Genes, Hormones, Sex and Gender
This chapter discusses the developmental origin of sex differences in behavior in humans. It focuses on the question, what is the role of genes or sex hormones in the ontogeny of sex differences in human behavior, a process referred to as psychosexual differentiation? The chapter describes most of the existing investigations of the relationship between fetal hormones and human psycho-sexual differentiation. There is evidence that fetal hormones alter brain development with respect to adult performance of sexual behavior in certain mammalian species, and are important in determining sex differences in copulatory pattern. The vast majority of the nonhuman experiments looked solely at copulation, whereas none of the human experiments have done so. The chapter discusses male homosexuality, which is often regarded as a disorder of psychosexual differentiation, and which has sometimes been assumed to be primarily biological in origin. Hormonal theories of homosexuality have been tested in part by looking for evidence that homosexuals have different androgen levels than heterosexuals.