Most of our basic knowledge of human biochemistry, physiology, endocrinology, and pharmacology has been derived from initial studies of mechanisms in animal models. Throughout history, scientists have performed experiments on animals with the aim of obtaining knowledge of animal and human biological structure and function (see, e.g., Held; Loew). Often such studies have not been and are not possible in the human. This may be due to ethical or religious considerations, but often practical, economic, and scientific reasons make initial studies in animals the best solution to studies of a biological phenomenon.