# Popular Science Monthly/Volume 60/March 1902/The Differentiation of the Human Species

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* THE DIFFERENTIATION OF THE HUMAN SPECIES.
By Professor LINDLEY M. KEASBEY,
BRYN MAWR COLLEGE.
ZOOLOGICALLY considered, the human race constitutes a single species which has in the course 'of time become subdivided into a number of ethnic varieties. Scientifically speaking, this differentiation of the human species into ethnic stocks is an instance of organic variation, and, as such, subject to biological interpretation. Applying the general principles of organic evolution to the particular case, ethnic differentiation may, accordingly, be regarded as the result of environmental agencies operating through the process of selection upon the attribute of variability inherent in the anthropoid line.
Recent paleontological evidence renders it reasonably certain that mankind was homogeneous before the ice-age, and that heterogeneity entered in during the glacial period. It may be taken for granted, therefore, that the first stages of ethnic differentiation were established by the great geographic changes that occurred at this time. As the ice-sheets advanced successively from the arctic and antarctic regions and the thermal equator oscillated at long intervals about the geographical equator, the climate of the northern and southern hemispheres alternated between equable and frigid conditions, and the surface of the earth was modified accordingly. Thus so long as the ice-age lasted, the human race was subjected to the influences of a varying environment. Upon the final retreat of the glaciers, the configuration of the earth gradually assumed its historic form and the globe became divided as at present into temperature zones. After this, time introduced no further changes in the general geographic conditions, but place peculiarities became permanently established and regions of the earth differed from each other in climate and topography. So instead of the human race being affected as before by a varying environment, varied environments henceforth influenced different portions of mankind. The effect of these varying and varied environments was first to alter, and then to diversify, the conditions of human survival. This necessitated adaptation on man's part, which in turn led to the differentiation of the human species; so that by the close of the glacial period heterogeneity was established where homogeneity had previously prevailed.
Owing to the numerous instances of migration and miscegenation that have occurred since the ice-age, the ramifications of race are ​nowadays extremely complex. Looking from above downward, it is consequently difficult to define the lines of ethnic division with any accuracy. The analytical method furnishes sufficient distinctions, however, to establish a general classification of humanity. Taking the shape of the skull, the texture of the hair, the pigment of the skin and general structural characters into account, ethnographers have concluded that there are four elementary divisions of mankind, known particularly as the Negro or Black race, the Mongolic or Yellow race, the Caucasic or White race and the American or Red race.
Looking from below upward, it is out of the question, of course, to follow the lines of racial ramification chronologically. But though the time factor fails for the most part, the place element can usually be determined with considerable accuracy. Ethnic consequents can, accordingly, be connected in each instance with their geographic antecedents, and the outcome of the interaction between variability and environment set forth in some detail. Thus though it is out of the question to establish the chronological sequence exactly, by supplementing the analytical with the geographical method of enquiry, it should at least be possible to indicate the general order of racial ramification and determine under what environmental conditions the ethnic differentiation of mankind took place.
Corresponding to the fourfold ethnic division of the human race, there are four more or less distinctly defined geographic sections of the globe. Three of these racial regions radiate from Indo-Malaysia, the cradle-land of mankind; the fourth is situated on the opposite side of the earth, though connected in the far north with the continental area of the eastern hemisphere. Considering the situation somewhat more in detail, the four habitats may be defined as follows: Toward the south, the Indo-Malaysian abode borders upon what we may call the 'eastern-equatorial section,' which stretches out between the tropics from the west coast of Africa, across the partially submerged Indo-African continent, to Melanesia and Australia. This intertropical belt has from time immemorial been the abode of the Negro or Black race. North of the Indo-Malaysian cradle-land lies the vast 'Asiatic section' of the eastern hemisphere, which is separated from the southern peninsulas by the Himalayan line, except along the Pacific coast where passage to the north is possible between the longitudinal ranges of Cochin-China. This continental area is the traditional abode of the Mongols or Yellow people. Between the equatorial belt and the Asiatic area, the 'Indo-Mediterranean-European section' spreads out towards the west from Indo-Malaysia to the Atlantic coast of the continent. This peninsular portion of the eastern hemisphere is the historical home of the White man, the field for the development of what we are in the habit of calling Caucasian ​civilization. On the opposite side of the globe the western hemisphere points south between the two seas.
