2.1 Genetic theories of criminality

• Cambridge studies in delinquent development findings


  Found out of 397 families, half of all criminal convictions came in just 23 familes
• Osborn + West findings


  Found that sons of criminal farthers were more likely to have a criminal record.
• What are monzogytocic twins (Mz)


  Identical- share 100% DNA
• What are dizygotic twins (Dz)


  Fraternal- share 50% DNA
• What is the concordance rate


  The probability (%) that if one twin has a characteristic, the other twin will have the characteristic
• Lange studies of Mz/DZ

  • 1929
  • investigated 13 Mz+ 17 Dz twins
  • found 10 of the 13 Mz twins had both been in prison
  • found only 2 of 17 Dz twins had both been in prison
• Christiansen Genetic studies of Mz/Dz

  • 1977
  • investigated 3586 twins
  • Found a 52% concordance rate between Mz ( one twin had a convivtion, the other had a 52% chance of the other twin also having one)
  • Dz Twins only 22%
• Hutchings 1975 adoption studies

  • studied 14,000 adopted children + found a high proportion of boys with criminal convictions had parents with convictions aswell.
  • This suggests that there is a strong link between genetics n criminality
• Mednick 1975 adoption studies


  studied adopted children and found 0 relationship between the number of criminal convictions adopted parents had and their adopted offspring
• XYY theory


  a chromosoic defect thought to explain the hightend criminal behaviour of some individuals
• what does the XYY theory cause

  • aggresion
  • low IQ
  • physical changes
• Jacob (1965) XYY findings

  • more aggresive and violent than men with a single Y chromosome
  • he found xyy men are over represented in prison
  • 15X more likely to be a criminal
• Case study XYY

  • John Wayne Gacy
  • it is highly suspected that he had the xyy mutation
  • he sexually assulted, tortured and murderd atleast 33 men and boys