Page:Popular Science Monthly Volume 74.djvu/378

374 regard as superfluous, although harmless, but it is heresy to study critically the working out of the theory of natural selection. Such has ever been the procedure of the infertile followers of great leaders. In the present instance the result is the more deplorable, since Darwin's own independence of the traditions of all schools, his careful study of facts, his emancipation from prejudice, are his lasting virtues. The NeoDarwinian, worshipping the letter of the law, forgets its import. Let us salute, and pass.

And now we come to the last twenty years of zoology as influenced by Darwin. This, I believe, is the brightest chapter of Darwinism, for the spirit of Darwin is once more abroad.

Foremost amongst the many debts that modern zoology owes to Darwin is this: he pointed out that in order to understand how evolution takes place, we must study the variations of animals and plants, for here is the material on which rests any solid superstructure. To my mind, the appreciation of this maxim and its application is the distinguishing feature of Darwin's work. Before his time the theory of evolution remained but a general idea, though one of profound significance. After Darwin, the theory of evolution rested its claims for recognition on a definite body of information relating to variations and their inheritance. It is these data that first convinced his greatest contemporaries of the reality of evolution, and finally convinced also the rank and file of thinking men. So extensive were the facts of variation accumulated by Darwin, so penetrating was his analysis of these facts, so keen was his insight, and so wise his judgment as to their meaning, that for thirty years afterwards little of importance in this direction was added. In their amazement at Darwin's accomplishment zoologists forgot that he had opened the door leading into an unexplored territory. During the last twenty years the march forward has once more begun and the reward has been immediate.

Let us tarry therefore a little in these rich and pleasant fields of discovery and examine in some detail what is being done. The study of variation has been actively pursued in three main directions. The biometricians have applied exact measurements to variation; the ecologists have studied the complex influences of the environment; the experimentalist has put to the test the supposed factors of change. Each of these methods has brought out results of significance.

A careful study of variations within each species has shown that taken as a group many variations conform to the law of probability. Popularly expressed, this means that chance determines variations, or, put more exactly, variations taken as a group and measured, give the same mathematical results that follow when any set of objects become arranged according to the laws of probability. There was a time when chance meant lack of conformity to law. Such a popular