Chapter XI: Section VI: Evolution of Man (1)

EVOLUTION OF MAN.

The detailed study of the development (ontogenetic and phylogenetic) of man is so vastly intricate and extensive a subject that it will be impossible in a work of this character to do more than refer to it in brief outline. One of the best and simplest methods to approach the study of such a subject is to acquire some idea of the _development of the frog_.

The fertilized frog’s egg, which is the starting point in the life of a new frog, is deposited in water and hatched by the warmth of spring. After fertilization the egg or cell divides into two cells, these two into four, the four into eight, the eight into sixteen, and so on till a large number of small cells, associated together, is formed (Fig. 10). These cell phases represent different stages in the life of the growing frog. It is thus seen that the frog, in its earliest stages, consists of nothing but many small cells. These cells, through the mysterious powers of heredity, are going to differentiate as development proceeds into the various organs (groups of various kinds of cells) that form the tadpole and finally the frog. For further stages in the development of the egg (oösperm) towards the tadpole, works upon Comparative Embryology should be consulted.

At length the tadpole is hatched from the egg, and then soon swims about in the water (Fig. 17).

The creature that comes from the egg looks nothing whatever like a frog. It has no limbs whatever, and consists mainly of a bulky head and tail. This is the tadpole stage in the development of the frog. It can exist only in water, breathing air therefrom by means of gills. Like the fish, it has a two-chambered heart. At this stage it has no lungs, and the gills consist of an external (Fig. 17, a) and an internal pair. The mouth is small, with only horny toothless jaws, with no tongue. The creature is herbivorous, living on decaying vegetable matter. The vertebræ of the spinal column are bi-concave, as in fishes. The tadpole is essentially a fish, and would be so classed if it did not develop further. An evolving fish does not go beyond this stage. But the developing frog does go beyond this stage to a higher one. As its evolution proceeds through the multiplication and differentiation of the cells that form its body, limbs begin to bud out, first posteriorly (Fig. 17, b) and then anteriorly (Fig. 17, c). The lungs now begin to develop, and the external gills dwindle more and more until they soon disappear, the internal ones persisting for a while longer. The tongue, at this stage, also makes its appearance. The creature now can breathe both air and water. This is the permanent condition of many adult amphibians belonging to a lower order than the mature frog, such as the _siren_, _menobranchus_, etc. The siren in developing also passes through the fish stage, but does not get beyond the siren stage. But the evolving frog does go beyond this stage, for with the growth of the legs the tail dwindles slowly by its gradual absorption (Fig. 17, d). The internal gills now disappear through absorption, and the lungs develop more thoroughly. Great changes take place in the blood-vascular system, the fish-like, two-chambered heart evolving into the three-chambered, amphibian heart. In spite of its dwindling, the tail is still a very conspicuous organ. In this phase of its development the frog can breathe only air, and must frequently come to the surface of the water for that purpose, and soon leaves the water altogether. Now this stage of the creature’s development corresponds to the permanent adult condition of another order of amphibians, which is higher than that to which the siren belongs but lower than the order of the adult frog. This intermediate order has such creatures in it as the _triton_. The triton in developing passes through the fish and siren stages, but does not get higher than the triton stage. But the evolving frog goes even higher than this triton-like condition. Its tail is more and more absorbed until it finally disappears, and then the young but perfect frog appears (Fig. 17, e). During this period the teeth develop and the creature becomes carnivorous, feeding on insects. It is thus seen that the developing frog passes by small gradations from one class (the fish class) to an altogether different and higher class (the amphibian class). When it has evolved to this higher class, it then passes from the lower order (“siren” order) to a higher one (“triton” order), and then to the highest order (“frog” order). The bi-concave vertebræ of the fish-like tadpole have now developed into vertebræ with the cup-and-ball joints of the higher amphibian. It is the same with all the complex organs of the adult frog; they evolve from the much simpler structures of the tadpole.

This study of the frog’s evolution from the fertilized egg is profoundly instructive. It reveals to us, through direct observation, that a creature varies in its form and structure at succeeding intervals of time. These variations diverge more and more, so that specific, generic, and even ordinal and class distinctions are revealed as the development proceeds. Owen, the distinguished comparative anatomist, in speaking of the transmutation of one species into another in the course of geologic history, says, though with a hostile purpose in view, that in the metamorphoses of the amphibians we seem to have such process carried on before our eyes to its extremest extent. Not merely is one specific form changed to another of the same genus; not merely is one generic modification of an order substituted for another, the transmutation is not even limited by passing from one order (Urodela) to another (Anura); it affects a transition from class to class. The fish becomes the frog (amphibian); the aquatic animal changes to the terrestrial one; the water-breather becomes the air-breather; an insect diet is substituted for a vegetable one. And these changes, moreover, proceed gradually, continuously, and without any interruption of active life. Such is the language of Owen in reference to these remarkable transmutations of the developing frog.

The development of the frog is a brief recapitulation, an epitome, through heredity, of the main transmutations of its ancestral forms in geologic time. It is not true that the embryonic phases in the development of a higher form always resemble the adult stages of lower forms. This may or may not be the case; but what always does occur is that the embryonic phases of a higher form resemble the corresponding phases of the lower forms. So far as the frog’s development is concerned, it is very instructive to know that the order of succession of its embryonic forms undoubtedly parallels the order of succession of corresponding forms in past geologic ages. Fishes appeared in the Upper Silurian rocks with amphibian characteristics. In the succeeding Carboniferous Ages the fishes still continued under new forms; but also the lowest forms of amphibians, the most fish-like forms, now appeared. They were somewhat like the sirens, they were perennibranchs. In the next succeeding rocks, the Permian and Triassic, higher, triton-like forms appeared. They were caducibranchs. Finally, in the Tertiary rocks, the highest forms of amphibians are found, such as the frogs.

