Read Ebook: Man And His Ancestor: A Study In Evolution by Morris Charles

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d will it be further asserted that the Deity placed similar stumbling-blocks to the human reason in the embryo, in order to deceive those who should extend their researches to this low level? It would be difficult to conceive of a more preposterous idea, yet there is no other escape from what seems a self-evident fact, that man is a product of evolution from the lower animals, and bears the marks of his ancestry thick upon him.

FOOTNOTES:

RELICS OF ANCIENT MAN

If now, instead of seeking for evidences of man's ancestry within the human body, in survivals of ancient anatomical structures, we seek for them within the crust of the earth, we find ourselves confronted with evidences of a great antiquity of the human race, partly in implements of human manufacture, partly in ancient or fossilized bones of primitive man. These indicate not only great remoteness of origin, but also a very gradual advance from the lowest stage of inventive ability to the high level now attained.

These relics of primitive man are divided by Dana into ten varieties, Buried human bones; stone arrow and lance heads, hatchets, pestles, etc.; flint chips, left in the manufacture of implements; arrow heads and other implements made of bone and deer horn; bones, teeth, and shells bored or notched by human hands; cut or carved wood; bone, horn, ivory, or stone graven with figures, or cut into the shapes of animals; marrow bones broken longitudinally to obtain the marrow for food; fragments of charcoal and other indications of the use of fire; fragments of pottery.

Relics of the kinds above cited have been found at intervals for many years past, but their age and significance were doubted, and only within some forty years has the great antiquity of man upon the earth been generally acknowledged by scientists. The most important early find of ancient implements was made by Boucher de Perthes in 1841 and subsequently, in the high level gravels of the valley of the Somme, in Picardy, France. In deep layers of these gravels, which were deposited at a period when the river occupied a wider and higher channel than at present, he found rude flint weapons and tools, bearing plain evidences of human workmanship, and mingled with the teeth and bones of animals, both of living and extinct species. Among the bones were those of the mammoth and the hairy rhinoceros, species evidently contemporary with man, though they have long since vanished from the earth. At a somewhat earlier date, implements of men, mingled with bones of the cave-bear, cave-lion, hyena, and other species, had been found in the caves of France and Belgium. These were frequently buried beneath deposits of stalagmite and other materials that must have taken a long time to accumulate.

The significance of these discoveries was long in forcing itself upon the attention of scientific men. Nearly twenty years passed before Boucher de Perthes could get the noted geologists of France and England to investigate the Somme gravels. When they did so they were quickly convinced of the genuine antiquity of these relics, and announced it as a fact beyond question that man had lived in the Somme valley and fashioned rude implements out of flint during what was known as the Quaternary or Drift Period of geology.

The discoveries here made set men actively at work investigating elsewhere. Excavations were made in other high level gravels, caverns were carefully and minutely examined, Kent's Cavern, England, was dug out to its rock bottom, dozens of important finds resulted, and the antiquity of man was proved to extend back from thousands to tens of thousands, if not to hundreds of thousands, of years. And the coexistence of man with the animals whose bones accompanied his relics was proved by unquestionable evidence, for drawings and carved forms of these animals were found, proving incontestably that man had gazed upon their living forms. Thus the sketch of a mammoth, showing the long hair which served to protect this animal from the cold, was found engraved upon a piece of mammoth ivory, and one of a group of reindeer on a piece of reindeer horn. There were also drawings of the cave-bear, the seal, etc., and one very interesting group showing the aurochs, a number of trees, and a man with a snake apparently biting his heel. The carvings consisted of the horn handle of a dagger, cut into the shape of a reindeer, and other forms.

That these relics belong to a far distant age is proved by the strongest evidence. It must suffice here to give some of the more striking of these proofs of antiquity. The flint hatchets found at St. Acheul, France, were obtained from a gravel bed which lay below twelve feet of sand and marl. On the surface was a layer of soil, in which were graves of the Gallo-Roman period, showing that it had been there for at least fifteen hundred years. The time needed for the slow accumulation of the whole series of deposits must have been very considerable.

