indicates that they are not purposeful, but we can not prove this. If they are not purposeful then the purposefulness of the living world has no direct relation to the origin of useful variations. The origin of an adaptive structure and the purpose it comes to fulfill are only chance combinations. Purposefulness is a very human conception for usefulness. It is usefulness looked at backwards. Hard as it is to imagine, inconceivably hard it may appear to many, that there is no direct relation between the origin of useful variations and the ends they come to serve, yet the modern zoologist takes his stand as a man of science on this ground. He may admit in secret to his father confessor, the metaphysician, that his poor intellect staggers under such a supposition, but he bravely carries forward his work of investigation along the only lines that he has found fruitful.
In the last analysis it is a matter of expediency; or if the word jars, a matter of instinct. Why forsake the gold mine at our feet, because the transmutation of metals is a philosophic possibility?
Whether definite variations are by chance useful, or whether they are purposeful are the contrasting views of modern speculation. The philosophic zoologist of to-day has made his choice. He has chosen undirected variations as furnishing the materials for natural selection. It gives him a working hypothesis that calls in no unknown agencies; it accords with what he observes in nature; it promises the largest rewards. He does not deny, if he is cautious, the possibility that there may be a purposefulness in the sense that organisms may respond adaptively at times to external conditions; for the very basis of his theory rests on the assumption that such variations do occur. But he is inclined to question the assumption that adaptive variations arise because of their adaptiveness. In his experience he finds little evidence for this belief, and he finds much that is opposed to it. He can foresee that to admit it for that all important group of facts, where adjustments arise through the adaptation of individuals to each other—of host to parasite, of hunter to hunted—will land him in a mire of unverifiable speculation. He fears to enter thereby on a field of exploitation of nature that has proved itself so sterile in the past.
We have reached the end of our theme. If I have led you too far into some of the remote corners of zoological thought, I must plead that such thoughts are the legitimate outgrowth of Darwinism.
I have tried to show you the modern zoologist at work on the great theory of evolution. We stand to-day on the foundations laid fifty years ago. Darwin's method is our method, the way he pointed out we follow, not as the advocates of a dogma, not as the disciples of any particular creed, but the avowed adherents of a method of investigation whose inauguration we owe chiefly to Charles Darwin. For it is this spirit of Darwinism, not its formula, that we proclaim as our best heritage.