From prenatal life into senescence, testosterone is essential requirement for manhood.

Prenatally, organisms have the bipotentiality to differentiate along either male or female lines, a process with different stages, each with a narrow window of time, during which testosterone plays a pivotal role in the case of male sexual differentiation. During puberty, the body directs the masculinization process with growth of the genitalia and prostate. Body contours become male, with an average height of 10-15 centimeters greater than that of females, a greater bone and muscle mass, a male hair pattern and a male-type fat distribution. These pubertal developments, largely reversible in case of severe androgen deficiency, require adult levels of testosterone throughout life. A new area of interest is in exploring how far age-related body changes (loss of bone and muscle mass, a shift into a higher ratio of body fat/lean body mass) are part of an age-related decline of testicular testosterone production. Therefore, throughout life, testosterone is essential for a normal male life.