The influence of high doses of testosterone and anabolic steroids on testicular endocrine function and on circulating steroid binding proteins, sex hormone binding globulin (SHBG) and cortisol binding globulin (CBG), were investigated in power athletes for 26 weeks of steroid self-administration and for the following 16 weeks after drug withdrawal. Serum testosterone and androstenedione concentrations increased (P less than ) but pregnenolone, 17-hydroxypregnenolone, dehydroepiandrosterone, 5-androstene-3 beta, 17 beta-diol, progesterone and 17-hydroxyprogesterone concentrations strongly decreased (P less than ) during steroid administration. Serum pregnenolone, 17-hydroxypregnenolone and dehydroepiandrosterone sulphate concentrations followed the changes of the corresponding unconjugated steroids but 5-androstene-3 beta, 17 beta-diol and testosterone sulphate concentrations remained unchanged during the follow-up time. During drug administration SHBG concentrations decreased by about 80 to 90% and remained low even for the 16 weeks following steroid withdrawal. Steroid administration had no influence on serum CBG concentrations. In conclusion, self-administration of testosterone and anabolic steroids soon led to impairment of testicular endocrine function which was characterized by low concentrations of testosterone precursors, high ratios of testosterone to its precursor steroids and low SHBG concentrations. Decreased concentrations of SHBG and testicular steroids were still partly evident during the 16 weeks after drug withdrawal. The depressed circulating levels of dehydroepiandrosterone and its sulphate may indicate that the androgenic-anabolic steroids also suppress adrenal androgen production.
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.