A much more decisive proof of antiquity is given by the position in which this and similar gravel beds lie. They are found along the sides of rivers at a height often of a hundred or two hundred feet above the flood level of the streams. When they were deposited, the rivers must have run at this elevation, so that time has since elapsed sufficient for the streams to cut down their valleys to the present depths. The streams may have formerly been of greater volume, and had superior cutting powers, and they may have been aided by the ice of the Glacial Age, yet, however we estimate, the conclusion is inevitable that the men who dropped their implements into those gravels must have lived upon the earth ages before the beginning of historical times.

The presence there of remains of animals which ages ago perished from the earth is another circumstance indicative of high antiquity. These embrace the mammoth,--the great hairy elephant of prehistoric times,--an extinct hair-clad rhinoceros, the large and powerful cave-bear and cave-lion, the great Irish elk, and still other animals of whose existence we know only by their bones. Others, which existed in common with men of later date, are the reindeer and the musk-ox, species of which now inhabit the coldest regions of the north, and whose presence in southern Europe at that era seems to indicate a much colder climate than that of historic times.

The evidences of human antiquity here briefly presented are accompanied by indications of a gradual development of the human intellect. If man has "fallen from his high estate," he has left no traces of this high estate on his downward path. We possess abundant indications of his upward climb, we find none of a preceding descent. If we base our opinions on known facts, the theory of development is the only one that can be sustained; the doctrine of a fall is absolutely without warrant outside the pages of Genesis.

The successive stages of man's mental development, as indicated in the work of his hands, are well and clearly marked. At the lowest level we find tools and weapons of the palaeolithic or old stone age, made of roughly chipped stone, rude in form, and never ground or polished. These present some evidence of gradual improvement, but we must go to a higher level to find implements of a decidedly higher order, the neatly shaped and polished stone implements of the neolithic or new stone age. With the coming of these appears a much greater diversity in tools and weapons, and evidences of a growing skill in manufacture and a considerably greater power of invention. Still higher lie the deposits of the bronze age, in which metal replaces stone in human implements. Finally appears the age of iron, that in which we still remain. We need merely refer in passing to the lake-dwellings of Switzerland, with their many interesting relics of man during the later stone, the bronze, and the early iron eras; and the kitchen-middens, or refuse-heaps, of the Danish islands and elsewhere, which extend from the old stone age far down toward the historic period.

These are but a portion of the evidences of man's antiquity and his gradual progress in the arts of manufacture. Others have been found in many parts of the earth. Many of them exist in America, proving that man resided on this continent at a very distant era. When we consider that late discoveries in Babylonia appear to carry back the age of civilization and historical relics to some ten thousand years, and that semi-civilization must have extended very considerably beyond that time, the vista of man's gradual progress seems to recede interminably and the era of primitive man to stretch backward to an enormously remote period. In truth, discoveries have been made which are claimed to carry man back beyond the Quaternary and into the Tertiary Period of geology, since cut and scratched bones have been found in Pliocene deposits, which some geologists of experience believe to have been the work of human hands. Still more remote are some seemingly chipped flints and bones cut in a way that suggests human action, which have been found in deposits of the very far-distant Miocene Age. The immense remoteness of this epoch and the rudeness of the work have cast much doubt on the human origin of these remains, though their authenticity as the work of man has been accepted by several competent observers, among them the able anthropologist, Quatrefages.

If we confine ourselves, however, to the conclusions regarding ancient man which are generally accepted, we must say that he has not been clearly traced back beyond the Glacial Period, though some of the relics found in the older river gravels and in the lowest cave accumulations may well be of pre-glacial age. Many geologists believe that he reached Europe as early as the extinct mammals with which he was contemporaneous there, but how far back in time this would carry his advent it is impossible to say.

Coming now to the consideration of more immediate human relics, the bones of man himself, it must be said that well-authenticated remains of palaeolithic or early neolithic man are not numerous. As long as man left his bones to the unaided agencies of nature, they were little likely to be preserved. Of the anthropoid apes of Europe, probably numerous in individuals, a few remains of one or two species alone survive. Of pre-glacial man none remain, but this may merely indicate that he has shared the fate of numerous other species that died out and left no trace. It was only when the growing cold drove man from the open woods to seek shelter in caves that remnants of his body were likely to be preserved, and only when a growing sense of human dignity led to the art of sepulture that the preservation of his bones became assured.

