Popular Science Monthly/Volume 23/September 1883/How the Earth was Peopled I
|HOW THE EARTH WAS PEOPLED.|
WHY should the study of prehistoric man excite bitter passions? Why should it trouble timorous souls? Its aim, with real scientific inquirers, is simply to attain an objective reality, worthy of the respect of all; and it has had the happy fortune to unite in a common pursuit minds of the most diverse character, having neither the same motives nor the same tendencies, but animated by the pure desire of increasing the domain of knowledge. In this way freethinkers and priests, men of the world and men of the study, collectors, pioneers, philosophers, and practicians, whether spiritualistic and Christian or positivists, resolute partisans of the doctrine of evolution or opponents of it, have labored hand-in-hand in prehistoric investigation—that is, in collecting all the signs, observations, and things which relate to the existence of man in the times anterior to history. The objects of this study also lie back of all chronology, and it is in question whether it is possible to make an estimate of the time within which they were embraced. History, as founded on documents and monuments of definite import and intelligible traditions, goes back to the foundation of the Egyptian empire by Menes, five thousand years before Christ, and there stops. At that time, the Egyptians had an organization, a well-developed civilization, and cities. It is not hazarding too much to add as many years to the figure we have named, or to accept Plato's statement that the Egyptian people were ten thousand years old in his time.
Prehistoric times begin at this period—twelve thousand years ago—and extend back into a much more remote past. Without written data, without even conjectural dates, is it possible to estimate their duration? All that we have are the marks that man has left on Nature, who, in her incessant action burying these marks under accumulations of successive strata, gives us a kind of relative chronology. It is now admitted by science that the life of man crosses the whole Quaternary period, and if we can measure the duration of that period we shall be able to fix approximately the age of our race. This is what M. de Mortillet attempts to do in formulating the conclusions of his book on the "Prehistoric Antiquity of Man."
The circles of growth of trees on American ruins and the rates of formation of river deltas and alluvions have been made the bases of partial and doubtless insufficient calculations from which an age of five or six thousand years has been assigned to the polished-stone period of Robenhausen, and thirteen thousand years for the accumulation of Nile-mud over a brick which was found beneath a statue of Rameses. The stalagmites of the Kent Cavern, England, which cover both Roman relics and palaeolithic implements of the Magdalenian period, have been made the basis of calculations which give an age of more than three hundred thousand years to the more ancient of the deposits. This, of course, is upon the supposition that the rate of incrustation has never been more rapid than it is now. Other calculations are more general in their bearing. The oscillations of the European lands under which Denmark, North Germany, and Russia have been raised from submergence during the Quaternary period, Scandinavia was depressed and has been slowly raised again, and England has been sunk till the connection that existed between it and the continent during the whole Quaternary period has been destroyed, required not less than seventy thousand years. Still another grand and surprising phenomenon, the extension of the Alpine glaciers, by which huge rocks were carried to distances of seventy or one hundred and seventy-five miles, required an enormous length of time. The maximum rate of progress of these blocks is not more than sixty metres a year; but in Quaternary times, when the slopes were not nearly so steep as now, the rate was, according to M. de Mortillet, five times slower, and each erratic block must have taken more than twenty thousand years to be carried from Mont Blanc to the lower Rhone. We may add that an enormous number of blocks were thus transported to form the terminal moraine. Add to the period of extension the period occupied in the retreat of the same glaciers, which must have been nearly as long as the other, and we shall find that the one hundred thousand years which M. de Mortillet asks for to express the duration of the glacial epoch is not an exaggeration. The epochs of the extension and retreat of the glaciers were, however, preceded by a pre-glacial period, and all the calculations together induce M. de Mortillet to adopt a total of two hundred thousand years to represent the entire duration of the Quaternary period, during which we are assured of the presence of man on European soil.
