291 IMPERFECTION 1 OF THE 



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 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 

 3ort 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 inter- 

 mediate between them. But this is a wholly false view ; 

 we should always look for forms intermediate between each 

 species and a common but unknown progenitor; and the pro- 

 genitor 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 become so 

 much modified, that, if we had no historical or indirect evi- 

 dence regarding their origin, it would not have been possible 

 to have determined, from a mere comparison of their struc- 

 ture 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 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, m all such cases, we should be unable to 

 recognize the purent 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 

 fo^ms might have descended from the other j for instance, a 