The burial art was seemingly not practised by the hunters of the river-drift period or by men of still earlier date. The only remains of primitive man known are those found in caves and rock shelters. A number of human skulls have been discovered in these situations, and in a few instances skeletons have been exhumed. In the neolithic period interment became more common and more carefully performed, and the progress of this period is marked by many remains of man, which in later times were buried in elaborately constructed stone sepulchres, sometimes massive in materials and covered by great earth-mounds.

What is meant by the Glacial Age is probably well-known to most readers, but its close relations to ancient man render it important for those who are not familiar with its meaning that a passing description of it should here be given. It will suffice to say that there are found over much of the northern portions of America and Europe accumulations of clays, sands, and gravels, sometimes laid down in stratified beds, sometimes rudely piled together. In these occur blocks of stone, large and small, and other blocks, occasionally of great size, are found in isolated localities. The solid rocks which lie beneath these heaps are often scratched or polished, as if the material had been pushed over them with great force.

All geologists now believe that these accumulations were made by ice, at some remote period when a very cold climate prevailed in the northern hemisphere, and great glaciers slowly made their way southward, grinding and rending as they went, and burying the land under their mountain-like heaps, which sometimes were a mile or more in depth. In North America the glacial ice pushed southward to the 40th degree of north latitude. In Europe it extended to the Alpine region, but failed to reach the countries bordering on the Mediterranean.

The elaborate and minute investigation of the glacial deposits has made it highly probable that there were two glacial eras, two periods in which the ice pushed down far to the south, and that these were separated by a period in which the ice retreated and an age of warmer weather intervened. This is known as the interglacial period. So far as can be positively ascertained, all the authentic relics of man belong to the Glacial Age. They seem first to become numerous in the interglacial period, and continue to increase and become diversified as we descend lower in time. How long ago it was that the sea of ice began its downflow over the earth it is impossible to say. Some place it back six hundred thousand or seven hundred thousand years. Some seek to bring it down to a quite recent date. It is still so uncertain and such a matter of controversy that the utmost we are able definitely to say is that it was very long ago.

While there is no positive proof that men dwelt in Europe before the coming on of the glacial chill, we have no just reason to doubt it. That he lived there during glacial times is unquestionable, and we may be very well assured that a naked tropical animal, destitute of the hairy covering of the other animals, would not have chosen that frozen period to migrate to the north. The fact that he was there during the ice age seems satisfactory evidence that he was there before that age, during the mild climate of late Tertiary times, and that--for a reason which we shall hereafter consider--he was caught there and unable to retreat, and was forced to adapt himself to the new conditions.

During the warm preceding period he probably wandered as a hunter through the European forests. But with the gradual coming on of a wintry chill, as the advance of the ice began, shelter of some kind became necessary, and he sought refuge in caves. From being a forest wanderer he became a troglodyte. Everywhere in southwestern Europe we find traces of this period of man's existence. There is hardly a cave or rock shelter in that region within which he has not left his marks. He made his way to England, which was probably then connected by land with Europe, and dwelt long in its caverns. His period of cave residence, indeed, appears to have been a very extended one. While it continued, deposits many feet in depth gradually accumulated on the floors of the caverns, slowly filling them up. And that, in some cases at least, this cave residence ended a very long time ago, we are assured, for since then a great thickness of stalagmite, which is deposited with extreme slowness, has spread over the lower cave deposits and sealed them in.

It is in these caves that we find, not only the rude stone spearheads, scrapers, hammers, etc., the bone awls, borers, and other implements of palaeolithic man, but the bones of man himself. And it is significant of his primitive condition that these earliest relics indicate a man of a very low grade of development, mentally far above the ape, it is true, but mentally and physically much below modern man.

The most ape-like of those human remains is the famous Neanderthal skull, found in 1856 in a limestone cavern of the Neanderthal Valley, between D?sseldorf and Elberfeld, in Rhenish Prussia. The relics discovered consist of the brain cap, two femori, two humeri, and other fragments. The fragment of the skull attracted wide attention by its bestial aspect, it presenting a low, narrow and receding forehead, and an enormous thickness of the bony ridges over the eyes, like that seen in the gorilla. This skull, which was associated with remains of the cave-bear, hyena, and rhinoceros, is, with one exception, the most ape-like human relic yet found. Yet its cranial capacity is far above that of the highest apes, and is assimilated with that of Hottentot and Polynesian skulls.