This period, long as it appears, is very short as compared with the myriads of ages of geological development that preceded it, and represents only the last and the shortest of the geological periods. The question arises, How has the human race been able to spread itself over the whole surface of the globe? Is it the product of different and independent origins in the several continents, or have all men sprung from a common cradle, a "mother-region"? On this point students are divided, Agassiz holding that men were created, and Carl Vogt that they were developed, at different centers, and Quatrefages and the theologians maintaining the unity of their origin. The fact is left that man, the same in all the essential characteristics of the species, has advanced into all the habitable parts of the globe, and that not recently, and when provided with all the resources that experience and inventive genius could put at his disposal, but when still young and ignorant. It was then that, weak and almost naked, having only just got fire and a few rude arms with which to defend itself and procure food, the human race conquered the world and spread itself from within the Arctic Circle to Terra del Fuego, from the Samoyed country to Van Diemen's Land, from the North Cape to the Cape of Good Hope. It is this primitive exodus, as certain as it is inconceivable, accepted by science as well as by dogma, that we have to explain, or at least to make probable; and that in an age when it is only after the most wonderful discoveries, by the aid of the most powerful machinery for navigation, through the boldest and most adventurous enterprises, that civilized man has been able to flatter himself that he has at last gone as far as infant man went in an age that is so far removed from us as to baffle all calculations.
We must insist on this point, for it brings into light an obstacle which those who have tried to trace out the connection between widely separated races and to determine the course that had been followed by tribes now separated by oceans and vast expanses have hitherto found insurmountable; for, if man is one—to which we are ready to agree—we must assign a single point of departure for his migrations. In these migrations, man has gone wherever he could, and, at every spot he has occupied and settled, has acquired characteristics peculiar to the place, and which differentiated him from the men settling in other places. Hence the varieties in human races. Some of these spots seem to have been peculiarly favorable to his advancement, and became centers of civilization. The number of such centers is, however, very limited, and their distribution is significant.
The continental masses are distributed in three principal groups, one feature in the configuration of which must strike every one who carefully examines a map of the world. It will be noticed that they are so expanded toward the north as to touch in that direction or be separated only by narrow passages, and that they also surround within the Arctic Circle a central polar sea with a bordering island-belt. Going down toward the south we find that the three continents, North America, Europe, and Northern Asia, which had approached each other so closely, give place to three appendages, South America, Africa, and Australia, which in their turn gradually taper off to mere points in an illimitable sea, long before they reach the Antarctic Circle. Within this circle the configuration of the land is precisely the reverse of that in the north; it is that of a solid cap of land around the pole, in the midst of the great ocean.
If we again observe these masses, we shall find that civilization was born in each of them under similar geographical conditions, viz., in the neighborhood of a smaller interior sea, near or rather north of the tropic of Cancer, between 20° and 35° north latitude. The most eastern of the centers is in China, near the Japan Sea. The most western, and apparently the most recent, was along the inner shores of the Gulf of Mexico. The last civilization was in the course of radiation and transformation when the Europeans came to America, and was wholly independent and autonomous; but, weak and relatively new, it was not able to resist the sudden onset of a stronger race.
Toward the center of the space whose extremes we have marked out must be placed two other centers of civilization, more ancient than either of the two already named, and in the same zone of latitude—Egypt, in the valley of the Nile, and near the Arabian Gulf, and Mesopotamia, near the head of the Persian Gulf. Thus, each continental mass had its particular center of civilization, except Asia, which had two—one in the extreme east, the other near the line which joins it to Europe. This peculiar grouping of the chief centers of civilization in such a relation of neighborhood constitutes the most considerable palæoethnic fact that we are able to record. The Nile and the Syrian sea on the west, upper Armenia and the Caspian on the north, the Hindoo-Koosh and the Indus on the east, and the Arabian Sea on the south, bound the region where Cushites, Semites, and Aryans, the first farmers, workers, and founders of cities, the second pastoral people, and the third mountaineers, afterward emigrants and conquerors, met, elbowed each other, and mingled, conquerors and conquered by turns, inventing arts and the use of metals, learning arms and how to organize themselves hierarchically, reaching their ideal through religion, and having in writing the most powerful instrument at the disposition of human intelligence. With them we have the beginning of history, and a continuous chain of social organizations, down to our own days. The growth of civilization in these centers leaves, however, still unaccounted for the diffusion of mankind all over the earth, which took place at a period far anterior to it.
The spread of man throughout Europe and Asia does not offer very great difficulties, for, in consequence of the long distance for which the two continents are joined, Europe is in reality only a dependency of Asia; and occupation of Europe from Asia is conformable to religious traditions. The difficulties are, however, formidable when we come to America, which we find occupied from one end to the other by races whose unity has struck the best observers. Not only, moreover, did the American man inaugurate on the soil of the New World an original and relatively advanced civilization, but he has left, chiefly in the north, indisputable traces of his presence in the most remote ages. Palæolithic implements have been found in the valley of the Delaware, at Trenton, New Jersey, and near Guanajuato in Mexico, so clearly characterized that they can not be mistaken, the situation of which at the base of the Quaternary alluvions and their coexistence with elephants and mastodons, indicate the existence of a race contemporaneous with that of the gravels of the Somme, having the same industry and doubtless the same manners and physical traits. Whence could this primitive American race, sister to the one that lived in Europe at the same date, have come, unless we suppose a direct communication between the two continents? The difficulty such men would have in crossing the Atlantic and the certainty which soundings give of the antiquity of the ocean remove all possibility of our believing either that the two continents were formerly joined, or that one of them was discovered by some unknown Columbus navigating the ocean a hundred thousand years before the later one.
