Biological explanations into aggression PSYA3

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Neural and Hormonal mechanisms - AO1


  • Serotonin- Low levels of serotonin related to increased aggression.
  • Serotonin is thought reduce the emotional stimuli which could lead to an aggressive response.
  • Drugs that deplete serotonin levels can cause men to become hostile and aggressive, this was shown using a questionare so could be invalid and could contain demands characteristics. (Mann)
  • Dopamine- Increase dopamine is related to increase aggression.
  • Amphetamines associated with increase dopamine levels.
  • Antipsychotics reduce dopamine activity in the brain have shown to reduce aggressive behaviour.
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Neural and Hormonal mechanisms - AO2


  • Research Support.
  • Serotonin- Monkeys who fed on foods high is serotonin showed lower levels of aggression that those that didnt. This could be due to the levels of serotonin in the brain. (Raleigh)
  • Drugs which decrease serotonin levels can increase irritability, hostility and aggression, an example of this drug is anti-depressents. (Bond)
  • Dopamine- In mice there is a reward pathway which after an aggressive event releases dopamine. This suggests that aggressive behaviour is done in order to feel a good feeling. (Coupis and Kennedy)
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Neural and Hormonal mechanisms - AO1

Hormonal Mechanisms.

  • Testosterone- High testosterone level associated with high levels of aggression.
  • Violent/Non-violent criminals testosterone levels measured from saliva, those with high levels had a history of violent crimes, those with low levels hadnt. (Dabbs)
  • The challenge hypothesis says that testosterone levels should only rise when social challenges do such as male-male rivalry.
  • Cortisol- High levels of Cortisol inhibit testosterone levels so inhibit aggression.
  • Low cortisol levels are also shown in violent people.
  • Combination of low levels of cortisol and high levels of testosterone lead to high levels of aggression.
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Neural and Hormonal mechanisms - AO2

Hormonal mechanisms.

  • Research Contradictions
  • Testosterone- There is little evidence to support a positive correlation between testosterone and aggressive behaviour. Studies which have used a small group of males in prison have used self evaluation and could be unreliable. (Albert)
  • Testosterone is not just used to show aggression but more likely dominance. In non human animals testosterone might influence dominance and aggression. But in humans the testosterone influences are expressed more varied and subtle (Mazur)
  • Research Support.
  • Cortisol- A study of a 4 year old boy showed that he had low levels of cortisol he showed anti-social behaviour at a younger age and showed 3x number of aggressive symptoms compare to boys with higher cortisol levels.
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Neural and Hormonal mechanisms -AO3

  • Reductionism and biological mechanisms- This theory does not take into consideration social factors and is much more established in non-human animals because of the fact it would be unethical to test this for human animals.
  • Real World Application- A stimulus such as gun or a knife can increase testosterone levels and therefore increasse aggression. Males were told to either play with toys or a real gun and those with the gun were the ones who had the highest testosterone levels. (Klinesmith)
  • Gender Bias- Testosterone could make women act nicer. Rather than directly increasing aggression it promotes status seeking which in men is aggression and women is compassion.
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Genetic factors in aggression - AO1

Is aggression inherited?

  • Twin Studies-  Identical twins share 100% of there DNA and so would be more alike in terms of aggression, this could be due to genes rather than the enviroment.
  • 50% of the variety in aggressive behaviour comes down to genetics. (Caccaro)
  • Adoption studies- If aggression found in biological parent to the adopted child than its a genetic effect. But if found in child and adopted parents then its an enviromental effect.
  • Studies have shown that children in Denmark who have gotten criminal convictions also have parents who have criminal convictions.
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Genetic factors in aggression - AO1

Is there a gene for aggression?

  • Monomine Oxidase MAOA- Regulates the production of serotonin in the brain.
  • A Dutch male family who were violent had a low amount of MAOA in there system this was caused by a defective gene.
  • Gene enviroment interaction- Children who had low levels of MAOA who had been maltreated showed anti-social behaviour.
  • However those with high who had been mistreated and low levels of MAOA who hadnt been mistreated showed little aggressive behaviour.
  • This suggests a link between genes and enviromental influence.
  • Genetics and violent crime- It shown in studies that if adoptied and biological parents have criminal convictions its likley the child will be convicted.
  • However this didnt work for violent crimes, only property crimes.
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Genetic factors in aggression- AO2

Genetic factors in aggression.

  • Research Contradiction.
  • It is difficult to define what is the genetic contribution because...
    • more than one gene may contribute
    • there are non-genetic factors which may contribute e.g enviroment.
  • A meta analysis of 24 studies showed that those done by self/parental reports shoed genetic factors to be the cause however observational studies show that the enviroment is the main cause. (Miles and Carey)
  • Studies fail to distinguish the difference between violent and non-violent crime making it more difficult to untangle the role of genetic factors in aggressive violence.
  • A meta analysis found low/moderate correlation between hereditary and crime (Walters)
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Genetic factors in aggression - AO3

  • Real World Application- Its questioned whether there should be genetic engineering to determine aggressive behaviours in the future for example chemical castration. However with the threat of ethical issues and them being deemed as a threat to society, it poses many limitations.
  • The value of animal research- Research including the selective breeding programmes and knockout techniques which is where a certain gene is eliminated from a group shows how aggression gene can push them out of that group. Also a research with mice showed that a mutation called 'feirce' causes them to be aggressive however the function of the gene is unknown.
  • Gender Bias- Most of the studies done were done on male participants and women show aggression too so more studies should be done on them so the conclusion of the research can be generalised.
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