246 ENTOMOLOGY 



plished in the most forcible way, namely, by shattering the 

 traditional belief in the immutability of species. Nowhere 

 does Darwin imply that nature is striving to produce " spe- 

 cies " for their own sake. A process of evolution was the 

 theme of Darwin and its key-note was adaptation. 



Indeed, for the purposes of the present generation, Dar- 

 win's immortal work would more properly be entitled The 

 Evolution of Adaptations by Means of Natural Selection. 

 And to us, who now ridicule the old notion of the special 

 creation of species, the doctrine of natural selection appears in 

 a fresh light, with a new mission. For, in the words of 

 Romanes, the theory is " primarily, a theory of adaptations, 

 and only becomes secondarily a theory of species in those com- 

 paratively insignificant cases where the adaptations happen to 

 be distinctive of the lowest order of taxonomic division." 

 The opposite view he compares " to that of an astronomer who 

 should define the nebular hypothesis as a theory of the origin 

 of Saturn's rings. It is indeed a theory of the origin of 

 Saturn's rings ; but only because it is a theory of the origin of 

 the entire solar system, of which Saturn's rings form a part. 

 Similarly, the theory of natural selection is a theory of the 

 entire system of organic nature in respect of adaptations, 

 whether these happen to be distinctive of particular species 

 only, or are common to any number of species." It should be 

 remembered, of course, in using this comparison, that not all 

 specific characters are adaptive. 



As regards the origin of species, however, there are several 

 processes at work besides natural selection. Indeed, Darwin 

 himself knew this, for he expressly stated : " I am convinced 

 that natural selection has been the most important, but not the 

 exclusive, means of modification." 



The Conception of " Species." What is a " species"? 

 The only practical criterion of species is isolation, or separate- 

 ness, of one kind or another. The majority of our " species " 

 are sharply separated from one another by structural differ- 

 ences; the minority, however, blend into one another, and 



