One would have thought that, by now, 150 years after the Origin, biologists could agree on a single definition of species. Many biologists had indeed begun to settle on the “biological species concept” in the late modern synthesis (1940–70), when new findings in genetics became integrated into evolutionary biology. However, the consensus was short-lived. From the 1980s until the present, it seems not unfair to say that there arose more disagreement than ever before about what species are. How did we get into this situation? And what does it have to do with Darwin? Here, I argue that a series of historical misunderstandings of Darwin’s statements in the Origin contributed at least in part to the saga of conflict among biologists about species that has yet to be resolved. Today, Darwinian ideas about species are becoming better understood. At long last, the outlines of a new and more robust Darwinian synthesis are becoming evident. This “resynthesis” (as it perhaps should be called) mixes Darwin’s original evolutionary ideas about species with evidence from modern molecular and population genetics.

What Did Darwin Mean by Species?

Darwin realized he had convincing proof that species were not created but evolved. But this understanding caused a terminological problem that he had to address in his book. Species were defined in the minds of many of his Creation-educated readers as members of real groups: all members of a species were related by descent, whereas no individual was descended from members of another species. A second idea, which had been promoted especially by the French naturalist Buffon, was that the intersterility of species was a protective mechanism with which species had been endowed by the Creator to maintain their purity (Fig. 11.1). Thus, the famous anatomist Richard Owen, a powerful creationist opponent of Darwin, had given this succinct definition in his 1858 treatise on chimpanzees and orangutans: “an originally distinct creation, maintaining its primitive distinction by obstructive generative peculiarities” (as cited by Huxley 1860, 544).