244 DIFFICULTIES OF NATURAL SELECTION. [Chap. YI. 



which the species has passed during its successive 

 adaptations to changed habits and conditions 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 indeed is shown by that old, but somewhat ex- 

 aggerated, canon in natural history of "Natura non 



DO ' f 



facit 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 niggard in innovation. Why, on the 

 theory of Creation, should there be so much variety 

 and so little real 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 structure to structure ? On the theory of natural 

 selection, we can clearly understand why she should 

 not ; for natural selection acts only by taking ad- 

 \ :.' _•■ of slight successive variations ; she can never 

 take a great and sudden leap, but must advance by 

 short and sure, though slow steps. 



