Hormones and Aggression

• Testosterone and aggression

  Observations across species have revealed that the males are more aggressive than females. These sex differences have been attributes to the male sex hormone testosterone. Testosterone is a male sex hormone (androgen) produced in the testes and secreted by the adrenal gland which is needed to produce sperm. Testosterone is also involved in the development of the male reproductive organs and produces male features, such as facial hair and a deep voice.  It is also said to be involved in aggression.
• Developmental psychology (antenatal exposure to testosterone)

  It has been shown that antenatal exposure to testosterone has an organising effect on the developing brain, leading to increased spatial ability and competitive aggression. Embryos that eventually develop to become males are exposed to higher levels of testosterone in the womb than females. This exposure to testosterone in the womb may help to explain postnatal difference in aggressive behaviour between the genders.
• Reciprocal- model.

  Not only does more testosterone result in more aggression; successful aggression (winning a fight) results in more testosterone. A monkey that wins a fight for dominance in a monkey colony secretes more testosterone into its bloodstream, resulting in still more aggressive behaviour, as well as more mating activity. This is called a reciprocal- model.
• Cortisol inhibiting Testosterone

  Low levels of cortisol (the stress hormone) have been linked with aggressive behaviour. The hormone cortisol is thought to inhibit aggression. It is thought to do this by having a mediating effect on other hormones related to aggression such as testosterone. A high level of cortisol inhibits testosterone and so inhibits aggression. This may be due to the fact that cortisol increases anxiety and the likelihood of social withdrawal. 
• Cortisol - not feeling stress = violence

  Cortisol, and therefore feelings of stress, mediate the acts that people carry out, but that some people produce less cortisol and therefore feel less stressed when committing acts of violence against others.