We are thus in the presence of the problem, always coming up before us, and always escaping us, of the origin of the American man. Evidently it can not be resolved by invoking an accidental colonization of Asiatic wanderers, or a shipwrecked company; but it is one in which we have to deal with primitive populations flowing as in Europe by successive waves, and attesting the continuous presence of man, whose gradual development and extension have followed in America the same course as on the old continent. The hypothesis of an immigration from Asia by way of the Aleutian Islands to Alaska might be acceptable, did not the certainty of the presence of an indigenous American population in the Quaternary age reduce it to the proportions of a secondary fact. The same is the case with the relations—contradictory, it is true, and therefore suspicious—which some have attempted to establish between the monuments, statues, and graphic signs of Central America and those of Egypt and Buddhistic Asia. These analogies, aside from their insufficiency, must fall before two paramount considerations: first, the certainty of the contemporaneousness of the American man with the great animals of the Quaternary age; and, second, the relative uniformity of the copper colored race, so like itself through the whole extent of the continent, except in that part which is occupied by the Esquimaux. The difficulty arises from the fact that the monogenists, having in view a single birthplace and a single point of departure for the whole human race, and placing neither in the New World, have supposed America to have been colonized by European or Asiatic immigrants following the direction of the parallels of latitude. Emigration in this direction at once meets an obstacle in the oceans, which grow wider the farther south we go. The obstacle disappears if we give up the idea of lateral emigrations, and suppose the movement to have taken place in the direction of the meridians from north to south. No obstacle of any kind offers itself to such migrations; and the relative uniformity of the Americans, from one end of the continent to the other, would never have excited astonishment, if we had not been preoccupied with the idea of their introduction at a later date.
We may remark, on this topic, that the extreme southern points of the three continents are occupied by races which came originally, without doubt, from somewhere else, and which are ranked, in Terra del Fuego, at the Cape of Good Hope, and in Tasmania, among the lowest of the species. These races, advancing in front of the others, have preserved the visible stamp of the relative inferiority of the stock from which they were prematurely detached. We have to believe, in effect, that these three branches—Fuegians, Bushmen, and Tasmanians—so little elevated in their physical, intellectual, and moral traits, have gone and planted themselves so far away only because the unoccupied space opened out before them. Scouts for the rest of mankind, they have reached, step by step, the extreme limits of the habitable land. They must have occupied for the moment, at least, the parts of the intermediate space, but they could not resist the push of the stronger races, and they could not have survived to our time, except under the condition of restriction to a small area in the most remote tract of their original domain. There is nothing surprising in the fact that MM. Quatrefages and Hamy, having described the most ancient European race of which we have the skulls, that of Canstadt, should have found its analogies only among these same natives of the extreme south—the Bushmen and the Australians.
It will be seen that we are inclined to remove to the circumpolar regions of the north the probable cradle of primitive humanity. From there only could it have radiated as from a center, to spread into several continents at once, and to give rise to successive emigrations toward the south. This theory agrees best with the presumed course of the human races. It remains to be shown that it is equally in accord with the most authentic and most recent geological data, and that, besides man, it is applicable to the plants and animals which accompanied him, and which have continued to be most closely associated with him in the temperate regions which afterward became the seat of his civilizing power.
The general laws of geology favor this hypothesis in a remarkable manner. To make it seem probable, we have only to establish two essential points that will not be seriously contested by any geologist. One is, that the polar regions, which were covered with large trees, enjoyed a climate more temperate than that of Central Europe, and were habitable and fertile to the eightieth degree, underwent a slow and progressive cooling down till the middle of the Tertiary period. Thence refrigeration made rapid progress till the ice gained exclusive possession of the country south of them. Under such circumstances, man as well as the animals and plants would have to remove or perish—to emigrate step by step, or find himself reduced to a daily more precarious state of existence.
