i86S] PANGENESIS. 263 



accumulated through natural selection, then as every degree 

 exists up to absolute barrenness, natural selection must have 

 the power of increasing it. Now take two species, A and B, 

 and assume that they are (by any means) half-sterile, i.e. 

 produce half the full number of offspring. Now try and 

 make (by natural selection) A and B absolutely sterile when 

 crossed, and you will find how difficult it is. I grant indeed, 

 it is certain, that the degree of sterility of the individuals A 

 and B will vary, but any such extra-sterile individuals of, we 

 will say A, if they should hereafter breed with other indi- 

 viduals of A, will bequeath no advantage to their progeny, by 

 which these families will tend to increase in number over 

 other families of A, which are not more sterile when crossed 

 with B. But I do not know that I have made this any clearer 

 than in the chapter in my book. It is a most difficult bit of 

 reasoning, which I have gone over and over again on paper 

 with diagrams. 



. . . Hearty thanks for your letter. You have indeed 

 pleased me, for I had given up the great god Pan as a still- 

 born deity. I wish you could be induced to make it clear 

 with your admirable powers of elucidation in one of the 

 scientific journals. . . . 



C. Darwin to J. D. Hooker. 



Down, February 28 [1868]. 

 My dear Hooker, — I have been deeply interested by 

 your letter, and we had a good laugh over Huxley's remark, 

 which was so deuced clever that you could not recollect it. I 

 cannot quite follow your train of thought, for in the last page 

 you admit all that I wish, having apparently denied all, or 

 thought all mere words in the previous pages of your note ; 

 but it may be my muddle. I see clearly that any satisfaction 

 which Pan may give will depend on the constitution of each 

 man's mind. If you have arrived already at any similar 

 conclusion, the whole will of course appear stale to you. I 

 heard yesterday from Wallace, who says (excuse horrid 



