INTRODUCTION xiii 



naturally more vivid to him. In his letter 1 to Otto 

 Zacharias (1877) he wrote, "On my return home in 

 the autumn of 1836, 1 immediately began to prepare 

 my Journal for publication, and then saw how many 

 facts indicated the common descent of species." 

 This again is evidence in favour of the view that 

 the later growths of his theory were the essentially 

 important parts of its development. 



In the same letter to Zacharias he says, " When 

 I was on board the Beagle I believed in the per- 

 manence of species, but as far as I can remember 

 vague doubts occasionally flitted across my mind." 

 Unless Prof. Judd and I are altogether wrong in 

 believing that late or early in the voyage (it matters 

 little which) a definite approach was made to the 

 evolutionary standpoint, we must suppose that in 

 40 years such advance had shrunk in his recollec- 

 tion to the dimensions of "vague doubts." The 

 letter to Zacharias shows I think some forgetting 

 of the past where the author says, " But I did not 

 become convinced that species were mutable until, 

 I think, two or three years had elapsed." It is 

 impossible to reconcile this with the contents of 

 the evolutionary Note Book of 1837. I have no 

 doubt that in his retrospect he felt that he had not 

 been "convinced that species were mutable" until 

 he had gained a clear conception of the mechanism 

 of natural selection, i.e. in 1838 9. 



But even on this last date there is some room, 

 not for doubt, but for surprise. The passage in 

 the Autobiography 2 is quite clear, namely that in 

 October 1838 he read Malthus's Essay on the 

 principle of Population and "being well prepared 

 to appreciate the struggle for existence..., it at 

 once struck me that under these circumstances 

 favourable variations would tend to be preserved, 



1 F. Darwin's Life of Charles Darwin (in one volume), 1892, p. 166. 



2 Life and Letters, i. p. 83. 



