ABSTRACT
This chapter focuses on the temporally and hormonally mediated processes underlying the development of structural sex differences in the brain. Obviously, appropriate moral and ethical restrictions preclude the manipulation of hormonal systems during human development. The chapter illustrates how during multiple critical periods, the hormonal environment alters the morphology of the reproductive system in a permanent fashion. It also focuses on the hormonally influenced mechanisms thought to produce structural sex differences in neural systems that underlie sexual behavior or reproductive function in laboratory animals. The traditional dogma of sexual differentiation has been that testosterone (T) and its metabolites act to masculinize and defeminize both the body and the brain of what would, in their absence, default to a female morphology. During fetal development, the presence of gonadal factors, including T and its metabolites, triggers the morphological differentiation of shared genital precursor organs into male or female genitalia.