It has been maintained that this is a pathological specimen, and does not represent normal man. But this theory has been disproved by the fact that other skulls of similar cranial characters are now known, indicating that the Neanderthal cranium represents a type of man, not an abnormal individual. In the Spy Cavern, in the province of Namur, Belgium, there were found, in 1886, two nearly perfect skeletons of a man and a woman, both of them with very prominent eye ridges, low, retreating foreheads, and large orbits. This was strikingly the case with the woman. The lower jaws in both were heavy, while the woman was almost destitute of a chin--a marked ape-like characteristic. The tibia was shorter than in any known race and stouter than in most. Its curious feature was the articulation with the femur, which was such that to maintain the equilibrium the head and body must have been thrown forward, as is the case in the anthropoid apes.

In the cave of Naulette, near Dinant, Belgium, has been found the lower jaw of a man of decidedly ape-like aspect. Its prognathism or protrusion is extreme, and the canine teeth were very strong, while the molars were evidently large and increased in size backward, a non-human characteristic. At La Denise, in the upper Loire, France, have been found the frontal bones of a man like the Neanderthal man in type, the forehead being depressed and retreating, and the superciliary ridges large and thick. Several other skulls of this general type are known, but the above will suffice as examples.

Remains of palaeolithic man of considerably higher type are not wanting. In the rock shelter of Cro-Magnon, France, were found the bones of three men, one woman, and one child, of more advanced character. These, however, are of late date and may have been early neolithic. At Engis, near Li?ge, Belgium, a deeply buried skull, associated with many remains of extinct animals, has been dug up, which is by no means ape-like in character. A still superior example of palaeolithic man is the skeleton found in a cavern at Mentone, east of Nice, France, which represents a man six feet in height, with rather large head, high forehead, and very large facial angle . The cave contained bones of extinct animals, but no trace of the reindeer.

There is no occasion to speak here of the many remains of neolithic man that have been exhumed. Sparse in the early part of the age of polished stone weapons, they gradually became numerous, and merged into the human remains of late prehistoric times. The American continent is not without its relics of ancient man, the most famous of which is the Calaveras skull, found in 1886 in the auriferous gravels of Calaveras County, California, at an extraordinary depth. The miners, in excavating a shaft, passed through several layers of lava and gravel, forming a total thickness of seventy-nine feet of lava and a considerable thickness of gravel, making nearly one hundred and thirty feet in all. At this depth a skull was found imbedded in the gravel, which, if authentic, must have been overflowed by several successive thick outpours of lava in the ancient volcanic era of that region. As its authenticity is, however, still a matter of controversy, nothing further need here be said about it.

The femur very closely resembles that of a human being of average size, and its shape, articulating surface, and other characters show clearly that the animal stood habitually erect. The principal significance lies in the tooth and the cranium. The former is like that of the chimpanzee in shape, but less rugose on its grinding surface. It seems to lie between the ape and the human type of dentition. The cranium has a low, depressed arch, with a very narrow frontal region and highly developed superciliary ridges. The cranial capacity was apparently about one thousand, that of man being from thirteen hundred to fourteen hundred. It is therefore said to be "the lowest human cranium yet described, very nearly as much below the Neanderthal as that is below the normal European."

We have here given a short review of a long story. The evidences of man's former existence upon the earth are multitudinous, but any extended consideration of them is aside from our purpose, which is merely to show that the proofs of man's descent found in his physical structure are strengthened by evidences which he has left strewn behind him in his long march down the ages. Only a single conclusion can be drawn from these vestiges of man excavated from caves and gravels, namely, that they indicate a gradual and steady progression upward from a very low condition, while they nowhere give evidence of the traditional fall of man.

