Evaluation

• Strength: support for diathesis-stress model of crime

  Mednick et al. studied 13000 Danish adoptees and criminality (operationalised as having at least one court conviction). When neither biological nor adoptive parents had conditions, the percentage of adoptees that had a conviction was 13.5%. This rose to 20% when either of the biological parents did, and 24.5% when both adoptive parents and biological parents did. These data suggest that both genetic inheritance and environment influence criminality- supporting the diathesis-stress model of crime
• Limitation: methodological problems with twin studies of criminality

  Lange's research was poorly controlled (e.g. judgements of whether twin pairs were MZ or DZ based on appearance not DNA testing). Also, most twins are reared in the same environment- so concordance rates may be due to shared experiences rather than genetics. Methodological issues such as confounding variables mean twin studies of criminality may lack validity
• Limitation: methodological problems with adoption studies

  Adoption studies are complicated by the fact that many children experience late adoption. So these children spent time with their biological parents before adoption. In addition, lots of adoptees maintain contact with their biological parents. Both of these points make it difficult to assess the environmental (nurture as well as nature) impact the biological parents may have had.
• Limitation: explanations are biologically determinist

  The notion of a 'criminal gene' presents a dilemma. The legal system is based on the premise that criminals have personal and moral responsibility for their crimes. Only in extreme cases (e.g. diagnosis of mental illness) can someone claim that they were not acting entirely of their own free will. This raises ethical questions about what society does with people who are suspected of carrying criminal genes and who therefore have a limited choice