The role of hormones and aggression

Male aggression and testosterone - in almost every culture, males are far more aggressive than females. Could this be because they have more testosterone? 

Testosterone is a male sex hormone. Hormones are chemicals produced by the body that send messages to organs of the body via the bloodstream.

Testosterone is secreted by the adrenal glands and testes and is needed to produce sperm, develop the male reproductive organs and produce male features - e.g. facial hair and a deep voice. 

Women also have testosterone, but males produce up to 10mg of testosterone every day, which is ten times more than women.

Aggression in animals - 
Psychologists have researched the role of testosterone in aggression by studying animals. Injecting animals with testosterone or removing the testes leads to increased or decreased levels of aggression.

Castrating a male animal lowers its testosterone levels. This makes the animal less aggressive. But if the same animal is then injected with testosterone its aggression is restored to a similar level to that before castration.

This is strong evidence that testosterone is responsible for aggression. We cannot say the same about humans…