Having located the four races in their respective habitats, we should next determine how each racial region was originally occupied, and then note the ethnic effects produced by geographic peculiarities.
The human species was differentiated from the other anthropoids within Indo-Malaysia, where the climate was moist and warm and the surface of the ground covered with a tropical forest growth. Such were the surroundings that impressed themselves upon primeval man and established the original type. These conditions were continued on either side of the cradle-land toward the south along the equatorial belt of the eastern hemisphere, which then stretched uninterruptedly from the west coast of Africa, across the now partially submerged Indo-African continent, into Melanesia and Australia. The shifting of the thermal equator north and south of the geographical equator no doubt caused the climate of this intertropical belt to vary slightly during the ice-age; but after the final retreat of the glaciers no further changes occurred; so that, ever since, the environmental conditions of the eastern-equatorial region have remained to all intents and purposes the same as they were in tertiary times. The Negro descendants of the original inhabitants of these parts have thus been subjected since time immemorial to somewhat the same external influences as impressed themselves upon primeval man. It is natural, therefore, that the blacks should conserve the conspicuous characteristics of the ape-like ancestor and resemble the human prototype more closely than any other people. Ethnically the Negroes are considered the lowest of the four races of man; while geographically they may be characterized as the children of the tropical forest. There are, to be sure, minor differences among them, arising from different lines of heredity, variations of environment, migration and miscegenation; so that from the primitive Pygmy people living in the recesses of the tropical forest, the line of ethnic evolution may be traced through the pure Negroes, who occupy the central equatorial belt, to the mixed Negroid types which have come into contact with other races on the borders of the region. But despite these differences the Blacks may still be regarded as ethnically similar and grouped together under one racial category; for, if we confine ourselves to general characteristics, the typical Negro can readily be distinguished from his human fellows by his black skin; his short curly hair, which is flat in cross section; his long head with protruding jaws, his flat foot, his broad nose and his round black eyes.
The rest of the races of mankind were differentiated within the northern hemisphere. Being affected from the first by the varying environment of the glacial era, these northern emigrants were influenced by different conditions from those to which their ancestors ​had become accustomed in the Indo-Malaysian abode. Furthermore, upon the final retreat of the ice the people of the north became marked off from the inhabitants of the south by climate bounds. Regarded collectively, therefore, Mongols, Caucasians and Americans alike may be distinguished from the tropical Negroes as products of the temperate zone. The several stocks that migrated northward from the Indo-Malaysian abode were, however, separated from each other from the start by the mountain barriers and open seas that intervened between the different lines of march. Thus though subjected to somewhat the same climatic conditions during the period of dispersion, upon settling in their respective habitats, the geographic groups were influenced by different surroundings. As a result, ethnic diversity was established along the northern latitudes, and the three temperate races became separated from one another by topographic differences. Taking this as our clue we may go back again to the original point of departure and follow the several lines of northerly dispersion in detail.
As was indicated above, the Indo-Malaysian cradle-land is cut off from the Asiatic area by the Himalayan line. Passage was possible, however, between the longitudinal ranges of Cochin-China, and, judging from the remains that have recently been discovered in this mountainous region, it is probable that primeval man proceeded northward along these lines during the interglacial epochs. The effect of the Himalayan barrier was, therefore, not so much to prevent migration into the continental area, as to shut the Asiatic immigrants in, and separate them from the inhabitants of the south. Those that remained in this region—Mongols in the forming—must, accordingly, have been subjected for long ages to the influences of their own surroundings.
This Asiatic area is not characterized by any such uniformity as the eastern equatorial region, but as nature has operated here upon so stupendous a scale, there is still a certain sameness in the salient features of the environment. Speaking generally, Asia is a continental territory, made up for the most part of bleak plateaux and deforested steppes. Such at least were the prevailing conditions which impressed themselves upon the majority of the original inhabitants and constituted the basic type. The Mongolians may thus be regarded as the product of temperate plains, much as the Negroes were considered to be the children of the tropical forest.
