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.     
Testosterone, an essential precursor of estrogen in women, is made in the ovaries and adrenal glands. There is a steady decline in testosterone levels from the 20s through menopause. With surgical menopause, the level of testosterone drops precipitously. No clear lower limit of testosterone has been established; however 15 ng per dL ( nmol per L) commonly is used. One study 38 found that women with 0 to 10 ng per dL (0 to nmol per L) had markedly decreased sexual desire in all situations and absent or markedly decreased orgasms. Because of studies like this, supplemented with anecdotal evidence, many women have been started on testosterone therapy.
Alkaline phosphatase, hemoglobin and hematocrit, and creatinine may vary depending on the patient's current sex hormone configuration. Several factors contribute to these differences, bone mass, muscle mass, number of myocytes, presence or lack of menstruation, and erythropoetic effect of testosterone. Many transgender men do not menstruate, and those with male-range testosterone levels will experience an erythropoetic effect. As such an amenorrheic transgender man taking testosterone, registered as female and with hemoglobin/hematocrit in the range between the male and female lower limits of normal, may be considered to have anemia, even though the lab report may not indicate so. Conversely, the lack of menstruation, and presence of exogenous testosterone make it reasonable to use the male-range upper limit of normal for hemoglobin/hematocrit. Using the male-range upper limit of normal for alkaline phosphatase and creatinine may also be appropriate for transgender men due to increased bone and muscle mass, respectively. In these cases the provider should reference the male normal ranges for their lab.