GOOD AND BAD SPECIES. 273 



themselves, and at length cease to be any longer connected 

 with the original primary species through intermediate forms 

 of transition. Thus arise " good species " out of varieties. 

 Thus, then, the struggle for life necessarily favours the 

 general divergence of organic forms, that is, the constant 

 tendency of organisms to form new species. This fact does 

 not rest upon any mystic quality, or upon an unknown forma- 

 tive tendency, but upon the interaction of Inheritance and 

 Adaptation m the struggle for life. As the intermediate 

 forms, that is, the individuals in a state of transition, of 

 the varieties of every species die out and become extinct, 

 the process of divergence constantly goes further, and from 

 the extremes forms develop which we distinguish as new 

 species. 



Although all naturalists have been obliged to acknowledge 

 the variability and mutability of all species of animals and 

 plants, yet most of them have hitherto denied that the 

 modification or transformation of the organic form surpasses 

 the original limit of the characters of the species. Our 

 opponents cling to the proposition — " However far a species 

 may exhibit deviations from its usual form in a collection of 

 varieties, yet the varieties of it are never so distinct from 

 one another as two really good species." This assertion, 

 which Darwin's opponents usually place at the head of 

 their arg-uments, is utterly untenable and unfounded. 

 This will become quite clear as soon as we critically 

 compare the various attempts to define the idea of species. 

 No naturalist can answer the question as to what is in 

 reality a " genuine or good species " (" bona species ") ; yet 

 every systematic naturalist uses this expression every day, 

 and whole libraries have been written on the question as to 