Here as elsewhere, however, variations from the characteristic environment made for corresponding modifications of the normal ethnic type. Being of such enormous extent and cut off on two sides from the sea, the climate of the Asiatic section is predominantly continental. Nevertheless, as the region stretches from the Arctic circle to the tropic of Cancer, and rises in altitude from 100 feet below to 25,000 feet above sea-level, there is naturally a wide range of temperature within ​its borders. Topographically, the Asiatic section is dominated on the south by the Tibetan table-land, culminating in the Pamir region, called the 'roof of the world,' from which the land falls off rather abruptly on the west, and more gradually toward the north and east to the level of the sea. The bleak plateaux are thus succeeded by grassy plains and deforested steppes, which in turn are bordered by a comparatively narrow Tiaga, or wooded belt, extending to the Arctic Tundra and in places to the Pacific shore. The heart of the continent contains deserts and enclosed seas, while the surrounding lands are furrowed by forest-bordered streams flowing to the north, and by more open rivers of uncertain course draining toward the east. In consequence of these climatic and topographic differences, the Mongolic race has in the course of time become subdivided into a number of geographic groups. There are plateaux people, desert folk and steppe tribes, forest dwellers and typical Hyperboreans, and the settled inhabitants of the eastern valleys. Migration has moreover been succeeded by miscegenation, so that the lines of heredity and environment have become confused. Withal, however, enough Mongolian traits have persisted everywhere over the region, and during all the centuries that have elapsed since the original type was constituted, to allow us to set the Yellow people in a separate racial category, and distinguish the typical Mongol from his human fellows by his round head with high cheek-bones; the texture and pigment of his skin; his coarse straight hair, which is cylindrical in cross section; his thin colorless lips; and his small oblique black eyes.
South of the Himalayan line the peninsular portion of the old world spreads out like a fan from the Indo-Malaysian cradle-land to the Atlantic coast of the continent. On the east, the Indian section of this territory is connected with the equatorial region through the southern peninsulas, which once formed part of the Indo-African continent; but cut off from the Asiatic area by the lofty Himalayan range. On the west the conditions are reversed, the Mediterranean and European sections of this territory being cut off from the equatorial region by the Sahara, and connected with the Asiatic area through what is called the open gateway of the east, lying between the Ural mountains and the Caspian sea. There was access to the Indo-Mediterranean-European section, therefore, from two sides; from the equatorial region on the southeast, and from the Asiatic area on the northwest. The ancestry of the so-called Caucasians can accordingly be traced back to two sources. From the southeast, dolichocephalic Negroids pushed westward from Indo-Africa into the Mediterranean region and overran Europe in very early times. Somewhat later successive streams of brachycephalic Asiatics poured in through the open gateway of the east and mingled with the primitive inhabitants of these parts. From ​the standpoint of heredity, therefore, the White people constitute a derived race, combining Negro and Mongolic affinities. For the rest, however, they are the products of their peculiar surroundings.
Unlike the other two regions, the peninsular portion of the old world contains an almost infinite variety of environments. With its apex in the subtropics, this triangular territory stretches out towards the northwest across the warm temperate, temperate and cold temperate zones, and consequently offers a series of climate transitions without striking contrasts. Topographically also the Indo-Mediterranean-European region is diversified throughout with deforested and forested river valleys, indented sea-shores, deserts, plains and steppes, alps and mountains, woodlands and dales, heaths and downs—in fact, with pretty nearly all the varied features the surface of the earth affords. On account of this diversity of environmental conditions, it is difficult to characterize the Indo-Mediterranean-European region as a whole. Negatively, at least, it may be distinguished from the equatorial belt by its temperature, and from the Asiatic area by its topography. Considered positively, its oceanic climate and its peninsular structure constitute its most striking characteristics. It should furthermore be noticed that the region is subdivided into three interconnected sections: The Indian section, which proceeds by insensible steps out of the eastern-equatorial region; the European section, which opens out of the Asiatic area; and the Mediterranean section, lying between, which combines the characteristics of the other two sections, and still possesses certain peculiarities of its own.
