Genetic influences on criminality from adoption studies

Biological factors may play a role in offending behaviour, though they do not fully determine it. Concepts such as concordance rates indicate the likelihood that both individuals in a pair share a trait if one has it. Biological disposition refers to a genetic tendency towards criminal actions, while biological dysfunction involves irregularities in bodily processes that could affect behaviour.

Adoption studies help isolate genetic factors by comparing criminality rates between adopted children and their biological versus adoptive parents.

Key findings from Mednick et al (1984)

• Method - Researchers examined records of 14,427 Danish adoptees, comparing criminal conviction rates with those of their biological and adoptive parents.
• Results - Among adoptees whose parents (biological or adoptive) had no convictions, 13.5% had convictions themselves. This rose to 14.7% if an adoptive parent had a conviction, 20% if a biological parent did, and 24.5% if both did.
• Conclusion - The higher rates linked to biological parents suggest a genetic component to criminality, but the low overall concordance indicates other influences are involved.
• Evaluation - These studies separate genetic from environmental effects effectively. However, a lack of conviction does not mean no crimes were committed, which could affect accuracy.

Twin studies on aggression and criminality

Aggression often contributes to offending, and twin studies explore genetic links by comparing monozygotic (MZ) twins, who share all genes, with dizygotic (DZ) twins, who share about half.

Christiansen (1977) study on criminal activity in twins

• This study reviewed 3586 twin pairs.
• Male MZ twins had 35% concordance for criminality, versus 12% for DZ twins.
• Female MZ twins showed 21% concordance, compared to 8% for DZ twins.

Rushton et al (1986) study on aggressiveness in twins

• This research involved 573 adult twin pairs.
• MZ twins had a 40% correlation in aggression scores, while DZ twins showed only 4%.

Concordance rates below 100% for MZ twins highlight that genetics alone do not explain criminality; environmental factors also contribute.

The role of extra Y chromosome in offending

Some chromosomal abnormalities may increase impulsivity or aggression, potentially leading to crime.

Jacobs et al (1965) study on XYY chromosome pattern

• Method - The study compared chromosome patterns in prison populations versus non-prison groups.
• Results - A higher proportion of prisoners had the XYY pattern (extra Y chromosome) than the general population.
• Conclusion - The extra Y may raise testosterone levels, boosting aggression and offending. Those with XYY often show hyperactivity, impulsivity, and lower IQ, which could contribute to criminal acts.

Neural explanations of offending behaviour

Brain dysfunctions may predispose individuals to violence and crime by affecting decision-making or impulse control.

Raine et al (1997) study on brain activity in murderers

• Method - PET scans were used to image brain function in 41 murderers (who pleaded not guilty by reason of insanity) and 41 matched controls.
• Results - Murderers displayed lower glucose metabolism in areas like the prefrontal cortex, superior parietal gyrus, and corpus callosum, plus uneven activity between brain hemispheres.
• Conclusion - These dysfunctions suggest a neural basis for violent predispositions.
• Evaluation - Controls were matched for age and sex, strengthening comparisons. However, participants could not be randomly assigned to groups, limiting claims about cause and effect.

Strengths and limitations of biological explanations

Biological approaches to offending provide insights but face challenges.

Strengths of biological explanations

• Supporting evidence - Various studies, including adoption, twin, and neural research, indicate biological factors contribute to criminal tendencies.
• Scientific testability - These theories can be empirically examined, enhancing their reliability.

Limitations of biological explanations

• Incomplete concordance - No research shows 100% agreement in criminality between MZ twins or biological relatives, implying environment matters.
• Indirect influences - As Andrews and Bonta (2006) noted, genetics might cause emotional instability or mental health issues that indirectly lead to offending, rather than directly causing crime.
• Reductionism and determinism - Critics argue these explanations oversimplify behaviour by ignoring social contexts and wrongly suggest biology fixes outcomes, limiting personal agency.