Jay Campbell has many excellent podcasts on testosterone and TRT. The podcasts he did a few years ago with Cernovich led me to get tested and as a 30 year old found 480ng/dl. Under the old labcorp values thats ~17%th percentile and what I’d expect if I was in my late 50’s or 60’s. That’s less than optimal for me. Urologist said, of course, that I was too young for TRT and my values were “fine”. The anti aging clinics near me in the north east cost around $3k a year but if you are enterprising and can figure out bitcoin you can devise your own course of treatment via online sources and it might only cost say $600/year. Do your own research, learn how to use a needle, and get your bloodwork done regularly. As Mangan always tells us, you are in charge of your own health, not your doctor, and if your hormones are out of whack you need to get that fixed!
So, how does one ensure that testosterone levels remain in balance? Some doctors suggest that monitoring testosterone levels every five years, starting at age 35, is a reasonable strategy to follow. If the testosterone level falls too low or if the individual has the signs and symptoms of low testosterone levels described above, testosterone therapy can be considered. However, once testosterone therapy is initiated, testosterone levels should be closely monitored to make sure that the testosterone level does not become too high, as this may cause stress on the individual, and high testosterone levels may result in some of the negative problems (described previously) seen.
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.