Nor was it an accident that the continents in their original form grew larger with the fat of the land that was added to them under the action of the chemistry of the air. You see Nature must understand chemistry or things wouldn't come out right in the laboratory, as they always do if you have made no mistakes. Ever think of that, Mr. High School Boy? II. The Strangest Thing of All That Didn't Happen But the strangest thing of all that didn't happen in this history of the world and its making I'm going to tell you about now. KINSHIP OF KITTENS AND APPLE-TREES You remember what I said of the apple-tree in Chapter V (page 93), how nobody who didn't know it to be true would believe that little Miss Greenleaf and old Mr. Root and rough Mr. Bark and lovely Miss Blossom were not only born under the same roof but were as closely related as a pussy-cat and her nest full of kittens. I didn't mention the kittens then, but just suppose I had done so; and then had gone on to say that kittens are relations of the apple family and that all birds are related to all kittens, and that both are kindred of that terrible Mr. Cetiosaurus that we met in the Bad Lands of Dakota. Would you have believed it? No? Well, I don't wonder. It was quite a while before the wise men of science believed it. Now not only is this idea of the origin of all living things--animal and vegetable--universally accepted by men of science, but every educated person is supposed to know about it. It is always, and as a matter of course, put into the school-books dealing with the history of nature; just as in all histories we are sure to see Columbus landing in 1492 and George Washington being inaugurated April 30, 1789. Most people, including the scientists, used to think that each kind of plant and animal was given its present form in the first place and that this form had never changed. This was known as the "special creation" theory; while the idea that the various kinds of plants and animals we now know gradually developed from quite different forms is called the theory of "evolution." Among the curious facts that finally led educated people everywhere to believe this strangest of all the strange fairy tales of the land of science were these: AS WE READ THE ROCKS FROM THE BOTTOM UP The remains and imprints of plant and animal life of long ago which we find in the rocks show successions of related but different forms in the rocks of different ages. At the beginning in the lowest rocks the forms are much alike, but grow more and more unlike as we climb these stairs of time. At first there are no animals with backbones; then there come animals with backbones that resemble each other in general build; and finally such wide varieties of backboned creatures as fish, birds, horses, and men. And so with endless varieties of birds and beasts and creeping things and the trees and the grasses of the field.