With this lack of environmental uniformity goes a corresponding diversity of ethnic types. The influx of original races from either side, migrations to and fro through the length and breadth of the land, adaptation to special surroundings, and the mingling of the blood of different peoples, have all contributed to the existing complexity. Stock has been added to stock in this way, and ancestral lines have become so confused that the ethnic diversity among the inhabitants of the Indo-Mediterranean-European region is as great as its environmental variety. Thus though it is easy enough to distinguish the white man from his human fellows, it is difficult to describe a typical Caucasian. In fact, only one physical characteristic runs through the whole race, namely, the hair, which is predominantly wavy and always oval in cross section. Generally speaking the Caucasian's features are also more regular than those of other people and his eyes are usually set straight. For the rest, amid the existing diversity, the most that can be done in the way of classification is to establish three types of white men, corresponding roughly to the three sections into which their territory is divided. In the center, there is the olive-skinned, brunette, Mediterranean type, which was originally recruited from the ​southeast, but which has in the course of time become differentiated from the Negroids and adapted to its peculiar surroundings. Toward the northwest we find the florid-skinned, blond-haired Europeans, whose ancestors are Mediterraneans and Asiatics, but whose distinguishing characteristics were undoubtedly acquired during the course of their wanderings across the plain lands between the Pamir region and the Baltic. In the southeast section finally, dwell the swarthy-skinned, black-haired Indians, who came down from the northern plain lands during prehistoric days and established their supremacy over the scarcely differentiated black people of the peninsula. These distinctions are not to be taken too definitely, however; for even as the three sections of the Indo-Mediterranean-European section are interconnected, so the corresponding ethnic types are blended along the lines of transition, in such a way that it is as easy to pass from diversity to unity as from unity to diversity in considering the characteristics of the Caucasians.
Before leaving the eastern hemisphere to consider the fourth racial region on the other side of the globe, we should take a hasty survey of the insular region of Oceania and determine the ethnic affinities of the South Sea Islanders. These islands of the Pacific are so scattered, and differ from one another so widely, that they cannot be said to constitute a separate racial region. The most that can be done in the way of classification, therefore, is to divide the archipelagoes into groups, establish their relations with each other, and indicate their connections with the mainland.
Topographically the islands may be divided into two classes: continental and oceanic. The continental islands are adjacent to the mainland and stretch out along the equator toward the east and southeast. The oceanic islands, on the other hand, are grouped between the tropics in isolated archipelagoes, extending more than halfway across the Pacific. The lines of entry into this insular region lead back to Indo-Malaysia, the cradle-land of mankind and the point of intersection of the three racial regions of the old world. Oceania was, accordingly, peopled from three sources, successive waves of Negro, Caucasic and Mongolic migration coming together in Indo-Malaysia and spreading out again over the islands of the Pacific.
The negro dispersion occurred first, probably in the early days when the eastern-equatorial region still extended uninterruptedly far out into the South Sea. As the configuration of the globe assumed its historic form, many of the earlier land-bridges were broken, leaving the blacks to become adapted to different insular environments. But as the islands occupied were for the most part continental and situated under the equator, the surrounding conditions differed but slightly from those prevailing throughout the eastern-equatorial region. As a ​result, the Oceanic negroes are ethnically similar to their African relatives. There is even the same succession of types, running from the pygmy Negritoes of Borneo and the Philippines, through the Negroes of Papua and Melanesia, to the Negroids of Micronesia. The Australians constitute the only exception. The racial affinities of this primitive people are somewhat doubtful, though they are in all probability derived from Negro stock. The Australians have lived so long isolated in their island continent, however, that in the course of time they have developed certain ethnic peculiarities.
Oceania is still connected through Malaysia with Indo-China. The Golden peninsula, in turn, is joined on the west with the Indo-Mediterranean-European region, and open on the north to the Asiatic area. During prehistoric times, migrations proceeded along both these lines in successive stages toward the east. From the peninsular portion, people belonging to the white race—Indonesians they are collectively called—passed through Malaysia and proceeded thence (probably in canoes or perhaps in proas) to the scattered islands of Polynesia. Monuments and stone records still mark the path of this Indonesian dispersion even as far as Easter island. Miscegenation with Negro natives doubtless occurred along the route, accompanied by adaptation to the different environments; but withal, the original type has been preserved, so that the surviving Indonesians, classified geographically as Polynesians, still show distinct Caucasic characteristics. The Mongols who pushed south somewhat later from the Asiatic area into the Golden peninsula became deeply impregnated with Indonesian blood in these parts. The mixed Malay race thus constituted subsequently spread out through the adjacent islands and eventually established their supremacy over Malaysia. Some of them, notably the Bujis, became a sea-faring folk, and by establishing commercial connections with the surrounding islands, extended Malaysian influence still further across the Pacific.
