Summary: Any effective drug or supplement has potential side-effects. Most of the gym whisperings and pop culture assumptions about steroids and their side effects are overblown at best. Usually they are out-and-out lies. These myths include “roid rage,” hair loss in men who aren’t already predisposed to baldness, and penile shrinkage. The side effects that have been reported from Test Propionate include slightly faster body and facial hair growth and an increased need to shave, slightly accelerated hair loss only in men who already are balding, and temporary mild acne even with low dosages. Please avoid this product.
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.