270 THE ORIGIN OF SPECIES 



also bear in mi ml that every highly developed organism 

 has passed through many changes; and that each modi- 

 fied structure tends to be inherited, so that each modifi- 

 cation 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 diffi- 

 cult 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 ex- 

 tinct and unknown, 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 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 experi- 

 enced naturalist; or as Milne Edwards has well expressed 

 it, Nature is prodigal in variety, but niggard in innova- 

 tion. 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 



