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Fig. 22. Side view of a human brain of high type, showing the chief areas of muscular control and of the sensory impressions of sight and hearing, also the prefrontal area in which the higher mental faculties are centred. Modified after M. Allen Starr.

The anatomy of man is full of remote reminders of this original arboreal existence, which also explains the very large and early development of the posterior portions of the brain, in which the various senses of sight, touch, and hearing are located.

The first advance from arboreal to terrestrial life is marked by the power of walking more or less erect on the hind limbs and thus releasing the arms; this power is developed to a greater or less degree in all the anthropoid apes; with practice they become expert walkers. The additional freedom which the erect attitude gives to the arms and to the movements of the hands and the separate movements of the fingers is especially noticeable in the gibbon. The cultivation of the powers of the hand reacts upon the further growth and specialization of the brain; thus the brain and the erect attitude react upon each other. In the gibbon there is a marked increase in the size of those portions of the brain which supply the centres of touch, vision, and hearing.

Fig. 23. The evolution of the brain. Outlines (side view) of typical human and prehuman brains, showing the early development of the posterior portions of the brain and the relatively late development of the anterior portions, the seat of the higher mental faculties.

Discussion as to how the ancestors of man were fashioned has chiefly dealt with the rival claims of four lines of structural evolution: first, the assumption of the erect attitude; second, the development of the opposable thumb; third, the growth of the brain; and fourth, the acquisition of the power of speech. The argument for the erect attitude suggested by Lamarck, and ably put by Munro(4) in 1893, indicates that the cultivation of skill with the hands and fingers lies at the root of man's mental supremacy. Elliot Smith's argument that the steady growth and specialization of the brain itself has been the chief factor in leading the ancestors of man step by step upward indicates that such an advance as the erect attitude was brought about because the brain had made possible the skilled movements of the hands.

Fig. 24. The evolution of the brain. Outlines (top view) of typical human and prehuman brains, showing the narrow forebrain of the primitive type and the successive expansion of the seat of the higher mental faculties in the successive races.

The true conception of prehuman evolution, which occurred during Miocene and Pliocene times, is rather that of the coincident development of these four distinctively human powers. It appears from the limb proportions in the Neanderthal race that the partly erect attitude and walking gait were assumed much earlier in geologic time than we formerly imagined. The intimate relation between the use of the opposable thumb and the development of the higher mental faculties of man is sustained to-day by the discovery that one of the best methods of developing the mind of the child is to insist upon the constant use of the hands, for the action and reaction between hand and brain is found to develop the mind. A similar action and reaction between foot and brain developed the erect gait which released the hand from its locomotive and limb-grasping function, and by the resultant perfecting of the motion of thumbs and fingers turned the hand into an organ ready for the increasing specialization demanded by the manufacture of flint implements.

This is the stage reached, we believe, in late Pliocene times in which the human ancestor emerges from the age of mammals and enters the age of man, the period when the prehistory of man properly begins. The attitude is erect, the hand has a well-developed opposable thumb, the centres of the brain relating to the higher senses and to the control of all the motions of the limbs, hands, and fingers are well developed. The power of speech may still be rudimentary. The anterior centres of the brain for the storing of experience and the development of ideas are certainly very rudimentary.

Change of Environment in Europe

Considering that the origin and development of any creature are best furthered by a struggle for existence sufficiently severe to demand the full and frequent exercise of its powers of mind and body, it is interesting to trace the sequence of natural events which prepared western Europe for the entrance of the earliest branches of the human race. The forests and plants portray even more vividly than the animals the changing conditions of the environment and temperature which marked the approach and various vicissitudes of the great Ice Age.

The forests of central France in Pliocene times, as well as those of the valley of the Arno in northern Italy, were very similar to the forests of the middle United States at the present time, comprising such trees as the sassafras, the locust, the honey-locust, the sumach, the bald cypress, and the tulip. Thus the regions which harbored the rich forest and meadow fauna of northern Italy in Upper Pliocene times abounded in trees familiar to-day in North and South Carolina, including even such distinctively American forms as the sweet gum (Liquidambar styraciflua), the sour gum (Nyssa sylvatica), and the bay, beside those above mentioned. To the south, along the Mediterranean, there also flourished trees incident to a more tropical climate, the bamboo, the sabal palm, and the dwarf fan-palm; most interesting is the presence of the sabal, which now flourishes in the subtropical rain forests of central Florida. The sequoia also was abundant. Toward the close of the Pliocene the first indications of the coming Glacial Epoch were a lowering of the temperature, and, in the higher mountainous areas perhaps, a beginning of the glacial stages.

