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Show 118 DARWINIAN A. because, by their complete extinction in South America the line of descent was there utterly broken~ U ~on the ordinary hypothesis, there is no scientific explanation possible of this series of facts, and of many others like them. Upon the new hypothesis, " the succession of the same types of structure within the same areas during the later geological periods ceases to be mysterious, and is simply explained by inheritance." Their cessation is failure of issue. Along with these considerations the fact (alluded to on page 98) should be remembered that, as a general thing, related species of the present age are geographically associated. The larger part of the plants, and still more of the animals, of each separate country are peculiar to it; and, as most species now flourish over the graves of their by-gone relatives of former ages, so they now dwell among or accessibly near their kindred species. Here also comes in that ·general "parallelism be-tween the order of succession of animals and plants in geological times, and the gradation among their livinO' representatives" from low to highly organized, from 5 simple and general to complex and specialized forms ; also " the parallelism between the order of succession of animals in geological times and the changes their living representatives· undergo during their embryological growth," as if the world were one prolonged gestation. Modern science has much insisted on this parallelism, and to a certain extent is allowed to have made it out. All these things, which conspire to prove that the ancient and the recent forms of life " are somehow intimately connected together NATURAL SELECTION, ETC. 110 in one grand system," equally conspire to suggest that the connection is one similar or analogous to generation. Surely no naturalist can be blamed for entering .somewhat confidently upon a field of speculative inquiry which here opens so invitingly; nor need former premature endeavors and failures utterly dishearten him. All these things, it may naturally be said, go to explain the order, not the mode, of the incoming of species. But they all do tend to bring out the generalization expressed by Mr. Wallace in the formula that "every species has come into existence coincident both in time and space with preexisting closely-allied species." Not, however, that this is proved even of existing species as a matter of general fact. It is obviously impossible to prove anything of the kind. But we must concede that the known facts strongly suggest such an iri:ference. And-since species are only congeries of individuals, since every individual came into existence in consequence of preexisting individuals of the same sort, so leading up to the individuals with which the species began, and since the only material sequence we know of among plants and animals is that from parent to progeny-the presumption becomes exceedingly strong that the connection of the incoming with the preexisting species is a genealogical one. Here, however, all depends upon the probability that :Mr. Wallace's inference is really true. Certainly it is not yet ge~erally accepted; but a strong current is setting toward its acceptance. So long as universal cataclysms were in vogue, and all life upon the earth was thought tp h~ve been |
