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.

Adoption Studies and Environmental Factors

This section examines how adoption studies contribute to our understanding of genetic versus environmental influences on criminal behavior.

Definition: Concordance rate refers to the percentage of twin pairs who share the same characteristic or behavior.

Example: Medrick's 1994 study of 14,000 adopted boys showed significant correlation between biological parents' criminal records and their offspring's behavior.

Highlight: The research demonstrates that while genetic factors play a role in criminal behavior, environmental triggers are often necessary for criminal tendencies to manifest.

Vocabulary: Biomedical factors refer to biological and chemical influences on behavior that are recognized by courts and sometimes incorporated into laws.

Brain Structure and Criminality

This section examines how brain structure and injuries can potentially influence criminal behavior.

The brain is divided into four lobes, each with distinct functions. The prefrontal cortex in the frontal lobe plays a crucial role in regulating behavior and decision-making. Damage to the temporal lobe can lead to behavioral issues. The amygdala, part of the limbic system, is vital for processing emotions, especially fear.

Highlight: Adrian Raine's research using PET scans revealed damage to the prefrontal cortex in impulsive killers, suggesting a link between brain structure and criminal behavior.

Famous cases illustrating brain injury and criminal behavior:

1. Phineas Gage: Severe frontal lobe damage in 1848 led to personality changes, highlighting the importance of this region in emotional control.

2. Charles Whitman: A brain tumor pressing on his amygdala may have contributed to his violent actions in the 1966 University of Texas shooting.

Example: Charles Whitman's case demonstrates how brain injury aggression treatment might be crucial in preventing violent behavior stemming from neurological issues.

Strengths of brain-based theories:

• Extreme cases provide clear evidence of brain injury leading to personality changes and criminal behavior.
• Correlation found between abnormal EEG readings and criminality.
• Higher prevalence of brain injuries among prisoners compared to the general population.

Limitations:

• Brain injuries are relatively rare and may not explain most criminal behavior.
• Personality factors likely play a more significant role in criminality.
• The higher rate of brain injuries in prisoners could be a result, rather than a cause, of criminal behavior.

Vocabulary: Undifferentiated frontal lobe syndrome refers to a condition where damage to the frontal lobe leads to various behavioral and cognitive changes, potentially including increased aggression or impulsivity.