Darwin, who had studied theology, was unshaken with regard to God himself. However, something occurred that occurs so often and with such good result in the history of thought. It appeared to him that the notion of a direct creation is by no means the simplest way of explaining things, but the most puzzling and complicated. Darwin believed in Lyell. There had been no destructive catastrophe at all to sweep away the megatherium and its companions. They had disappeared gradually, by natural means. Was it not much more rational to suppose that the actual sloths and armadilloes came into being gradually, by natural means? Part of the old animal population had not perished, but been transformed into the actual species. There was a bond of relationship between the past and the present. One or other grotesque and perhaps helpless giant form may have completely disappeared in the course of time. But the golden thread of life was never entirely broken. Other and more fortunate species had preserved the type of the sloth, the armadillo, and the llama; they had developed naturally into the living animals of America. God might remain at the groundwork of things. He had launched matter into space, and impressed natural laws on it. But these sufficed for the further work. They created America. They developed the mammal into the sloth and the armadillo in the days of the megatherium and the glyptodon. They maintained these types in the country, in a straight line of development; the progressive principle of life bringing about the extinction of certain forms, and transforming others by a more fitting adaptation to their environment.
Darwin always looked back on this first conflict of his ideas in presence of the dead shells and bones of the ancient pampas animals as an hour of awakening. It was the birth of his humanity in the higher sense. It is of interest to us because it coincides exactly with the date of Haeckel’s birth in the ordinary sense.
In Darwin’s fine account of his voyage, which is mostly arranged in the form of a diary, we find a passage written on the east coast of Patagonia on January 9, 1834, and the next on April 13th. In the meantime the ship had made a short zigzag course, which is spoken of in another connection. But the interval between the two dates is taken up with a passage on these gigantic animals, the reasons for their extinction and the striking fact of their bodily resemblance to the living animals of South America. “This remarkable resemblance,” we read, “between the dead and the living animals of one and the same continent will yet, I doubt not, throw more light on the appearance of organic beings on the earth than any other class of facts.” This is clearly a summary of Darwin’s deepest thoughts at the time. Haeckel was born on February 16th of the same year, 1834. Thus the bodily birth of one of the two men whom we conceive to-day as Dioscuri coincides with the spiritual rebirth of the other. But it would be nearly thirty years before they would meet in spirit never to part again. At the very beginning of their acquaintance Darwin wrote a letter to Haeckel (October 8, 1864) in which he speaks of the earliest suggestions of his theory. The Hamlet-hour comes back vividly to his memory. “I shall never forget my astonishment when I dug out a gigantic piece of armour, like that of a living armadillo. As I reflected on these facts and compared others of a like nature, it seemed to me probable that closely related species may have descended from a common ancestor.”
However we take it, Darwin then saw for the first time that his difficulty about the mutability of species was from the first, in his own mind, a difficulty about God. He began his doubts with the ancient armadillo; he ended with God.
On the return journey from South America, which amounted to a circumnavigation of the globe, the struggle was renewed at the Galapagos islands. Volcanic forces had raised these islands from the bed of the ocean in comparatively recent times. They were, therefore, bound to be a virgin province at the time. Now, however, the walls of the crater were clothed with vegetation, birds flew after insects, and gigantic turtles and lizards lived on the shores. Whence did these plants and animals come? Darwin examines them. They have an unusual appearance, and seem to point to America. Yet not a single species is now wholly American; each has its peculiarities. An historical controversy arises over the islands, and men range themselves in parties once more. Empty islands emerge from the blue waters. How are they to be populated? There are two possibilities. One is that God has created the animals and plants—Galapagos animals and plants. But in that case why has he created them entirely on the American model, while diverging from it in small details? The second possibility is that the animals and plants were brought by the current or the wind from the neighbouring American coast; they are American plants and animals. After landing on the islands, they adapted themselves to their new surroundings, and were altered. Hence both the resemblance and the difference. The theory assumes, of course, that species are mutable. If that is so, we can explain everything—without God.
But the greatest and tensest struggle began when Darwin returned home. He approached the most audacious, but most striking fact, for his purpose. Up to this the question had been whether new species were produced by God or by natural necessity. Now a third element was introduced, man himself. He also alters species, as a breeder of pigeons, rabbits, sheep. He has done it with success for ages—only the Linnés and Cuviers had not noticed the fact. How does he accomplish it?
A breeder desires to give his sheep finer wool. He examines the wool of a thousand sheep. The difference between them is so slight that it is of no practical consequence. But the farmer selects the male sheep out of the thousand that has the best quality of wool, and the corresponding female. He crosses the two. Their young have wool of a slightly improved quality, and he picks out the best amongst them once more for crossing. He continues this through several generations. At last, with his continuous selection and crossing, the quality of the wool increases so much that any one can recognise it at once, and it has a distinct cultural value. In this way improved races of animals and large numbers of fine flowers have been produced by breeders: by artificial selection of the fittest to reproduce in each generation. This was done by man—not by God, not by nature in remote times, but under our very eyes, by man.
Now for an analogous process without man. Let our sheep live wild in any country. No human breeder has any interest in them: God does not seem to interfere with them. They live on and on, for thousands of years, generation after generation. Here again, in the wild state, we find the same slight variations in the quality of the wool. One sheep has a thicker coat than another. For thousands of years the fact is without significance. Then occurs a slow change of the environment. The climate becomes colder. Perhaps an ice-age sets in, such as our earth seems to have passed through many times. There are two alternatives. A very hard winter may set in at once and all the sheep perish, because their woolly coat is too thin in all cases. That would mean the extinction of a whole species. But the severe cold may come on gradually. The winters are more trying. So many sheep perish in the first winters; but so many others survive. Which will survive? Naturally, those that happened to have the thicker coats. Those alone live on to the spring, and reproduce. The following year the coat is thicker all round, as the lambs all came from relatively thick-coated parents. The winter decimates them again, and the thickest coated survive once more, and so on. The pressure of external conditions, the “struggle for life,” selects just as man does. Only the best adapted individuals survive and reproduce.
The whole earth is a vast field of splendid adaptations. The tree-frogs are green because only green frogs are preserved; all the others are destroyed. The arctic hare is white on the snow, the desert-fox yellow. For a thousand reasons in the course of the earth’s development these backgrounds—white, yellow, green; snow, desert, forest, &c.—have themselves been constantly changing under the action of Lyell’s changes in the crust of the earth. Hence constantly fresh adaptations, with a certain percentage of complete extinctions. In these ceaseless new adaptations we see a picture of an eternal progressive development. Always a finer selection: always better material: natural things always selecting and being selected. Man is superfluous in this world-old, eternal process. And God, too, is superfluous.
That was Darwin’s last and decisive thought. Divine action was excluded from the whole province of animal and plant species. It does not matter whether or no the shrewd idea of natural selection solves the whole problem. Why speak of “whole,” when all problems are really unfathomable? He left open the question of the origin of the first slight variations, the first increase in the fineness or thickness of the sheep’s wool, for instance. He left open the question of the inner nature of the process—and a good deal more. But these things did not affect the great issue.