Biological theories into Criminality

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  • Biological theories into criminality
    • Genetic theories
      • XYY theory
        • Presence of an extra y chromosome
        • 'Super males' are more of an interests to criminologists
        • Jacobs et al found that XYY men are more aggressive and violent
        • Found that XYY is overpopulated in prisons
        • John Wayne Gacy had XYY syndrome and murdered and tortured 33 young males.
      • Twin studies
        • Monozygotic- identical twins
        • Dizygotic- non identical twins
        • Lange found that MZ twins shared a higher degree of concordance than DZ twins for criminal behaviour
        • Christiansen found higher rates for MZ twins too
      • Adoption studies
        • Comparison of biological and adoptive parents
        • Hutching and Mednick studied adopted children and found a high proportion with criminal convictions also had biological parents with criminal convictions
        • Mednick et al found no connection between adopted children and adoptive parents
    • Physiological theories
      • Lombroso
        • Argued that criminal is a separate species, between modern and primate humans
        • Argued that a 'born criminal' could be determined by physical shape of head/features
          • Atavistic or primitive features
        • Examined facial features of 4,000 living criminals and 400 dead.  40% accounted for by atavistic features
        • Study in Chinese uni researched ID pics, half with criminal convictions. Correctly identidied 80% of real criminals
      • Sheldon
        • Advanced Lombroso's theory, linked criminal behaviour to physical form
        • Examined 4000 scantily clothed men and put forward fundamental somatotypes
        • Endomorphic- fat and soft, tend to be sociable and relaxed
        • Ectomorphic- thin and fragile, introverted and restrained
        • Mesomorphic- muscular and hard, aggressive and adventurous
        • Found criminals were more prone to being mesomorphic and least likely ectomorphic
      • Brain scans
        • Raine et al used PET scans to study the brains of impulsive killers
          • Found damage on the pre frontal cortex,  controls impulsive behaviour
        • Case study: Phineas Gage
          • Iron rod went through his head, destroyed left frontal lobe. Behaviour and personality changed
          • He became anti-social, used bad language and had bad manners
      • Neuro-chemical
        • Brain can be affected by diet and blood sugar levels
        • Low serotonin levels are linked with higher agression
        • Large about of steroids can increase violence


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