In order to understand the relation of Ontogeny to Phylogeny, it must be carefully borne in mind that the simple and lowly organized creatures on the globe at the first appearance of life were performing the two great functions that all living creatures perform, viz.: those of nutrition and reproduction. These functions imply that organisms were reacting to environment, and, therefore, undergoing modifications and adaptations; and at the same time the organisms were giving origin to offspring—they were reproducing their kind through heredity. As these simple organisms lived through the ages and became more and more complex by modifications and adaptations to an ever-changing environment, they still evolved their kind in reproduction. Every new adaptation gained by the parent was transmitted by heredity, in the course of time, to the offspring; every form and structure modified in the parent was modified by heredity in the offspring; and every structure lost by the parent was finally lost in the offspring. Just in proportion as the parents, through the ages, became modified, often becoming more complex by the addition of adaptation to adaptation, retaining some structures of their ancestors by heredity (through use) and losing others, eventually, through disuse; so the offspring of these modifying parents became correspondingly modified, and acquired by heredity the modified structures and habits of the parents, while losing other structures in time that the parents had lost. Just as complex _organisms_ of later ages have been evolved from the simpler organisms of earlier ages by the addition of adaptation to adaptation, in an orderly sequence (Phylogeny); so, therefore, the complex _offspring_, while growing, unfold these inherited adaptations in the order of their acquisition. This last process is called Ontogeny or Embryology. Ontogeny is undoubtedly an illustration of the results of Natural Selection’s activity; for, during the phylogeny of the frog throughout the incalculable ages of the past its ancestors undoubtedly assumed innumerable forms and structures which were adaptations to the times and surroundings. But with the advancing time and changing environment, some of the old forms and structures continued useful and were retained, while others became useless and were eliminated by Natural Selection. In addition to the old useful structures that were retained changing environment often modified some of the retained structures and added still other adaptations to these. And so on, throughout the ages, in building up a frog, through geologic embryos, geologic “infants,” geologic “children,” and finally geologic adult frogs, Natural Selection has retained during ontogeny many useful structures in the order of their first appearance, and eliminated innumerable others that became useless. The ontogeny of the frog, which has been built up by its phylogeny, reveals the useful structures that have been retained, and in the order of their appearance; often showing structures that have been lost in the parent, but are not yet quite lost in the embryo, while it fails to show innumerable useless structures that have been lost in the past. This is the reason why we say that the ontogeny of a frog is a brief outline recapitulation of the main points in the phylogeny of the frog, with even some main points occasionally omitted altogether. The geologic ancestors of the frog were the scaffoldings by which it climbed from simple creatures up to its present complex organization; just as the embryological phases at present are the scaffoldings by which a simple, unicellular, fertilized ovum climbs up through heredity to the huge complexity of the multicellular adult frog. What is true of the development of the frog, ontogenetically and phylogenetically, is also true of all living creatures, and is therefore true of =man=.

Man, in his individual development, commences life as a small, microscopic cell—the fertilized ovum—which is only one-fifth of a millimeter in size. His first stage resembles an encysted protozoan animal. As cell-multiplication proceeds he soon gets into the morula stage, which resembles a colony of undifferentiated protozoans. He soon evolves into a stage which may be compared to a colony of protozoans some of the members of which have undergone differentiation. Then comes the gastrula stage, which is distinctly suggestive of a low metazoan, and in which the developing germ assumes fundamental anatomical qualities such as characterize lowly animals like polyps. Then, by gradual transmutations, the vertebrate characteristics appear; but it could not be said at this stage of development, if one did not know, whether one is observing a fish, an amphibian, a reptile, or a mammal. Finally, the developing man passes through his fish and reptile phases and reaches the mammal stage. But as yet it cannot be said to which order the animal belongs. The evolution of the individual continuing, he finally assumes those anatomical characteristics that stamp him as belonging to the order of man.

The theory of evolution, then, teaches that this development of man in the course of a few short months, like the development of the frog, is a very condensed and abbreviated epitome of the evolution of mankind from primitive protozoans during the incalculable ages of the past.

Drummond has prettily written that “the developing human embryo is like a subtle phantasmagoria, a living theater in which a weird transformation scene is being enacted and in which countless strange and uncouth characters take part. Some of these characters are well known to science, some are strangers. As the embryo unfolds, one by one these animal-actors come upon the stage, file past in phantom-like procession, throw off their drapery, and dissolve away into something else. Yet, as they vanish, each leaves behind a vital portion of itself, some original and characteristic memorial, something itself has made or won, that perhaps it alone could make or win,—a bone, a muscle, a ganglion, or a tooth,—to be the inheritance of the race. And it is only after nearly all have played their part and dedicated their gift that a human form, mysteriously compounded of all that has gone before, begins to be discerned as the resultant.”

