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.     
So if your testosterone level is below average, regardless of whether you as a male are experiencing classic Low Testosterone Symptoms , , you may want to natural methods, dietary and lifestyle factors, that can naturally boost. I cover many dietary and lifestyle factors on my site that can naturally boost testosterone. Read this link, for example, on How to Boost Your Testosterone Naturally . And, yes, that even includes Sex ! It may be possible to boost your testosterone levels 20-40%, and possibly get them into the normal and acceptable range, simply by changing certain lifestyle factors.