DIFFICULTIES OF THE THEORY 271 



advantage of slight successi ve__variations ;__shfi— caa-a^veF- 



takg^a^reat an d sudden, leap, but must , advance bj short 



and sure|jthou^h_sk)WL,steps. ,^ 



Organs of little apparent Importance^ as affected hy Natural 



Selection 



As natural selection acts by life and death — by the 

 survival of the fittest, and by the destruction of the less 

 well-fitted individuals — I have sometimes felt great diffi- 

 culty 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 consti- 

 tutional differences or from determining the attacks of 

 insects, might assuredly be acted on by natural selec- 

 tion. 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 



