OF NATURAL SELECTION. 175 



should there be so much variety and so little real novelty ? 

 Why should all the parts and organs of many independent 

 beings, each supposed to have been separately created for 

 its own proper place in nature, be so commonly linked to- 

 gether by graduated steps ? Why should not Nature take 

 a sudden leap from structure to structure ? On the theoiy 

 of natural selection, we can clearly understand why she 

 should not ; for natural selection acts only by taking advan- 

 tage of slight successive variations ; she can never take a 

 great and sudden leap, but must advance by short and sure, 

 though slow steps. 



ORGANS OF LITTLE APPARENT IMPORTANCE, AS AFFECTED 



BY NATURAL SELECTION. 



As natural selection acts by life and death, by the sur- 

 vival of the fittest, and by the destruction of the less well- 

 fitted individuals, I have sometimes felt great difficulty in 

 understanding the origin or formation of parts of little 

 importance ; almost as great, though of a very different 

 kind, as in the case of the most perfect and complex organs. 



In the first place, we are much too ignorant in regard to 

 the whole economy of any one organic being to say what 

 slight modifications would be of importance or not. In a 

 former chapter I have given instances of very trifling 

 characters, such as the down on fruit and the color of its 

 flesh, the color of the skin and hair of quadrupeds, which, 

 from being correlated with constitutional differences, or 

 from determining the attacks of insects might assuredly 

 be acted on by natural selection. The tail of the giraffe 

 looks like an artificially constructed fly-flapper; and it 

 seems at first incredible that this could have been adapted 

 for its present purpose by successive slight modifications, 

 each better and better fitted, for so trifling an object as to 

 drive away flies ; yet we should pause before being too 

 positive even in this case, for we know that the distribution 

 and existence of cattle and other animals in South America 

 absolutely depend on their power of resisting the attacks of 

 insects; so that individuals which could by any means 

 defend themselves from Ijhese small enemies, would be able 

 to range into new pastures and thus gain a great advantage. 

 It is not that the larger quadrupeds are actually destroyed 

 (except in some rare cases) by flies, but they are in- 

 cessantly harassed and their strength reduced, so that they 



