By observing emasculated male domestic animals, eunuchs in the imperial harems of ancient China, and castrated singers in 18th-century Italy, people realized that typically male characteristics of physiology and behavior were determined by the presence of testes, otherwise known as testes. Over time, science has discovered that these glands are the main source of testosterone, the main male hormone. Who has a bigger Adam's apple, a deeper voice and a hairier chest? Who has a higher rate of physical abuse, a greater desire for privileged status, and an insatiable desire for multiple sexual partners? Just keep an eye on your testosterone levels. What we know about testosterone and differences between the sexes in no way means that we should accept current levels of sexual violence, harassment, discrimination or coercion. On the contrary, social progress depends on scientific progress. Understanding the forces that determine our priorities and behavior, as well as how genes, hormones and the environment interact, helps combat the manifestations of the dark side of our nature. Although we humans are able to study and evaluate our behavior, we are also animals, products of evolution lasting for millions of years. Astounding research in animals from iguanas to chimpanzees shows how high levels of testosterone help males produce offspring while outperforming their competitors. And men are no exception. Although most of us agree that sex differences in human behavior objectively exist, we disagree about their causes. But science is inexorable here: testosterone is a powerful force that acts both in the human body and in human society to separate the male from the female sex. However, as Harvard evolutionary biologist Carol Hoeven argues in her book, it does so in concert with genetics and culture to create enormous diversity in male and female behavior. And, crucially, the fact that many sex differences are based on biology does not mean that either restrictive gender norms or patriarchal values are justified. By understanding the mechanics of testosterone, we will better understand ourselves and each other, and how we can build a fairer and safer society. Sex chromosomes themselves do not stimulate (or suppress) the development of female characteristics. This is the task of sex hormones, and sometimes they the action, contrary to expectations, is not consistent with the presence of certain sex chromosomes. For whom For anyone who is interested in how men differ from women. The main evolutionary function of testosterone is to coordinate, for the purpose of reproduction, the anatomy and physiology of the male body, on the one hand, and behavior - on the other. To this end, in many male mammals (including humans), early exposure to testosterone masculinizes the brain, determining the development of neural circuits that are activated later during puberty.