156 Organs of little Importance Chap, vi 



instances, can we understand the graduated scale of complexity 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 modi- 

 .fication 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 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 advantage of slight successive varia- 

 tions ; she can never take a great and 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 well-fitted indi- 

 viduals, — I have sometimes felt great difficulty in understanding 

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



