All modern horned animals have been evolved from ancestors that were without horns. The progenitors of the deer, the elk, the caribou, the moose, before the Miocene period, were entirely destitute of horns. Then the first horns appeared, each as a simple prong. As the succeeding ages passed away, the horns gradually increased in size and took on more prongs. The fossil antlers, found in the successive rock formations from the Miocene period onward, show the gradual evolution of the horns that adorn the heads of living animals (Fig. 34). But this is only half the story. The history of an individual creature is called ontogeny. The history of a race of creatures is called phylogeny. Now, it is a biological law that ontogeny is always a recapitulation of phylogeny; that is to say, that every creature in the course of its development, especially before birth, passes through the various stages permanently occupied by its ancestors. We see this law beautifully illustrated in the growth of the antlers of one living deer (Fig. 35). During the first year, or thereabout, the deer develops one plain horn, and each year thereafter another prong is added, until after a series of years, the antlers are full grown and full-pronged. In other words, each and every deer, in the development of his horns, repeats the long experience of his race in acquiring horns. [Illustration: FIG. 33.—EOHIPPUS, THE “DAWN HORSE,” FROM THE LOWER EOCENE ROCKS. Restored from a skeleton in the American Museum of Natural History, New York. Reprinted with the permission of the author and publishers from Prof. William B. Scott’s “A History of Land Mammals in the Western Hemisphere.” The Macmillan Co., New York.] Now, this process of recapitulation applies to man as well as to all other creatures. This brings us to another line of evidence which proves the truth of evolution—embryology, or development before birth. Dogs, cattle, sheep, elephants, horses, apes, men and all other mammals had the same origin. Therefore, the early stages in the evolutionary process were the same for all these creatures. That is to say, the course of life’s development, before diverging toward these respective forms, followed for a time a general line of advance.