Fig. 2. Evolution of pole arms. (Metropolitan Museum. After Dean.)
What has the evolution of the stars, of the horse and of human inventions in common? Only this, that in each case from a simple beginning through a series of changes something more complex, or at least different, has come into being. To lump all these kinds of changes into one and call them evolution is no more than asserting that you believe in consecutive series of events (which is history) causally connected (which is science); that is, that you believe in history and that you believe in science. But let us not forget that we may have complete faith in both without thereby offering any explanation of either. It is the business of science to find out specifically what kinds of events were involved when the stars evolved in the sky, when the horse evolved on the earth, and the steam engine was evolved from the mind of man.
Is it not rather an empty generalization to say that any kind of change is a process of evolution? At most it means little more than that you want to intimate that miraculous
intervention is not necessary to account for such kinds of histories.
We are concerned here more particularly with the biologists' ideas of evolution. My intention is to review the evidence on which the old theory rested its case, in the light of some of the newer evidence of recent years.
Four great branches of study have furnished the evidence of organic evolution. They are:
Comparative anatomy.
Embryology.