Genetic theories

• if crime is inborn, meaning it runs through the family.

  1961-Cambridge Study in Delinquent Development found that out of 397 families, half of all criminal convictions came in just 23 families.

  Osborn and west found that sons of criminal fathers were much more likely to have a criminal record
• what are the two types of twins?

  Dizygotic Twins- born at the same time but come from two separate eggs and share 50% of the dna.

  Monozygotic twins- born at the same time but come from one egg and share 100% of the dna
• what are concordance rates? 


  The probability (as a percentage) that if one twin has a characteristic the other twin will have the characteristic
• what does crime often run in family?

  family members (blood relatives) share many of the same genes so if one member has ‘criminal genes’ then it is likely that their relatives will have them.

  
  

  Identical (monozygotic) twins share exactly the same genes, they both developed from the same fertilised egg. Therefore, if one twin is criminal, the other twin ought to be criminal too.
• What was Christensen's (1977) twin studies?

  He investigated 3586 twin pairs born in Denmark,

  He found there was 52% concordance rate between MZ twins

  Whereas only 22% concordance rate between DZ twins

  
  

  Ishikawa and Raine found a 44% concordance rate for MZ twins and 21.6% concordance rate for DZ twins.
• What was Lange's (1929) twins studies?

  Lange investigated 13 MZ twins and 17 DZ twins

  Found that 10/13 MZ twins had both served time in prison.

  Only 2/17 DZ twins has both served time in prison.
• Criticisms of twin studies

  Twins share genes but also share the same environment-so how can it be argued that behaviour is only genetic?

  Twins look the same or similar and so will be treated the same by the people around them so is it genetics causing the similarities or environment?
• Adoption studies 


  this theory is that an adopted (at birth) child shares the same environment as their adoptive parents/carers but, the same genes as their biological parents.

  if we find that the adopted child's behaviour in relation to criminality is the same as that of their birth parents then would this support a genetic theory of crime?
• What was Mednick et al.'s (1984) adoption studies?


  They studied 14,000 adopted children in Denmark from 1924-1947, found that a high proportion of boys with criminal convictions had biological parents with a concordance rate of 20%, in contrast they found that only 14.7% had a criminal record if their adoptive parent had one.
• What was Hutchings et al.'s (1944) adoptive study?


  found no relationship between the number of criminal convictions of adoptive parents and their adoptive children but, found significant correlation between number of criminal convictions of biological parents and children.
• What was Crowe's (1972) adoption study?

  When the child's biological mother had a criminal record, the child ran a 50% risk of acquiring one by the age of 18, compared with only a 5% risk if the biological mother did not have a criminal record.
• Strengths of Twin and Adoption Studies

  -Twin and adoption studies give some support to genetic explainations.

  -Adoption studies overcome the problem of isolating genes and environment.

  -Research design of adoption studies is logical (nature vs nurture)
• Weaknesses of Twin and adoption studies.

  -If criminality was only genetic, MZ twins would have 100% concordance.

  -It is impossible to isolate genetic effects fully from environmental ones.

  -Adopted children often placed with similar families to their birth family.
• XXY theories.

  • chromosomes: strands of 'condensed DNA'. On these chromosomes you find individual genes for every physical characteristic.
  • Genes: 'units' of DNA which code for one or more characteristics and are inherited from a person's parents.
• What chromosomes do we inherit from our parents?

  If we are a female (XX) we will get an X from each parent.

  If we are a male (XY) we will get an X from our mother and a Y from our father

  However sometimes their are abnormalities.
• One abnormality is an extra Y chromosome, this is known as XYY syndrome and has been labelled 'super male syndrome'. Men with XYY syndrome tend to be very tall and well built and of low intelligence.
• What is Jacob et al.s (1965) XYY theory?

  Claims that men with XYY syndrome are more aggressive and potentially violent than other males.

  
  

  They studied imprisoned criminals in psychiatric hospitals and found that XYY men are over-represented in prison.

  
  

  15/1000 men have the condition in prison compared to 1/1000 in the general population.

  
  

  Many of the men studied has histories of aggression and violent assault.

  
  

  Price and Whatmore found XYY males to be immature and unstable, with a strong tendency to commit seemingly motiveless property crimes.
• MAOA "the warrior gene"

  • X-chromosome genes are responsible for breaking down neurotransmitters in the brain, such as dopamine and serotonin.
  • Various studies have linked the 'warrior gene; to increased risk-taking and retaliatory behaviour (MAOA-L or an absence of MAOA)
  • MAOA mutations are exclusive to men despite being X-based
• Brunner et al. 1993 (MAOA study)


  Studied a Dutch family whose male generations displayed extreme violent aggression.

  
  

  He found that 9 males from the family had a defect, they were missing the MAOA gene and exhibited low levels of IQ.
• Lea and chambers (2007) (MAOA study)

  found a high incidence of the low activity MAOA variant among Maori (56% in a small study). This figure was used to explain problems of risk taking behaviour, aggression and violent crime.
• Caspi et al. (2002) (MAOA and the environment)

  • compared childhood maltreatment in those with genetic MAOA deficiencies against those without.
  • Monitored subjects from birth through into adulthood.
  • Those who suffered maltreatment and possessed the 'warrior gene' showed higher levels of criminality (12% of cohort were responsible for 44% of convictions)
  • 10x more likely to be convicted of violent crime by the age of 26.
  • Those possessing the gene variant, who were not abused during childhood, were found to be less aggressive.