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.