464 THE CAUSES OF THE xi 



assault, ought to be able to demonstrate the possi 

 bility of developing from a particular stock by se 

 lective breeding, two forms, which should either 

 be unable to cross one with another, or whose 

 cross-bred offspring should be infertile with one 

 another. 



For, you see, if you have not done that you have 

 not strictly fulfilled all the conditions of the prob 

 lem ; you have not shown that you can produce, 

 by the cause assumed, all the phenomena which 

 you have in nature. Here are the phenomena of 

 Hybridism staring you in the face, and you cannot 

 say, &quot; I can, by selective modification, produce 

 these same results/ Now, it is admitted on all 

 hands that, at present, so far as experiments have 

 gone, it has not been found possible to produce 

 this complete physiological divergence by selective 

 breeding. I stated this very clearly before, and I 

 now refer to the point, because, if it could be 

 proved, not only that this has not been done, but 

 that it cannot be done ; if it could be demonstrated 

 that it is impossible to breed selectively, from any 

 stock, a form which shall not breed with another, 

 produced from the same stock ; and if we were 

 shown that this must be the necessary and inevit 

 able results of all experiments, I hold that Mr. 

 Darwin s hypothesis would be utterly shattered. 



But has this been done ? or what is really the 

 state of the case ? It is simply that, so far as we 

 have gone yet with our breeding, we have not pro- 



