Psychology Topic E

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  • Compares family trees of criminals and non-criminals to show biological link.
  • Some show a child is more likely to be criminal if a parent/grandparent is too.


  • Looks at relatives, siblings and twins adopted at a young age.
  • They share genes but not environment to focus on genetics as a criminality cause.
  • Mednick (1984) studied 14,427 adopted children and compared their criminal records to their adoptive and biological parents ones. He found that adopted children with criminal records for property theft had criminal biological fathers; true even when siblings had been placed in different adoptive homes.


  • Either monozygotic or fraternal/dizygotic twins. 
  • Identical twins share all genes, non-identical share half of their genes. Two criminal identical twins shows strong genetic link to criminality.
  • Christiansen (1977) studied 3586 pairs of twins in Denmark and found that if an identical twin was criminal, 52% of the time the other was too. True with only 22% of non-identical twins. He looked at property crime not violent crime. 


  • Family/twin studies show we are more likely to turn to crime if a family member has, but you could argue that family members are raised together, so their criminality could be due to upbringing or observational learning.
  • The above studies are based on only criminals who have been caught.


  • Male sex genes are XY and female sex genes are XX.
  • Blood samples can show if criminals have a chromosome abnormality.
  • In 1960s, XYY chromosome was found that can make males more criminal and violent.
  • XYY is not inherited and is rare but men with this have been more aggressive and slower learners.
  • Theilgaard (1984) found XYY males were more masculine and aggressive.
  • The murderers Richard Speck, John Wayne Gacy and Arthur Shawcross had XYY.


  • Not all violent criminals have XYY.
  • The samples of XYY are not large enough to be sure of a link.
  • The criminals may have turned to crime because of slow learning having caused them to not succeed at school.



  • Family patterns are experiences children could have during their family life, such as divorce, separation from main caregiver or family size.
  • Divorce can lead to broken homes which can make children twice as likely to become criminal. Boys become aggressive with no father and girls become depressed. Children could suffer worse if there were arguments before the divorce. Divorce can come with other issues such as moving schools and home, or financial problems and maternal deprivation.
  • Maternal deprivation is when a child becomes distressed from being separated from their caregiver. If the bond between them is broken, mainly during the first two years of life, the child could suffer lasting effects. They lose sense of safe world and feel rejected.
  • John Bowlby (1946) questioned 44 boy offenders about their crimes and relationships with their parents. He found that 14 boys


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