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.     
Arginine is the immediate precursor of nitric oxide (NO), urea , ornithine , and agmatine ; is necessary for the synthesis of creatine ; and can also be used for the synthesis of polyamines (mainly through ornithine and to a lesser degree through agmatine), citrulline , and glutamate . As a precursor of nitric oxide, arginine may have a role in the treatment of some conditions where vasodilation is required.  The presence of asymmetric dimethylarginine (ADMA), a close relative, inhibits the nitric oxide reaction; therefore, ADMA is considered a marker for vascular disease , just as L -arginine is considered a sign of a healthy endothelium .