Testosterone and the heart
Forget clothes. In a very real sense, testosterone makes the man.
It is responsible for the deep voice, increased muscle mass, and strong bones that characterize the gender. It stimulates the production of red blood cells by the bone marrow. The hormone also has crucial, if incompletely understood, effects on male behavior: it contributes to aggressiveness, and it is essential for the libido, or sex drive, as well as for normal erections and sexual performance. Testosterone stimulates the growth of the genitals at puberty and is responsible for sperm production throughout adult life.