Page images

of the designs of Providence missed their mark, because in placing man in the first place, and the distribution of life in the second, they reversed not merely the chronological order of affairs, but subverted the real aspect of the case. Thus, clearly, no explanation of the “ whys” of distribution was forthcoming from former aspects of this study, just as the "hows” of the science were equally neglected. The newer era of research inaugurated by the publication and growth of Mr. Darwin's opinions, derived no small share of its power and progress from its ability to explain the “how” and “why," not merely of distribution, but of other departments of biology. Evolution, for example, gave a reasonable explanation of the metamorphosis or series of changes through which many animals pass, externally to the egg, in their development. The tadpole, as every schoolboy knows, grows to be a frog through successive changes converting it from a fish-like organism into the type of the air-breathing terrestrial adult. The caterpillar, through equally well marked alterations of form, becomes the butterfly or moth. Under the old idea of zoological causation, either form undergoes metamorphosis, because, to quote the words of Kirby and Spence, “it is the will of the Creator.” “This, however," as Sir John Lubbock remarks, “is a confession of faith, not an explanation of metamorphosis.” Evolution satisfactorily and finally replaces the want of rational ideas of metamorphosis by a higher idea of satisfactory causation, namely, heredity. The frog passes in its development through a metamorphosis, because its ancestor was a fish-like organism. It repeats, as an individual frog, the history of its race. So, also, an insect may directly or indirectly be credited with demonstrating, by the course of its development, its origin from lower stages of life. The development of every animal is a brief recapitulation of the descent of its species. Obscured, and often imperfect, that biography may be, but nevertheless it is plainly outlined before the seeking eye and understanding mind.

If evolution has thus assisted our comprehension of why an animal passes through apparently useless stages in the course of its develop. ment, no less clearly has that theory brought to light the meaning of the previously isolated facts of distribution. It was evolution which played to these facts the part of a guardian genius; marshalling their ranks into order and arrangement, and demonstrating that relationship between them which it is the province of science to explain. It is necessary to dwell upon the influence which evolution has exerted upon the study of distribution, simply because the latter science practically dates its origin from the day when the modifica

tion of existing species as a means of natural creation of new races of animals and plants was recognised. And it is with the greater satisfaction that one may dwell upon this mutual relationship of distribution and the theory of development, since the due appreciation of the clear explanation which the facts of distribution receive from evolution at large, constitutes a powerful counterproof of the truth of that theory. It is not surprising, therefore, to find Professor Huxley saying that “no truths brought to light by biological investigation were better calculated to inspire distrust of the dogmas intruded upon science in the name of theology, than those which relate to the distribution of animals and plants on the surface of the earth. Very skilful accommodation was needed," continues Huxley, “if the limitation of sloths to South America, and of the ornithorhynchus to Australia, was to be reconciled with the literal interpretation of the history of the deluge; and with the establishment of the existence of distinct provinces of distribution, any serious belief in the peopling of the world by migration from Mount Ararat came to an end. Under these circumstances, only one alternative was left for those who denied the occurrence of evolution-namely, the supposition that the characteristic animals and plants of each great province were created as such within the limits in which we find them. And as the hypothesis of " specific centres ” thus formulated was heterodox from the theological point of view, and unintelligible from the scientific aspect, it may be passed over without further notice as a phase of transition from the creational to the evolutional hypothesis. In fact," adds Huxley, “the strongest and most conclusive arguments in favour of evolution are those which are based upon the facts of geographical taken in conjunction with those of geological, distribution.”

Or if we turn for a moment to the opinion of Mr. Darwin himself, we shall find an equally clear expression of the futility of the attempt to explain distribution on any other save an evolutionary understanding. In his classical work, the “Origin of Species,” Darwin remarks the fact that “neither the similarity nor the dissimilarity of the inhabitants of various regions can be wholly accounted for by climatal and other physical conditions.” He secondly notes the fact, “ that barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions of various regions ;” and a third fact noted by Darwin is “the affinity of the productions of the same continent or of the same sea, though the species themselves are distinct at different points and stations.” Again, Darwin remarks that, “in discussing

this subject we shall be enabled at the same time to consider a point equally important for us, namely, whether the several species of a genus, which must on our theory all be descended from a common progenitor, can have migrated, undergoing modification during their migration, from some one area. If, when most of the species inhabiting one region are different from those of another region, though closely allied to them, it can be shown that migration from the one region to the other has probably occurred at some former period, our general view will be much strengthened, for the explanation," adds Darwin, “is obvious on the principle of descent with modification. A volcanic island, for instance, upheaved and formed at the distance of a few hundreds of miles from a continent, would probably receive from it in the course of time a few colonists, and their descendants, though modified, would still be related by inheritance to the inhabitants of that continent. Cases of this kind are common, and are, as we shall hereafter see, inexplicable on the theory of independent creation."

