150 MAN AND THE LOWER ANIMALS n 



tion in which I wish to find myself is that of an 

 advocate for Mr. Darwin's, or any other views ; if 

 by an advocate is meant one whose business it is 

 to smooth over real difficulties, and to persuade 

 where he cannot convince. 



In justice to Mr. Darwin, however, it must be 

 admitted that the conditions of fertility and 

 sterility are very ill understood, and that every 

 day's advance in knowledge leads us to regard the 

 hiatus in his evidence as of less and less import- 

 ance, when set against the multitude of facts 

 which harmonize with, or receive an explanation 

 from, his doctrines. 



I adopt Mr. Darwin's hypothesis, therefore, sub- 

 ject to the production of proof that physiological 

 species may be produced by selective breeding; 

 just as a physical philosopher may accept the 

 undulatory theory of light, subject to the proof of 

 the existence of the hypothetical ether ; or as the 

 chemist adopts the atomic theory, subject to the 

 proof of the existence of atoms ; and for exactly 

 the same reasons, namely, that it has an immense 

 amount of prima facie probability : that it is the 

 only means at present within reach of reducing 

 the chaos of observed facts to order ; and lastly, 

 that it is the most powerful instrument of investi- 

 gation which has been presented to naturalists 

 since the invention of the natural system of classi- 

 fication, and the commencement of the systematic 

 study of embryology. 



