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 treatment was largely prescribed and marketed as a potential therapy to treat symptoms of aging. Testosterone levels decrease progressively with aging and low testosterone levels were associated with an increase risk of cardiovascular events and death. Controversies persist whether this association is causal or mediated by confounders of the general health. Systematic screening of testosterone is not recommended in a check-up visit, but only in case of suggestive symptoms. Furthermore a recent meta-analysis and large prospective cohort studies have reported a concern regarding the safety of testosterone therapy and the associated risk of major cardiovascular events. The decision to prescribe testosterone should be made with the patient after evaluating the risks and benefits.
“My family doctor basically told me that I had to live with my Low T problem which was not something I wanted to hear. He told me this for 2 years and in fact it made me so mad that I am no longer his patient. I decided to get checked at TCT. After a thorough evaluation, including checking my blood, they told me that Low T was not something that I had to live with and in fact, they have helped with my other medical problems. They are treating my blood pressure, cholesterol and erection problems as well. I’m in my late forties and finally feel like I have been “tuned-up”. I feel better than I have in years which allows me to focus less on me and more on the things I find important. Thank you to everyone who helped get me where I am, including my ex-doctor. Keep up the good work TCT!” — Todd J.