338 DARWINISM TO-DAY. 



through gradual selection continued for hundreds or thou- 

 sands of years, but by jumps (stuf enweise) through sudden, 

 though small, transformations. In contrast with variations 

 which are changes in a linear direction the transformations 

 to be called mutations constitute divergence in new directions. 

 They take place, so far as experience goes, without definite 

 direction." And even if transition forms exist between 

 the species produced by mutations, they are no evidence 

 against the mutations, ''for," says de Vries, "the transitions 

 do not appear before the new species, at most only simul- 

 taneously with this, and generally only after this is already 

 in existence. The transitions are therefore no intermediates 

 or preparations for the appearance of the new forms. The 

 origin takes place, not through them, but wholly independ- 

 ently of them." 15 



Too often de Vries's theory is said not to be alternative 

 with Darwin's, but auxiliary to it. As regards the forma- 

 tion of new species, the two theories are directly 

 De Vries's in opposition. But as regards the general 

 opposition to course of organic evolution (which is another 

 Darwin's as con- matter) the mutations theory is not in contra- 



cerns species- . 



forming, diction to the theory of descent through 



selection. De Vries himself says : "Notwith- 

 standing all these apparently unsurmountable difficulties, 

 Darwin discovered the great principle which rules the evolu- 

 tion of organisms. It is the principle of natural selection. 

 It is the sifting out of all organisms of minor worth through 

 the struggle for life. It is only a sieve, and not a force of 

 nature, no direct cause of improvement, as many of Dar- 

 win's adversaries, and unfortunately many of his followers 

 also, have so often asserted. It is only a sieve, which de- 

 cides which is to live, and what is to die. . But evolutionary 

 lines are of great length, and the evolution of a flower or 

 of an insectivorous plant is a way with many side-paths. It 

 is the sieve that keeps evolution on the main line, killing- 