This is certainly the case with the relics of human workmanship. They begin with the rudest chipped stones, and very slowly improve in form and finish and become more varied, as we move upward in our search. The ground and polished stones follow, and the variety of implements considerably increases, until at length the age of metal, with its developed industries, is reached. The only seeming evidence of superior intellect to be found in this gradual progress is that of the drawings and carvings left us by one group of palaeolithic men. But the actual mental development indicated by these becomes problematical when we consider that similar drawings are made to-day by the Bushmen of South Africa, a race of men occupying a very low mental stage. From this fact we may fairly conclude that the possession of a simple graphic art does not necessarily indicate any considerable intellectual advance.

If we consider the remains of man himself, the few bones which mark his early pathway through time, a similar conclusion must be drawn. Beginning with Pithecanthropus, which science is yet in doubt whether to class with the apes or with men, we pass upward to the bestial Neanderthal man and his fellows of the same low type. Of the sparse remains of palaeolithic man that exist, the most are of this degraded type. The cranial capacity is usually not small. They had the full brain development of man. But this simply assimilates them with the low races of existing savages, many of whom have not developed the simple art of chipping stone to form weapons and yet have brains of normal human weight.

In truth, the influences under which the development of the brain took place were not what we now call intellectual. Developing man used his mental powers actively in his dealings with the hostile forces of surrounding nature, and nearly all the forces of evolution were brought to bear upon the organ of the mind, the body remaining practically unchanged. His senses became acute, his cunning and alertness high, his use of weapons skilful, but his field of mental exercise was still the outer world, and the inner world of thought remained in its embryo state. The more recent development of the mind has been in its intellectual powers, while its physical aptitudes have somewhat declined. This has not yielded any marked increase in the dimensions of the brain, but it may have had a decided effect upon the proportion of its parts, the regions of the cerebrum devoted to intellectual activity probably increasing at the expense of the motor and sensory regions, while the convolutions may have grown considerably more complicated.

FROM QUADRUPED TO BIPED

In the question which now confronts us, that of the evolution of man from the lower world of animals, it is necessary first to state in what particulars he has evolved, what are the conditions which distinguish him from the lower animals. Four marked distinctions may be named: his erect attitude, with the freeing of the fore limbs from use as agents in locomotion; his employment of natural objects, instead of his bodily organs, as tools and weapons; his development of vocal language; and his great mental superiority, with the general use of the mind in his dealings with nature.

In none of these particulars does man stand quite alone; in all of them an affinity with the lower animals exists. Steps of progress in these directions have been made by many animals, though none of them have gained any considerable advance. In man's strikingly developed social habit and organization he has no close counterpart among the vertebrates, but several among the insects. And it is of much interest to find that in the highest field of man's progress, his employment of the mind in his dealings with nature, he is chiefly emulated by such lowly-organized creatures as the ants and the bees.

We do not need to look far among the lower animals for the species which come nearest to man in structure and which seem to have immediately preceded him in the line of descent. We find these forms in the monkeys or apes, and especially in their highest representatives, the anthropoid apes. These possess in a partial degree all the special characteristics of man. They are social in habit; some of them are semi-erect in posture, and their fore limbs partly freed from use in locomotion; they possess some imperfect means of vocal communication; they employ the mind to some extent in place of the body; in short, they seem arrested forms on the road from brute to man, signal-posts on the highway of evolution. In physical organization their approach to man is singularly close. In anatomy man and the higher apes are in most respects counterparts of each other. The principal anatomical distinction has been considered to be in the foot, which from the opposable character of the great toe was classed by Cuvier with the hand, the apes being named Quadrumana, or four-handed, and man Bimana, or two-handed. Fuller research has shown that this distinction does not exist, the foot of the ape being found to agree far more closely with the foot than with the hand of man. Estimated according to use, the hand is, in the whole order, the special prehensile organ; the foot, however prehensile it may be, is predominantly a walking organ. And the opposability of the great toe is approached in some men, who have great mobility in this organ, and can use it for grasping.

