Testosterone. The hormone that divides and rules

By observing the castrated males of domesticated animals, eunuchs in the imperial harems of ancient China, and castrati singers in 18th century Italy, people understood that typically male characteristics of physiology and behavior are determined by the presence of testicles, otherwise known as balls. Over time, science has determined that these glands are the primary source of testosterone, the main male hormone. Who has a larger Adam's apple, a lower voice, and a hairier chest? Who has higher rates of physical aggression, sharper desire for privileged status, and an insatiable urge to have multiple sexual partners? Just watch the testosterone levels. Although we, humans, have the ability to study and evaluate our behavior, we are also animals, products of evolution lasting millions of years. Astonishing studies of animals from iguanas to chimpanzees show how high levels of testosterone help males produce offspring, outmaneuvering their competitors in this. And men are no exception here. While most of us agree that sexual differences in human behavior objectively exist, we disagree on their causes. But science is relentless here: testosterone is a powerful force acting both in the human body and in human society to separate the male sex from the female. However, as Harvard evolutionary biologist Carol Hooven proves in her book, it does so in conjunction with genetics and culture, creating a vast diversity of male and female behavior. And, importantly, the fact that many sexual differences are based on biology does not justify either restrictive gender norms or patriarchal values. By understanding the mechanics of how testosterone works, we will better understand ourselves and each other, as well as how to build a more just and safe society.