362 MY LIFE [Chap. 



case of animals also ; and as animals usually breed much more 

 rapidly than does mankind, the destruction every year from 

 these causes must be enormous in order to keep down the 

 numbers of each species, since they evidently do not increase 

 regularly from year to year, as otherwise the world would long 

 ago have been densely crowded with those that breed most 

 quickly. Vaguely thinking over the enormous and constant 

 destruction which this implied, it occurred to me to ask the 

 question, Why do some die and some live ? And the answer 

 was clearly, that on the whole the best fitted live. From the 

 effects of disease the most healthy escaped ; from enemies, 

 the strongest, the swiftest, or the most cunning ; from famine, 

 the best hunters or those with the best digestion ; and so on. 

 Then it suddenly flashed upon me that this self-acting process 

 would necessarily improve the race, because in every genera- 

 tion the inferior would inevitably be killed off and the 

 superior would remain — that is, the fittest would survive. 

 Then at once I seemed to see the whole effect of this, that 

 when changes of land and sea, or of climate, or of food- 

 supply, or of enemies occurred — and we know that such 

 changes have always been taking place — and considering the 

 amount of individual variation that my experience as a 

 collector had shown me to exist, then it followed that all 

 the changes necessary for the adaptation of the species to 

 the changing conditions would be brought about ; and as 

 great changes in the environment are always slow, there 

 would be ample time for the change to be effected by the 

 survival of the best fitted in every generation. In this way 

 every part of an animal's organization could be modified 

 exactly as required, and in the very process of this modifica- 

 tion the unmodified would die out, and thus the definite 

 characters and the clear isolation of each new species would 

 be explained. The more I thought over it the more I 

 became convinced that I had at length found the long-sought- 

 for law of nature that solved the problem of the origin of 

 species. For the next hour I thought over the deficiencies in 

 the theories of Lamarck and of the author of the " Vestiges," 

 and I saw that my new theory supplemented these views and 



