330 DARWINISM STATED BY DARWIN HIMSELF. 



formerly existed, I have found it diflBcult, when looking 

 at any two species, to avoid picturing to myself forms 

 directly intermediate between them. But this is a wholly 

 false view ; we should always look for forms intermediate 

 between each species and a common but unknown pro- 

 genitor ; and the progenitor will generally have differed 

 in some respects from all its modified descendants. To 

 give a simple illustration : the fantail and pouter pigeons 

 are both descended from the rock-pigeon ; if we possessed 

 all the intermediate varieties which have ever existed, we 

 should have an extremely close series between both and 

 the rock-pigeon ; but we should have no varieties directly 

 intermediate between the fantail and pouter ; none, for 

 instance, combining a tail somewhat expanded with a 

 crop somewhat enlarged, the characteristic features of 

 these two breeds. These two breeds, moreover, have be- 

 come 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 com- 

 parison of their structure with that of the rock-pigeon, 

 G. livia, whether they had descended from this species or 

 from some other allied form, such as O. oenas. 



p 2 g 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 be- 

 tween 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 child and parent, will render this a 

 very rare event ; for in all cases the new and improved 