The ancestors of the modern forests of Europe predominated in central France: the oak, the beech, the poplar, the willow, and the larch. It is these forests, which survived the vicissitudes of glacial times, that gave descent to the forests of Postglacial Europe, while all the purely American types disappeared from Europe and are now found only in the temperate regions of the United States.(5)

We have seen that anthropoid apes have not been discovered either in the Middle or Upper Pliocene of Europe; the gibbon-ape line disappears with the Pliohylobates of the Upper Pliocene. These animals are, however, rarely found in fossil form, owing to their retreat to the trees in times of flood and danger, so that we need not necessarily assume that the anthropoids had actually become extinct in France. The primates which are found in the Upper Pliocene belong to the lower types of the Old World monkeys, related to the living langur of India and to the macaque and baboon. The evidence, as far as it goes, indicates that the ancestors of man were at this time evolving in Asia and not in Europe. This evidence, nevertheless, would be completely offset if it could be proven that the eoliths, or primitive flints, found in various parts of Europe from Oligocene to Pleistocene times are really artifacts of human or prehuman origin.

The mammals of Europe in Pliocene times were derived by very remote migrations from North America and, more directly, from southern Asia. The Oriental element is very strong, including types of rhinoceroses now peculiar to Sumatra and southern Asia, numerous mastodons very similar to the south Asiatic types of the times, gazelles and antelopes, including types related to the existing elands, and primitive types of horses and of tapirs. Among the carnivores in Europe similar to south Asiatic species were the hyænas, the dog bears (Hyænarctos), the civets, and the pandas (Ailurus); there were also the sabre-tooth tigers and numerous other felines. In the trees were found the south Asiatic and north African monkeys; and in the forests the axis deer, now restricted to Asia. But the most distinctive African-Asiatic animal of this period was found in the rivers; namely, the hippopotamus, which arrived in Italy in the early Pliocene and ranged south by way of the Sicilian land bridge into northern Africa and east along the southern shores of the Black Sea to the Siwalik hills of India. Thus, many of the ancestors of what we have termed the African-Asiatic mammal group of Pleistocene times had already found their way into Europe early in Pliocene times. In middle and late Pliocene times there arrived three very important types of mammals which played a great rôle in the early Pleistocene. These are:

The true horses (Equus stenonis) of remote North American origin.

The first true cattle (Leptobos elatus), originating in southern Asia.

The true elephants, first Elephas planifrons and later E. meridionalis, better known as the southern mammoth, both originating in Asia.

The forests and river borders of the valley of the Arno, near Florence, contained all these African-Asiatic animals in Upper Pliocene times. Here they received their names which remind us of this region of Italy as it is to-day, such as the Etruscan rhinoceros (Dicerorhinus etruscus), the Florentine macaque (Macacus florentinus), Steno's horse (Equus stenonis), the Etruscan cattle (Leptobos etruscus), which was the earliest ox to reach Europe.

In Italy and France these African-Asiatic mammals were mingled with ancestors of the more hardy Eurasiatic forest and meadow group. Of these the most graceful were a variety of deer with very elaborate or many-branched antlers, hence known as the 'polycladine' deer. In the forests roamed the wild boars of Auvergne (Sus arvernensis), also the bears of Auvergne (Ursus arvernensis), lynxes, foxes, and wildcats. In the rivers swam the otter and the beaver, closely allied to existing forms. Among the rocks of the high hills were the pikas or tailless hares (Lagomys), also hamsters, moles, and shrews.

Many of the most characteristic animals of the dry modern plateaus of Africa had disappeared from Europe before the close of Pliocene times, namely, species of gazelles, antelopes, and the hipparion horses, all of which were adapted to the dry uplands or deserts of Africa. In the remaining faune Pliocène récente of French authors we find evidence that the Pliocene in all of western Europe closed with a moist, warm, temperate climate, with wide-spread forests and rivers interspersed with meadows favorable to the life of a great variety of browsing deer as well as of grazing elephants, horses and cattle. The flora of the Middle Pliocene as found at Meximieux indicates a mean annual temperature of 62° to 63° Fahr.

