explanation of tHe origin of species. Darwin's discovery converted them en bloc. It was easy to understand, by means of the clew he afforded, not merely that organisms had been naturally evolved from simple primitive forms, but also how and why they had been so evolved. Darwin's great work, then, consisted in this — that he made credible a theory which most people before him had thought incredible; that he discovered a tenable modus operandi for what had before been rather believed or surmised than definitely imagined.
I do not mean to say that Darwin did no more than this. He supplied the great key of natural selection; but he also added much in other ways to the doctrine, especially in the direction of piling up facts and meeting objections. His work had thus a double value. On the one hand, it is not probable that the general biological public would have been converted to evolutionism half so quickly if it had not been for the enormous mass of confirmatory evidence adduced by Darwin. In the second place, even those who, like Spencer, were already evolutionists — evolutionists in fiber, incapable of taking any supernaturalist view of the universe in which they lived — gladly availed themselves of Darwin's discovery of natural selection, as an explanation of one important set of features in organic evolution, thitherto most imperfectly and inadequately explained. Or, let us put it another way. From the point of view of contribution to thought, it is natural selection that forms Darwin's great glory. But from the point of view of mere effective persuasion, it is the weight of evidence he brought up in favor of the older principle of descent with modification that told and still tells with the average mind. Hence it has happened, and perhaps will always happen, that Darwin has received more credit for that part of his theory which was not of his own invention than for that part of which he can justly claim the almost exclusive glory. Almost, I say, because the modifying adverb is demanded by justice to Mr. Alfred Russel Wallace, whose partial coincidence with Darwin in the discovery of natural selection now needs no advertisement.
As thinker, then, it is on natural selection as a vera causa of specialization and adaptation among plants and animals that Darwin most securely rests his claim to celebrity. As prophet and apostle, on the other hand, it must be frankly admitted that he ranks first as a preacher of organic — but only of organic — evolution. In this respect, his importance, in England especially, can hardly be overrated. For it is a peculiarity of the practical English mind that it is more moved by a vast array of evidence, a serried mass of cumulative instances, than by any possible cogency of logical reasoning. Darwin's own mind was in this way intensely English. He piled up fact after fact, added case