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.
Sometimes the differences between these apparently related forms, as we find them in the rocks, are very great; but everything goes to show that this is because there are missing pages, so to speak, in the great stone book. When you remember how long it takes to make one of these layers of stone, and what they go through in cracking and twisting and wearing down on their way back to dust and the sea, and how quickly the remains of big animals—to say nothing of plants and insects—are destroyed, you must agree that the wonder is that we have any records at all. Yet so enormous has been the number of plants and animals that have died in the course of the world's history that there have been found hundreds and thousands of these remains and imprints between the layers of stone. In all cases the fashions in form change from age to age; and the longer the time, as shown by the thickness of the rock, the greater the change.
THE RABBIT THAT TURNED INTO A HORSE
The horse, which has been such a faithful carrier for man since man and horse arrived from the lower ranges of life, also brought with him on the way up one of the most complete of these strange autobiographies that our brother animals have recorded with their bones. The most of this story of the horse was found in the rocks of our Western States, but the first chapter of it saw the light about forty years ago in England. When the bones were found in the rock deposits of that country known as London Clay they looked so unhorselike that a famous paleontologist (as the students of these ancient anatomies are called) gave it a name which means "rabbit-like beast." But in rock of the same age in Wyoming they afterward found the bones of an animal that looked a little more like a horse, but plainly a close relation of the rabbit-like beast. They went on finding different forms, through thirteen successive stages of rock history, and with each new period the form kept getting larger and more horselike until they came to a horse with three toes; and finally to one with the single big toe which we call a hoof. Instead of the other two toes there were those two little lumps that you can feel in any horse's foot just above the hoof. These are the ends of two small splintlike bones that are all there is left of the other two toes.