The long series of animal forms which we must regard as the ancestors of our race has been confined within narrower and narrower circles as our phylogenetic inquiry has progressed. The great majority of known animals do not fall in the line of our ancestry, and even within the vertebrate stem only a small number are found to do so. In the most advanced class of the stem, the mammals, there are only a few families that belong directly to our genealogical tree. The most important of these are the apes and their predecessors, the half-apes, and the earliest Placentals (Prochoriata).

The Placentals (also called Choriata, Monodelphia, Eutheria or Epitheria) are distinguished from the lower mammals we have just considered, the Monotremes and Marsupials, by a number of striking peculiarities. Man has all these distinctive features; that is a very significant fact. We may, on the ground of the most careful comparative-anatomical and ontogenetic research, formulate the thesis: “Man is in every respect a true Placental.” He has all the characteristics of structure and development that distinguish the Placentals from the two lower divisions of the mammals, and, in fact, from all other animals. Among these characteristics we must especially notice the more advanced development of the brain. The fore-brain or cerebrum especially is much more developed in them than in the lower animals. The corpus callosum, which forms a sort of wide bridge connecting the two hemispheres of the cerebrum, is only fully formed in the Placentals; it is very rudimentary in the Marsupials and Monotremes. It is true that the lowest Placentals are not far removed from the Marsupials in cerebral development; but within the placental group we can trace an unbroken gradation of progressive development of the brain, rising gradually from this lowest stage up to the elaborate psychic organ of the apes and man. The human soul—a physiological function of the brain—is in reality only a more advanced ape-soul.

The mammary glands of the Placentals are provided with teats like those of the Marsupials; but we never find in the Placentals the pouch in which the latter carry and suckle their young. Nor have they the marsupial bones in the ventral wall at the anterior border of the pelvis, which the Marsupials have in common with the Monotremes, and which are formed by a partial ossification of the sinews of the inner oblique abdominal muscle. There are merely a few insignificant remnants of them in some of the Carnivora. The Placentals are also generally without the hook-shaped process at the angle of the lower jaw which is found in the Marsupials.

However, the feature that characterises the Placentals above all others, and that has given its name to the whole sub-class, is the formation of the placenta. We have already considered the formation and significance of this remarkable embryonic organ when we traced the development of the chorion and the allantois in the human embryo (pp.165–9) The urinary sac or the allantois, the curious vesicle that grows out of the hind part of the gut, has essentially the same structure and function in the human embryo as in that of all the other Amniotes (cf. Figs. 194–6). There is a quite secondary difference, on which great stress has wrongly been laid, in the fact that in man and the higher apes the original cavity of the allantois quickly degenerates, and the rudiment of it sticks out as a solid projection from the primitive gut. The thin wall of the allantois consists of the same two layers or membranes as the wall of the gut—the gut-gland layer within and the gut-fibre layer without. In the gut-fibre layer of the allantois there are large blood-vessels, which serve for the nutrition, and especially the respiration, of the embryo—the umbilical vessels (p. 170).In the reptiles and birds the allantois enlarges into a spacious sac, which encloses the embryo with the amnion, and does not combine with the outer foetal membrane (the chorion). This is the case also with the lowest mammals, the oviparous Monotremes and most of the Marsupials. It is only in some of the later Marsupials (Peramelida) and all the Placentals that the allantois develops into the distinctive and remarkable structure that we call the placenta.

The placenta is formed by the branches of the blood-vessels in the wall of the allantois growing into the hollow ectodermic tufts (villi) of the chorion, which run into corresponding depressions in the mucous membrane of the womb. The latter also is richly permeated with blood-vessels which bring the mother’s blood to the embryo. As the partition in the villi between the maternal blood-vessels and those of the foetus is extremely thin, there is a direct exchange of fluid between the two, and this is of the greatest importance in the nutrition of the young mammal. It is true that the maternal vessels do not entirely pass into the foetal vessels, so that the two kinds of blood are simply mixed. But the partition between them is so thin that the nutritive fluid easily transudes through it. By means of this transudation or diosmosis the exchange of fluids takes place without difficulty. The larger the embryo is in the placentals, and the longer it remains in the womb, the more necessary it is to have special structures to meet its great consumption of food.

In this respect there is a very conspicuous difference between the lower and higher mammals. In the Marsupials, in which the embryo is only a comparatively short time in the womb and is born in a very immature condition, the vascular arrangements in the yelk-sac and the allantois suffice for its nutrition, as we find them in the Monotremes, birds, and reptiles. But in the Placentals, where gestation lasts a long time, and the embryo reaches its full development under the protection of its enveloping membranes, there has to be a new mechanism for the direct supply of a large quantity of food, and this is admirably met by the formation of the placenta.

