adoptive and biological parents had convictions.

  This shows that genetic inheritance plays an important role in offending but environmental influence is clearly also important