The biological explanations of aggression say that aggression is caused by differences in the biological make-up of individuals. One example of these biological differences that could cause aggression is hormonal mechanisms.
Testosterone is the male sex hormone and is thought to influence aggression as it affects the areas of the brain which are involved in controlling aggression. There are several pieces of research which back up this theory.
Dabbs et al – took saliva samples to test of criminals for levels of testosterone. They found that those with the higher levels of testosterone had a history of violent crime, whereas those with low levels of testosterone had committed only non-violent crimes.
Lindman et al (1987) – found that young males who behaved aggressively when drunk had higher levels of testosterone then those who did not act aggressively.
Although cortisol alone isn’t thought to increase aggression directly, Dabbs et al found that high levels of cortisol inhibit testosterone and this in turn inhibits aggression. So by inhibiting testosterone, cortisol can affect aggression levels.
Vukkenen 1985 found that studies have reported low levels of cortisol in habitual violent offenders and in violent school children, this supports the theory that high levels of cortisol reduces aggression.