THE ORIGIN OF NEW FORMS 189 



makes it evident that Darwin was not the discoverer of the law 

 of evolution, contrary to what is often assumed. In an historical 

 sketch of the progress of opinion on the origin of species previous 

 to the appearance of his own book, Darwin himself summarizes 

 the views of twenty biologists who gave entire or partial support 

 to the idea of evolution. The action of natural selection as a 

 factor in evolution, the discovery of which has been commonly 

 attributed to Darwin, was first suggested by Wells in 1813. Matthew 

 in 1831 and Naudin in 1852 held the same view of the importance 

 of natural selection as that advanced independently by Darwin 

 and Wallace in 1859. Nevertheless, while it is incorrect to ascribe 

 the discovery of evolution and natural selection to Darwin, he 

 must receive the fullest credit for bringing about the final accept- 

 ance of origin by descent. His twenty years of painstaking study 

 of evolution left no doubt of its being a universal process, even 

 though he was unable to prove the exact way in which it acts. 



Darwin recognized that new forms arose through the direct 

 action of the habitat and through the production of sports. He 

 considered that the action of the habitat led to definite or in- 

 definite variation, while it was impossible to connect the origin 

 of sports with external causes. Definite variation occurs when 

 all or nearly all individuals respond in the same way, while in- 

 definite variation, called also fluctuating variability, takes place 

 when the individuals are slightly modified in all directions. While 

 Darwin believed that definite variation, i.e., adaptation, as well 

 as sports, i.e., mutation, occasionally produced new forms, he 

 held that species ordinarily arise in consequence of indefinite 

 variation. The minute variations of individuals were assumed 

 to be preserved and accumulated through natural selection, or 

 the survival of the fittest. The latter, moreover, was sujiposed to 

 be due entirely to the competition between individuals and not 

 to the direct action of the physical factors of the habitat. Dar- 

 win's conclusions were based chiefly upon the study of domesticated 

 plants and animals, and upon observation instead of upon ex- 

 periment. These two facts serve to explain why he found it 

 possible to put the greatest emphasis upon origin by vai-iatioii 

 and natural selection, which is, of the three methods recognized 

 by him, the only one not experimentally proven. 



205. Evolution after Darwin. As frequently happens after the 

 appearance of a great work, the "Origin of Species" ushered in a 