Branches of the blood-vessels penetrate into the chorion-villi from within, starting from the gut-fibre layer of the allantois, and bringing the blood of the foetus through the umbilical vessels (Fig. 273 chz). On the other hand, a thick network of blood-vessels develops in the mucous membrane that clothes the inner surface of the womb, especially in the region of the depressions into which the chorion-villi penetrate (plu). This network of arteries contains maternal blood, brought by the uterine vessels. As the connective tissue between the enlarged capillaries of the uterus disappears, wide cavities filled with maternal blood appear, and into these the chorion-villi of the embryo penetrate. The sum of these vessels of both kinds, that are so intimately correlated at this point, together with the connective and enveloping tissue, is the placenta. The placenta consists, therefore, properly speaking, of two different though intimately connected parts—the foetal placenta (Fig. 273 chz) within and the maternal or uterine placenta (plu) without. The latter is made up of the mucous coat of the uterus and its blood-vessels, the former of the tufted chorion and the umbilical vessels of the embryo (cf. Fig. 196).

The manner in which these two kinds of vessels combine in the placenta, and the structure, form, and size of it, differ a good deal in the various Placentals; to some extent they give us valuable data for the natural classification, and therefore the phylogeny, of the whole of this sub-class. On the ground of these differences we divide it into two principal sections; the lower Placentals or Indecidua, and the higher Placentals or Deciduata.

To the Indecidua belong three important groups of mammals: the Lemurs (ProsimiÆ), the Ungulates (tapirs, horses, pigs, ruminants, etc.), and the Cetacea (dolphins and whales). In these Indecidua the villi are distributed over the whole surface of the chorion (or its greater part) either singly or in groups. They are only loosely connected with the mucous coat of the uterus, so that the whole foetal membrane with its villi can be easily withdrawn from the uterine depressions like a hand from a glove. There is no real coalescence of the two placentas at any part of the surface of contact. Hence at birth the foetal placenta alone comes away; the uterine placenta is not torn away with it.

The formation of the placenta is very different in the second and higher section of the Placentals, the Deciduata. Here again the whole surface of the chorion is thickly covered with the villi in the beginning. But they afterwards disappear from one part of the surface, and grow proportionately thicker on the other part. We thus get a differentiation between the smooth chorion (chorion laeve, Fig. 273 chl) and the thickly-tufted chorion (chorion frondosum, Fig. 273 chf). The former has only a few small villi or none at all; the latter is thickly covered with large and well-developed villi; this alone now constitutes the placenta. In the great majority of the Deciduata the placenta has the same shape as in man >(Figs. 197 and 200)—namely a thick, circular disk like a cake; so we find in the Insectivora, Chiroptera, Rodents, and Apes. This discoplacenta lies on one side of the chorion. But in the Sarcotheria (both the Carnivora and the seals, Pinnipedia) and in the elephant and several other Deciduates we find a zonoplacenta; in these the rich mass of villi runs like a girdle round the middle of the ellipsoid chorion, the two poles of it being free from them.

Still more characteristic of the Deciduates is the peculiar and very intimate connection between the chorion frondosum and the corresponding part of the mucous coat of the womb, which we must regard as a real coalescence of the two. The villi of the chorion push their branches into the blood-filled tissues of the coat of the uterus, and the vessels of each loop together so intimately that it is no longer possible to separate the foetal from the maternal placenta; they form henceforth a compact and apparently simple placenta. In consequence of this coalescence, a whole piece of the lining of the womb comes away at birth with the foetal membrane that is interlaced with it. This piece is called the “falling-away” membrane (decidua). It is also called the serous (spongy) membrane, because it is pierced like a sieve or sponge. All the higher Placentals that have this decidua are classed together as the “Deciduates.” The tearing away of the decidua at birth naturally causes the mother to lose a quantity of blood, which does not happen in the Indecidua. The last part of the uterine coat has to be repaired by a new growth after birth in the Deciduates. (Cf. Figs. 199, 200, pp. 168–70.)

In the various orders of the Deciduates, the placenta differs considerably both in outer form and internal structure. The extensive investigations of the last ten years have shown that there is more variation in these respects among the higher mammals than was formerly supposed. The physiological work of this important embryonic organ, the nutrition of the foetus during its long sojourn in the womb, is accomplished in the various groups of the Placentals by very different and sometimes very elaborate structures. They have lately been fully described by Hans Strahl.

The phylogeny of the placenta has become more intelligible from the fact that we have found a number of transitional forms of it. Some of the Marsupials (Perameles) have the beginning of a placenta. In some of the Lemurs (Tarsius) a discoid placenta with decidua is developed.

