280 IMPERFECTION OF THE Chap. IX. 



pends on the very process of natural selection, through 

 which new varieties continually take the places of and 

 exterminate their parent-forms. But just in proportion 

 as this process of extermination has acted on an 

 enormous scale, so must the number of intermediate 

 varieties, which have formerly existed on the earth, 

 be truly enormous. Why then is not every geo- 

 logical formation and every stratum full of such inter- 

 mediate links ? Geology assuredly does not reveal any 

 such finely graduated organic chain ; and this, perhaps, 

 is the most obvious and gravest objection which can be 

 urged against my 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 my 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 

 unknown progenitor ; and the progenitor will generally 

 have differed in some respects from all its modified de- 

 scendants. To give a simple illustration : the fantail and 

 pouter pigeons have 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 some- 

 what 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 evidence regarding 

 their origin, it would not have been possible to have 



