Biological causes of aggression

Hormonal and neural factors/causes of aggression.

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Role of hormones

A look into aggression in many animals has found that males tend to be more aggressive. Over 80% of homicides are committed by males. There have been looks into the role of hormones in aggression, mainly androgen's. The main androgen of interest is testosterone. 

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Testosterone 1

Testosterone in produced in the adrenal cortex and testes. It is suggested that because males have testes (therefore have more testosterone) males are more aggressive. Studies have supported this theory, Wagner et al found that male mice that were castrated had lower levels of aggression. when those mice were injected with testosterone, they became more aggressive.


Castration has been used for years to make pets and farm animals more manageable. 

However, it is difficult to generalise because the study was done on rodents, not on humans, so social factors were not taken into account. The study cannot be conducted on humans, as it is unethical to castrate humans and inject them with testosterone. 

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Testosterone 2

Dabbs et al measured tested testosterone levels in 692 male prisoners and found that the more violent criminals (e.g. ******) had higher levels of aggression than the less violent criminals (e.g. thieves). 


This study is gender biased as the study only looked at males, however, it is assumed that elevated levels of testosterone have the same impact on females. Also, these types of studies only provide a correlation, but don't establish a cause and effect. 

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Testosterone 3

The double blind procedure was used in a study, participants were either given testosterone or a placebo. Participants were told  they had a partner (they didn't actually have a partner). They were told they  had to push a button as much as possible to reduce the amount of money the partner would receive. Those injected with testosterone were found to press the button significantly more times than those injected with the placebo.


This study allows scientist to be more confident in claiming that testosterone increases aggression. The double blind procedure also removes the possibility of experimenter bias and demand characteristics. However, the long term effects of injecting testosterone is unknown. 

Simpson (2001) argues that testosterone is only one factor that increases aggression. There are other factors such as the environment (e.g. temperature, overcrowding, noise, etc).

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Frontal lobe - Phineas Gage

The frontal lobes are in charge of restraining inappropriate behaviors, to allow a person to act more socially acceptably. Therefore damage to the frontal lobe can cause aggression. 

There has been evidence to link damage to the frontal lobe and aggression since the 1800s. In 1848, Phineas Gage had a accident at work, A temping iron was projected through his skull, it is believed the iron went through the frontal lobe.He was described to be more aggressive, impulsive and impatient after the accident. 


This suggests that the frontal lobe is important in controlling aggression. However, it is impossible to be 100% certain where to the damage was done, as this was over 150 years ago. Also this i a case study, therefore it cannot be generalized to the general population. 

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Frontal lobe - Serial killers

Many serial killers have also been found to have damaged frontal lobes. Albert Fish was a *********, torturer, murderer and cannibal. He suffered frontal lobe damage as a child. 

Fred West was a sadistic, serial killer, who tortured and dismembered his victims. He suffered frontal lobe damage on to occasions. 


This theory is argued to be reductionist, as damage to the brain is unlikely to be confined to one specific area of the brain. Also many serial killers have experienced abusive childhoods. Fred West was abused by his father and Albert fish was placed in a orphanage from a early age and witnessed beating on a daily basis. The combination of abusive childhoods and damage to the frontal lobe could led to increased aggression.

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Freewill vs Determinism (AO3)

The brain is argued to be a complex machine, but still a machine. Since it is a machine there is no freewill and if the brain in damage then there is a high chance of unpredictable behaviors/acts, which are not voluntary. Therefore the idea of moral responsibility irrelevant. If biological processes override free will then a person should not be held liable for their actions.

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