Seite - 350 - in The Origin of Species

r 350 ORIGIN OF SPECIES Supposing B and C to be two species, and a third, A, to be found in an older and underlying bed ; even ifA were strictly intermediate between B and C it would simply be ranked as a third and distinct species, unless at the same time it could be closely connected by intermediate varieties with either one or both forms. Nor should it be forgotten, as before explained, that A might be the actual progenitor of B and C, and yet would not necessarily be strictly intermediate between them r in all respects. 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 gradations, we should not recognise their blood-relationship, and should consequently rank them ^ 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 concholo- gists 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 de- posits, which include many shells believed by the majority of naturalists to be identical with existing species ; but some ex- cellent naturalists, as Agassiz and Pictet, maintain that all these tertiary species are specifically distinct, though the dis- tinction 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 representa- tives, 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 oc- currence 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 specific- ally different, yet are far more Josely related to each other than are the species found in more widely separated forma- tions; so that here again we have undoubted evidence of