 But this feature of Darwin’s discussion of species only in part captures the complexity of his argument. Drawing also on the tradition of species realism developed within the Buffonian tradition, Darwin also affirmed that species and varieties are defined by common descent and material relations of interbreeding. Darwin then employed the ambiguity of the distinction between species and varieties created by taxonomic variation in practical taxonomy to undermine the ontological fixity of “natural” species. Varieties are not simply the formal taxonomic subdivisions of a natural species as conceived in the Linnaean tradition. They are, as he terms them, “incipient” species (Origin 1859: 52). This subtly transformed the issue of local variation and adaptation to circumstances into a primary ingredient for historical evolutionary change. The conclusions to be drawn from this argument were, however, only to be revealed in chapter four of the text.