DIFFICULTIES ON THEORY 175 



prodigal in variety, but niggard in innovation. Why, 

 on the theory of Creation, should this be so? ^v hy 

 should all the parts and organs of many independent 

 beings, each supposed to have been separately created 

 for its proper place in nature, be so commonly linked 

 together by graduated steps ? Why should not Nature 

 have taken a leap from structure to structure? On 

 the theory of natural selection, we can clearly under- 

 stand why she should not ; for natural selection can 

 act only by taking advantage of slight successive varia- 

 tions ; she can never take a leap, but must advance by 

 the shortest and slowest steps. 



Organs of little apparent importance. — As natural 

 selection acts by life and death, — by the preservation 

 of individuals with any favourable variation, and by the 

 destruction of those with any unfavourable deviation of 

 structure, — I have sometimes felt much difficulty in 

 understanding the origin of simple parts, of which the 

 importance does not seem sufficient to cause the pre- 

 servation of successively varying individuals. I have 

 sometimes felt as much difficulty, though of a very 

 diiferent 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 its 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 distribu- 

 tion and existence of cattle and other animals in South 



