56 THE ORIGIN OF SPECIES 



pouter; none, for instance, combining a tail somewhat 

 expanded with a crop somewhat enlarged, the character- 

 istic features of these two breeds. These two breeds, 

 moreover, have become so much modified that, if we had 

 no historical or indirect evidence regarding their origin, 

 it would not have been possible to have determined, 

 from a mere comparison of their structure with 4hat of 

 the rock-pigeon, C. livia, whether they had descended 

 from this species or from some other allied form, such 

 as C. oenas. 



So, with natural species, if we look to forms very 

 distinct, for instance, to the horse and tapir, we have 

 no reason to suppose that links directly intermediate 

 between them ever existed, but between each and an 

 unknown common parent. The common parent will have 

 had in its whole organization much general resemblance 

 to the tapir and to the horse; but in some points of 

 structure may have differed considerably from both, even 

 perhaps more than they differ from each other. Hence, 

 in all such cases, we should be unable to recognize the 

 parent-form of any two or more species, even if we 

 closely compared the structure of the parent with that of 

 its modified descendants, unless at the same time we had 

 a nearly perfect chain of the intermediate links. 



It is just possible by the theory that one of two 

 living forms might have descended from the other; for 

 instance, a horse from a tapir; and in this case direct 

 intermediate links will have existed between them. But 

 such a case would imply that one form had remained for : 

 a very long period unaltered, while its descendants had! 

 undergone a vast amount of change; and the principle 

 of competition between organism and organism, between 



