126 Thomas Henry Huxley 



On the other hand, Huxley all through his life, 

 while holding that natural selection was by far the 

 most probable hypothesis as to the mode in which evo- 

 lution had come about, maintained that it was only a 

 hypothesis, and, unlike evolution, not a proved fact. 

 In 1863, in a course of lectures to workingmen, he 

 declared : 



" I really believe that the alternative is either Darwinism or 

 nothing, for I do not know of any rational conception or theory 

 of the organic universe which has any scientific position at all 

 beside Mr. Darwin's. . . . But 3'ou must recollect that 

 when I say I think it is either Mr. Darwin's hypothesis or 

 nothing ; that either we must take his view, or look upon the 

 whole of organic nature as an enigma, the meaning of which 

 is wholly hidden from us ; you must understand that I mean 

 that I accept it provisionally, in exactly the same way as I 

 accept any other hypothesis." 



In 1878 he wrote : 



" How far natural selection suffices for the production of 

 species remains to be seen. Few can doubt that, if not the 

 whole cause, it is a very important factor in that operation ; 

 and that it must play a great part in the sorting out of varieties 

 into those which are transitory and those which are per- 

 manent." 



The diflSculty in accepting natural selection as more 

 than a hypothesis is simply that we have no experi- 

 mental knowledge of its being able to produce the 

 mutual infertility which is so striking a character of 

 species. This difficulty is, in the first place, the diffi- 

 culty of proving a negative. It might be possible to 

 prove that its operation actually does produce species ; 

 it will always be impossible to prove that, in the past, 

 natural selection, and no other known or unknown 



