criminology ~ genetic theories

• genetic theories


  explains how family members who are blood relatives can own a 'criminal gene' and can explain why criminality can run through the family
• dizygotic twins


  non-identical twins - two separate eggs - share 50% of DNA
• monozygotic twins


  identical twins - come from one egg - share 100% of DNA
• concordance rate


  the probability that if one twin has a characteristic the other twin will have it (as a percentage)
• johannes lange theory (1929)


  10/13 MZ twins had both served time in prison and 2/17 DZ had both served time in prison
• christiansen (1977)


  investigated approximately 3600 pairs of twins and he found that out of all the twins he studied that male twins were more likely to be criminals than female
• adoption studies


  children are compared to their biological and adopted parents to see which has more of an influence - nature vs nurture
• hutchings and mednick


  studied 14,000 adopted children and found a high proportion of boys with criminal convictions had biological parents with a criminal conviction
• mednick et al (1975)


  studied adopted children and found no relationship with the criminal conviction and adopters
• XYY theory


  the idea that violent behaviour in males can in part be attributed to the presence of an extra Y chromosome in male offenders
• supermales


  XYY
• example of a supermale


  john wayne gacy -> tortured and killed at least 33 men
• jacob et al


  15 in 1000 men have this condition in prison - compared to 1 in 1000 in the general population
• strength of XYY theory


  price and whatmore found some links between the syndrome and property of crime
• limitation of XYY theory


  this syndrome is very rare as only 1/1000 men have it therefore is cannot explain as much crime
• strength of twin theories


  because mz twins are genetically identical, it is logical to examine whether the offending behaviour is also identical
• limitation of twin theories


  higher concordance rates may be due to the same home, school and lifestyle rather than criminality
• strength of adoption studies


  the research design is logical and allows us to see the relative importance of 'nature'
• limitation of adoption studies


  many children are not adopted immediately after birth and therefore they may remain with their biological family for a while first