Neural and hormonal causes of aggression:

  • Limbic system - includes hypothalamus and amygdala. Acts as an alarm system triggering an aggressive response to certain types of threats. Giving testosterone to new-born female mice made them act like males with increased aggression. This suggests that testosterone masculinises androgen-sensitive neural circuits underlying aggression in the brain. The amygdala evaluates the emotional importance of sensory information and prompts an appropraite response. Damage to this area can lead to inappropriate behaviours such as not being aggressive when you should.
  • AO3 - Research in Greece found that removing the amygdala reduced aggressive incidents by between 33% and 100%, although the sample was small (13 patients). The Phineas Gage study provides evidence that brain damage may have an effect on personality including aggression.
  • The hippocampus records past experiences which help elicit an appropriate response. If it is damged it can lead to aggression. 
  • AO3 - Boccardi (2010) found that habitually violent offenders exhibited abnormalities in the hippocampus.
  • Serotonin research - PET-1 gene is linked to the production of serotonin which inhibits aggression. Damage to the gene in mice raised aggression. Drugs that increases serotonin levels decrease aggression which suggests low levels of serotonin are linked to increased aggression. 
  • AO3 - most evidence is corrolational so doesn't indicate causality.
  • Testosterone - produces male characteristics which are associated with aggression. Acts on areas of the brain involved in controlling aggression. Increases in testosterone is linked to high levels of aggression. Men are more aggressive than women and have higher testosterone. Dabbs (1990) found that violent criminals had higher levels of testosterone than non-violent ones. 
  • AO3 - individuals with high testosterone levels display signs of aggression but rarely commit aggressive acts, suggesting social and cognitive factors play a role. Testosterone doesn't simply cause aggression but makes it a more likely response to frustration.
  • General AO3 - much of the evidence is only correlational. It isn't clear whether hormones promote aggression or aggressive behaviour stimulates hormone production. A lot of the work done on aggression is tested on animals so may not easily apply to humans. Is reductionist as it sees only biological factors and overlooks social issues such as de-individuation/environment and the effects of socialisation and environmental stressors.

Genetic origins of aggression:

  • Basic evidence of genetics - uses twin studies and adoption studies. McGuffin and Gootesman found concordance of 87% in MZ and 72% in DZ but also highlighted the importance of environmental factors. 
  • AO3 - criminality is not always the same as aggression. Also, aggrression can't be solely down to genetics as concordance rates for MZ twins are not 100%.
  • MAOA - a gene responsible for producing MAOA has been linked to aggressive behaviour. MAOA regulates the metabolism of serotonin and low levels are associated with impulsivity and aggression. A deficiency in the MAOA gene has shown higher levels of aggression in males. 
  • AO3 - in the 1980s research was done on a Dutch family with many males invlved in violent and serious crimes. It was found…


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