genetic factors in aggression

genetic factors in aggression

1. aggression can be inherited through our genes

2. twin and adoption studies

   • twin studies
     • coccaro
       • studied male MZ and DZ twins for aggressive behaviour
         • direct physical assault
         • the concordance rate of aggression for MZ twins = 50%
         • the concordance rate of aggression for DZ twins = 19%
         • genetics influence aggression
           • higher percentage of genetics shared = higher concordance rate for aggression
   • adoption studies
     • can see whether the child is more similar to biological parent or adoptive parent in terms of aggression
       • whether genetics or environment plays more of a role in aggression
     • mednick, gabrielli, hutchings
       • over 14,000 participants
       • studied criminal records of danish children adopted outside of biological family
         • having a criminal biological father increased the risk of the child's criminality and aggression more than having an adoptive criminal father

3. MAOA gene

   • monoamine oxidase
   • affects levels of neurotransmitters
   • MAOA is controlled by MAOA gene
     • enzyme that breaks down neurotransmitters in the brain
   • defective gene can lead to...
     • less of the enzyme = MAOA-L
       • research shows MAOA-L causes aggression
         • less of the enzyme = less breaking down of serotonin
           • high serotonin levels = high levels of aggression
     • more of the enzyme = MAOA-H
   • everyone has this gene
   • cases et al
     • genetically engineered mice with MAOA-L
       • mice had atypical serotonin levels and behaviour
       • increased levels of aggression

4. evaluation

   • :) evidence to support
     • brunner - studied 28 male members of one large dutch family
       • repeatedly involved in aggressive, violent crime
         • rape
         • attempted murder
         • assault
       • all had MAOA-L
   • :( MAOA gene can only explain a small amount of aggression
     • MAOA-L is only in 1/3 of men in western populations
       • cannot explain aggressive behaviour in 2/3 of men and in any women
     • often not shown in women
   • :( too simplistic
     • :) can investigate in detail with biological tests
       • see how genes influence aggression
     • genetics can't be the only factor affecting aggression
       • otherwise, MZ twins' aggression concordance rate would be 100%, not 50%
       • eg. upbringing
   • :( animal research
     • :) unethical to genetically engineer humans to manipulate their MAOA levels to see the effects on aggression
     • :( unethical to conduct on animals too
     • :( humans are more complex in brain structure and genetics
       • may have different forms of aggression and varying affecting factors
   • :( could be other explanations
     • rutter - found MZ and DZ twins' criminality concordance rate
       • MZ = 51%
       • DZ = 22%
       • genetics isn't the only factor affecting aggression
         • otherwise, MZ twins' concordance rate would be 100%
         • other factors contributing to aggression