The second point is the relative stability of the existing continental masses, and of their distribution around a sea occupying the Arctic pole; while the other pole was occupied with a cap of land surrounded by an immense ocean. The importance of the Arctic pole in respect to the production of animals and plants, and to their migrations, and the nullity of the other hemisphere in relation to this feature, result from such a grouping. The essential point is, that there is nothing capricious in such an arrangement of lands and seas, and that there have been, if not always, at least from a very ancient period, emerged lands occupying a considerable part of the northern hemisphere, advancing very far toward the pole, and describing around the Arctic Sea a belt of more or less contiguous countries and islands. This is, in effect, what geology teaches. The changes, immersions, and emersions have never been anything but partial and successive, while the skeletons of the continents go back to the most remote ages. There have always been a Europe, an Asia, an America, and Arctic lands. We know certainly that there have always been around the Arctic pole extensive territories, if not continents, long the home of the same plants as the rest of the globe, and that, beginning with an epoch that corresponds with the end of the Jurassic, the climate, at first as warm there as elsewhere, has tended gradually to become colder. The depression of temperature was at first manifested very slowly, and was far from having attained its present degree in the tertiary; for the trees that then grew in Greenland—the sequoias, magnolias, and plane-trees—now attain their full development in Southern Europe, and are not suited with the climate of Central Europe. We are, then, assured of the ancient existence, near the Arctic pole, of a zone of lands covered with a rich vegetation. The permanent existence of a polar sea is none the less attested by fossils from all parts of the region. The neighborhood of the pole was long habitable, and inhabited by man in a time near that in which the vestiges of his industry begin to show themselves alike in Europe and America. In passing thus from the Arctic lands to those bordering on the polar circle, and through the latter into Asia, Europe, and America, man would only have taken the road which a host of plants and animals followed, either before him or at the same time, and under the stress of the same circumstances.
It is, in fact, by the aid of migrations from the neighborhood of the pole that we can generally explain the phenomenon of scattered or disjoined species, a phenomenon identical with the one which man of the Old World and man of the New World present when they are compared. Combining present notions with the indications furnished by the fossils, we discover numerous examples of disjunction—in which allied forms, often hardly distinguishable, have been distributed at the same time in scattered regions, at extremely remote points in the boreal hemisphere, without any apparent connection along the parallels, to explain the common unit. Europe attests by undeniable fossils that it had formerly a host of vegetable types and forms that are now American, which it could have received only from the extreme north. It had, for example, magnolias, tulip-trees, sassafras, maples, and poplars, comparable in all respects to those which grow in the United States. The two plane-trees, that of the West and that of Asia Minor, to which we may add an extinct fossil European plane-tree, illustrate the same phenomenon of dispersion. Europe in the Tertiary period witnessed the growth of a ginko similar to the one in the north of China. It had sequoias and a bald cypress corresponding with the trees of those names that are now growing in California and Louisiana. The beech seems to have been growing in the Arctic circumpolar zone before it was introduced and extended throughout the northern hemisphere. The same is doubtless the case with the hemlock, of which distinguishable traces have been found in Grinnell-land, above the eighty-second degree of latitude, of a date much earlier than that of its introduction into Europe. The well-established presence in both continents of many animals peculiar to the northern hemisphere must be attributed to emigrations, if not from the pole, at least from countries contiguous to the polar circle. This is obvious in the case of the reindeer, bison, and stag; but it ought to be equally true in respect to animals of more ancient times, and, although we have no other direct proofs of it than the abundance of the remains of mammoths in upper Siberia, the same law doubtless includes the elephants and mastodons. We mean here the species of these two genera which were propagated from the north to the south, and were, in America and Europe, the companions of primitive man. The connection of the continental masses with their belt of hardly discontinuous lands around the polar circle gives the key to all these phenomena. The cause on which they depend would be constantly producing radiations and consequently disjunctions of species and races, whatever kingdom we may consider.