As has been stated in the introductory part of this book, if all the animals that have ever lived on the globe should be represented by a tree those existing on the earth to-day would be indicated by the topmost twigs and leaves, while the extinct forms would be represented by the trunk and main branches. Just as the leaves, twigs, branches, and trunk of the tree have a common origin, viz., the seed that developed into the tree, so all the different species of animals of the present and the past are the trunk, branches, twigs, and leaves of the “tree of life,” and have had a common origin from a primitive protozoan cell (see Diagram of Development, Fig. 18). Therefore all creatures, living and past, have a more or less blood relationship.

The Diagram of Development will indicate in a very general way the possible track taken by a man as he evolved,—grew higher and higher as the central, straight trunk of the expanding tree of life,—during the geologic ages; and finally appeared as the inflorescence of the topmost branch of this central trunk. It is seen from this scheme that the tree of life commenced in a primitive cell. Without entering into any discussion of the various theories of evolution and epigenesis, we may say that the primitive protozoan contained potentially all the animal forms (each being a cell or group of cells) that have existed on the globe, just as the fertilized egg contains potentially all the tissues and organs (groups of cells) of the adult man.

As the tree of animal life unfolded and expanded—like a germinating seed—from the primitive protozoan, certain of the descendants evolved along the straight and central branch, through the primitive colonial protozoans, on through primitive vermes, and still on through primitive fishes (elasmobranchii), amphibians, reptiles, and on through primitive ornithodelphia (monotremes), and didelphia (marsupials) to a primitive order of monodelphia, viz.: primitive primates. The evolution of man continued through primitive anthropoidea to primitive anthropopithecus. At this point we meet with the common ancestors of the _higher anthropoid apes_ (chimpanzee and gorilla) and _man_.

At each stage of the evolution some of the descendants of the animals of this stage diverged obliquely, modifying the characters they possessed at this stage in a direction that varied more and more from those characters that led on to man. So that all along the central trunk of the tree of animal life collateral branches were given off. The collateral branches given off at each upward stage of evolution represent animals higher in the scale than those that departed from the central trunk lower down. To illustrate what has occurred at each stage in the evolution of man, pause for a moment to consider that phase of progress represented by the primitive reptilia. If we study the anatomy of the specialized reptiles, birds, and monotremes of the present, we will find that they all have many characters in common. These characters are _reptilian_. Each class has its own distinctive specialized peculiarities in addition to its common reptilian characters. The study of the fossils of the rocks shows that in the Jurassic and Cretaceous ages animals existed that were undoubtedly reptiles, but had also very distinct bird characters; also reptiles existed that had distinct monotreme characters. These reptiles came from those of earlier times that were still more generalized. As the ages passed, some of the generalized reptiles (primitive reptiles) lost more and more the reptilian features and gradually assumed more and more distinct bird characters, until finally the highly specialized modern birds (“glorified reptiles”) were evolved as a branch from primitive reptiles. The specialized reptiles of modern times likewise came from the primitive reptiles. In like manner those primitive reptiles that had mammalian (monotreme) characters, by getting into a suitable environment, gradually lost more and more their reptilian characters and assumed with increasing accentuation the characters of primitive monotremes—the lowest of the mammalian class. But observe particularly that the earliest introduced monotremes were not the specialized monotremes on the globe to-day, but generalized, primitive monotremes. These gave origin to the specialized modern monotremes, and also to the generalized primitive marsupials. The evolution of man continued through the primitive marsupials to primitive anthropoidea.

Here we meet with the common, generalized ancestors of man and the monkeys. These creatures contained, potentially at least, _anthropoid_ as well as _pithecoid_ characters. From them were derived the primitive New World monkeys (primitive Platyrrhines) and the primitive Old World monkeys (primitive Catarrhines). Some of the descendants of the primitive Old World monkeys, migrating into an environment which favored particularly the pithecoid characters, eventually developed into the tailed monkeys of the Old World (Cercopithecidæ). Others of their descendants, migrating into a different environment, found conditions that favored the anthropoid characters especially, and by greater and greater use of these, with the diminished use of the pithecoid ones, the characters of the anthropoid apes (primitive Simiidæ and primitive Simiinæ) became clearer and clearer until, in time, primitive anthropopithecus appeared,—a tailless anthropoid ape of the Old World. More than likely this anthropoid ape bore a close resemblance, as Dr. Theodore Gill long since taught, to the modern chimpanzee. If there were any differences they could scarcely have been of even a generic value. This primitive chimpanzee was undoubtedly a quadrupedal, quadrumanous creature leading an arboreal life. His descendants specialized along two distinct but closely related lines. Those that continued to live in trees specialized along the oblique path that led finally to the gorilla on the one hand and the chimpanzee on the other. Those descendants that abandoned the trees and lived on the ground used the feet more and more for purposes of locomotion and less for grasping; while they employed with increasing frequency the hands for grasping exclusively. Associated with these adaptations were many other correlated adaptations, such as the upright posture, an enlarging brain, a change in the character of the face and of the dentition, etc. As man evolved further and further along the central trunk of the tree of life, he discarded, through disuse, many of the characters that are peculiar to the anthropoid apes; and assumed with increasing emphasis, through use, many of the characters that are distinctive of man. He passed through the phases of pithecoid man and pre-palæolithic (primitive) man, until eventually, in palæolithic man, the visage of humanity is clear and unmistakable.

