Adaptation by divergence--for the most part by slow stages--is the movement of evolution. While occasional leaps or sudden changes occur in the process, they are by no means the rule. In most cases of "saltatory evolution," the suddenness is in appearance only. It comes from our inability to trace the intermediate stages. When an epoch-making character is acquired, as the wings of a bird or the brain of man, the process of readjustment of other characters goes on with greatly increased rapidity. But this rapidity of evolution is along the same lines as the slower processes. Radical changes from generation to generation never occur. We do not expect to find birds arising from a "flying-fish in the air, whose scales are disporting into feathers." A flying-fish is no more of the nature of a bird than any other fish is. A cow will never give birth to a horse, nor a horse to a cow. The slow operation of existing causes is the central fact of organic evolution, as it is of the evolution of mountains and valleys. Seasons change as the relations which produce them change. But midsummer never gives way to midwinter in an instant. Nor does the child in an instant become a man, though in some periods of growth epoch-marking causes may make development more rapid. Life is conservative. The law of heredity is the expression of its conservatism. It changes slowly, but it must constantly change, and all change is by necessity divergence. There is in nature no single "law of progress," nor is progress in any group a necessity regardless of conditions. That which we call progress rests simply on the survival of the better adapted, their survival being accompanied by their reproduction. Those that live repeat themselves. The "innate tendency towards progression" of the early evolutionists is a philosophic myth. Progress and degeneration are alike the resultants of the various forces at work from generation to generation on and within a race or species. The same forces which bring progress to a group under one set of conditions will bring degradation under another. In their essence the factors of evolution are no more laws of progress than the attraction of gravitation is. Cosmic order comes from gravitation. Organic order comes from the factors of evolution. Evolution is simply orderly change.