278 Darwin, and after Darwin. 



cause of specific change. But, apart altogether 

 from this a priori refutation of the dogma, our 

 analysis went on to show that, in point of actual 

 fact, there are not a few well-known causes of high 

 generality, which, while having no connexion with 

 the principle of utility, are demonstrably capable 

 of originating species and specific characters if by 

 " species " and " specific characters " we are to under- 

 stand organic types which are ranked as species, 

 and characters which are described as diagnostic 

 of species. Such causes I grouped under five dif- 

 ferent headings, viz. Climate, Food, Sexual Selection, 

 Isolation, and Laws of Growth. Sexual Selection 

 and Isolation are, indeed, repudiated by Mr. Wallace ; 

 but, in common I believe with all biologists, he 

 accepts the other three groups of causes as fully 

 adequate to produce such kinds and degrees of 

 modification as are taken to constitute specific dis- 

 tinction. And this is amply sufficient for our present 

 purposes. Besides, under the head of Sexual Selection, 

 it does not signify in the present connexion whether 

 or not we accept Darwin's theory on this subject. 

 For, in any case, the facts of secondary sexual char- 

 acters are indisputable: these characters are, for the 

 most part, specific characters: and they cannot be 

 explained by the principle of utility. Even Mr. 

 Wallace does not attempt to do so ; and the ex- 

 planation which he does give is clearly incompatible 

 with his doctrine touching the necessarily life-serving 

 value of all specific characters. Lastly, the same has 

 to be said of the Laws of Growth. For we have just 

 seen that on the grounds of this principle likewise 

 Mr. Wallace abandons the doctrine in question. As 



