248 DIPERFECTION OF THE [CHAP. X. 



process of extermination has acted on an enormous scale, so must 

 the number of intermediate varieties, which have formerly existed, 

 be truly enormous. Why then is not every geological formation 

 and every stratum full of such intermediate links ? Geology 

 assuredly does not reveal any such finely-graduated organic chain ; 

 and this, perhaps, is the most obvious and serious objection which 

 can be urged against the theory. The explanation 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 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 inter- 

 mediate 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 ex- 

 panded with a crop somewhat enlarged, the characteristic 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 that 

 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 organisation 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 recognise 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, whilst its descendants 



