The trail led first to Joseph Hooker and Thomas Huxley, who had been both the theory's strongest supporters and its most penetrating critics, and eventually to Darwin's young research associate, the Victorian Georges Romanes, and to the Victorian-Edwardian, William Bateson. Although these men were well-known, their resolution of the origin of species paradox has either been ignored (Romanes), or ignored and reviled (Bateson). Four years after Darwin's death, Romanes published a theory of the origin of species by means of "physiological selection" that resolved the inconsistencies in Darwin's theory and introduced the idea of a "peculiarity" of the reproductive system that allowed selective fertility between "physiological complements." Forsdyke argues that the chemical basis of the origin of species by physiological selection is actually the species-dependent component of the base composition of DNA, showing that Romanes thus anticipated modern biochemistry. Using this new perspective Forsdyke considers some of the outstanding problems in biology and medicine, including the question of how "self" is distinguished from "not-self" by members of different species. Finally he examines the political and ideological forces that led to Romanes' contribution to evolutionary biology which has remained unappreciated until now.