Genetic factors in aggression

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  • Created by: KCharlish
  • Created on: 31-05-16 11:15

AO1 Twin studies

MZ twins - share all of their genes

DZ twins - share max, 50%

If MZ twins are more alike = strong genetic influence

Studies suggest at least 50% variance can be explained in terms of genetic factors

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AO1 Adoption studies

Adoption studies can help determine the relative contributions of environment and heredity in aggression.

Mednick and Hutchings

  • interaction between genes and their environment
  • criminal records of adopted Danish children
  • criminal biological father - increased criminality
  • criminal biological and adopted father - highest risk
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Gene coding for the production of MAOA.

MAOA regulates the metabolism of serotonin 


  • studied a violent dutch family 
  • many of the men haad abnormally low levels of MAOA
  • defective gene for the production of MAOA
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AO2 Twin studies

Miles and Carey

  • meta analysis of 24 studies
  • evidence of a strong genetic influence
  • younger individuals - genetic and environmental influences
  • older - genetic influences

Genes are influential in ALL individuals 

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AO2 Rutter


  • meta analysis of twin studies on criminality
  • DZ twins have concordance rates between 13-22%
  • MZ twins 26-51%
  • difference likely due to genetics

consider MZ twins do not show 100%

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AO2 Gene - environment interaction


  • 500 male children
  • low levels of MAOA significantly more likely to grow up to exhibit antisocial behaviour
  • ONLY if they had been maltreated as a child
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IDA Sampling

  • focused on individuals convicted of violent crime
  • represent a small minority of those who regularly engage in aggressive behaviour
  • single offence e.g. murder is not necessarily a consistently violent criminal

Validity may be suspect 

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IDA Genetic engineering

  • Real life applications
  • genetic engineering to prevent crime
  • using chemical castration to treat potential violent offenders
  • Ethical concerns about labelling someone a threat
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IDA Self reports

Methodological issues

  • self reports and observations
  • meta analysis - file drawer effect - support have used parental or self reports 
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