Genetic theories

• Genetic theories


  Linked to Lombroso's theory that if individuals are born criminal then it must be a genetic trait passed down from parent to child
• Jacob's XYY Study


  Suggests that some crime might be attributable to a chromosomal abnormality 47, XYY
• XYY (supermale) chromosomal syndrome


  • Involves the presence of an extra Y chromosome
  • May act on the brain's limbic system (which regulates man's most primitive drives, including his impulses toward violence)
  • Can somehow help trigger violent criminal acts
• Twin Studies


  Support the idea that a heritable trait may increase the risk of criminal behaviour
• Monozygotic (MZ) twins


  • Share 100% of DNA
• Dizygotic (DZ) twins


  • Share 50% of DNA
• Studies have proven that identical twins (MZ) have more concordance than non-identical twins (DZ)
• Studies


  • Johannes Lange (1929) found that 13 MZ twins had both served time in prison compared to 17 DZ twins
  • Christiansen (1977) studied 3,580 twins from Danish Islands and found concordance rates of 52% between MZ twins; that is, where one identical twin had a conviction, there was a 52% chance of the other twin also having a conviction. But, among DZ twins, there was only a 22% chance
• Adoption Studies


  Compare criminals with their biological and adoptive parents to examine the impact of nurture on children raised by non-biological parents
• If an adopted child is more like their biological parents than their adoptive parents, a genetic basis of criminality may be suggested
• If an adopted child is more like their adoptive parents, there is an argument that their environment is the main reason for criminality
• Adoption Studies


  • Mednick et al studied 14,000 adopted children in Denmark from 1924 to 1947. They found that some were more likely to have a criminal record if a birth parent also had a record (concordance rate of 20%). By contrast, only 14.7% had a criminal record if their adoptive parent had one. This suggests a genetic risk in terms of criminality