Chap. VI. ORGANS OF LITTLE IMPORTANCE. 195 



understanding the origin of simple parts, of which the 

 importance does not seem sufficient to cause the preser- 

 vation of successively varying individuals. I have some- 

 times felt as much difficulty, though of a very different 

 kind, on this head, as in the case of an organ as perfect 

 and complex as the eye. 



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 

 most trifling characters, such as the down on fruit and 

 the colour of the flesh, which, from determining the 

 attacks of insects or from being correlated with con- 

 stitutional differences, 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, for so trifling an object as driving 

 away flies ; yet we should pause before being too posi- 

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

 and existence of cattle and other animals in South 

 America absolutely depends on their power of resisting 

 the attacks of insects : so that individuals which could 

 by any means defend themselves from these 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 the flies, but they are incessantly harassed and 

 their strength reduced, so that they are more subject to 

 disease, or not so well enabled in a coming dearth to 

 search for food, or to escape from beasts of prey. 



Organs now of trifling importance have probably in 

 some cases been of high importance to an early pro- 

 genitor, and, after having been slowly perfected at a 



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