In regard to the brain, the organ of the mind, the difference between the higher apes and man is almost solely one of comparative size, the lower intelligence of the apes being indicated by the smaller size of their brains. The largest ape brain is scarcely half the size of the smallest human brain. But anatomically they are nearly identical. All the structural features of the brain are common to both, and the details are largely filled out in the anthropoid apes, the convolutions being all present and the pattern of arrangement the same. The brain of the orang may be said to be like that of man in all respects except size and the greater symmetry of its convolutions, which are less complicated with minor convolutions than in man. In truth, the difference between the brains of man and the orang is almost insignificant as compared with the difference between those of the orang and the lowest apes. Mr. E. W. Taylor, who has recently made an exhaustive study of the minute anatomy of the brain of the chimpanzee, remarks, "The similarity between the brain of the anthropoid apes and of man is one of the most singular and interesting facts of which we have knowledge."

In any attempt, then, to consider the origin of man from the point of view of evolution, we are irresistibly drawn to the ape tribe as the next lower link in the long chain of development, and are led to consider the characteristics of the apes as the intermediate stage between the quadruped and the biped, the bridge crossing this great gulf in organic development. This is by no means to suggest that some one of the existing anthropoid apes is the direct ancestor of man. Such an idea has never been entertained by scientists. These animals cannot even fairly be considered as brothers to man's ancestor, but must be looked upon as more or less distant cousins, with a physical organization less favorable to high development than that of man. Man's ancestry lies much farther back in time, and his progenitor must have been constituted differently from any of the existing large apes.

In the ape tribe we are able to trace nearly every step by which the gulf between quadruped and biped has been crossed, from the quadrupedal baboon to the nearly erect gibbon. And in seeking to follow this development through its successive stages, the first point to be considered is how the apes gained their special power of grasping, that characteristic to which they undoubtedly owe the partial freedom of their hands and their tendency to assume the erect attitude.

The most distinguishing characteristic of the apes and of the nearly related lemurs has not hitherto been definitely pointed out. This is that they form the only group of strictly arboreal animals. The tree is not alone their native habitat, but they are specially adapted to it in their organs of motion, a fact which cannot be affirmed of any other animal group. If we consider, for instance, the squirrels, one of the best-known groups of tree-living animals, we find them to be members of the great order of rodents, whose native habitat is the land surface. Though the squirrels have taken to the trees, there has been no adaptive change in the structure of their limbs and feet. The same may be said of almost all tree-dwellers except the lemurs and apes. The sloth, indeed, is specially adapted in organization to an arboreal residence, but this change is individual, not tribal, this animal being an aberrant form of the ground-dwelling edentata. In the apes and lemurs, on the contrary, the ground-dwellers are the aberrant forms, stray wanderers from the host. Nearly all the species live in trees, to which they are specially adapted by the formation of their feet. It remains to inquire how this deviation in structure arose, what were the steps of development of the grasping foot and hand, the special characteristic of this group.

In considering this question, the first fact to appear is that the apes and lemurs are plantigrade animals. Their natural tendency is to walk on the sole of the foot, a habit which few other tribes of animals possess. Most of the larger animals walk on the knuckles or the toes, and develop claws or hoofs, but the ancestral form of the ape, ages in the past, was doubtless a sole-walking quadruped, its toes apparently provided with nails instead of claws. What the story of this very ancient quadruped was we are quite unable to say. It may, in the exigencies of existence, have come to a parting of the ways; a section of the group, drawn by a love of fruit, developing the climbing habit; the remaining section continuing on the ground and following a separate line of evolution. Perhaps only a single species took to the trees; for it is quite possible for a single form, in a new and advantageous habitat, to vary in time into a great number of species.

Of all this we can know nothing: but of one thing we may feel assured, which is that the plantigrade foot is the only one that could have developed into a grasping organ; such a development being impossible to the digitigrade or the hoofed animals. One can readily see how the habit of walking on the sole might tend to a spreading of the toes, in order to obtain a wider and firmer footing. And it is equally easy to see how a free and wide motion in the great toe would aid in this result. The animal may have been at first light in weight and able to support itself on its unchanged foot, but as it increased in size and weight it would need a firmer grasp, and the final result of spreading its toes for this purpose may well have been the opposable great toe.

It must be borne in mind, in this consideration, that the apes differ from the other tree-dwellers in being destitute of claws. The squirrels, the opossums, and other arboreal animals have sharp claws, by whose aid they can easily cling to the surface of the bark-covered boughs. The nails of the apes are incapable of affording them this service, and it is not easy to perceive how a foot like theirs could become adapted to locomotion in the trees otherwise than by the gaining of mobile action and grasping power in the toes.

