Claude Bernard, the father of scientific physiology, believed that if medicine was to become truly scientiifc, it would have to be based on rigorous and controlled animal experiments. Bernard instituted a paradigm which has shaped physiological practice for most of the twentieth century. ln this paper we examine how Bernards commitment to hypothetico-deductivism and determinism led to (a) his rejection of the theory of evolution; (b) his minima/ization of the role of clinical medicine and epidemiological studies; and (c) his conclusion (...) that experiments on nonhuman animals were, "entirely conclusive for the toxicology and hygiene of man". We examine some negative consequences of Bernardianism for twentieth century medicine, and argue that physio/ogy's continued adherence to Bernardianism has caused it to diverge from the other biological sciences which have become increasingly infused with evolutionary theory. (shrink)