146 ORGANS OF LITTLE IMPORTANCE [CHAP. VI. 



How, it may be asked, in the foregoing and in innumerable 

 other instances, can we understand the graduated scale of com- 

 plexity and the multifarious means for gaining the same end. 

 The answer no doubt is, as already remarked, that when two 

 forms vary, which already differ from each other in some slight 

 degree, the variability will not be of the same exact nature, and 

 consequently the results obtained through natural selection for the 

 same general purpose will not be the same. We should also bear 

 in mind that every highly developed organism has passed through 

 many changes ; and that each modified structure tends to be 

 inherited, so that each modification will not readily be quite lost, 

 but may be again and again further altered. Hence the structure 

 of each part of each species, for whatever purpose it may serve, is 

 the sum of many inherited changes, through 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 exaggerated, canon in natural history of "Natura non 

 facit saltum." We meet with this admission in the writings of 

 almost every experienced naturalist ; or as Milne Edwards has well 

 p 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 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 advantage of slight suc- 

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

 but must advance by short and sure, though slow steps. 



S Organs of little apparent Imjxn'tance, 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 well-fitted in- 

 dividuals, I have sometimes felt great difficulty in understanding 

 . the origin or formation of parts of little importance ; almost as 