It is extremely interesting to attempt to form some rough picture of primitive man. It may help us to do so if we recall what Darwin has said about the Fuegians, who are among the lowest of savages. He has written that they are men whose very signs and expressions are less intelligible to us than those of the domesticated animals—men who do not possess the instinct of those animals, nor yet appear to boast of human reason, or at least of arts consequent on that reason.

The Fuegians are much nearer to the ape than to a Shakespeare or Sir Isaac Newton. In the words of Clodd, primitive man was doubtless much lower than the lowest Fuegians. “He was a powerful, cunning biped, with keen sense organs (always sharper, in virtue of constant exercise, in the savage than in the civilized man, who supplements them by science), strong instincts, uncontrolled and fitful emotions, small faculty of wonder, and nascent reasoning power; unable to forecast to-morrow or to comprehend yesterday, living from hand to mouth on the wild products of nature, clothed in skin or bark, or daubed with clay, and finding shelter in trees and caves; ignorant of the simplest arts, save to chip a stone missile, and perhaps to produce fire; strong in his need of life and vague sense of right to it and to what he could get, but slowly impelled by common perils and passions to form ties, loose and haphazard at the outset, with his kind, the power of combination with them depending on sounds, signs, and gestures.”

Through the theory of evolution it can readily be understood why the anatomical characters of the anthropoid apes and of man are so very closely alike. They have a common origin, and are blood relations—the one group of animals having specialized from common ancestors in one direction (obliquely), and the other group having specialized in another (straight) direction. (Vid. Diagram of Development.)

Man, in his individual development from a fertilized ovum, comes from a source infinitely lower than the ape. Why, therefore, should he feel such reluctance to believe that he has passed, during geologic ages, through the phase of generalized simian ancestors? Is there not much more of hope in the knowledge that he has risen higher and higher through the æons of the past than in the belief that he was created an innocent and noble character and then fell to utter wretchedness through great temptation? The motto of evolution is Excelsior. For it shows that the human race, through all the incalculable ages of the past, has risen to higher and higher levels,—to nobler and nobler phases of being. His progress in the almost infinite past suggests the hope that he will mount higher and higher towards perfection during the limitless future. Not only may we hope that there will be boundless improvement of the human race, but boundless evolution of each individual human being as well. Evolution’s motto for each individual may also be Excelsior. And, therefore, may we say with some assurance of hope that love, while kissing the pathetic lips of death, need not entertain in vain the splendid hope of immortality. For if there be no immortality of personal consciousness, then the evolution of the cosmos, of man, of the highest mind in man, have no intelligible meaning for us; they are unfathomable enigmas—idiot stories without meaning.

Man, in specializing along certain lines since separating from the ancestral simian stock, has displayed more and more that structure of his skeleton and of the soft parts molded upon it that is best adapted to the needs of the mind resident within him. His bones are not merely the jointed framework of an animal, but a framework adapted to that erect attitude which so befits his intellectual nature. His feet are not the climbing and grasping feet of the ape, but organs for giving firmness to the tread and dignity to the bearing of a creature capable of high thought. The arms and hands are not for strength alone, for these members are much stronger in many a brute; but they also give greater expression and power to the thoughts that come from within. The hands possess such molding of fingers, thumbs, and palms, such delicacy for tactile impressions, and such capacity for nice adjustments, that they are not alone used for feeding the mouth and fighting antagonists; but they also contribute pre-eminently to the desires of a large mind, and are the efficient servants of its promptings. As Dana well says, “The face, with its expressive features, is formed so as to respond not solely to the emotions of pleasure and pain, but to shades of sentiment and interacting sympathies the most varied, high as heaven and low as earth,—ay, lower, in debased human nature; the whole being, body, limbs, and head, with eyes looking, not towards the earth, but beyond an infinite horizon, is a majestic expression of the divine feature in man and of the infinitude of his aspirations.”

But it is well to remember that man’s structure is riddled with evidences that he passed from an ancestral, quadrupedal condition, through the semi-erect to his present upright posture, slowly and laboriously. His erect attitude, geologically speaking, is a very recent accomplishment, and his anatomy, therefore, reveals many imperfect adaptations to his newly acquired posture. These imperfect adaptations are the sources of many grave diseases in mankind. It would require too technical a knowledge of anatomy to explain these imperfect adaptations, and I will therefore simply mention _rupture_ and _uterine displacements_ as due to imperfect adaptations to the upright attitude.

The common origin of man and the ape accounts for many interesting and otherwise inexplicable facts in anatomy. There is, for instance, a muscle that is normally present in the orang-outang known as the Opponens Hallucis. This muscle enables the orang to oppose his big toe to the other toes, just as we can oppose our thumb to the other fingers of our hand. This muscle is absent from the foot of man ordinarily. But occasionally it is found in man, in the dissecting-room, as a rarity—as an anomaly. The question naturally arises, why should this muscle be present normally in the orang and absent normally in man, occurring in the latter only as an abnormality? The theory of evolution gives the only rational answer. The man-like, ape-like generalized ancestors of man and the orang possessed this muscle, which was useful to them in grasping the branches of the trees among which they lived. These ancestors used the feet and hands alike for purposes of grasping (prehension) and locomotion. But those descendants that evolved more and more man-ward used the feet more for purposes of locomotion and less for grasping, while they used the hands more for grasping and less for locomotion, until, finally, man was created—a creature that uses his feet exclusively for locomotion, and the hands entirely for grasping. Through disuse, therefore, the _opponens hallucis_ gradually disappeared in man; so that now it occurs only as a rare abnormality. The hereditary units that make this muscle still lie dormant in most men are usually so weak, through disuse, that they do not develop. Some unusual stimulus occasionally causes the latent hereditary units to develop and makes it appear in man. The same is the case with many other muscles and structures that are normal in the modern anthropoid apes, and only occur as rarities in man. The appearance of those muscles in man are instances of _atavism_, i. e., reversions to conditions that were normal in the ancestors of man and the apes, as they are still normal in the latter.

