In June, 1842, he wrote a brief account of the theory, occupying thirty-five pages. In Lyell’s and Hooker’s introduction to the joint paper by Darwin and Wallace in the Linnean Society’s Journal (1858) it is stated that the first sketch was made in 1839, but Francis Darwin shows (“Life and Letters,” 1887, Vol. II. pp. 11, 12) that in all probability this is an error—a note of Darwin’s referring to the first complete grasp of the theory after reading Malthus, being mistaken for a reference to the first written account.
In 1844 the sketch was enlarged to a written essay occupying 231 pages folio—“a surprisingly complete presentation of the argument afterwards familiar to us in the ‘Origin of Species’” published fifteen years later. Professor Huxley, after reading this essay, observed that “much more weight is attached to the influence of external conditions in producing variation, and to the inheritance of acquired habits than in the ‘Origin,’” while Professor Newton pointed out that the remarks on the migration of birds anticipate the views of later writers.[C]
The explanation of divergence of species during modification (divergence of character) had not then occurred to him, and he tells us in the “Autobiography”:—
“I can remember the very spot in the road, whilst in my carriage, when to my joy the solution occurred to me; and this was long after I had come to Down. The solution, as I believe, is that the modified offspring of all dominant and increasing forms tend to become adapted to many and highly diversified places in the economy of nature.”
A good example of this tendency is seen in the relations of three great vertebrate classes—mammals, birds, and fishes—to the environments for which they are respectively fitted: earth, air, and water. Competition is most severe between forms most nearly alike, and hence some measure of relief from competition is afforded when certain members of each of these classes enter the domain of one of the others. Hence, we observe that although mammals as a whole are terrestrial, a small minority are aërial and aquatic; although birds are aërial, a minority are terrestrial and aquatic; although fishes are aquatic, a minority tend to be, at any rate largely, terrestrial and aërial.
Huxley considered it “curious that so much importance should be attached to this supplementary idea. It seems obvious that the theory of the origin of species by natural selection necessarily involves the divergence of the forms selected” (“Obituary,” 1888, reprinted in “Darwiniana,” 1893; see pp. 280, 281). But Darwin showed that divergence might be a great advantage in itself, and would then be directly (and not merely incidentally and indirectly) encouraged and increased by natural selection.
RESOLVE TO PUBLISH.
As soon as the 1844 sketch was finished, Darwin wrote a letter (July 5th) as his “solemn and last request” that his wife would, in the case of his death, devote £400, or if necessary £500, in publishing it, and would take trouble in promoting it. He suggests Lyell as the best editor, then Edward Forbes, then Henslow (“quite the best in many respects”), then Hooker (“would be very good”), then Strickland. After Strickland he had thought of Owen as “very good,” but added, “I presume he would not undertake such a work.” If no editor could be obtained, he requested that the essay should be published as it was—stating that it was not intended for publication in its present form. In August, 1854, he wrote on the back of the letter: “Hooker by far best man to edit my Species volume.”
All this shows how certain he felt that he was on firm ground, and that his theory of natural selection was of vast importance to science. This same strong conviction appears clearly in the first edition of the “Origin,” and is undoubtedly one of the secrets of its power to move the minds of men. Although the author is above all others fair-minded; although he is most keen to discover and to bring forward all opposing evidence, and to criticise most minutely everything favourable; nevertheless, looking at the evidence as a whole, he has no doubt as to its bearing, and feels, and shows that he feels, a magnificent confidence in the truth and the importance of his theory.