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Adoption Studies and Criminality
Adoption studies compare adopted children to their biological and adoptive parents to determine whether genetics or environment has a greater influence on criminal behaviour.
Nature vs Nurture in Adoption Studies
If an adopted child's criminal behaviour is more similar to their biological parents, it suggests a genetic influence. If it is more similar to their adoptive parents, it suggests an environmental influence.
Mednick et al. (1984) Adoption Study
Mednick, a US psychologist and geneticist, conducted a large-scale adoption study to investigate whether criminality is more influenced by nature or nurture. He studied 14,000 adopted males in Denmark (1924-1947) and found a 20% concordance rate for criminality with biological parents, compared to 14.7% with adoptive parents. This suggests a genetic link to criminality, though environmental factors still play a role.
Mednick and Hutchings Study
Further research by Mednick and Hutchings reinforced the genetic link to criminality. They compared adopted children with and without a criminal record and found that those with a criminal record were more likely to have biological parents who also had criminal records. This strengthens the argument that genetic factors contribute to criminal behaviour. However, it does not completely rule out environmental influences.
Purpose of Adoption Studies
Adoption studies attempt to rule out environmental effects by studying children raised by adoptive parents with no genetic similarity. Unlike twin studies, which cannot fully separate nature from nurture if twins are raised in the same home, adoption studies allow researchers to see whether criminal behaviour persists even when environmental factors change. This provides stronger evidence for genetic influences on criminality while also acknowledging the role of upbringing.
Crowe (1972) Adoption Study
Crowe compared a group of adopted children whose biological mother had a criminal record to a control group whose biological mother did not. He found that 50% of children whose biological mother had a criminal record also had one by 18, compared to only 5% in the control group. This suggests that criminal tendencies may be biologically inherited, even when children are raised in a different environment.