USELESS SCAFFOLDING LEFT IN THE BODY.

Man, in his post-natal growth, as well as during his embryological development, exhibits reminiscences of his animal ancestry. In the structure and movement of the new-born babe, as well as in the adult frame, we find continuous witnesses to the ancient animal strain.

On the theory that men in bygone ages were closely allied to simian creatures in habit as well as structure; that they led an arboreal life; and that, like the baby-monkeys to-day, the baby-men of other ages clung to their mothers as they climbed among the trees, Dr. Louis Robinson predicted that a =baby’s power for grasping= would likely be found to equal that of a young monkey which had reached a corresponding period of growth. He tested a large number of new-born infants in reference to this power by extending his finger or a cane, to imitate the branch of a tree, and observed how long they would hang there without any other support (Plate XI). He made experiments on about sixty children under a month old. About thirty of the children experimented upon were not over an hour old. Dr. Robinson states that each of the infants, with two exceptions, was able to hang to the finger or cane by its hands, like an acrobat from a horizontal bar, and sustain the whole weight of its body for at least ten seconds. Twelve of the infants, less than an hour old, held on for half a minute before the grasp relaxed; while four of this age held on for one minute. Over fifty of the infants when four days old could continue the grip for half a minute. Three weeks after birth the faculty for holding on reached its maximum, for at this age several succeeded in hanging on for a minute and a half; two held on for over two minutes; and one infant held on over two minutes and a half. One infant that was less than an hour old hung by both hands to Dr. Robinson’s finger for ten seconds, and then deliberately let go with his right hand, as if to seek a better hold, and continued his grasp with the left hand only, for five seconds longer. In none of these experiments did the limbs of the infants hang down in the attitude of the erect position, but the thighs were invariably in the baby-monkey attitude, at right angles to the body. The doctor says that this attitude and the disproportionately large development of the arms compared with the legs give the photographs of the infants a striking resemblance to a well-known picture of the celebrated chimpanzee, Sally, at the Zoölogical Garden in London. In these experiments the infants very seldom gave any sign of distress, and uttered no cry until the grasp began to give way. The fact that the flexor muscles of the forearm of a new-born infant show such remarkable strength while the other parts of the muscular system are so conspicuously weak and flaccid,—that they are able to perform a feat of muscular strength that will tax the powers of many a healthy adult,—can be explained only on the theory of inherited instinct from simian ancestors that lived in trees. This instinct is no longer useful to an infant. It is a vestigial instinct, a useless scaffolding in its life history.

=Club-foot.= There is an ordinary case of malformation in the foot of a child known as club-foot. The most common kind of this deformity is that where the sole is turned inwards and upwards and the heel is raised. Before birth all children pass through this condition as a perfectly normal and natural one, and only gradually outgrow it (evolve beyond it). But some children fail to evolve beyond this condition and have club-feet throughout life, unless relieved by the surgeon. It is a very instructive fact that this particular form of club-foot is the normal condition of the adult gorilla and orang-outang. The foot of every child passes through this gorilla phase, and if it does not develop beyond this phase it retains the simian characters, and we call it an abnormality. In this abnormality the anatomist finds that those bones that enter into the formation of the ankle joint have the pronounced anatomical characters of the adult orang-outang.

=Ribs.= Adult man possesses twelve pairs of ribs. The chimpanzee and gorilla possess fourteen pairs. An older comparative anatomy predicted that in an early embryonic condition man would be found to possess thirteen or fourteen pairs. The prophecy has been verified.

=Hair.= The apes have hair over the entire body. At the sixth month of the embryonic development the human fœtus is thickly covered with a somewhat long, dark hair over all the body, except those parts that are uncovered in the apes, viz.: the palms of the hands and the soles of the feet. This covering of hair is called lanugo. Since it covers all the body except the points noted, it extends, of course, all over the ears, face and forehead. It is usually shed before birth. It is a simian characteristic, and sometimes fails to disappear, but persists and develops greatly. Therefore there are occasionally found such men (“dog-faced men”) as the Russian Jeftichjeff. The Ainos of one of the Japanese Islands also possess this extreme hairiness.

=Vermiform Appendix.= There are a number of vestigial structures in man that are not only useless but even a menace to life. The most striking of the vestigial structures that come under this category is a portion of man’s large intestine which is called the Appendix Vermiformis. This useless structure is a veritable death trap. In some animals, such as the herbivorous ones, the appendix is very large, sometimes longer than the body itself, and is of great use in digestion. But in man it has shrunken to a small rudiment varying from two to six inches in length, which is very liable to a grave form of disease that frequently causes death unless timely treated by the surgeon. In the early embryo the appendix is equal in caliber to the rest of the bowel, but at a certain date ceases to grow _pari passu_ with it. At birth it has become a small rudiment of the large intestine. In the new-born infant the appendix is often of the same size as it is in the adult. This precocity of an organ is always an indication that it was of great importance to the ancestors of the human species.

