Christiansen studied over 3500 twin pairs in Denmark, finding a concordance for offender behaviour of 35% for MZ males and 23% for DZ males (slightly lower rates for females). 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.
A genetic analysis of about 800 offenders by Tilhonen suggested two genes that 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 the MAOA and CDH13 genotypes.
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 (diathesis).
A biological or psychological stressor or trigger' (e.g. criminal role models or dysfunctional upbringing).
