DARWINISM DEFENDED. 139 



ciently useful and advantageous to turn the scale in the intra- 

 or inter-specific struggle for existence in favour of the 

 individuals possessing them, and they must occur in suffi- 

 ciently many individuals to avoid being swamped or 

 extinguished by cross-breeding : that is, they must be useful 

 enough to be selected and numerous enough to perpetuate 

 themselves. Do Darwinian variations ever meet these re- 

 quirements ? Unfortunately our proof is rather indirect : 

 observation reveals their abundance, but does not actually 

 show their utility. 6 To answer the question our judgment 

 and reason, based on our knowledge and experience of the 

 existing conditions of animal and plant life, will have to 

 be trusted for answer. How real is the rigour ; how keen 

 the struggle ; how crowded the square yard or square mile ; 

 how great or how little must be the differences in a part to 

 give a life-or-death decision in the competition? Each 

 naturalist must answer this for himself, and the layman 

 must take the general consensus of opinion of the natural- 

 ists, if there is one, for his answer. 



The objection to the linear and quantitative character of 

 the Darwinian variations has been recently especially urged 

 by de Vries in connection with his exposition 

 of the theor y f species-forming by mutations. 



coining the The selection theory reckons with linear hence 



linear and quan- . , . . 



titative charac- strictly quantitative variations, says he, and yet 



teroffluctnating j s presumed to create new forms for which in 



variation, . 



reality qualitative variations are necessary as 

 a basis, so that in fact selection can only increase or 

 diminish, add to or subtract from characters already in 

 existence and cannot create anything new, this appear- 

 ance of new characteristics being, however, precisely the 

 principal peculiarity of new species, taken by and large. This 

 position of de Vries has been discussed by Plate T as follows : 

 "I call attention in advance to the fact that de Vries 

 understands by 'linear variations' what are more usually 



