Following Watson and Crick's determination of the structure of DNA in 1953, the growth and self-confidence of molecular biology led not only to unparalleled understanding of fundamental biological processes, but also to divergence between molecular and cellular biology, on one hand, and what was often termed "whole-organism biology" on the other. Evolutionary biology was practiced largely by whole-organism biologists, and although they often proclaimed that evolution was the central, if not sole, unifying theory of biology, such unification, or even broad ratification of the claim, could be hard to discern.