Short answers, pulled from the story.
Testosterone is the primary male sex hormone and androgen, produced mainly by the Leydig cells of the testes. It drives development of male reproductive tissues, secondary sexual characteristics such as muscle and bone mass, and plays roles in mood, cognition, metabolism, cardiovascular health, and the prevention of osteoporosis in both sexes.
Adolf Butenandt and Hanisch achieved the first chemical synthesis of testosterone from cholesterol in August 1935. One week later, Leopold Ruzicka and A. Wettstein at the Ciba group in Zurich published an independent synthesis. Both Butenandt and Ruzicka received the joint 1939 Nobel Prize in Chemistry for this work.
Most studies support a link between adult criminality and testosterone levels, with the highest testosterone found among the most violent criminals in prison. Researchers propose two main explanations: the challenge hypothesis, which ties testosterone to competitive and reproductive behavior, and the evolutionary neuroandrogenic theory, which argues the hormone motivates males to pursue competition even at personal risk.
Testosterone is used to treat male hypogonadism, gender dysphoria, and certain types of breast cancer, and is included on the World Health Organization's list of essential medicines. The American College of Physicians' 2020 guidelines support discussing testosterone treatment for adult men with age-related low testosterone who have sexual dysfunction.
In adult males, testosterone levels are about seven to eight times as great as in adult females, and daily production is roughly twenty times greater in men. Mean total testosterone in adult men has been reported as 630 ng/dL, compared to a mean of 32.6 ng/dL in women.
Fatherhood decreases testosterone levels in men. Higher investment in direct child care correlates with lower average testosterone levels, and temporary drops in a father's testosterone when his infant cries are associated with more nurturing behavior and better outcomes for the child.