GENEEAL REMARKS ON DEVELOPMENT OF SPECIES. 329 



bably remain ever unsolved. But .all that we have learned, but they 

 of the variability of form and function in organisms, tends ^ith'^the 

 to diminish the diflficulties of this hypothesis ; while all advance of 

 that we have learned concerning the facts of development, ledo-e. 

 embryology, morphology, and classification, tends to in- 

 crease its probability; and that probability is, as I think, 

 raised to the rank of a certainty by the discovery of rudi- 

 mentary and useless structures, both in mature and in 

 embryonic forms. 



It appears to be a prevalent notion, that, whatever may 

 be hereafter concluded on as true, the presumption is at 

 present in favour of the theory of separate creations, and 

 will continue to be so until the argument is closed. I 

 cannot admit this ; I think that it has no logical foundation No pre- 

 whatever, and that it owes the force it has in men's minds sumption 



against the 



merely to the theory of separate creations being familiar ; develop- 



while the theory of the origin of species by descent with ^eory. 



modification (or, briefly, the development theory) is still 



comparatively strange. It is not to be hoped that the 



difficulties of the development theory can be cleared up 



at once, or that they can be fully cleared up at all. The 



evidence is too scanty, and the experimental method, 



which has created the sciences of physics and chemistry, is 



scarcely applicable here. But the ordinary objections to 



the development theory are utterly futile. It is said that Argu- 



we have never seen a new species come into existence bv ^^^^^ 



... TO irom ex- 



descent. This IS scarcely true, for many races of plants perience 



and animals have come into existence under domestication, ^S^^'^^* ^'^ 



which it is nearly if not quite impossible to distinguish 



from true species.^ But it is quite true that we have never 



seen any such change as the descent of a bird from a 



reptile would be ; and yet the birds and the reptiles are 



both vertebrates, and must, therefore, on the development 



theory, be descended either the one class from the other, or 



both from a common origin. It is true, I say, that such a 



change is quite out of our experience ; but the separate are worth- 



and special creation of any organic form out of dust, or out *'^'^' 



of nothing, is equally outside of our experience, and far 



1 See Note at end of chapter. 



