19 



the reviewer to be entirely misrepresented when it is said to 

 "offer itself as an explanation of adaptation," and to be a 

 " claimant for recognition as the great cause of descent." Unless 

 I have entirely misunderstood de Vries, mutation was never put 

 forward by him as an explanation of adaptation, nor as a " cause " 

 of anything, but as a method only ; the method of variation (by 

 saltation) whose results are held most probably to furnish the 

 material for natural selection (the great " sieve," as de Vries calls 

 it) to act on. Adaptation, for the de Vnesian mutationist, as well 

 as for the Darwinian, results from the survival of the fittest 

 (because best adapted) in the struggle for existence. It were 

 much nearer the truth to say that mutation offers an explanation 

 for the lack of adaptation, i. e., for the origin of characters that 

 are not adaptive. It is on this point that the weakness of natural 

 selection is greatly in evidence. 



The last chapter is a kind of confession of faith, or scientific 

 creed, of the author, in which he makes it more clear, if possible, 

 than do the above quotations, that he is not a mutationist. " Dar- 

 winism," he says, "as the natural selection of the fit, the final 

 arbiter in descent control, stands unscathed, clear and high above 

 the obscuring cloud of battle. At least, so it seems to me. But 

 Darwinism, as the all-sufficient or even the most important causo- 

 mechanical factor in species-forming and hence as the sufficient 

 explanation of descent, is discredited and cast down." The 

 author urges us, "with Osborn," to "join the believers in the 

 * unknown factors in evolution,' " and inclines to a belief that there 

 is " an automatic modifying principle which results in purposive 

 change, that is, in the change needed as the indispensable basis 

 for the upbuilding of the great fabric of species diversity and de- 

 scent " (p. 387). 



The reading of the book is rendered easier and more pleasant 

 by the paragraph headings in heavy type, and less so by numer- 

 ous lengthy quotations in German and French in the appendices 

 to the chapters. The citations to original papers serve to render 

 the book even more helpful and indispensable. All students of 

 evolution-theories and kindred problems will warmly welcome it. 



C. Stuart Gager. 



