DIFFICULTIES ON THEORY 179 



precise cause of the slight analogous differences be- 

 tween species. I might have adduced for this same 

 purpose the differences between the races of man, 

 which are so strongly marked ; I may add that some 

 little light can apparently be thrown on the origin of 

 these differences, chiefly through sexual selection of a 

 particular kind, but without here entering on copious 

 details my reasoning would appear frivolous. 



The foregoing remarks lead me to say a few words 

 on the protest lately made by some naturalists, against 

 the utilitarian doctrine that every detail of structure 

 has been produced for the good of its possessor. They 

 believe that very many structures have been created 

 for beauty in the eyes of man, or for mere variety. 

 This doctrine, if true, would be absolutely fatal to my 

 theory. Yet I fully admit that many structures are of 

 no direct use to their possessors. Physical conditions 

 probably have had some little effect on structure, quite 

 independently of any good thus gained. Correlation 

 of growth has no doubt played a most important part, 

 and a useful modification of one part will often have 

 entailed on other parts diversified changes of no direct 

 use. So again characters which formerly were useful, 

 or which formerly had arisen from correlation of 

 growth, or from other unknown cause, may reappear 

 from the law of reversion, though now of no direct 

 use. The effects of sexual selection, when displayed 

 in beauty to charm the females, can be called useful 

 only in rather a forced sense. But by far the most 

 important consideration is that the chief part of the 

 organisation of every being is simply due to inherit- 

 ance ; and consequently, though each being assuredly 

 is well fitted for its place in nature, many structures 

 now have no direct relation to the habits of life of each 

 species. Thus, we can hardly believe that the webbed 

 feet of the upland goose or of the frigate-bird are of 

 special use to these birds ; we cannot believe that the 

 same bones in the arm of the monkey, in the fore-leg 

 of the horse, in the wing of the bat, and in the flipper 

 of the seal, are of special use to these animals. We 



