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EVOLUTION see them to-day. We have treated our question as an historical question, and have gone searching for clues in the past as an archæologist explores the past of buried cities, by digging, and collecting coins, implements, records, etc. and putting the facts together into a history. In the museums at Yale University are preserved upward of 30 steps or stages in the history of the horse-family, showing that it arose by evolution or gradual changes from a four or five-toed ancestor about the size of a fox and that it passed through many changes besides increase in size in the 2,000,000 years in which we can get facts as to its history. These facts, taken in connection with a multitude of others pointing in the same direction, give us the answer to the question: Were the immense number of living forms created just as we find them, or were they created by a process of evolution?

The series of shells and horses mentioned above are called evolutionary series. They were not known at the time of the publication of Darwin's great book on The Origin of Species.

The most interesting evidences of evolution bearing on all animal life are found in the various stages through which animals pass on their way from the egg to the fully formed animal. Every animal, above the Protozoa, begins its life as a single cell and passes through every gradation from that condition upward. As animals develop in this way, they become successively more and more complex, and many rudimentary organs arise and disappear. For example, in the young chick, developing within the hen's egg, there appear, after four days, gill-slits or openings into the throat, like the gills of lower fishes. These organs belong entirely to water-life, and are not of direct use to the chick. The heart and blood-vessels at this stage are also of the fish-like type, but all this disappears in a few days, long before the chicken is hatched. Similar gill-slits appear also very early in the development of the young rabbit and of all higher animals. The best way of explaining their presence—which certainly means something—is to say that they are inherited from remote parents. Animals in the course of their development repeat certain stages of their past histories. The presence of gill-clefts in the embryos of birds and rabbits probably means that both these animals sprang from ancestors that had gill-clefts, or water breathing animals. Such traces are like hieroglyphics and inscriptions on temples and columns—they are clues to ancient history and they weigh heavily on the side of evolution. If space permitted, the evidences in favor of evolution might be very much multiplied.

Having illustrated what the doctrine of

evolution is, the main part of our task is done, for the questions regarding the different theories of evolution and the rise of evolutionary thought must be dealt with very briefly, and the reader directed to the best books for further information. The doctrine of evolution is regarded as established beyond controversy. The controversies about evolution to-day are not as to whether it was or was not the method of creation, but as to how evolution of different forms was brought about. Therefore we must distinguish between the facts of evolution and the factors. Although several theories have been advanced to account for evolution, only three command any particular amount of attention at the present time: those of Lamarck, Darwin and Weismann. Lamarck's theory was founded in the early part of the 19th century. Being greatly impressed with the differences produced in animal-life by surroundings—climate, temperature, moisture, elevation above the sealevel, etc., he came to believe that all variation in animals had been produced by different surroundings, and the effects of use and disuse of organs. The use of the muscles of the blacksmith's arm, for example, develops it greatly; the disuse of the wings of the wingless birds has led to the disappearance of their wings. The differences thus produced are inherited. While the explanation of Lamarck has two factors, that offered by Darwin has three. He showed that animals vary in a state of nature, that these variations are inherited and, thirdly, that nature selects the fittest to survive, through the failure and death of the weaker ones in the struggle for existence. The variations that prove of advantage to the individual would be the ones preserved and handed along by heredity. This theory was arrived at, independently, by A. R. Wallace, and should be known as the Darwin-Wallace theory of natural selection. But this is not evolution; it is an attempt to explain how evolution was brought about. Weismann's theory is difficult to state briefly and clearly. It is called the theory of continuity of the germ-plasm. He accepts Darwin's natural selection, and shows that the germ-plasm, or substance from which animals arise, is continuous from generation to generation. Heredity is explained in a simple way, viz., the offspring is like the parent, because some of the same stuff enters into all its cells. He concludes, further, that the germ-plasm must be impressed by surroundings before changes in the animal can be inherited. There is at present a disposition to revive Lamarck's ideas in a modified form and to unite them with Darwin's. The theory of Weismann is losing ground.

Let us now look briefly at the rise of the doctrine of evolution. Osborn has shown