248 Darivin, and after Darwin. 



appearance, destitute of significance from a utilitarian 

 point of view, 



(C.) 



Thus far in the present chapter we have been 

 dealing exclusively with the case of "climatic varia- 

 tion,'' or change of specific type due to changes in 

 the external conditions of life. But it will be remem- 

 bered that, in the preceding chapter, allusion was 

 likewise made to changes of specific type due to 

 internal causes, or to what Darwin has called " the 

 nature of the organism." Under this division of 

 our subject I mentioned especially Sexual Selection, 

 which is supposed to arise in the aesthetic taste 

 of animals themselves ; Isolation, which is supposed 

 to originate new types by allowing the average 

 characters of an isolated section of an old type to 

 develop a new history of varietal change, as we shall 

 see more fully in the ensuing part of this treatise ; 

 and the Laws of Growth, which is a general term for 

 the operation of unknown causes of change incidental 

 to the living processes of organisms which present the 

 change. 



Now, under none of these divisions of our subject 

 can there be any question touching the criterion of 

 Heredity. For if new species — or even single specific 

 characters of new species — are ever produced by any 

 of these causes, they must certainly all ' reproduce 

 their like." Therefore the only question which can 

 here obtain is as to whether or not such causes ever do 

 originate new species, or even so much as new specific 

 characters. Mr. Wallace, though not always consis- 

 tently, answers this question in the negative ; but tlie 



