One limitation of the genetic explanation of criminal behaviour is that the environment may act as a confounding variable:
Evans and Martin suggest parents, teachers etc. treat MZ twins more similarly than DZ twin
Therefore, greater similarity in terms of criminal behaviour may also be due to greater similarity of experiences
Support for the DSM
One strength is support for the diathesis-stress model of offending:
Mednick et al. analysed 13000Danish adoptees and found that when neither set of parents had convictions, 13.5% of adoptees did
This rose to 20% when either of the biological parents had criminal convictions, and 24.5% when both sets of parents did
Therefore, both genetic inheritance and environmental influence play a role in determining offending behaviour
Nature vs nurture
One strength of adoption studies is that they offer support to the nature vs nurture debate:
Adoptees are exposed to different environments than that of their biological parents, so it is easier to separate the effects of nature and nurture than for twin studies
However, there may be trauma with being adopted, which can act as a confounding variable
Furthermore, adoption after birth means biological contact may have been maintained