Jacobs et al

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  • XYY Theory
    • Facts
      • Jacobs is a Scottish geneticist
      • She was the first to describe discovery of abnormal chromosome in humans.
      • Born: 8 October 1934.
    • 1.Claims
      • Men with XYY syndrome were more aggressive than 'XY' men.
      • This abnormality is the presence of an extra Y chromosome.
      • XYY men=supermale.
      • Supermales more inclined to be violent.
    • 2.Components
      • Correlational study comparing men in prison to general population- seeing how prevalent XYY was.
        • 15 sufferers per 1000 in prisons and 1 per 1000 in general society.
      • Prevalence of XYY men in prison was 25-60x as high then general society.
      • Early assumptions- XYY made men more aggressive and below-average intelligence.
      • Accepted symptoms now- more physically active, tendency to be more impulsive.
    • 3.Credibility
      • Scientific status
      • Been studied by other geneticists for 40-50 years.
      • Reductionist- reduces criminal behaviour down to one explanation.
      • Deterministic- implies that males with extra Y chromosome inevitably are more aggressive than males without it.
      • This theory doesn't attempt to explain why women commit crime.
      • Richard Speck-known alcoholic.
        • Killed 8 people, could be due to alcohol not XYY chromosome.
    • 4.Analysis
      • John Wayne Gacy
        • Has XYY syndrome.
        • Sexually assaulted 33 men in USA.
          • Could be due to the XYY chromosome.
      • Richard Speck
        • Sid to have XYY chromosome.
        • Known for killing 8 student nurses.
        • Was an alcoholic so murder could've been down to this.
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    • 5.Refuting Evidence
      • Focuses too much on genetics ignoring environmental triggers.
        • Richard speck- degenerate alcoholic.
      • Theilgaard- took blood samples from 30,000 criminals.
        • Found characteristics of aggression not linked to XYY men.
    • 6.Supporting Evidence
      • Nature Genetics published discovery.
        • Supporting idea that a chromosomal addition was possible.
      • American Journal of Medical Genetics
        • compared XYY males with XY siblings and found XYY sibling scored lower on intelligence tests.
          • However, no link between low intelligence and criminal behaviour.


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