y \ 





Chap. x. Imperfection of the Geological Record. 265 



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 inter- 

 mediate 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 some- 

 what 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 



