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[18 November 1880]

Sir Wyville Thomson and Natural Selection

I HAVE at least great reason to be thankful that my stupidity has not prevented me from thoroughly enjoying the teachings of Mr. Darwin and Mr. Wallace, which I confess to having regarded as chiefly masterly and charming "studies in variation," for the last twenty years. The title of the epoch-marking book which came of age last month was, however, "The Origin of Species by Means of Natural Selection.'' Mr. Darwin, as I am well aware, has put forward this mode of the origin of species as a part only of a hypothesis which is universally looked upon as a supreme effort of genius.

It seemed to me, rightly or wrongly, that the fauna of the enormous area forming the abyssal region existed under conditions which held out the hope that It might throw some light upon a question which appears to underlie the whole matter, and which is still unanswered. Are physiological species the result of the_ gradual modification of pre-existing species by natural selection, or by any similar process; or are they due to the action of a law as yet utterly unknown, by which the long chain of organisms rolls off in a series of definite links?

I fear I scarcely follow Mr. Darwin's illustration. If one were to pay his first visit to a breeder's, and be shown a flock of Leicesters, never having seen or heard of a sheep before, and would see nothing but a flock of sheep, and would certainly without justly incurring the contumely of the breeder, be entitled to set them down merely as a group of animals of the same species, that is to say, animals fertile with one another and producing fertile progeny. He would judge so from their common resemblance, and without previous observation or information I do not see how he could know more about them. But give him an opportunity of comparing the results of breeding throughout a long period of time, or of observing the process of breeding over half the world, which comes to much the same thing; the breeder might then have cause to rail if he had not picked up the stages of the process.

The close examination of the newer tertiaries and the careful analysis of the fauna of the deep sea seem to me fairly to represent these two methods; both of these promise to yield a mass of information in regard to the course of evolution, but as to the mode of the origin of species both seem as yet equally silent.

I will ask you in a week or two for space for a short paper on "The Abyssal Fauna in Relation to the Origin of Species."

C. Wyville Thomson