The Doctrine of Evolution | Page 5

to other than everyday processes for an explanation of the present order of things.
Wherever we look we see evidence of nature's change; every rain that falls washes the earth from the hills and mountains into the valleys and into the streams to be transported somewhere else; every wind that blows produces its small or greater effect upon the face of the earth; the beating of the ocean's waves upon the shore, the sweep of the great tides,--these, too, have their transforming power. The geologists tell us that such natural forces have remodeled and recast the various areas of the earth and that they account for the present structure of its surface. These men of science and the astronomers and the physicists tell us that in some early age the world was not a solid globe, with continents and oceans on its surface, as now; that it was so very hot as to be semi-fluid or semi-solid in consistency. They tell us that before this time it was still more fluid, and even a mass of fiery vapors. The earth's molten bulk was part of a mass which was still more vast, and which included portions which have since condensed to form the other bodies of the solar system,--Mars and Jupiter and Venus and the rest,--while the sun remains as the still fiery central core of the former nebulous materials, which have undergone a natural history of change to become the solar system. The whole sweep of events included in this long history is called cosmic evolution; it is the greater and more inclusive process comprising all the transformations which can be observed now and which have occurred in the past.
At a certain time in the earth's history, after the hard outer crust had been formed, it became possible for living materials to arise and for simple primitive creatures to exist. Thus began the process of organic evolution--_the natural history of living things_--with which we are concerned in this and later addresses. Organic evolution is thus a part of the greater cosmic process. As such it does not deal with the origin of life, but it begins with life, and concerns itself with the evolution of living things. And while the investigator is inevitably brought to consider the fundamental question as to the way the first life began, as a student of organic forms he takes life for granted and studies only the relationships and characteristics of animals and plants, and their origins.
But even as a preliminary definition, the statement that organic evolution means natural change does not satisfy us. We need a fuller statement of what it is and what it involves, and I think that it would be best to begin, not with the human being in which we are so directly interested, nor even with one of the lower creatures, but with something, as an analogy, which will make it possible for us to understand immediately what is meant by the evolution of a man, or of a horse, or of an oak tree. The first steam locomotive that we know about, like that of Stephenson, was a crude mechanism with a primitive boiler and steam-chest and drive-wheels, and as a whole it had but a low degree of efficiency measured by our modern standard; but as time went on inventive genius changed one little part after another until greater and greater efficiency was obtained, and at the present time we find many varied products of locomotive evolution. The great freight locomotive of the transcontinental lines, the swift engine of the express trains, the little coughing switch engine of the railroad yards, and the now extinct type that used to run so recently on the elevated railroads, are all in a true sense the descendants of a common ancestor, namely the locomotive of Stephenson. Each one has evolved by transformations of its various parts, and in its evolution it has become adapted or fitted to peculiar circumstances. We do not expect the freight locomotive with its eight or ten powerful drive-wheels to carry the light loads of suburban traffic, nor do we expect to see a little switch engine attempt to draw "the Twentieth Century Limited" to Chicago. In the evolution, then, of modern locomotives, differences have come about, even though the common ancestor is one single type; and these differences have an adaptive value to certain specific conditions. A second illustration will be useful. Fulton's steamboat of just a century ago was in a certain true sense the ancestor of the "Lusitania," with its deep keel and screw propellers, of the side-wheel steamship for river and harbor traffic like the "Priscilla," of the stern-wheel flat-bottom boats of the Mississippi, and of the battleship, and the tug boat. As in the first instance, we know that each modern