One of the proofs of the gradual lowering of temperature toward the close of Pliocene times in Europe is the southward retreat and disappearance of the apes and monkeys; the Upper Miocene gibbon is found as far north as Eppelsheim, near Worms, Germany; in Lower Pliocene times the monkeys and apes are found only in the forests of the south of France; in Upper Pliocene times they are recorded only in the forests of northern Italy; the evidence, so far as it goes, indicates a gradual retreat toward the south.

Finally, at the end of the Pliocene there existed very close geographic relations eastward with the mammalian life of India by way of what was then the isthmus of the Dardanelles and southward with the mammalian life of Africa by way of the Sicilian land bridge. This would indicate that the long lines of eastward and westward migration were open and favorable to the arrival in western Europe of new migrants from the far east, including perhaps the most primitive races of man. There is not the least evidence that Pliocene man or ancestors of man existed in Europe, excepting such as may be afforded by the problematic eoliths, or most primitive flints.

The First Glaciation

In Upper Pliocene times cold marine currents(6) from the north began to flow along the southeastern coast of England, with indications of a gradually lowering temperature culminating at a time when the sea abounded in the arctic mollusks, which have been preserved in the 'Weybourn Crags,' a geologic formation along the coast of Norfolk. This arctic current was the herald of the First Glacial Stage.

It does not appear that a glacial cap of any considerable extent was formed in Great Britain at this stage, but about this time the first great ice-cap was formed in British North America west of Hudson Bay, which sent its ice-sheets as far south as Iowa and Nebraska. In the latter State forests of spruce and other coniferous species indicate the appearance of a cool temperate flora in advance of the glaciation. In the Swiss Alps the snow descended 1,200 meters below the present snow-line, and in Scandinavia and northern Germany the first great ice-sheets were formed from which flowed the glaciers and rivers conveying the 'Old Diluvium,' or the 'oldest drift.' Accompanying the cold wave along the eastern coast of England we note, in the famous fossil deposits known as the 'Forest Bed of Cromer,' which overlie the Weybourn Crags, the arrival from the north of the fir-tree (Abies). This is most significant, because it had hitherto been known only in the arctic region of Grinnell Land, and this was its first appearance in central Europe. Another herald of northern conditions was the first occurrence of the musk-ox in England, which is attributed(7) to the 'Forest Bed' deposits.

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Fig. 25. The First (Günz) Glacial Stage was far less extensive than that in the above map, which shows Europe in the Second Glacial Stage, during the greatest extension of the ice-fields and glaciers (dots), a period of continental depression in which the Mediterranean, Black, and Caspian Seas were connected. The line from Scandinavia to the Atlas Mountains corresponds with the section shown in Fig. 13, p. 37. Drawn by C. A. Reeds, after James Geikie and Penck.

While Great Britain was less affected at this time than other regions, there is no doubt as to the vast extent of the First Glacial Stage in British America, in Scandinavia, and in the Alps; in the latter region it has been termed 'the Günz stage' by Penck and Brückner. The 'drift' deposits have a general thickness of 98½ feet (30 m.), but they are largely covered and buried by those of the far more extensive Second Glacial Stage. The Scandinavian ice-sheet(8) not only occupied the basin of the Baltic but overflowed Scania—the southern part of Sweden—and extended as far south as Hamburg and Berlin. In the Alps the glaciers passed down all the great mountain valleys to the low grounds of the foreland, implying a depression of the snow-line to 4,000 feet below its present level.

Fig. 26. The musk-ox, belonging to the tundra region of the arctic circle, which is reported to have migrated as far south as the southern coast of England during the First (Günz) Glacial Stage.

The First Interglacial Stage. Eoliths

Proofs that a prolonged cool wave passed over Britain during the first glaciation are seen in its after effects, namely, in the modernization of the forests and in the disappearance both in Britain and France of a very considerable number of animals which were abundant in Upper Pliocene times. Yet by far the greater part of the Pliocene mammal life survived, a fact which tends to show that, while very cold conditions of climate and great precipitation of moisture may have characterized the regions immediately surrounding the ice-fields, the remainder of western Europe at most passed through a prolonged cool period during the climax of the First Glacial Stage. This was followed during the First Interglacial by the return of a period somewhat warmer than the present.