Before leaving the questions that touch on the presumed origin of man, we can not refrain from speaking of the relations which it has been sought to establish between him and the pithecan apes. Primitive man, according to some authors of the transformist school, was an anthropomorphic ape, perfected physically as to his walk and erect attitude, intellectually by the development of his cranial capacity, till the moment when reasoning, or the faculty of abstraction and the power of using articulate language, took in him the place of instinct. Numerous and undeniable anatomical or physiological analogies of the human body and those of the more highly organized monkeys, which have no tails nor callosities on their paws, and whose faces and ways have something singularly human, favor this system, at least in appearance. The pithecans have, however, other contiguities than purely human ones. Their ways are rather analogous than directly assimilable to those of man; with other adaptations, they seem to have followed a wholly different course of evolution. They are essentially climbers, while man is exclusively a walker, and has always been predisposed to the erect position. The highest monkeys, the anthropomorphous apes, walk badly and with difficulty. When they leave the trees in which they live, their position is a stooping one, and they bend down their toes so as not to touch the ground with the soles of their feet. We have, then, reason not to admit the simian origin of man without decisive proofs. Moreover, the pithecans seem to have been evolved in an inverse direction from man. Rejoicing in the heat, they perish rapidly when brought into the temperate zones, and this is especially the case with the anthropoid apes. Thus, while man, coming from the north, advances toward the south only when the depression of temperature favors his progress in that direction, the monkeys, to which a strong heat is a vital element, were developed in an age when Europe had a sub-tropical climate, and disappeared from that continent as soon as the climate became temperate, so that their departure coincides with the arrival of man. They fled south to find the heat they needed, precisely when the diminution of the heat opened to man the region from which it excluded his predecessors. The necessity of placing the cradle of the pithecans in a hot country enables us to separate the monkeys of the Eastern and Western Continents into two distinct groups marked by differences in dentition important enough to oblige us to assume an extreme antiquity for their separation. Both are descended from the lemurians, now represented only in Madagascar, but of which early tertiary fossils are found in Europe. The most recent lemurians in Europe are found at the end of the Eocene. It is later, in the Miocene and that not the lowest, that we meet pithecans similar to those of the equatorial zone of the Eastern Continent. At this epoch, which was nearly that of Oeningen and the Mollassic Sea, which divided Europe from east to west, a subtropical climate still prevailed in the center of the continent, and the palm-trees extended up into Bohemia, along the northern banks of the great interior sea. By favor of this temperature the monkeys occupied Europe to near the forty-fifth degree, but without going above it, to disappear forever as soon as it became cool enough for men and elephants.
The Mesopithecus Pentelici, of which M. Gaudry has discovered twenty-five individuals at Pikermi, was small, walked on its four paws, and lived on twigs and leaves. The Dryopithecus of St. Gauclens had the characteristics of the highest anthropomorphs, with the bestial face of the gorilla; but it is to this animal that M. Gaudry is inclined to attribute the flints, intentionally chipped, according to the Abbe Bourgeois, of the Beauce limestone at Thénay, in the St. Gaudens geognostic horizon. The Pliopithecus of Sansan (Gers) resembles a gibbon. To find the present analogues of the Pliopithecus and Dryopithecus of Miocene Europe, it is necessary to go across the tropic of Cancer to about 12° north latitude, or more than thirty degrees south of the locality of these fossils. If, as is probable, the same interval existed between the perimeter frequented by the European anthropomorphs and the natal region in which man was originally confined, we shall find the latter in the latitude of Greenland, at 70° or 75°. This is indeed an hypothetical calculation, but it is based on a double argument hard to refute.
We can reach almost the same conclusion by a little different reasoning. The abundance of large-flaked instruments in the contiguous valleys of the Somme and the Seine marks the existence at that point of external conditions evidently favorable to the diffusion of man, whose race was then multiplying for the first time. The flora of that epoch, as observed near Fontainebleau, indicates the presence of conditions similar to those now existing in the south of France, near the forty-second degree of latitude. Now, to reach, starting from the forty-second degree, the nearly tropical regions where palm, camphor, and southern laurel trees are associated together, we have to go twelve or fifteen degrees south, to the thirtieth or twenty-eighth degree of latitude, where we see the same climatological conditions existing as prevailed in Miocene Europe when it was hardly warm enough for the anthropomorphic apes. Between these conditions and those which seem to have been first favorable to the growth of the human race, there existed a space of twelve or fifteen degrees of latitude. But when palm-trees were growing near Prague, and camphor-trees grew as far north as Dantzic, man, if he existed then, might have lived without inconvenience beyond or around the Arctic Circle, within equal reach of North America and Europe, which he was destined to people. If it be objected to this view that man now lives in the hottest regions as well as in temperate ones, we answer that that shows simply that he has developed a capacity of adapting himself to them; but he flourishes best and has reached his highest development in temperate latitudes.—Translated for the Popular Science Monthly from the Revue des Deux Mondes.