AO3 Genetic Explanation

• -Assuming equal environment. It’s often assumed that environmental factors are the same for MZ and DZ twins because they experience similar environments. However, because MZ twins look identical, people tend to treat them more similarly which, in turn, affects their behaviour. Therefore higher concordance rates for Ms may be because they are treated more similarly than DZs, suggesting conclusions lack validity.
• +Support for diathesis-stress model of offending. Mednick studied 13,000 Danish adoptees having at least one court conviction. Conviction rates 13.5% (biological or adoptive parents had no convictions), 20% (one biological parent), 24.5% (both adoptive and biological parents). This data suggests that both genetic inheritance and environment influence criminality - supporting the diathesis-stress model of crime.
• Nature v Nurture

  Adoption studies separate nature and nurture - similarities due to biological parents can only be genetic. However, many adoptions occur when children are older and many adoptees maintain contact with biological family, so still environmental influences. This suggests that adoption studies cannot fully separate nature and nurture.