Genetics and Biochemistry in Criminality
This section explores the role of genetics and biochemical factors in criminal behavior through twin and adoption studies.
Twin Studies:
Twin studies compare concordance rates (likelihood of both twins engaging in criminal behavior) between monozygotic (identical) and dizygotic (fraternal) twins.
Definition: Concordance rate is the percentage of twin pairs where both individuals exhibit the same trait or behavior.
Key findings:
- Lange (1929): Higher concordance rate for criminality in MZ twins (10/13) compared to DZ twins (2/17).
- Christiansen (1977): 52% concordance rate for MZ twins vs. 22% for DZ twins.
- Another study showed 44% concordance for MZ twins vs. 21.6% for DZ twins.
Adoption Studies:
Adoption studies compare adopted children to their biological and adoptive parents to separate genetic and environmental influences.
Mednick et al. (1975) findings:
- 20% concordance rate for criminal records if biological parent had one.
- 14.7% concordance rate if adoptive parent had a criminal record.
Mednick (1994) study of 14,000 adopted boys:
- Significant correlation between biological parents' criminal convictions and their offspring's.
- No correlation between adoptive parents' convictions and adopted children's behavior.
Quote: "If the cause of criminality is genetic, you would expect that if one MZ twin engages in criminal activities then the other twin will do the same."
Biochemical Factors:
- Strong medical evidence supports the influence of substances and hormone levels on behavior.
- Courts recognize biomedical factors in some laws.
- May create a predisposition to offending but often require environmental triggers.
Highlight: The relationship between prefrontal cortex damage and criminality is a key area of study in biological theories of crime.
Strengths of genetic and biochemical explanations:
- Explain why crime often runs in families.
- Supported by twin and adoption studies showing higher concordance rates in genetically related individuals.
Limitations:
- The effect of biochemicals on aggression might be overstated, more likely to lead to verbal than physical aggression.
- Environmental factors still play a crucial role in criminal behavior.
Example: The statement "There is a correlation between head trauma and violent behavior. True or false" can be answered as true, based on the evidence presented, but with the caveat that correlation does not imply causation.
