Part 3

• Criminality


  Biological theories of criminality
• Genetic theories


  Theories that suggest criminality is inherited through genes
• Chromosomes


  • Strands of 'condensed DNA'
  • Humans have 46 chromosomes divided into 23 'pairs'
  • Genes are 'units' of DNA which code for one or more characteristics and are inherited from a person's parents
• XYY Theory


  Theory that crime might be attributed to a chromosomal abnormality where an extra Y chromosome appears
• XYY Syndrome


  • Also known as 'super-male disease'
  • Behaviours displayed include: explosive temper, hyperactivity, impulsivity, defiant actions, lack of empathy, and in some cases, antisocial behaviour
• XYY men are over-represented in prison - 15 in 1000 men have the condition in prison compared to 1 in 1000 in the general population
• John Wayne Gacy


  • Sexually assaulted, tortured and murdered at least 33 men
• Humans typically have 46 chromosomes
• XYY Syndrome is sometimes known as the 'super-male disease'
• Behaviours associated with XYY Syndrome


  • Explosive temper
  • Hyperactivity
  • Impulsivity
  • Defiant actions
  • Lack of empathy
  • Sometimes anti-social behaviour
• Jacobs found 15 in 1000 people had XYY in prison, compared to 1 in 1000 in the general population
• John Wayne Gacy sexually assaulted, tortured and murdered at least 33 men
• Dizygotic Twins


  Born at the same time, come from two separate eggs and share 50% of the DNA (Fraternal Twins)
• Monozygotic Twins


  Born at the same time, come from one egg and share 100% of the DNA (Identical Twins)
• Concordance Rates


  The probability (as a percentage) that if one twin has a characteristic the other twin will have the characteristic
• Christensen found a 52% concordance rate between MZ twins, compared to 22% for non-identical twins
• Higher concordance rates for MZ twins


  Suggests a potential genetic cause to criminal behaviour
• Limitations of twin studies


  • If genetics were the only cause of criminality, identical twins would show 100% concordance
  • Higher rates for MZ could be due to them sharing the same home and environment, not just genetics
  • Other environmental factors could impact on their criminality
• Adoption studies


  Studies in which adopted children are compared to their biological and adopted parents to see which has more influence - biology or environment
• Mednick's adoption study found a 20% concordance rate for criminal convictions in adopted children with biological parents who had criminal convictions, compared to 14.7% if their adoptive parent had a criminal record
• Higher concordance rates for adopted children with criminal biological parents


  Suggests a potential genetic cause to criminal behaviour
• We usually have 46 chromosomes arranged in 23 pairs
• Women have one X and one Y chromosome
• Adoption studies can be used to test the nature vs nurture theory
• XYY males are generally smaller and more intelligent
• Genetic theories: True or false?
• Genetic theories that are true


  • Many twin studies show a 100% concordance rate
  • Twin studies can provide support for genetic theories if MZ twins both engage in criminal behaviour
  • If genes are the only cause of crime, the concordance rates in twin studies would be 100%
  • Adoption studies overcome the problem with twin studies when twins have been raised in the same household
  • Jacob et al claim that men are more likely to be violent and aggressive if they have an extra X chromosome
  • Women have one X and one Y chromosome
• Genetic theories that are false
• Monozygotic twins


  Identical twins who share 100% DNA
• Josh has frequently been involved with the police since the age of 12 years when he got involved in a fight with another child from school. Since then, he has been arrested for other violent offences and shoplifting
• Jordan has never been involved with the police and is a hardworking, A grade student
• Despite being twins, Josh and Jordan have not lived together since the age of 6 months as their mother couldn't cope. Josh lived with a friend of the family and Jordan went to live with his grandmother
• Explain how genetic theories can be applied to Josh and Jordan's situation

  1. Consider twin studies - concordance rates in MZ twins

  2. Consider adoption studies - role of environment vs genetics
• Describe how genetic researchers might use twin studies to investigate criminality


  1. Identify criminal behaviour in MZ twins

  2. Look for concordance in criminal behaviour

  3. High concordance supports role of genes
• Ronnie and Reggie were identical twins, therefore sharing 100% DNA


  Were they born criminals?