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