The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.     
Hypoactive sexual desire disorder (HSDD) is a deficiency of sexual desire that causes marked personal or interpersonal distress. It occurs in approximately 1 in 10 adult women. A number of potential contributory factors (hormonal, neurobiological and psychosocial) have been identified. Testosterone plays an excitatory role in sexual desire but the mechanism is not yet well understood. Treatment with testosterone has been shown to improve sexual desire in menopausal women with HSDD. However, there are limited data concerning premenopausal women and long-term safety. At present, physiological testosterone preparations for use in women are not available in Switzerland.