During the middle ages Saracen traders reached these parts from Arabia, and from very early times Chinese emigrants have continued to establish out-post settlements upon the littoral islands of Asia; but with these later influences we have not at present to deal. It is enough to know that the inhabitants of Oceania trace their ethnic origin to the three great races of the old world. In the tropical continental islands of Melanesia, the Oceanic Negroes predominate. Scattered over the oceanic islands of Polynesia are the Indonesian descendants of an ancient Caucasic line. Throughout Malaysia the Mongolic Malays prevail. The island continent of Australia contains a peculiar population, probably derived originally from Negro stock, while the tiny islets of Mikronesia support scanty settlements of mixed Melanesian-Polynesian people.
​Entry into the fourth racial region was not from Indo-Malaysia but from the Arctic peninsulas of the eastern hemisphere. During the period of dispersion, continuous connections probably existed along these high latitudes, joining America with northwest Europe, on the one hand, and with northeast Asia, on the other. It was possible, therefore, during these early ages, for dolichocephalic Mediterranean people to continue the course of their northwesterly migrations until they reached the Atlantic shores of the new world; and for brachycephalic Asiatics to pursue their way northeastward until they came to the Pacific coast of the continent. That the western hemisphere was originally occupied in this manner by emigrants from Europe and Asia appears probable from the prevalence among the American aborigines of the long-head type in the east and the broad-head type in the west. The incursion along the Atlantic could not have lasted as long as that proceeding by way of the Pacific, for the ancient land-bridge joining northwest Europe with northeast America was broken long before the prehistoric period, and the islands left between were too far apart to afford further access from this direction. On the Pacific side, however, the old miocene bridge, with its temporary glacial extensions, probably endured until quaternary times, and after this, approaches still remained across the narrow Behring strait and along the Aleutian island chain. We should think of Asia, therefore, as the source of the main stream of migration that spread southeastwards over the new world.
In these early days, before the knowledge of ocean navigation, America was not as now a Durchgangsland, but rather a cul-de-sac. There was entry on either side from the north, but no exit in any other direction. The aboriginal people pouring in from above must, therefore, have been pushed down by the later comers through the constricted central space, like the sands in an hourglass, to spread out along the equator and become contracted again in the apex of the continent. Moreover, as the main stream of migration proceeded from Asia, the emigrants from Europe were probably confined from the first to the eastern edge of the hemisphere. Cut off completely from further contact with other people, the American aborigines, long-heads and round-heads alike, were henceforth subjected to the influences of their new surroundings and modified accordingly.
Geographically speaking, the American continent differs from the other regions of the earth, and at the same time possesses certain positive characteristics of its own. This isolation of the western hemisphere, taken together with such environmental uniformity as exists within its borders, had the effect of differentiating the aboriginal inhabitants from their European and Asiatic ancestors and blending them gradually into one racial variety, possessing pronounced Oriental affinities.
​Topographic and climatic differences led, however, to lines of minor ethnic variation, which, for environmental reasons, cross each other at right angles. Topographically considered, the western hemisphere combines longitudinal uniformity with latitudinal diversity, so that in this respect the two sections of the continent are very much alike. Both North and South America have their mountain ranges along the west and the mural masses of each section are succeeded by deforested plains and forested river valleys extending to the Atlantic coast. As a result, there is a corresponding variation of ethnic types running through both continents from west to east, showing more or less marked distinctions between the men of the mountain, the men of the plain, the men of the forest and the men of the shore. Owing to its extension across almost all the degrees of latitude, the western hemisphere offers, on the other hand, an extreme longitudinal range of climate, so that in this respect there is a striking difference between the two Americas. Both triangular sections have their bases on the north and their apexes turned towards the south in such a way that the northern continent is mostly temperate and the southern continent predominantly tropical. As a result, there are likewise lines of ethnic variation running along the longitudes, which distinguish the inhabitants of the northern or temperate continent from the inhabitants of the southern or tropical continent. From the fact that they cross each other at right angles, however, these longitudinal and latitudinal variations tend to neutralize each other to a large extent and leave a relatively uniform type. It is possible on this account, despite the diversity that exists among the American aborigines, to distinguish the Eed man from his human fellows by his brown or copper-colored skin; his lank black hair, which is nearly round in cross section; his deep-set beady black eyes; his aquiline nose; his massive jaws; and his finely formed figure.
There has been no attempt in the foregoing, either to make an exact analysis of the ethnic make-up of mankind, or to follow the process of varietal differentiation in detail. The sole purpose of the enquiry has been, by combining the analytical and geographical methods of investigation, to indicate the probable order of racial ramification and to determine in a general way under what environmental conditions the ethnic differentiation of mankind occurred.