Testosterone is a steroid hormone molecule that is found in human males and females as well as many other species. In humans testosterone serves as the primary male sex hormone, and it plays a crucial role in the development of the male reproductive system. In males it is secreted from the tesisticles, and in females it is secreted from within the ovaries. Males use significantly more testosterone than females, and for this reason males produce testosterone at about twenty times the rate of females. Oddly enough, males are also less sensitive to testosterone than females.