1859.] NATURAL SELECTION. 53! 



or " principle of improvement ; " it requires only diversified 

 variability, and man to select or take advantage of those 

 modifications which are useful to him ; so under nature any 

 slight modification which chances to arise, and is useful to any 

 creature, is selected or preserved in the struggle for life ; any 

 modification which is injurious is destroyed or rejected ; any 

 which is neither useful nor injurious will be left a fluctuating 

 element. When you contrast natural selection and " improve- 

 ment," you seem always to overlook (for I do not see how 

 you can deny) that every step in the natural selection of each 

 species implies improvement in that species in relation to its 

 conditions of life. No modification can be selected without 

 it be an improvement or advantage. Improvement implies, I 

 suppose, each form obtaining many parts or organs, all excel- 

 lently adapted for their functions. As each species is im- 

 proved, and as the number of forms will have increased, if 

 we look to the whole course of time, the organic condition of 

 life for other forms will become more complex, and there will 

 be a necessity for other forms to become improved, or they 

 will be exterminated ; and I can see no limit to this process 

 of improvement, without the intervention of any other and 

 direct principle of improvement. All this seems to me quite 

 compatible with certain forms fitted for simple conditions, 

 remaining unaltered, or being degraded. 



If I have a second edition, I will reiterate " Natural Selec- 

 tion," and, as a general consequence, " Natural Improve- 

 ment." 



As you go, as far as you do, I begin strongly to think, 

 judging from myself, that you will go much further. How 

 slowly the older geologists admitted your grand views on 

 existing geological causes of change ! 



If at any time you think I can answer any question, it is 

 a real pleasure to me to write. 



Yours affectionately, 



C. Darwin. 