=Tail.= Man, like the anthropoid apes, has no external tail; but, exactly like them, he has a rudimentary one concealed beneath the skin. The embryos of man and the ape at an early stage of growth possess a very conspicuous tail, which is even longer than the limbs. In the embryo of man even the muscles for wagging the tail are still found. In the adult man these muscles are represented, normally, by bands of fibrous tissue. In the dissecting-room one occasionally finds these muscles well developed in the adult man. Man and the anthropoid apes have descended from more primitive simian ancestors that possessed tails.

=Hearing.= Prominent among vestigial structures, though less easy for beginners to understand, are those that point to piscine ancestors and which, therefore, smack of the sea. Embryology points indubitably to the fact that the ancient, geologic progenitors of man once lived a marine life. In the history of the globe there was a time when all the animals lived in the sea. Land animals appeared as later creations. Man, in evolving from the primitive protozoan, passed through a marine-worm phase and finally, through the ages, attained to the fish stage. The chief characteristic of a fish is its apparatus for breathing the air dissolved in the water. This apparatus consists of gills—strong bars with delicate, highly vascular, fringe-like curtains hung on them, and through which the blood is continually circulating. The circulating blood throws out its impure gases and takes in from the water the pure air, thus breathing. These bars or arches are five or seven in number in many fishes. Slits extend from the surface of the fish between the bars to the throat, so that the water which the fish takes into its mouth is forced out between the bars, thus bathing the delicate curtains on them by which air is breathed from the water. Sometimes the slits between the bars are open and unprotected, as in the sharks; but in the modern fishes (teleosts) they are protected by a lid (operculum). If these slits did not exist in the neck all fishes would quickly perish. They are of so great use to the fish that Natural Selection has taken exceptional care in perfecting their mechanism.

It is one of the most interesting facts in evolution that these slits in the fish’s neck are still represented in the neck of man. One of the most prominent features in every mammalian embryo is the presence of four clefts of the old gill-slits. So persistent are these characters that children are occasionally born with persistent fissures leading to the throat, so that milk, when swallowed, will come out on the neck through an opening. Thus we have a persistent piscine characteristic as an abnormality in the child.

When the fish-like ancestors of man left the water the elaborate breathing apparatus was no longer needed for respiration. Nature, in creating new adaptations for the land animal, did not discard the elaborate gill apparatus that had been evolved through the ages; but utilized this old apparatus for the new adaptations. Nature is exceedingly economical and does not discard old organs when they can be molded for new functions.

In the course of ages, through minute gradations, the first gill-slit and portions of its adjacent bars were molded for purposes of hearing. In man there are two passages leading to the drum or middle ear; one is the external auditory canal (the opening which is seen in what is popularly called the ear), and the other is a canal leading from the throat to the middle ear. In the adult these two channels are partitioned off from each other by the membrane of the drum. These canals are the counterpart or homologues of the spiracle associated in the shark with the first gill-slit. The external ear is developed by the coalescence of six rounded tubercles appearing in the bars or branchial arches that surround the first gill-slit. In the course of ages the remaining gill-bars (branchial arches) were also modified for special uses.

In relation with the external ear of man are found rudimentary muscles that are no longer useful and ordinarily are not under the control of the will. These muscles are the exact counterparts of well developed functional muscles found in great numbers of the lower animals. They are present in man as vestigial structures, because he is descended from animals in whom these muscles were well developed and functional.

The anatomy of man reveals so many additional vestigial structures that we may look upon him as a museum of obsolete anatomies; he is an old curiosity shop containing many discarded tools, many outgrown and aborted organs. The lower animals as well as man contain so many useless (vestigial) structures among their useful organs, and they are so significant of a former state of things in which they were useful, that anatomists are willing to stake the theory of evolution upon their presence alone. Evolution explains a multitude of other facts about man that are inexplicable on any other theory.

In addition to pointing out the possible track along which man has evolved from a primitive protozoan it would be interesting as well as exceedingly instructive to trace the development of each structure and organ in his body. But the subject is a vast one, and cannot be presented here even in briefest outline. Yet it will be very valuable to trace the unfolding of one organ, and that the highest, as a sample of what occurs with every part of the body. I refer to the _development of the brain_.

THE DEVELOPMENT OF THE BRAIN IN PHYLOGENY AND ONTOGENY.

Fig. 19 represents the brain of an average bony fish. It consists of six swellings in a line, one before the other. Beginning from the end towards the spinal cord, they are designated as follows, viz.: a single median lobe, the medulla (Metencephalon), m; then in front of this is another single median lobe, the cerebellum (Epencephalon), cb; then the optic lobes (Mesencephalon), right and left, ol; then the thalami (Thalamencephalon), which are small and hidden from view by the encroachment of the two adjacent segments; then the cerebrum (Prosencephalon), cr; then, finally, the olfactory lobes (Rhinencephalon), of. In this fish the largest of the segments are the optic lobes, ol.

The reptile’s brain (Fig. 20) shows similar parts with the same serial arrangement. The reptile is a higher creature, a more intelligent animal, than the fish; and in consonance with this fact the cerebrum, cr, is the larger and more dominant part of the brain instead of the optic lobes, ol.

