284 THE ORIGIN OF SPECIES 



that A might be the actual progenitor of B and C, and yet would 

 not necessarily be strictly intermediate between them in all re- 

 spects. So that we might obtain the parent-species and its several 

 modified descendants from the lower and upper beds of the same 

 formation, and unless we obtained numerous transitional grada- 

 tions, we should not recognize their blood-relationship, and 

 should consequently rank them as distinct species. 



It is notorious on what excessively slight differences many 

 palaeontologists have founded their species; and they do this 

 the more readily if the specimens come from different sub-stages 

 of the same formation. Some experienced conchologists are now 

 sinking many of the very fine species of D'Orbigny and others 

 into the rank of varieties; and on this view we do find the kind 

 of evidence of change which on the theory we ought to find. 

 Look again at the later tertiary deposits, which include many 

 shells believed by the majority of naturalists to be identical with 

 existing species; but some excellent naturalists, as Agassiz and 

 Pictet, maintain that all these tertiary species are specifically 

 distinct, though the distinction is admitted to be very slight; so 

 that here, unless we believe that these eminent naturalists have 

 been misled by their imaginations, and that these late tertiary 

 species really present no difference whatever from their living 

 representatives, or unless we admit, in opposition to the judgment 

 of most naturalists, that these tertiary species are all truly dis- 

 tinct from the recent, we have evidence of the frequent occur- 

 rence of slight modifications of the kind required. If we look to 

 rather wider intervals of time, namely, to distinct but consecutive 

 stages of the same great formation, we find that the embedded 

 fossils, though universally ranked as specifically different, yet 

 are far more closely related to each other than are the species 

 found in more widely separated formations; so that here again 

 we have undoubted evidence of change in the direction required 

 by the theory; but to this latter subject I shall return in the 

 following chapter. 



With animals and plants that propagate rapidly and do not 

 wander much, there is reason to suspect, as we have formerly 

 seen, that their varieties are generally at first local ; and that such 

 local varieties do not spread widely and supplant their parent- 

 form until they have been modified and perfected in some con- 

 siderable degree. According to this view, the chance of discover- 

 ing in a formation in any one country all the early stages of 

 transition between any two forms, is small, for the successive 

 changes are supposed to have been local or confined to some one 



