Hormonal mechanisms of aggression

• Testosterone 


  A hormone from the androgen group that is produced mainly in the male testes and in small amounts in the female ovaries. It is linked with aggression. It is responsible for the development of masculine features.
• Daly and Wilson 1988


  Many people have observed that men are typically more aggressive than women. Men become more aggressive towards other men at a a time where testosterone levels are at their highest, at around 20 years old. Testosterone has a role in regulating social behaviour via its influence on certain areas of the brain implicated in aggression.
• Giammanco et al 2005- castration studies


  Castration studies of animals show that removing the testes, the source of testosterone, reduces levels of aggression in males of many species. Giving injections of testosterone back to the same animals restores aggressive behaviour.
• Mairead Dolan et al- violent offenders


  Dolan found a positive correlation between testosterone levels and aggressive behaviours in a sample of 60 male offenders in UK maximum security hospitals. These men mostly had personality disorders such as psychopathy and histories of violently impulsive behaviour.
• Progesterone 


  There is evidence that progesterone plays a role in aggression within women, levels of progesterone are lowest during and after menstruation as they vary during the cycle.
• Anna Ziomkiewicz et al- progesterone and aggression

  Ziomkiewicz found a negative correlation between progesterone levels and self reported aggression. This suggests that low levels of progesterone are linked to increased aggression in women.
• Evaluation- strength in animal research


  One strength of hormonal explanations is support from research with non-human animals. Marco Giammanco et al‘s review of studies confirm the role of testosterone. For example in male rhesus macaque monkeys there is an increase in both testosterone levels and aggressive behaviour during mating season. In rats castration of males reduces testosterone and also mouse-killing behaviour. Injecting female rats with testosterone increases mouse killing. These findings show the role of testosterone in a range of animal species.
• Evaluations- limitation dual hormone hypothesis 


  One limitation is mixed evidence of the link between testosterone and aggression in humans. Justin Carre and Pranjal Mehta developed a dual hormone hypothesis to explain why. They claim that high levels of testosterone lead to aggressive behaviour only when levels of cortisol are low. When cortisol is high, testosterones influence on aggression is blocked. Cortisol plays a central role in the body’s response to chronic stress. Therefore the combined activity of testosterone and cortisol may be a better predictor of aggression than one alone.