Although concepts of fertility and reproduction can be traced to ancient times, most of our current understanding of endocrinology has evolved during the past 150 years.^[2] The structures of the major glands and ducts were initially captured in drawings by Renaissance anatomists and artists. The publication of De Humani Corporis Fabrica in 1543 by Vesalius provided a turning point in studies of human anatomy. Fallopio, also of the Padova School, published Observationes Anatomicae in 1561, which included a detailed description of the “slender and narrow seminal passage that arises from the horn of the uterus.”

A timeline for selected advances in endocrinology is depicted in Fig. 1-1. Berthold recorded the physiologic consequences of castration in 1849. He demonstrated that castration of a cock caused regression of secondary sex characteristics and mating behavior. Transplantation of the testes into the abdominal cavity restored these features, proving a role for the …