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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.     
In addition to this function of testosterone supplements, expect that you will also have better endurance, leaner muscles, improved sexual performance and vigor. This will surely add vitality to your life as you want to, right where you want it. To be able to get all these benefits, better check on each facet of the supplement you want to order. You have to be certain you get ultimate results. Even if results may vary from one person to another, you can be assured that you will be able to see outcomes accordingly as long as the product is efficient enough.