Aggression (biological and genetic explanations)

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  • Aggression
    • Biological explanations
      • Testosterone-an androgen produced by Leydig cells in male testes and adrenal cortex.
        • During puberty aggression increases when androgen levels are higher.
        • Wagner et al (1979)-a castrated mouse showed less aggression.
          • ...after testosterone treatment, aggression increased again.
          • Evaluation
            • Aggression didnt disappear after castration
            • it cannot be stated that tesosterone causes aggression
            • Other studies have found that aggressive-ness in mice is only reduced if castration occurs before puberty.
            • Testosterone contributes to the development of aggression-its effects are relatively permanent.
      • Testosterone in humans
        • Dabbs et al (1995)-the relationship between testosterone, crime and prison behaviour.
          • Measured the testosterone levels in the saliva of 692 adult male prisoners
            • Findings: those who committed major crimes (murder, rape etc) had the highest levels.
          • Evaluation
            • Deterministic
            • High testosterone levels could be a result of the crime.
        • Further findings:
          • High testosterone = boisterous and macho
          • Low testosterone = attentive and helpful
        • Problems with research
          • Does not establish the cause.
          • There may be other factors
          • How do we operationalise aggression?
        • Women and testosterone
          • Dabbs et al (1985)
            • 84 female prison inmates, testosterone highest in cases of unprovoked violence, lowest in defensive aggression.
          • Pillay (2006)
            • Testosterone levels varied across sports, males and females in aggressive sports had the highest levels of testosterone.
        • Models of testosterone.
          • Reciprical model
            • Aggression causes raised testosterone levels.
          • Basal model
            • Testosterone is the cause of aggression.
              • The levels of T influences dominance-the more T, the more competitive and hence more dominant they become. Dominance is the effect of T.
      • Low serotonin = aggression
        • Mann et al (1990)
          • Dex-fenfluramine (DXF) treatment in males was associated with an increase in hostility and aggression scores.
            • Supports the bio-chemical explanation of aggression because DXF is known to deplete soerotonin levels
            • Evaluation
              • Why doesn't it affect women?
              • Deterministic
              • Real life applications: give it to criminals?
        • Raleigh et al (1991)
          • Giving monkeys a diest rich in tryptophan (Trypt.) (which increased their levels of serotonin) decread their levels of aggression
            • Supports the bio-chemical explanation of aggression because DXF is known to deplete soerotonin levels
            • Evaluation
              • Deterministic
              • Low in generalis-ability to humans as these are monkeys not humans.
        • Popova et al (1991)
          • Animals bred for domestication had an increase in serotonin levels over generations.
            • Low in generalis-ability to humans as these are monkeys not humans.
    • The role of genes
      • Is aggression passed on?
        • Nelson (2006)-found selective breeding (e.g. pitbulls & bulls) can lead to more aggressive behaviour in animals.
        • Lagerspetz (1979)
          • Selectively bred mice for aggression.
          • By the 19th generation, rates of aggression (biting etc) in the agressive mice was 52%
            • Only 5% in ordinary mice.
          • These mice had heavier testes and heavier forebrains
          • Altered levels of serotonin in the forebrain and noradrenaline in the brain.
          • However...
            • Lagerspetz: Selectively bred aggressive mice can be conditioned to be less aggressive.
              • Aggressive wild animals can be tamed.
            • In humans, there are environ-mental factors as well.
      • A combination of structural (muscles)  and functional (test. and serotonin) genetic effects contribute to aggressive behaviour.
      • Twin studies
        • Findings are extremely variable
        • Canter (1973)found a correlation of 0.14 for MZs reared together.
          • However, O'Connor (1980) looked at the same set of twins and found 0.72.
        • Not one, single gene.
        • Many non-genetic influences
        • Gene-environment interaction (Caspi et al, 2002).
      • Monoamine Oxidase A (MAOA)
        • The gene responsible for producing MAOA has been associated with aggressive behaviour.
        • Regulates serotonin levels
        • Brunner et al (1993)
          • Discovered a mutation of the MAOA gene in a Duthc family.
            • Family records showed a history of violence in the males.
              • Found a low level of MAOA and a defect in the gene.
          • Evaluation
            • Not generalisable-only done on one family, in one country etc.
            • Environment plays a key role- grew up in a violent household violence is bound to be passed on.
            • Cause or effect?
        • Cases et al (1995)-disabled the MAOA gene in mice
          • serotonin levels decreased, males became very aggressive-females were unaffected.
        • Caspi et al (2002)
          • 500 male children, children with the gene for low levels of MAOA were more likely to exhibit antisocial behaviour if they had been maltreadted as children.
      • Evaluation
        • Violent Vs non-violent crimes (not all crimes are violent)
        • Habitual Vs one-off criminals.
        • Often contradictory findings-how are we operation-alising aggression?
        • More than one gene contributes to most behaviours.
        • Genes and environment interact with each other.

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