100 OEGANS OF LITTLE IMPORTANCE Chap. VL 



changes, through which that species has passed during its suc- 

 cessive adaptations to changed habits and conditions of life. 



Finally, then, although in many cases it is most difficult 

 even to conjecture by what transitions many organs have ar- 

 rived at their present state; yet, considering how small the 

 proportion of living and known forms is to the extinct and un- 

 known, I have been astonished how rarely an organ can be 

 named, toward which no transitional grade is known to lead. 

 It certainly is true that new organs, appearing as if specially 

 created for some purjDOse, rarely or never appear suddenly in 

 any class ; as indeed is sho^\'n by that old, but somewhat ex- 

 aggerated, canon in natural history of " Natura non facit sal- 

 tum." Vio meet with this admission in the writings of almost 

 every experienced naturalist ; or, as Milne Edwards has well 

 expressed it, Nature is prodigal in variety, but niggard in inno- " 

 vation. Why, on the theory of Creation, should there be so 

 much variety and so little novelty ? "Why 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 take a sudden leap from structm-e to struct- 

 ure ? On the theory of natural selection, we can clearly un- 

 derstand why she should not; for natural selection acts only 

 by taking advantage of slight successive variations ; she can 

 never take a 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 survival 

 of the fittest, and by the destruction of the less wcll-litted indi- 

 viduals — I have sometimes felt great dilllculty in understand- 

 ing the origin or formation of parts of little importance ; al- 

 most as great, though of a very different kind, as in the case 

 of the most perfect and complex organs. 



In the fii-st 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 for- 

 mer chapter I have given instances of very trifling characters, 

 such as tlie down on fruit and the color of its ilesh, the color 

 of the skin and hair of quailrupeds, which, from being corre- 

 lated with constitutional differences or from determining the 



