148 MAN AND THE LOWER ANIMALS n 



At the present moment, therefore, the question 

 of the relation of man to the lower animals re- 

 solves itself, in the end, into the larger question 

 of the tenability, or untenability, 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 alto- 

 gether 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 