In the marsupial (Fig. 21), a more intelligent animal still, the cerebrum, cr, has grown so large that it extends backwards and partially covers the optic lobes. It is to be observed that in the marsupial the cerebellum, cb (like the cerebrum, cr), has evolved to a higher phase. It consists of a median lobe, cb, which is larger than the median cerebellum of the lower creatures mentioned, and of two lateral lobes, one on either side, which have been acquired in the course of evolution. The median lobe, the homologue of the single, median cerebellum of lower animals, is larger than the lateral ones. The cerebellum of the marsupial has its surface increased by fissures, while that of the fish and reptile is smooth. The fissured cerebellum is a higher evolution than the smooth ones. In the groups of animals referred to so far the cerebrum is smooth and the olfactory lobes are still in front, though much encroached upon in the marsupial by the enlarging cerebrum. In those animals still higher in the scale of life, such as the prosimiæ (Lemurs), the cerebrum has reached yet larger proportions and complexity, and has grown still farther backwards towards the medulla, so that it hides from view a considerable portion of the cerebellum (Fig. 22); it has also grown forward, thus concealing largely the olfactory lobes. The cerebrum is no longer smooth, but has a number of simple fissures and convolutions (the higher animals have numerous complex fissures and convolutions). The lateral lobes of the cerebellum have increased relatively more than the central lobe, and the whole organ has advanced in complexity of fissures. In the higher simiæ (monkeys and apes) the cerebrum has grown so far backwards as to almost completely cover the cerebellum and medulla, and its convolutions have become much more numerous and complex. The cerebellum has also grown greatly, and its lateral lobes are now larger and more complex than the central lobe.

Finally, in man (Plate XII), the whole brain has grown so enormously that it is three times larger than the brain of the highest simian creature. The cerebrum, especially, has increased enormously in size. It has grown not only backwards (overlapping cerebellum), upwards, and downwards on the sides, it has grown so far forwards as not only to cover the olfactory lobes, but also to project far beyond them. The cerebellum has also increased in size and complexity, especially the lateral lobes. The ideal vertical section (Fig. 23) shows diagrammatically in one figure all these stages in the evolution of the human brain through the geologic ages.

Modified from Le Conte.]

It is a very interesting and instructive fact that in the development of the human brain from the fertilized ovum these same stages, which are permanent conditions in the zoölogical (taxonomic) series, are passed through by it as transient stages.

One of the earliest conditions of the human brain is that in which it presents three swellings in a serial arrangement. They are known from behind, forwards as hindbrain, midbrain, and forebrain. For our purposes it is sufficiently accurate to say that the =fœtal brain=, in developing from this early condition to a later and higher condition, differentiates the hindbrain into the _medulla_ (Fig. 24, m) and the _cerebellum_ (cb); the midbrain becomes the _optic lobes_ (ol); and the forebrain differentiates into the _thalami_ (th) and the _cerebrum_ (cr). A little later the cerebrum buds forth the olfactory lobes (of), so that the human brain will consist of six fundamental segments,—one behind the other. This is the _fish stage_ in the growth of the human brain. (Compare Fig. 24 with Fig. 19.)

FIG. 25.—Dorsal view of the brain of a human fœtus of about seven weeks. Representing the reptilian phase in the ontogeny of the human brain. cr, cerebrum; th, thalami; ol, optic lobes; cb, cerebellum; m, medulla.

FIG. 26.—Side view of the brain of a human fœtus of about three months. Representing the marsupial phase in the ontogeny of the human brain. cr, cerebrum; ol, optic lobes; cb, cerebellum; m, medulla. The thalami are completely, and the optic lobes partially, covered by the greatly enlarged cerebrum.]

As development proceeds the most conspicuous growth of the brain is observed in connection with the cerebrum and cerebellum. The cerebrum particularly grows relatively and actually larger and larger, but does not yet cover any portion of the optic lobes. This is the _reptile stage_, represented in Fig. 25. The cerebrum, continuing to grow, finally covers the front portion of the optic lobes. This is the _marsupial stage_, and is shown in Figs. 26 and 27. Growing further, it soon covers a greater or less portion of the cerebellum. These are the prosimian (Lemur) and simian stages. Finally it grows so far backward as to completely cover the cerebellum, and so far forward as to project much beyond the olfactory lobes. This is the human stage (Plate XII).

In the study of the phylogeny of the brain we found that the cerebrum in fish, reptile, and lower marsupial is smooth. In the primitive primates (Lemuroidea) it is convoluted; in the simiidæ it is still more convoluted, while in man it reaches the climax of complexity in the size, number, and sinuosity of its convolutions. The object of these convolutions is to increase the surface of the cortex of the brain, the cortex being the seat of psychic phenomena. Other things being equal, the greater the amount of cortex the greater is the intelligence. During its embryonic development the human cerebrum passes also through the stage of smoothness to a convoluted condition; then through stages of increasing complexity of convolutions. Simultaneously with this advance of cerebral organization, there is an unfolding of increasing intelligence.

The cerebellum presides over the co-ordination of the muscular movements of the body. It also, like the cerebrum, passes through the fish, reptile, marsupial, lemur, and simian phases. At first it consists only of the median lobe; then the lateral lobes appear, at first small in size, but getting larger and larger until they greatly surpass in bulk the more primitive median portion. At first the cerebellum is smooth, but as it develops, its fissures become greater and greater, thus increasing its cortex, which presides over the muscular movements. With the developing cerebellum are associated increasing powers of muscular co-ordination; increasing delicacy and complexity of muscular movements. Thus the ontogeny of the brain recapitulates its phylogeny.

