XI PHENOMENA OF ORGANIC NATURE 463 



this enormous lapse of time while almost every- 

 thing else was changed and modified. 



Thus I have no doubt that Mr. Darwin's hypo- 

 thesis will be found competent to explain the ma- 

 jority of the phenomena exhibited by species in 

 nature ; but in an earlier lecture I spoke cautiously 

 with respect to its power of explaining all the 

 physiological peculiarities of species. 



There is, in fact, one set of these peculiarities 

 which the theory of selective modification, as it 

 stands at present, is not wholly competent to 

 explain, and that is the group of phenomena which 

 I mentioned to you under the name of Hybridism, 

 and which I explained to consist in the sterility of 

 the offspring of certain species when crossed one 

 with another. It matters not one whit whether 

 this sterility is universal, or whether it exists only 

 in a single case. Every hypothesis is bound to 

 explain, or, at any rate, not be inconsistent with, 

 the whole of the facts which it professes to account 

 for; and if there is a single one of these facts 

 which can be shown to be inconsistent with (I do 

 not merely mean inexplicable by, but contrary to) 

 the hypothesis, the hypothesis falls to the ground, 

 it is worth nothing. One fact with which it is 

 positively inconsistent is worth as much, and as 

 powerful in negativing the hypothesis, as five 

 hundred. If I am right in thus defining the obli- 

 gations of an hypothesis, Mr. Darwin, in order to 

 place his views beyond the reach of all possible 



