EVOLUTION — CONKLIN" 207 



son seemed very improbable to another. Cope accepted all the La- 

 marckian factors, Romanes rejected use and disuse but accepted 

 the others, Weismann rejected all of them. The fact of evolution 

 was accepted by practically all scientists, but the factors of evolu- 

 tion were largely matters of opinion, and in general persons believed 

 what they preferred to believe. Indeed this whole subject had 

 become so speculative that it seemed to be a field for the exercise of 

 the imagination rather than of scientific research, and one of the 

 eminent younger biologists, disgusted with this flood of speculation, 

 announced, " I am done with this entire phylogeny business." 



Then in 1900 Mendel's principles of heredity, which had re- 

 mained unrecognized for 35 years, were rediscovered, and a new 

 science of accurate, experimental knowledge of heredity was born 

 and was christened " genetics " by Bateson. Almost at once many 

 perplexing problems of heredity were solved ; " prepotency " was 

 found to be Mendelian dominance, " reversions " or " atavism " were 

 the reappearance of Mendelian recessives, the results of hybridiza- 

 tion were no longer unpredictable and the laws of heredity were 

 at last in process of being discovered. 



One year later (1901) De Vries published his great work on the 

 mutations of the evening primrose, Oenothera Imtmrckiana^ upon 

 which he had been engaged for 15 years and in the course of which 

 he observed under rigid experimental conditions among the off- 

 spring of this one species the appearance of 9 constant mutants, 3 

 inconstant and 1 infertile mutant, all of which differed so much from 

 the parent form and from one another that he called them elementary 

 species, and maintained that they furnished actual, living evidence 

 of experimental evolution. Galton had previously (1892) expressed 

 his belief that " sports ", or sudden variations, were the real steps 

 in the evolution of species and Bateson had published his great 

 work on "Discontinuity in the Origin of Species" (1894), but long 

 before this, Darwin had given it as his opinion that evolution had 

 occurred by means of minute variations rather than by " sports ", 

 and in this he was followed by Cope and practically all other pale- 

 ontologists. Consequently it was not until De Vries had actually 

 demonstrated the sudden appearance of mutations in his cultures 

 that this method of evolution was widely accepted. Since then 

 mutations have been found in almost all organisms that have been 

 carefully studied through successive generations, and in spite of 

 occasional objections on the part of paleontologists or other natural- 

 ists who are unable to carry on breeding experiments with their ma- 

 terials, the mutation theory of evolution is now well established, 

 although it is known that mutations may be small as well as great. 