THE BRAIN AND PSYCHIC PHENOMENA.

The bearing of the theory of evolution on ideas of creation, design, and kindred subjects may briefly be referred to in connection with our views about the relation of psychic phenomena to the brain.

The study of the human brain in its anatomical, physiological and psychological aspects has brought great thinkers, in all ages, into the presence of phenomena that still baffle some of the most subtle philosophers. Here we meet with such realities as self-consciousness, perception, intellection and volition. Are these material entities of such character that we may say they are exclusively products of the activity of the brain, as the secretion of bile is the product of the activity of the liver, as Cabanis taught? To us it seems clear that such is not the case. One cannot take the specific gravity of love or hate, of fear or joy, as one can that of bile; one cannot find a single physical characteristic in any psychic phenomenon. The most physical of all mental processes, viz., perception, has its psychological as well as its physiological phases. The instreaming, through the senses, of impressions from the external world, may be traced by the physiologist along the different nerves of the body to the cortex cells of the brain. All the phenomena that occur at and between these cortex cells and the peripheral endings of the nerves may be formulated in terms of molecular physics. But not so with that consciousness of these impressions which we call perception. In the light of the present knowledge that we possess, it seems to us that the only induction which the physiologist is warranted in making is that, associated with molecular movements in the brain is the phenomenon of perception. This leaves the field clear for each thinker to speculate about the subject in such manner as seems to him most rational. And the history of philosophy shows that many thinkers have formulated theories upon the subject that range in character from the materialism of Büchner to the idealism of Berkeley.

The view which teaches that psychic phenomena are correlated with the physiological phenomena of the brain; that these phenomena have undergone parallel[17] evolution, and “are as inseparable as are the two sides of a sheet of paper” (Dr. Carus), appeals to us as the most comprehensible one and at the same time the one most in consonance with the known phenomena. We accept the view, then, that there is a mind immanent in the brain.[18] The mind is conscious of its personality; conscious of the external world through the innumerable perceptions which reach it through the nervous system; conscious of its power to build its percepts into concepts, and to reason about them; conscious of its power of choice and of causing motion; and conscious of itself, therefore, as a cause in producing effects; and, finally, it is conscious of its power to adapt means to an end,—in short, it knows that it has the power to design.

These facts are at the bottom of much of the philosophy of the present and the past. The untutored savage, knowing that his personality can cause motion, and beholding moving objects in nature, instinctively made the induction that all these objects had personalities behind them. He saw a spirit in his own voice that came back to him as an echo from the rocks; he saw a personality in his shadow; he saw personalities in falling stones, in running brooks, in waving foliage; he beheld them in the raging tempest, in the thunder and the lightning, as well as in the blazing sun and the twinkling stars; he saw spirits in the dead that came back to him in dreams. In short, he recognized a separate personality in every isolated phenomenon in nature. The child talking to its doll, petting it, rebuking it, or whipping it; Xerxes castigating the ocean for wrecking his ships, are illustrations of the strong human tendency to project (or eject)[19] personalities into the inanimate objects of nature. This natural, but lowly, phase of culture and philosophy is known as _Fetichism_.

As encephalic and psychic evolution advanced; as men, with wider knowledge and broadening experience, ascertained the laws that govern the isolated phenomena of nature, the separate beings in every distinct object and occurrence vanished from thought; but they still beheld a separate personality in every great department of nature. The Romans, for instance, saw Neptune as God of the Ocean, Pluto as God of the lower world, Jupiter as God of the Heavens, and so on. This phase of culture and philosophy, and therefore of religion, is _Polytheism_.

In the two phases of culture now briefly outlined the personalities were grossly anthropomorphic. They were like human beings, capricious, revengeful, subject to flattery, good and evil, and were therefore to be placated and cajoled by sacrifices and offerings.

Psychic evolution continuing, there appeared from time to time great thinkers who saw one “Infinite Personality” behind the cosmos.[20] This “personality” is still in every phenomenon, though no longer as a separate soul, but only as the separate manifestation of the Soul of the Universe. This is _Monotheism_, a phase of culture which marks the culmination of philosophy and religion through psychic evolution.

Our knowledge of the universe can be only a shadowy symbol of the reality. The poverty of language is so great and the power of thought so limited that the most subtle philosopher can form only an empty symbol of the cosmic soul. The most ethereal symbols of the greatest thinkers are necessarily incomplete in detail and anthropomorphic, in order to be intelligible. The history of philosophy and religion shows that with the evolution of mind and the acquisition of knowledge, the anthropomorphic ideas of the soul of the cosmos become less crudely coarse and vulgar, until the most elevated and refined ideas of monotheism are reached. But even these refined ideas about the soul of the universe are necessarily anthropomorphic, though in a vastly less degree than in the lower phases of culture. One’s conceptions of this all-pervading soul immanent in the universe are therefore profoundly modified by one’s kind and degree of culture. In the words of Professor Fiske, the great scholar and subtle thinker who has delved in the deepest mines of philosophy and come forth weary and heavy-laden with their boasted treasures, has framed a very different conception of God from that entertained by the priest at the confessional.

A study of the human brain, then, and the soul resident therein prepares us to believe that the cosmos has a soul (God) immanent in it. We can readily grasp the idea that the soul of the cosmos may be self-conscious, wills, thinks, acts, and designs.