So much, then, for the argument from geographical distribution--the many facts of crucial importance which it affords almost resembling so many experiments devised by Nature to prove the falsity of the special creation hypothesis. For now, let it in conclusion be observed, that there is no _physiological_ reason why animals and plants of the different characters observed should inhabit different continents, islands, seas, and so forth. As Darwin observes, "there is hardly a climate or condition in the Old World which cannot be paralleled in the New ... and yet how widely different are their living productions." And that it is not the suitability of organisms to the areas which they inhabit which has determined their creation upon those areas, is conclusively proved by the effects of the artificial transportation of species by man. For in such cases it frequently happens that the imported species thrives quite as well in its new as in its old home, and indeed often supplants the native species. As the Maoris say,--"As the white man's rat has driven away the native rat, so the European fly has driven away our fly, so the clover kills our fern, and so will the Maori himself disappear before the white man."
Upon the whole then we are driven to the conclusion, that if the special creation theory is true, the various plants and animals have not been placed in the various habitats which they occupy with any reference to the suitability of these habitats to the organisations of these particular plants and animals. So that, considering all the evidence under the head of geographical distribution, I think we are driven to the yet further conclusion, that if the special creation theory is true, the only principle which appears to have been consistently followed in the geographical deposition of species, is the principle of so depositing them as in all cases to make it appear that the supposition of their having been thus deposited is not merely a highly dubious one, but one which, on the face of it, is conspicuously absurd.
There is still another important line of evidence which we cannot afford to overlook; I mean the argument from embryology. To economise space, I shall not explain the considerations which obviously lead to the anticipation that, if the theory of descent by inheritance is true, the life history of the individual ought to constitute a sort of condensed epitome of the whole history of its descent. But taking this anticipation for granted, as it is fully realised by the facts of embryology, it follows that the science of embryology affords perhaps the strongest of all the strong arguments in favour of evolution. From the nature of the case, however, the evidence under this head requires special training to appreciate; so I will merely observe, in general terms, that the higher animals almost invariably pass through the same embryological stages as the lower ones, up to the time when the higher animal begins to assume its higher characters. Thus, for instance, to take the case of the highest animal, man, his development begins from a speck of living matter similar to that from which the development of a plant begins. And, when his animality becomes established, he exhibits the fundamental anatomical qualities which characterise such lowly animals as the jelly-fish. Next he is marked off as a vertebrate, but it cannot be said whether he is to be a fish, a snake, a bird or a beast. Later on it is evident that he is to be a mammal; but not till still later can it be said to which order of mammals he belongs.