270 THE ORIGIN OF SPECIES 



links? Geology assuredly does not reveal any such finely-gradu- 

 ated organic chain; and this, perhaps, is the most obvious and 

 serious objection which can be urged against the theory. The ex- 

 planation lies, as I believe, in the extreme imperfection of the 

 geological record. 



In the first place, it should always be borne in mind what sort 

 of intermediate forms must, on the theory, have formerly existed. 

 I have found it difficult, 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 un- 

 known progenitor; and the progenitor will generally have dif- 

 fered 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 inter- 

 mediate varieties which have ever existed, we should have an ex- 

 tremely close series between both and the rock-pigeon; but we 

 should have no varieties directly intermediate between the fan- 

 tail and pouter; none, for instance, combining a tail somewhat 

 expanded with a crop somewhat enlarged, the characteristic fea- 

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

 come so much modified, that, if we had i^o historical or indirect 

 evidence regarding their origin, it would not have been possible 

 to have determined, from a mere comparison of their structure 

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

 from this species or from some other allied form, such as C. cenas. 



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 re- 

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

 structure may have differed considerably from both, even per- 

 haps 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 



