288 ON THE RELATIONS OF MAN 



the end, into the larger question of the tenability or un- 

 tenability of Mr. Darwin's views. But here we enter 

 upon difficult ground, and it behoves us to define our exact 

 position with the greatest care. 



It cannot be doubted, I think, that Mr. Darwin has 

 satisfactorily proved that what he terms selection, or 

 selective modification, must occur, and does occur, in 

 nature ; and he has also proved to superfluity that such 

 selection is competent to produce forms as distinct, 

 structurally, as some genera even are. If the animated 

 world presented us with none but structural differences, 

 I should have no hesitation in saying that Mr. Darwin 

 had demonstrated the existence of a true physical cause, 

 amply competent to account for the origin of living species, 

 and of man among the rest. 



But, in addition to their structural distinctions, the 

 species of animals and plants, or at least a great number 

 of them, exhibit physiological characters what are known 

 as distinct species, structurally, being for the most part 

 either altogether incompetent to breed one with another ; 

 or if they breed, the resulting mule, or hybrid, is unable 

 to perpetuate its race with another hybrid of the same 

 kind. 



A true physical cause is, however, admitted to be such 

 only on one condition that it shall account for all the 

 phenomena which come within the range of its operation. 

 If it is inconsistent with any one phenomenon, it must be 

 rejected ; if it fails to explain any one phenomenon, it is 

 so far weak, so far to be suspected ; though it may have 

 a perfect right to claim provisional acceptance. 



Now, Mr. Darwin's hypothesis is not, so far as I am 

 aware, inconsistent with any known biological fact ; on 

 the contrary, if admitted, the facts of Development, of 

 Comparative Anatomy, of Geographical Distribution, and 

 of Palaeontology, become connected together, and exhibit 

 a meaning such as they never possessed before ; and I, 

 for one, am fully convinced, that if not precisely true, 

 that hypothesis is as near an approximation to the truth 

 as, for example, the Copernican hypothesis was to the 

 true theory of the planetary motions. 



But, for all this, our acceptance of the Darwinian hypo- 

 thesis must be provisional so long as one link in the chain 

 of evidence is wanting ; and so long as all the animals 

 and plants certainly produced by selective breeding from 



