genetic

• suggets would be offenders inherit a gene or combo of genes that predispose them to commit crime
• twin and adoption studies

  Karl Christiansen studies over 3500 twin pairs in Denmark and found concordance rates for offender behaviour of 35% for MZ male twins and 13% DZ males - included all twins born between 1880 and 1910 in region of denmark and offender behaviour checked against Danish police records

  Crowe - found adopted children whose biological mother had a criminal recordhad 50% risk of having criminal record by 18 but adopted kids whose bio mother didn't have criminal record had 5% risk
• Candidate genes 


  Tiihonen et al studied 800 Finnish offerenders - suggested two genes may be associated with violent crime

  MAOA gene regulates serotonin in the brain and has been linked to agressive behaviour and the CDH13 gene linked to substance abuse and ADHD - 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 this is at least partly moderated by effects of environment

  tendency towards offending may come about through combo of genetic predisposition and biological or psychological trigger eg being raised in dysfunctional environment or having criminal role models.