244 BIFFICULTIES OP NATURAL SELECTION. [Chap. VI. 



its successive adaptations to changed habits and con- 

 ditions of life. 



Finally then, although in many cases it is most 

 difficult even to conjecture by what transitions organs 

 have arrived at their present state; yet, considering 

 how small the proportion of living and known forms is 

 to the extinct and unknown, I have been astonished 

 how rarely an organ can be named, towards which no 

 transitional grade is known to lead. It certainly is true, 

 that new organs appearing as if created for some special 

 purpose, rarely or never appear in any being; — as in- 

 deed is shown by that old, but somewhat exaggerated, 

 canon in natural history of " Natura non f acit saltum." 

 We 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 nig- 

 gard in innovation. Why, on the theory of Creation, 

 should there be so much variety and so little real nov- 

 elty? Why should all the parts and organs of many in- 

 dependent 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 structure to struc- 

 ture? On the theory of natural selection, we can clearly 

 understand why she should not; for natural selection 

 acts only by taking advantage of slight successive 

 variations; she can never take a great and sudden leap, 

 but must advance by short and sure, though slow 

 steps. 



