i863 SPECIES AND STERILITY 257 



In addition to the work mentioned in the following 

 letters, I note three lectures at Hull on April 6, 8, and 10; 

 a paper on " Craniology " (January 17), and his " Letter on 

 the Human Remains in the Shell Mounds," in the Ethno- 

 logical Society's Transactions, while the Fishery Commission 

 claimed much of his time, either at the Board of Trade, or 

 travelling over the north, east, and south coasts from the 

 end of July to the beginning of October, and again in 

 November and December. 



Jermyn Street, April 30, 1863. 



My dear Kingsley — I am exceedingly pleased to have your 

 good word about the lectures,* — and I think I shall thereby be 

 encouraged to do what a great many people have wished — that 

 is, to bring out an enlarged and revised edition of them. 



The only difficulty is time — if one could but work five-and- 

 twenty hours a day ! 



With respect to the sterility question, I do not think there is 

 much doubt as to the effect of breeding in and in in destroying 

 fertility. But the sterihty which must be obtained by the selec- 

 tive breeder in order to convert his morphological species into 

 physiological species — such as we have in nature — must be quite 

 irrespective of breeding in and in. 



There is no question of breeding in and in between a horse 

 and an ass, and yet their produce is usually a sterile hybrid. 



So if Carrier and Tumbler, e.g., were physiological species 

 equivalent to Horse and Ass, their progeny ought to be sterile 

 or semi-sterile. So far as experience has gone, on the contrary, 

 it is perfectly fertile — as fertile as the progeny of Carrier and 

 Carrier or Tumbler and Tumbler. 



From the first time that I wrote about Darwin's book in the 

 Times and in the Westminster until now, it has been obvious to 

 me that this is the weak point of Darwin's doctrine. He has 

 shown that selective breeding is a vera causa for morphological 

 species; he has not yet shown it a vera causa for physiological 

 species. 



But I entertain little doubt that a carefully devised system 

 of experimentation would produce physiological species by selec- 

 tion — only the feat has not been performed yet. 



I hope you received a copy of Man's Place in Nature, which 

 I desired should be sent to you long ago. Don't suppose I ever 



* See p. 223. 