This First Interglacial Stage is known as the Norfolkian, from the fact that it was first recognized in Europe in the deposits known as the 'Forest Bed of Cromer,' Norfolk, which contain rich records not only of the forests of the period, but of the noble forms of mammals which roamed over Great Britain and France in Norfolkian times. The forests of Norfolk, in latitude 52° 40' N. mainly abounded in trees still indigenous to this region, such as the maple, elm, birch, willow, alder, oak, beech, pine, and spruce, a forest flora closely corresponding to that of the Norfolk and Suffolk coasts of England at the present time, although we find in this fossil flora several exotic species which give it a slightly different character.(9) From this tree flora Reid concludes that the climate of southeastern England was nearly the same as at present but slightly warmer.

We note especially that a very great change had taken place in the entire disappearance in these forests of the trees which in Pliocene times were common to Europe and America, as described above; in other words, the flora of Europe was greatly impoverished during the first cold wave.

In southern France, as at the present time, the interglacial climatic conditions were milder, for we find numerous species of plants, which are now represented in the Caucasus, Persia, southern Italy, Portugal, and Japan. Thus the First Interglacial Stage, which was a relatively short one, enjoyed a temperature now belonging about 4° of latitude farther south.

This First Interglacial Stage is also known as the St.-Prestien, because among the many localities in France and Italy which preserve the plant and mammal life of the times that of St. Prest, in the Paris basin, is the most famous. Here in 1863 Desnoyers(10) first reported the discovery of a number of mammal bones with incision lines upon them, which he considered to be the work of man. These deposits were regarded at the time as of Pliocene age, and this gave rise immediately to a wide-spread theory of the appearance of man as early as the Pliocene. The human origin of the incisions discovered by Desnoyers has long been a matter of dispute and is now regarded as very improbable. Similar lines may be of animal origin, namely, marks left by claws or teeth, or due to accidental pressure of sharp cutting surfaces. However, we do not pretend to express an opinion of any value as to the cause of these incisions. Supposed confirmation of the evidence of Desnoyers of the existence of Pliocene man was the alleged finding by Abbott of several worked flints, two in situ, in the 'Forest Bed of Cromer,' Norfolk. Many years later in similar deposits at St. Prest were discovered the supposed 'eoliths' which have been referred to the Étage Prestien by Rutot. The age of the St. Prest deposits is, therefore, a matter of the very highest interest and importance.

Fig. 27. The giant deer (Megaceros), which first appears in western Europe during the First Interglacial Stage, probably as a migrant from the forested regions of Eurasia. After a painting by Charles R. Knight, in the American Museum of Natural History.

St. Prest is not Pliocene; it is rather the most ancient Pleistocene deposit in the basin of Paris,(11) and these incised mammal bones probably date from the First Interglacial Stage. The bed which has yielded the incised bones and the rich series of fossils consists of coarse river sands and gravels, forming part of a 'high terrace,' 98½ feet (30 m.) above the present level of the river Eure. This, like other 'high terraces,' contains a characteristic First Interglacial fauna, including the southern mammoth (E. meridionalis), and Steno's horse (E. stenonis). We also find here other very characteristic early Pleistocene mammals, such as the Etruscan rhinoceros (D. etruscus), the giant hippopotamus of early Pleistocene times (H. major), the giant beaver of the early Pleistocene (Trogontherium), three forms of the common beaver (Castor), and one of the bison (Bison antiquus). This mammalian life of St. Prest is very similar to that of Norfolk, England; to that of Malbattu in central France, Puy-de-Dôme; of Peyrolles, near the mouth of the Rhône, in southern France; of Solilhac near Puy; of Durfort, Gard; of Cajarc, Lot-et-Garonne; and finally to that of the valley of the Arno, in northern Italy.

One reason why certain authors, such as Boule and Depéret, have placed this stage in the Upper Pliocene is that the mammals include so many surviving Pliocene forms, such as the sabre-tooth tigers (Machærodus), the 'polycladine' deer with the elaborate antlers (C. sedgwicki), the Etruscan rhinoceros, and the primitive Steno's horse. But we have recently discovered that, with the exception of the 'polycladine' deer, these mammals certainly survived in Europe as late as the Second Interglacial Stage, and there is said to be evidence that some even persisted into the Third Interglacial Stage.