The existing habits of the ape tribe lead us to the conclusion that the ancestral animal may have soon begun to seek support from upper limbs. The plantigrade foot is one capable of readily curving into an organ of support, and in the case of the forefoot the toes would tend to spread and gain flexibility of motion, and the first toe to become opposable to the others and yield a more complete grasping power. It does not seem difficult to comprehend, from this point of view, how the feet of a five-toed plantigrade animal may in time have developed into grasping organs, since there would be required only an increased flexibility of the joints, and a wider and fuller movement of the great toes. That such a change took place in this instance the facts appear to indicate, the most simple and probable explanation of the development of the grasping power in the hands and feet of the ape being seemingly that given above.

The relation of the lemurs to the apes is not clearly defined. It may be an ancestral one, or the two animals may represent distinct lines of descent. In the latter case we would have two lines of animal evolution in which the grasping power was gained and adaptation to arboreal life completed. Whatever their relationship, they both possess the opposable thumb as the hall-mark of their arboreal habitat, and whenever found walking on the ground they may be looked upon as estrays from their native place of residence.

Once the grasping power was gained, the first step of change from the quadrupedal to the semi-erect attitude was completed. The process may have begun in the effort to fit the sole of the foot to the rounded surface of boughs; or its first stage may have been in the seizing of overhead branches with the flexible hand; or both influences may have acted simultaneously. We see the result only, we cannot trace the exact process; but we have as an outcome the adoption of a method of locomotion different from that of all other tree-dwellers, the forefoot developing into the hand with its opposable thumb, and the hindfoot gaining a similar grasping power in the toes.

The power of walking on a lower limb and grasping an upper one once attained, a succeeding step in evolution quickly appeared, and one of prime importance to our inquiry. The animal had ceased to be in a full sense a quadruped, while not yet a biped, and a variation in the length of its limbs was almost sure to take place. This is an ordinary result when animals cease to walk on all fours. In the leaping kangaroo and jerboa a shortening of the arms and lengthening of the legs appear. Here the arms are relieved from duty and a double duty is laid on the legs, with the consequence stated. In the ancient dinosaurian reptiles, upright walkers, the same was the case. Those varied from quite small to very large animals, but in all known instances the fore limbs were greatly reduced in size. A similar condition may be seen in the birds, the bones of whose fore-limbs have largely aborted from lack of employment as walking organs.

In the case of the apes and lemurs, while a similar effect has taken place, an interesting difference appears, due to the difference in conditions. In these animals the fore limbs are not freed from duty as organs of locomotion. In many cases, on the contrary, they have an extra duty put upon them, with the result that they have grown longer instead of shorter. Very likely these animals differed considerably in the past, as they do to-day, in the degree of use of their legs and arms. Many of them walk in the quadruped manner, either on the ground or in trees. Others make much use of their hands and arms in grasping and swinging. Great differences in the use of the arms and legs may have arisen in different species. In some, the legs may have been mainly trusted to for support, and the hands used for steadying. In others the arms may have been the chief locomotive organs and the feet have given steadiness. Here the legs may have grown the longer, there the arms, the limbs developing in accordance with their degree of employment. In the lower monkeys and the lemurs, the bones of the pelvis are altogether quadrupedal in character. This is not the case in the higher forms, and in the highest apes the pelvic bones approach those of man.

Highly interesting examples of these varied results may be seen in the existing anthropoid apes. In all of them it would appear that the arm was a prominent factor in locomotion, for in each instance it is longer than the leg,--but it differs in proportional length in every instance. It is shortest in the chimpanzee, somewhat longer in the gorilla, still longer in the orang, and remarkably long in the gibbon. In all these instances the fact that the arms exceed the legs in length indicates that they must have played a large and important part in the work of locomotion, and especially so in the case of the gibbon. It is well known, in fact, that the gibbons progress very largely by the aid of their arms, swinging from limb to limb and from tree to tree with extraordinary strength and facility. The legs lend their aid in this, but the arms are the principal organs of motion, and seem to have developed in length accordingly.

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