Lyell wrote a magnificent work in which he proved, from the point of view of scientific geology, that the whole story of these terrible revolutions was a fiction. There are no such sharp sections in the early history of the earth. Everything goes to show that throughout the whole period of the earth’s development the same natural laws have been at work as we find to-day. It is true that the relative positions of sea and land, hill and valley, forest and desert, have often changed; but very, very slowly, in the course of millions of years. A single drop of water, constantly falling, will hollow out a stone. In these millions of years the water has swept away rocks here, and formed new land by the accumulation of sand there. In these millions of years the sand has been compressed into the gigantic masses that tower above us to-day as sandstone mountains; they are formed of sand that was originally laid like mud, layer by layer, on the floor of the ocean.
It was all very plausible; it seemed to picture an eternal flow of things in which there was no room for God. The changes in the earth’s surface were easily brought about without catastrophes, in the course of incalculable ages. God was excluded from geological discussions of the formation of hill and dale. And when it was fully realised, it brought the question of species to the front once more.
It was impossible to retreat simply to Linné’s position. Lyell by no means denied Cuvier’s various periods in the earth’s development as such. He believed, moreover, that the plant and animal populations were different in these epochs. When the forests flourished which have formed the mass of our coal-measures there were no ichthyosauri; when the ichthyosauri came there were no longer any carboniferous forests; with the ichthyosauri there were no megatheria, and the last ichthyosaurus was extinct before the megatheria arrived. All that Lyell rejected was the great divine catastrophes. But when these were abandoned, it was no longer possible to attribute the “end” of the extinct species to a divine act. We were faced with the slow and natural conversion of terrestrial things in the course of endless ages.
Species must have been liable to be destroyed by purely natural causes. The catastrophes were abandoned, yet species had been destroyed. And when that was granted—it was the devil’s little finger—a further conclusion was inevitable. If species have died out slowly and naturally in the history of the earth, and new species have made their appearance at the same time, may not these new species have arisen slowly and naturally? Suppose these simple and purely natural causes, that had brought about the extinction of certain species, had been for others the very starting-point of development? In one word: if the extinction was not due to a mighty divine interference, was it not conceivable that the origin also may not have needed such?
One more deduction, and the demon of knowledge had hold of the entire hand. May not this natural extinction and natural new-birth have been directly connected in many cases? As a fact, some of the species had been wholly extirpated. But others had provided the living material of the new arrivals; they had been transformed into these apparently new species. That was the decisive deduction. It did away with the need of any sudden creation. It merely made a claim that was appalling to the Linnean principles: namely, that species may change. In the course of time and at a favourable spot one species may be transformed into another.
Another fairly obvious deduction could be made. Who brought about the transformation? Lyell proved that, without any catastrophes, terrestrial things are constantly changing—the water and the land, the mountains and the valleys, and even the climate. In this gradual change the environments of living things were at length altered to such an extent that they were bound to cause a change in the organisms. However, different species reacted in different ways. Some gradually died out. Others adapted themselves to the new conditions; just as, in human affairs, one race breaks down under changed conditions while another rises to a higher and richer and new stage on that very account. No creation! Merely transformations of species, development of new forms from older ones by adaptation to new, naturally modified conditions. Even zoology and botany were without the finger of God from the earliest days.
Of course there was no trace of these latter deductions in Lyell. But they pressed themselves with an irresistible and decisive force on the mind of one of his first readers, Darwin.
He took Lyell’s book with him to South America. Step by step the logic of it forced him to admit that this was what must have taken place somewhere. First the idea of “extinct species” became a concrete picture to him there, a sort of diabolic vision. The whole substratum of the pampas is one colossal tomb of strange monsters. The bones lie bare at every outcrop. Megatheria, or giant-sloths, as large as elephants, and with thighbones three times as thick as that of the elephant, able to break off branches in the primitive forests with their paws: armadilloes as big as rhinoceroses, with coats as hard as stone and curved like barrels; gigantic llamas, the macrouchenias, compared with which the modern specimens are Liliputians; mastodons and wild horses, of which America was entirely free even in the days of Columbus, and lion-like carnivores with terrible sabre-teeth. There they all are to-day—extinct, lost, buried in the deserted cemetery of the pampas-loam.
When the young Darwin stood by these groves, like Hamlet, he did not know how closely this ghost-world came to our own day. At that time the armour of the gigantic armadillo, the glyptodon, that had formed shelters over the heads of the human dwellers in the pampas, like Esquimaux huts, had not yet been discovered. The cave of Ultima Esperanza in Patagonia had not been searched, and no one had seen the red-haired coat of the sloth as large as an ox, the gryptotherium (a relative of the real megatherium), cut by some prehistoric human hand, amongst a heap, several yards deep, of the animal’s manure—in such peculiar circumstances as to prompt the suggestion that the giant-sloths had been kept tame in the cavern, as in a cyclopean stable, by prehistoric Indians. Darwin thought the remains were very old, though this by no means lessened the inspiration.
As our geological Hamlet speculated over these bones of extinct monsters, the ideas of Linné and Cuvier struggled fiercely in his mind with the new, heretical ideas inspired by Lyell. How was it that these ancient, extinct animal forms of America resembled in every detail and in the most marked characteristics certain living American animals? Before him were the relics of past sloths, armadilloes, and giant-llamas. In the actual America, also, there were sloths, armadilloes, and llamas, though with some difference. And nowhere else on earth, either in past or present time, were there sloths, armadilloes, and llamas. Cuvier had replied, God had pleased to create those ancient megatheria, glyptodons, and macrouchenias of America. Then, one day, he sent his destructive catastrophe, and swept them all away, as a sponge goes over the table. Then, in the empty land, he created afresh the sloths, armadilloes, and llamas of to-day. But why had God made the new animals so like the old that the modern zoologist has to class the megatherium in the same narrow group as the actual sloth, the ancient glyptodon with the modern armadillo, and so on?