It is, therefore, the extinction or disappearance from Europe of many of the animals very abundant even in late Pliocene times which marks this fauna as early Pleistocene. Anthropoid apes are no longer found; indeed, there is no evidence of the survival of any of the primates, except macaques, which survive in the Pyrenees to late Pleistocene times; the tapir has entirely disappeared from the forests of Europe; but the most significant departure is that of the mastodon, which is believed to have lingered in north Africa and which certainly survived in America into very late Pleistocene times. The animal life of western Europe, like the plant life, has lost one part of its Pliocene aspect while retaining another part, both in its mammalian fauna and in its forest flora.

Fig. 28. The sabre-tooth tiger (Machærodus), which survives from the Upper Pliocene and is widely distributed over western Europe until the Middle Pleistocene. After a painting by Charles R. Knight, in the American Museum of Natural History.

The living environment as a whole, moreover, takes on a novel aspect through the arrival, chiefly from the north, of the more hardy animals and plants which had been evolving for a very long period of time in the temperate forests and meadows of Eurasia to the northeast and northwest. From this Eurasiatic region came the stag, or red deer (Cervus elaphus), also the giant deer (Megaceros), and from the northerly swamps the broad-headed moose (Alces latifrons). The presence of members of the deer family (Cervidæ) in great numbers and representing many different lines of descent is one of the most distinctive features of First Interglacial times. Beside the new northerly forms mentioned above, there was the roe-deer (Capreolus), which still survives in Europe, but there is no longer any record of the beautiful axis deer (Axis), which has now retreated to southern Asia. The 'polycladine' deer, first observed in the valley of the Arno, is represented in First Interglacial times by Sedgwick's deer (C. sedgwicki), in Norfolk, and by the species C. dicranius of northern Italy, where there also occurs the 'deer of the Carnutes' (C. carnutorum).

We observe that browsing, forest-living, and river-living types predominate. Among the forest-frequenting carnivores were the wolverene, the otter, two kinds of bear, the wolf, the fox, and the marten; another forest dweller was a wild boar, related to the existing Sus scrofa of Europe.

Thus in the very beginning of Pleistocene times the forests of Europe were full of a wild life very similar to that of prehistoric times, mingled with which was the Oriental element, the great elephants, rhinoceroses, and hippopotami connecting Europe with the far east. Among these eastern migrants in the early Pleistocene were two new arrivals, the primitive wild cattle (Bos primigenius), and the first of the bison (Bison priscus).

The theoretical map of western Europe during First Interglacial times (Fig. 12, also Fig. 56) enables us to understand these migrations from the northeast and from the Orient. As indicated by the sunken river channels discovered on the old continental shelf, the coast-line extended far to the west to the borders of the continental plateau which is now sunk deep beneath the ocean; the British Isles were separated from France not by the sea but by a broad valley, while the Rhine, with the Thames as a western tributary flowed northward over an extensive flood-plain, which is the present floor of the North Sea basin.(12) It is not improbable that the rich mammalian life deposits in the 'Forest Bed of Cromer,' Norfolk, were washed down by tributaries of this ancient Rhine River.

In all the great rivers of this enlarged western Europe occurred the hippopotami, and along the river borders and in the forests browsed the Etruscan rhinoceros. Among the grazing and meadow-living forms of the Norfolk country of Britain were species of wild cattle (Bos, Leptobos), together with two species of horses, including a lighter form resembling Steno's horse (E. stenonis cocchi) of the Val d'Arno and a heavier type probably belonging to the forests. The giant elephant of this period is the southern mammoth (E. meridionalis trogontherii), a somewhat specialized descendant of the Pliocene southern mammoth of the valley of the Arno; this animal is best known from a superb specimen discovered at Durfort (Fig. 42) and preserved in the Paris Museum. It is said to have attained a height of over 12 feet as compared with 11 feet 3 inches, the height of the largest existing African elephants. It is probable that all these south Asiatic migrants into Europe were partially or wholly covered with hair, in adaptation to the warm, temperate climate of the summers and the cool winters. To the south, in the still milder climate of Italy, the arrival of another great species, known as the 'ancient' or 'straight-tusked elephant' (E. antiquus), is recorded. This animal had not yet reached France or Britain.

Preying upon the defenseless members of this heterogeneous fauna were the great machærodonts, or sabre-tooth tigers, which ranged over Europe and northern Africa and into Asia. It does not appear that the true lions (Felis leo) had as yet entered Europe.

An intercommunication of life over a vast area extending 6,000 miles from the Thames valley on the west to India on the southeast is indicated by the presence of six or more similar or related species of elephants and rhinoceroses. Twenty-five hundred miles southeast of the foot-hills of the Himalayas similar herds of mammals, but in an earlier stage of evolution, roamed over the island of Java, which was then a part of the Asiatic mainland.

