ZOOLOGY 45i 



In one fundamental respect the doctrine is incomplete, as it fails 

 to explain the causes for the variations with which selection deals. It 

 accounts for the perpetuation of favoring variations, but it does not 

 account for their inception. Because of this defect, investigators 

 reacted from the academic discussion of Darwin's original doctrine, 

 and returned to deeper and wider study of heredity and variation with 

 brilliant success. Some neo-Darwinians have endeavored to make the 

 selective process an originative influence — notably Koux, and Weismann 

 in his theory of germinal selection. Darwin himself added the sub- 

 sidiary process of sexual selection, which regards the preference by 

 one sex of characteristics of the opposite sex as a conserving influence. 

 But while such attempts have failed, zoologists believe, to explain the 

 whole method of evolution, much of the process has been demonstrated 

 more and more clearly with further study. The laws of fluctuating 

 variations have now been formulated with mathematical accuracy, 

 through the employment of the statistical methods used earlier by 

 anthropologists like Quetelet. The studies of Galton and Pearson, 

 Boas, Weldon and Davenport have demonstrated that structural and 

 physiological characters of men, of other animals, and of plants as 

 well, vary according to the formulas of chance or error — a result they 

 say that follows from the combined influence of innumerable and inde- 

 pendent factors. Variation is a natural phenomenon of chance. 

 Furthermore, the reality of the selective process has also been proved 

 by statistical methods. Bumpus's English sparrows, Weldon's snails 

 and crabs, and many other cases show that the individuals which depart 

 widely from an average condition, or that are uncorrected in their 

 organization, are marked for destruction. 



In brief, while natural selection has not been established as in any 

 sense an originative process, it has been demonstrated, I believe, as a 

 judicial process. For we may liken the many varied vital conditions 

 to jurymen, before whom every organism must present itself for judg- 

 ment; and a unanimous verdict of complete or at least partial approval 

 must be rendered, or the organism must perish. 



The phenomena of biological inheritance, however, have demanded 

 the greater attention of Darwinian and post-Darwinian investigators. 

 A complete statement of the whole of evolution must show how species 

 maintain the same general characteristics through inheritance, how the 

 type is held true with passing generations, and it must also show how 

 new characters may enter into the heritage of any species to be trans- 

 mitted as organisms transform in evolution. 



The earliest naturalists had accepted the fact of inheritance as self- 

 sufficient. The resemblance between parent and offspring did not 

 demand an explanation any more than variation. When Buffon, how- 

 ever, added the element of species transformation, he held that external 



