1859-1863] STERILITY OF HYBRIDS 137 



that Ramsay l is a convert, and I am extremely glad to get Letter 91 

 pure geologists, as they will be very few. Many thanks for 

 your very pleasant note. What pleasure you have given me. 

 I believe I should have been miserable had it not been for 

 you and a few others, for I hear threatening of attacks which 

 I daresay will be severe enough. But I am sure that I can 

 now bear them. 



To T. H. Huxley. Letter 92 



The point here discussed is one to which Mr. Huxley attached great, 



in our opinion too great, importance. 



Down, Jan. nth [1860?], 



I fully agree that the difficulty is great, and might be 

 made much of by a mere advocate. Will you oblige me by 

 reading again slowly from pp. 267 to 272.2 I may add to 

 what is there said, that it seems to me quite hopeless to 

 attempt to explain why varieties are not sterile, until we 

 know the precise cause of sterility in species. 



Reflect for a moment on how small and on what very 

 peculiar causes the unequal reciprocity of fertility in the 

 same two species must depend. Reflect on the curious case 

 of species more fertile with foreign pollen than their own. 

 Reflect on many cases which could be given, and shall be 

 given in my larger book (independently of hybridity) of very 

 slight changes of conditions causing one species to be quite 

 sterile and not affecting a closely allied species. How pro- 

 foundly ignorant we are on the intimate relation between 

 conditions of life and impaired fertility in pure species ! 



The only point which I might add to my short discussion 

 on this subject, is that I think it probable that the want of 

 adaptation to uniform conditions of life in our domestic 

 varieties has played an important part in preventing their 

 acquiring sterility when crossed. For the want of uniformity, 

 and changes in the conditions of life, seem the only cause of 

 the elimination of sterility (when crossed) under domestica- 

 tion. 3 This elimination, though admitted by many authors, 



1 See a letter to Huxley, Nov. 27th, 1859, Life and Letters, II., p. 282. 



2 The reference is to the Origin, Ed. I. : the section on "The Fertility 

 of Varieties when crossed, and of their Mongrel Offspring " occupies 

 pages 267-72. 



3 The meaning which we attach to this obscure sentence is as 

 follows : Species in a state of nature are closely adapted to definite 



