374 THE POPULAR SCIENCE MONTHLY 



regard as superfluous, although harmless, but it is heresy to study criti- 

 cally 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 Neo- 

 Darwinian, 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 evolu- 

 tion 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 distin- 

 guishing feature of Darwin's work. Before his time the theory of 

 evolution remained but a general idea, though one of profound signifi- 

 cance. 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 con- 

 temporaries 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 ecolo- 

 gists have studied the complex influences of the environment ; the experi- 

 mentalist 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 interpreta- 



