Page:Popular Science Monthly Volume 75.djvu/547

Rh form-series were not available at the time of the "Origin" or before, the evolutionist of the period could still find in paleontology one sort of evidence decidedly unfavorable to the chief hypothesis then opposed to his own—that of extensive "revolutions of the globe," wholesale obliterations of faunas, and thorough-going new creations of the entire organic world. This evidence lay in the persistence of many orders and certain species through more than one geological epoch. The classic of the special creation doctrine was the introduction to the third edition of Cuvier's "Récherches sur les ossements fossiles"; and the principal argument of that work was, in the words of one of Cuvier's disciples, to the effect that "no fossil species, at least among the two classes of mammalia and reptilia, has any analogue among living species, or, in other words, that every fossil species is extinct," If this could be shown by positive evidence not to be the case, one of the principal supports of the special creation hypothesis was taken away from it. Huxley made much of this line of attack in a paper of 1859 and in his address before the Geological Society in 1862. He pointed out, for example, that lingula and certain mollusca "have persisted from the Silurian epoch to the present day, with so little change that competent malacologists are sometimes puzzled to distinguish the ancient from the modern species." He noted that the "group of crocodilia was represented at the beginning of the Mesozoic age, if not earlier, by species identical in the character of their organization with those now living"; and that, probably, even certain types of the ancient mammalian fauna, such as that of the marsupialia, have persisted with no greater change throughout as vast a lapse of time."

But the argument Huxley here used had not newly become available. Cuvier's generalization had gone far beyond any evidence which he had offered, or which could, in the nature of the case, be offered. The proposition was, indeed, insusceptible of proof, save by a sort of reasoning in a circle. For when the special creationists denied the survival of species from one epoch to another, they were using the word "species" in a sense different from that in which they, at least, usually employed it. In their zoology, the final test of specific difference between two forms was the sterility of the hybrid. But extinct forms can not be subjected to this test. In paleontology, therefore, differences of species had to be determined solely on grounds of morphological dissimilarity; while it was, at the same time, recognized that in living animals an immense range of such dissimilarity might be consistent with identity of physiological species. If the pug dog and the greyhound had been extinct, it is at least questionable whether paleontologists would have assigned them to the same species—especially if their remains had been found at different geological horizons. Under such