136 Evolution and Adaptation 



variations, which sooner or later became constant through the 

 nature of the organism and of the surrounding conditions, as 

 well as through the intercrossing of distinct individuals, but 

 not through natural selection; for as these morphological 

 characters do not affect the welfare of the species, any slight 

 deviations in them could not have been governed or accumu- 

 lated through this latter agency. It is a strange result which 

 we thus arrive at, namely, that characters of slight vital im- 

 portance to the species are the most important to the system- 

 atist; but, as we shall hereafter see when we treat of the 

 genetic principle of classification, this is by no means so para- 

 doxical as it may at first appear." 



If all this be granted, it is once more evident that the only 

 variations that come under the action of selection are the 

 limited number that are of vital importance to the organism. 

 How little the theory of natural selection can be used to 

 explain the origin of species will be apparent from the above 

 quotation. This is, of course, not an argument against the 

 theory itself, which would still be one of vast importance if it 

 explained adaptive characters alone ; but enough has been 

 said, I think, to show that it is improbable that the origin of 

 adaptive and non-adaptive characters are to be explained by 

 entirely different principles. 



In reply to a criticism of Mivart, Darwin makes the 

 further admission as to the insufficiency of the theory of 

 natural selection : " When discussing special cases, Mr. 

 Mivart passes over the effects of the increased use and 

 disuse of parts, which I have always maintained to be highly 

 important, and have treated in my ' Variation under Domes- 

 tication' at greater length than, as I believe, any other 

 writer. He likewise often assumes that I attribute nothing 

 to variation, independent of natural selection, whereas in the 

 work just referred to I have collected a greater number of 

 well-established cases than is to be found in any other work 

 known to me." If this is admitted, and if it can be shown 



