genetic factors in aggression

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  • genetic factors in aggression
    • Twin studies
      • Monozygotic (MZ – identical) twins and dizygotic (DZ- share 50% DNA). If MZ twins are alike in aggressive behaviour it is due to their genes not environment
        • Coccao et al – nearly 50% of variance in direct aggressive behaviour could be due to genetic factors
    • Adoption studies
      • If positive correlation between aggressive behaviour in adopted kids and aggressive behaviour in their biological parents then genetic effect implied
        • If positive correlation found between adoptee and rearing family’s aggressive behaviour then environmental effect
          • 14000 adoptions, Denmark - significant number of adopted boys w/ criminal convictions had biological parents w/ criminal convictions – Hutchings and Mednick
    • a gene for aggression
      • the role of MAOA
        • There is no individual gene but gene responsible for producing a protein (monoamine oxidase A - MAOA) is associated with aggression and low levels of serotonin
          • Dutch family, many male members behaved in very aggressive manner e.g. arson/rape and found to have low levels of MAOA – Bruner et al
      • Gene-environment interaction
        • Caspi et al – 500 male kids. Those with low levels of MAOA more likely to grow up and exhibit antisocial behaviour but only if they had been maltreated as kids
          • Children with high levels of MAOA who were maltreated and those with low levels who were not maltreated did not display antisocial behaviour
            • Shows interaction between genes and environment determines behaviour.
    • Genetics and violent crime
      • Researchers claim inherited temperament or personality characteristics place some people more at risk
        • When adopted children have both biological and adoptive parents with a history of violent crime they are at more risk of committing violent crime
          • Gene-environment interaction theory
            • Genetic influences were significant in cases of property crime but not in case of violent crime – Brennan and Mednick
    • Difficulties of determining role of genetic factors
      • Hard to establish genetic cause because more than one gene contributes to a given behaviour
        • Many genetic and non genetic factors
          • Influences may interact with each other
            • Supports Caspi’s gene-environment interaction study
    • Problems of assessing aggression
      • Parent or self-report or observational techniques
        • Miles and Carey – Meta analysis – mode of assessment found to be a significant moderator of aggressive behaviour
          • Genetic factors explained in large proportion of variance in aggressive behaviour in studies using parental/self-reports
            • Observational techniques showed significantly less genetic contribution and more influence of environmental factors
              • Bandura et al – Bobo doll study – no difference in correlations between MZ and DZ twins
                • Suggesting individual difs in aggression were more product of environmental influence than genetic factors – Plomin et al
    • Methodological limitations
      • Studies using genetic factors often fail to distinguish between violent and non-violent crime, making it more difficult to untangle the role of genetic factors in specifically aggressive violence
        • Also fail to distinguish between criminals who are habitually violent and those who performed the violent crime as a one-off
    • IDA - Real World Application
      • Too unstable for actual immediate application but raises concerns because some links have been shown



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