There is no doubt about it, in the world of anabolic androgenic steroids testosterone is king and in the human body itself it is an imperative hormone. Yes, there are side effects of testosterone use but they are manageable, largely preventable and often of no concern if were responsible. There is a very real risk to reward ratio that exist around exogenous testosterone use; the more we use the greater the reward but the more we use the greater the potential for negative or adverse side effects. Further and often overlooked, a healthy diet can greatly improve our odds; as cholesterol and blood pressure can be a concern we should consume diets that promote healthy levels of both.
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.