The Trinil Race of Java

The human interest in this great life throng lies in the fact that the migration routes opened by these great races of animals may also have afforded a pathway for the earliest races of men. Thus the discovery of the Trinil race in central Java, amidst a fauna closely related to that of the foot-hills of the Himalayas and more remotely related to that of southern Europe, has a more direct bearing upon our subject than would at first appear.

Fig. 29. Restoration of Pithecanthropus, the Java ape-man, modelled by the Belgian artist Mascré, under the direction of Professor A. Rutot, of Brussels, Belgium.

Fig. 30. The Solo or Bengawan River in central Java. Scene of the discovery of the type specimen of Pithecanthropus erectus in 1894. After Selenka and Blanckenhorn. Compare map (Fig. 32, p. 75).

On the Bengawan River in central Java, a Dutch army surgeon, Eugen Dubois, had been excavating for fossils in the hope of finding prehuman remains. In the year 1891 he found near Trinil a deposit of numerous mammal bones, including a single upper molar tooth which he regarded as that of a new species of ape. On carefully clearing away the rock the top of a skull appeared at about a meter's distance from the tooth. Further excavation at the close of the rainy season brought to light a second molar tooth and a left thigh-bone about 15 meters from the spot where the skull was found, imbedded and fossilized in the same manner. These scattered parts were described by Dubois(13) in 1894 as the type of Pithecanthropus erectus,[O] a term signifying the upright-standing ape-man. The specific term erectus refers to the thigh-bone, of which the author observes: "We must therefore conclude that the femur of Pithecanthropus was designed for the same mechanical functions as that of man. The two articulations and the mechanical axis correspond so exactly to the same parts in man that the law of perfect harmony between the form and function of a bone will necessitate the conclusion that this fossil creature had the same upright posture as man and likewise walked on two legs.... From this it necessarily follows that the creature had the free use of the upper extremities—now superfluous for walking—and that these last were no doubt already far advanced in that line of differentiation which developed them in mankind into tools and organs of touch.... From a study of the femur and skull it follows with certainty that this fossil cannot be classified as simian.... And, as with the skull, so also with the femur, the differences that separate Pithecanthropus from man are less than those distinguishing it from the highest anthropoid.... Although far advanced in the course of differentiation, this Pleistocene form had not yet attained to the human type. Pithecanthropus erectus is the transition form between man and the anthropoids which the laws of evolution teach us must have existed. He is the ancestor of man."

Thus the author placed Pithecanthropus in a new family, of the order Primates, which he named the Pithecanthropidæ.

Fig. 31. Geological section of the volcano of Lawoe in the Solo River basin.

Drawn by C. A. Reeds.

Fig. 32. Map of the Solo River, showing the Pithecanthropus discovery site, also two excavations (Pit No. 1, Pit No. 2) in the ancient gravel of the river-bottom, made by the Selenka-Blanckenhorn expedition of 1907. After Selenka and Blanckenhorn.

The geologic age of the bones referred to is a matter of first importance. The remains of Pithecanthropus lay in a deposit about one meter in thickness, consisting of loose, coarse, tufaceous sandstones, below this a stratum of hard, blue-gray clay, and under that marine breccia. Above the Pithecanthropus layer were the 'Kendeng' strata, a many-layered tufaceous sandstone, about 15 meters in thickness. This geologic series was considered by Dubois and others to be of late Tertiary or Pliocene age; Pithecanthropus accordingly became known as the long-awaited 'Pliocene ape-man.' Subsequent researches by expert geologists have tended to refer the age to the early Pleistocene.(17) According to Elbert(18) the Kendeng strata overlying the Pithecanthropus layer correspond to an early pluvial period of low temperature and, in point of time, to the Ice Age of Europe. For even in Java one can distinguish three divisions of the Pleistocene period, including the first period of low temperature to which the Pithecanthropus layer is referred.

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Fig. 33. Section corresponding to line A-B in Fig. 32, showing the river-drift gravels and sands at the point where the skull-top of Pithecanthropus was found. Drawn by C. A. Reeds.

Recent		7 River wash, blue-black clay.
Pleistocene	{ { { { {	6 Light-colored sandstone, like tuff.
5 Gray tuff with balls of clay, fresh-water shells.
4 White streaked sandstone resembling tufa.
3 Blue-black clay with plant remains.
2 Bone-bearing stratum. Pithecanthropus.
1 Lahar conglomerate.