If further evidence were desirable concerning the influence of evolution as explanatory of the distribution of living beings in the past and present of the earth, such opinion might be culled from Sir Charles Lyell. The late eminent geologist remarks, that Buffon, when speculating on “philosophical possibilities,” in 1755, urged, " that whilst the same temperature might have been expected, all other circumstances being equal, to produce the same beings in different parts of the globe, both in the animal and vegetable kingdoms, yet it is an undoubted fact, that when America was discovered, its indigenous quadrupeds were all dissimilar to those previously known in the Old World.” “ Thus Buffon,” says Lyell, “ caught sight at once of a general law in the geographical distribution of organic beings, namely, the limitation of groups of distinct species to regions separated from the rest of the globe by certain natural barriers." In conformity with the doctrine of special centres of creation, as Lyell remarks, the “natural barriers” of Buffon held a perfectly logical place. Separate creations in the New World, and special creations in the Old, separated by intervening oceans, served fully to explain the reasons of the divergence between the animal populations in question. “But,” adds Lyell (in further alluding to the close correspondence between the fossil forms and the living beings of any given area), “the intimate connection between the geographical distribution of the fossil and recent forms of mammalia, points to the theory (without absolutely demonstrating its truth), that the existing species of animals and plants . . . . are of derivative origin, and not primordial or independent creations.” Last of all, Mr. Alfred Russel Wallace-to whose labours we owe much, if not the greater part, of the light which has been thrown on the formerly obscure problems of distribution-testifies in the most direct terms to the value of the theory of evolution. Towards the firm establishment of this theory he himself has made many important contributions, and has thus aided its place and power in explaining the laws regulating the development of life on the surface of the globe. “We further have to make use of the theory of descent with modification,'” says Mr. Wallace, “as the only possible key to the interpretation of the facts of distribution; and this theory," he adds, " has only been generally accepted within the last twenty years. It is evident that so long as the belief in special creations' of each species prevailed, no explanation of the complex facts of distribution could be arrived at, or even conceived; for, if each species was created where it is now found, no further inquiry can take us beyond that fact, and there is an end of the whole matter.” Again, we find a sentence worth quoting, and worth bearing in mind, when Mr. Wallace remarks, that “if we keep in view these facts—that the minor features of the earth's surface are everywhere slowly changing; that the forms, and structure, and habits of all living things are also slowly changing; while the great features of the earth, the continents, and oceans, and loftiest mountain ranges, only change after very long intervals, and with extreme slowness; we must see that the present distribution of animals upon the several parts of the earth's surface is the final product of all these wonderful revolutions in organic and inorganic nature.”

The proposition that in the existing world we may find a reflex of those causes which have wrought out the scheme of life's distribution over the surface of the globe, has received the tacit sanction and approval of all competent biologists. This result has been attained through the slow but sure and progressive advance of modern ideas concerning the uniformity of natural law and physical causation. The teachings of evolution in biology are but the reflections of “uniformity” in geology. As the doctrine of uniformity has taught us that the physical forces represented in and by the internal heat, water, frost, snow, and chemical action, are the agencies which from all time past have been sculpturing and moulding our earth's features -as we trace in the physical actions of the present the key to the activities of the past-so in biology we assume, and assume logically, that the ordinary activities of life, the processes of variation and change, and the influence of environments on the living form, are the agencies which mould the world of life now, as in the earliest æons, and as in the beginning itself. Rejecting the idea of uniformity in science, we fall back on the catastrophism of primitive geology and on the “special creation ” of those early times of biology, when fabulous theory represented the exact observation of to-day. Accepting, however, the theories of “uniformity” in the inorganic world and of“ evolution” in the living universe, we unite the sciences in a circle, outside the magnificent unity of which no fact of inorganic nature or of the living world can be presumed to exist.

The division of the world's surface for the purposes of ordinary geography is obviously unsuited to the wants of the biologist. The geographical survey of the earth is of necessity a matter of politics. The greater nation tends to obliterate the smaller; allocation of territory is largely a matter of division of spoil; and the outlines and boundaries of the countries of the world reflect the kaleidoscopic change which marks the arena of political strife and its concomitant warfare for its own. For scientific purposes, then, the standpoints of the political geographer are unavailable. Save in so far as the march of civilisation means and implies the destruction and repression of the animals and plants which are either useful or useless and dangerous to man, the distribution of life on the globe is comparatively unaffected by the divisions whereby man demarcates his territorial possessions from those of his neighbours. A rat may pass as placid an existence under the Czar as under British rule : a kangaroo will live as successfully beneath Dutch as under English sovereignty; but there may be more prospect of length of days for the hippopotamus under existing circumstances than under an extension of civilisation in the north of Africa. Neglecting, then, the political divisions of the world, the biologist divides the earth's surface into regions, the boundaries of which are determined solely by the distribution of the animals and plants included within their limits. Sweeping aside the lines of demarcation which human powers and aims have constructed, the naturalist constructs a new biological geography, whose continents and countries are under the unceasing sway and sovereignty of those natural forces, agencies, and laws which from all time past have affected the destinies of the earth and its tenants. It is on the very threshold of distribution that we begin to note the wide variations between the former and present methods of studying life's development over the globe's surface. Formerly, the range of any living being was denoted simply by the name of the country or continent in which it occurred.

But it is evident that such a method of indicating an animal's

« PreviousContinue »