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.     
It is also important to remember that the use of an injectable testosterone will quickly suppress endogenous testosterone production. It is therefore mandatory to complete a proper post cycle therapy, constisting of HCG and Clomid or Nolvadex at the conclusion of a cycle. This should help the user avoid a strong “crash” due to hormonal imbalance, which can strip away much of the new muscle mass and strength. This is no doubt the reason why many athletes claim to be very disappointed with the final result of steroid use, as there is often only a slight permanent gain if anabolics are discontinued incorrectly. Of course we cannot expect to retain every pound of new bodyweight after a cycle. This is especially true whenever we are withdrawing a strong (aromatizing) androgen like testosterone, as a considerable drop in weight (and strength) is to be expected as retained water is excreted. This should not be of much concern; instead the user should focus on ancillary drug therapy so as to preserve the solid mass underneath. Another way athletes have found to lessen the “crash”, is to first replace the testosterone with a milder anabolic like Deca-Durabolin. This steroid is administered alone, at a typical dosage (200-400mg per week), for the following month or two. In this “stepping down” procedure the user is attempting to turn the watery bulk of a strong testosterone into the more solid muscularity we see with nandrolone preparations. In many instances this practice proves to be very effective. Of course we must remember to still administer ancillary drugs at the conclusion, as endogenous testosterone production will not be rebounding during the Deca therapy.