In this chapter the author claim that until Charles Darwin's theory was formalized in the language of mathematics, its implications, predictions, and use in explanations was far from fully realized. Indeed, the confusion and controversies in the six decades following the publication of the Origin illustrate and underscore this point. First, the author set out the theory as Darwin structured and expounded it in the Origin, giving it the axiomatic, albeit informal, rendition that he contend Darwin intended. Second, he examines the early attempts to employ mathematics. The focus is on the underdeveloped elements in Darwin's exposition: heredity and variation. Darwin's theory had been given a rigorous mathematical formalization. The mathematical formalizations of Fisher, Haldane, Wright, and Weinberg map neatly on to Darwin's formulation. The author uses Fisher's 1930 The Genetical theory of Natural Selection to demonstrate this point.