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Show 246 IMPERFECTION OF THE (CHAP. IX. process of extermination has act~d on a:r; e;normo~s scale, so must the number of intermediate vanetles, ·which have fonnerly existed on the earth be truly enol'lnous. Why then is not every geological' formation and every stratum full of such intermediate links? G-eology assuredly does not reveal any such finely gr!1duated organic cha~n; and this, perhaps, is the mos~ obvious and gravest obJ ection which can be urged agamst my theory. The explanation lies, as I believe, in the extreme imperfection of the geological record. - Ih 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 spe?ies, to avoid picturing to n~y~elf, forms d~rectly Intermediate between them. But this Is a wholly false view; we should always look for forms in· termediate between each species and a common but un known progenitor ; 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 have both descended from the rock-pigeon; if we possessed all the intermediate varieties which have ever existed, we should have an extrmnely close series between both and the rock-pigeon ; but we should have no varieties direct1y intermediate between the fantail and pouter; none, for instance, combining a tail somewhat expanded with a crop ~omewhat enlarged, the characteristic features of these two breeds. These two breeds, moreover, have become so n1uch modified, that if we had no historical or indirect evidence regarding their origin, it would not have been possible to have determined f:ron1 a mere comparison of their structure with that _of the rockpigeon, whether they had descended from this species or from some other allied species, 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 ever existed directly intermediate between them, but between each and an unknown common parent. The common parent will have had in its whole organisation much general resemblance to the CHAP. IX.l GEOLOGICAL RECORD. 24'7 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. lienee 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 my 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 had undergone a vast amount of change; and the principle of competition between organism and organism, between child and parent, will render this a very rare event ; for in all cases the new and improved forms of life will tend to supplant the old and unimproved forms. By the theory of natural selection all living species have been connected with the parent-species of each genus, by differences not greater than we see between the varieties of the same species at the present day; and these parent-sl>ecies, now generally extinct, have in their turn been similarlv connected with more ancient species · and so on backwaur ds, always converging to the comrnon' · ancestor of each great class. So that the number of in· termediate and transitional links, between all living and extinct species, must have been inconceivably great. But assuredly, if this theory be true, such have lived upon this earth. On the lapse of Tim e.-Independently of our not finding fossil remains of such infinitely numerous connecting links, it may be objected, that time will not have sufficed for .so great an amount of organic change, all changes having been effected very slowly through natural selection. It is hardly possible for me even to recall to the reader _who I?-ay not be a practical geologist, the facts lead~ the mind feebly to comprehend the lapse of time. He |