The fossil mammals contained in the Pithecanthropus layer have also been thoroughly studied,(19) and they tend to confirm the original reference to the uppermost Pliocene. They yield a very rich fauna similar to that of the Siwalik hills of India, including the porcupine, pangolin, several felines, the hyæna, and the otter. Among the primates beside Pithecanthropus there is a macaque. Among the larger ungulates are two species of rhinoceros related to existing Indian forms, the tapir, the boar, the hippopotamus, the axis and rusa deer, the Indian buffalo, and wild cattle. It is noteworthy that three species of late Pliocene elephants, all known as Stegodon, and especially the species Stegodon ganeza, occur, as well as Elephas hysudricus, a species related to E. antiquus, or the straight-tusked elephant, which entered Europe in early Pleistocene times. Fossils of the same animals are found in the foot-hills of the Himalayas of India, about 2,500 miles distant to the northwest. The India deposits are considered of uppermost Pliocene age,(20) for this is the closing life period of the upper Siwaliks of India.

Certainly Java was then a part of the Asiatic continent, and similar herds of great mammals roamed freely over the plains from the foot-hills of the Himalaya Mountains to the borders of the ancient Trinil River, while similar apes inhabited the forests. At this time the orang may have entered the forests of Borneo, which are at present its home; it is the only ape thus far found in the uppermost Pliocene of India. We may, therefore, anticipate the discovery, at any time, in India of a race similar to Pithecanthropus.

The geologic age of the Trinil race is, therefore, to be considered as late Pliocene or early Pleistocene.

Fig. 34. The top (1) and side (1a) views of the skull-top of Pithecanthropus erectus. After Dubois. One-third life size.

This great discovery of Dubois aroused wide-spread and heated discussion, in which the foremost anatomists and palæontologists of the world took part. Some regarded the skull as that of a giant gibbon, others as prehuman, and still others as a transition form. We may form our own opinion, however, from a fuller understanding of the specimens themselves, always keeping in mind that it is a question whether the femur and the skull belong to the same individual or even to the same race. First, we are struck by the marked resemblance which the top of the skull bears, both on viewing it from the side and from above, to that of the Neanderthal race. This fully justifies the opinion of the anatomist Schwalbe(21) that the skull of Pithecanthropus is nearer to that of Neanderthal man than to that of even the highest of the anthropoid apes. As measured by Schwalbe, the index of the height of the cranium (Kalottenhöheindex) may be compared with others as follows:

Lowest human race		52 per cent.
Neanderthal man		40.4 per cent.
Pithecanthropus, or Trinil race		34.2 per cent.

Fig. 35. Head of chimpanzee—front and side views—exhibiting a head of somewhat similar shape to that of Pithecanthropus, with prominent eyebrow ridges, but much smaller brain capacity. Photograph from the New York Zoological Park.

This accords with the estimate of the brain capacity[P] of 855 c.cm. (Dubois) as compared with 1,230 c.cm., the smallest brain capacity found in a member of the Neanderthal race. Second, as seen from above, we are struck with the great length of the calvarium as compared with its breadth, the cephalic index or ratio of breadth to length being 73.4 per cent (Schwalbe) as compared with 73.9 per cent in the Neanderthal type skull; this dolichocephaly accords with the fact that all of the earliest human races thus far found are long-headed, although according to Schwalbe(22) all anthropoids are broad-headed. This is a very important distinction. The third feature is the prominence and width of the bony eyebrow ridges above the orbits, which are almost as great as in the chimpanzee and greatly exceed those of the Neanderthal race and of the modern Australian. The profile of the Trinil head restored by McGregor (Fig. 38) exhibits this prominent bony ridge and the low, retreating forehead. In the latest opinion of Schwalbe(23) Pithecanthropus may be regarded as one of the direct ancestors of Neanderthal man and even of the highest human species, Homo sapiens. He also considers that when the lower jaw of the Trinil race becomes known, it will be found to be very similar to that of the Heidelberg man, the final conclusion being that Pithecanthropus and the nearly allied Heidelberg man may be regarded as the common ancestors of the Neanderthal race, on the one hand, and of the higher races on the other. There are, however, reasons for excluding Pithecanthropus from the direct ancestral line of the higher races of man.