genetic theories

• Jacob XYY study:

  • KEY IDEA = XYY syndrome in males makes them genetically pre disposed to criminality
  • he compared rate of XXY in imprisoned criminals with general population
  • found that there were a higher than average proportion of inmates who had XYY
  • features include: very tall, well built, violent, high aggression
• strength of Jacob XYY

  • price and Watmore found links with XYY and property crime
  • Jacob Et Al found association with XYY and violent prisoners
• limitation of Jacob XYY:

  • having syndrome doesn't mean that it is cause of crime
  • XYY men fit stereotype of violent offenders- labelling theory
  • low intelligence of XYY may give higher chance to being caught
  • syndrome is too rare to explain crime
• twin studies:

  • TWIN KEY IDEA = if crime is genetic (MZ) twins should have identical criminality
  • TWIN STUDY FINDINGS = Christiansen found concordance in criminality MZ twins being 52% and DZ twins 22%
• adoption studies:

  • KEY IDEA = adoptees share environment of adoptive parents/ genes of biological parents. if genetic criminality will match bio parents more
  • ADOPTION STUDY FINDINGS: MEDRICK Et Al found birth parent concordance was 20% vs adopted parent concordance 14.7%
• strengths of twin+adoption studies:

  • twin and adoption studies give some support to genetic explanations
  • adoption studies overcome the problem of isolating genes and environment
  • research design of adoption studies is logical due to nature vs nurture
• limitation of twin+adoption studies:

  • if criminality was only genetic MZ twins would have 100% concordance
  • impossible to isolate genetic effects fully from environmental ones
  • adopted children often placed with similar families to their birth family