While these important results of comparative embryology have been throwing further light on the close blood-relationship of man and the anthropoid apes in the last few years (p. 172), the great advance of paleontology has at the same time been affording us a deeper insight into the stem-history of the Placental group. In the seventh chapter of my Systematic Phylogeny of the Vertebrates I advanced the hypothesis that the Placentals form a single stem with many branches, which has been evolved from an older group of the Marsupials (Prodidelphia). The four great legions of the Placentals—Rodents, Ungulates, Carnassia, and Primates—are sharply separated to-day by important features of organisation. But if we consider their extinct ancestors of the Tertiary period, the differences gradually disappear, the deeper we go in the Cenozoic deposits; in the end we find that they vanish altogether. The primitive stem-forms of the Rodents (Esthonychida), the Ungulates (Chondylarthra), the Carnassia (Ictopsida), and the Primates (Lemuravida) are so closely related at the beginning of the Tertiary period that we might group them together as different families of one order, the Proplacentals (Mallotheria or Prochoriata).

Hence the great majority of the Placentals have no direct and close relationship to man, but only the legion of the Primates. This is now generally divided into three orders—the half-apes (ProsimiÆ), apes (SimiÆ), and man (Anthropi). The lemurs or half-apes are the stem-group, descending from the older Mallotheria of the Cretaceous period. From them the apes were evolved in the Tertiary period, and man was formed from these towards its close.

The Lemurs (ProsimiÆ) have few living representatives. But they are very interesting, and are the last survivors of a once extensive group. We find many fossil remains of them in the older Tertiary deposits of Europe and North America, in the Eocene and Miocene. We distinguish two sub-orders, the fossil Lemuravida and the modern Lemurogona. The earliest and most primitive forms of the Lemuravida are the Pachylemurs (Hypopsodina); they come next to the earliest Placentals (Prochoriata), and have the typical full dentition, with forty-four teeth (3.1.4.3. over 3.1.4.3.). The Necrolemurs (Adapida, Fig. 274) have only forty teeth, and have lost an incisor in each jaw (2.1.4.3. over 2.1.4.3.). The dentition is still further reduced in the Lemurogona (Autolemures), which usually have only thirty-six teeth (2.1.3.3. over 2.1.3.3.). These living survivors are scattered far over the southern part of the Old World. Most of the species live in Madagascar, some in the Sunda Islands, others on the mainland of Asia and Africa. They are gloomy and melancholic animals; they live a quiet life, climbing trees, and eating fruit and insects. They are of different kinds. Some are closely related to the Marsupials (especially the opossum). Others (Macrotarsi) are nearer to the Insectivora, others again (Chiromys) to the Rodents. Some of the lemurs (Brachytarsi) approach closely to the true apes. The numerous fossil remains of half-apes and apes that have been recently found in the Tertiary deposits justify us in thinking that man’s ancestors were represented by several different species during this long period. Some of these were almost as big as men, such as the diluvial lemurogonon Megaladapis of Madagascar.

Next to the lemurs come the true apes (SimiÆ), the twenty-sixth stage in our ancestry. It has been beyond question for some time now that the apes approach nearest to man in every respect of all the animals. Just as the lowest apes come close to the lemurs, so the highest come next to man. When we carefully study the comparative anatomy of the apes and man, we can trace a gradual and uninterrupted advance in the organisation of the ape up to the purely human frame, and, after impartial examination of the “ape problem” that has been discussed of late years with such passionate interest, we come infallibly to the important conclusion, first formulated by Huxley in 1863: “Whatever systems of organs we take, the comparison of their modifications in the series of apes leads to the same result: that the anatomic differences that separate man from the gorilla and chimpanzee are not as great as those that separate the gorilla from the lower apes.” Translated into phylogenetic language, this “pithecometra-law,” formulated in such masterly fashion by Huxley, is quite equivalent to the popular saying: “Man is descended from the apes.”

In the very first exposition of his profound natural classification (1735) LinnÉ placed the anthropoid mammals at the head of the animal kingdom, with three genera: man, the ape, and the sloth. He afterwards called them the “Primates”—the “lords” of the animal world; he then also separated the lemur from the true ape, and rejected the sloth. Later zoologists divided the order of Primates. First the Gottingen anatomist, Blumenbach, founded a special order for man, which he called Bimana (“two-handed”); in a second order he united the apes and lemurs under the name of Quadrumana (“four-handed”); and a third order was formed of the distantly-related Chiroptera (bats, etc.). The separation of the Bimana and Quadrumana was retained by Cuvier and most of the subsequent zoologists. It seems to be extremely important, but, as a matter of fact, it is totally wrong. This was first shown in 1863 by Huxley, in his famous Man’s Place in Nature. On the strength of careful comparative anatomical research he proved that the apes are just as truly “two-handed” as man; or, if we prefer to reverse it, that man is as truly four-handed as the ape. He showed convincingly that the ideas of hand and foot had been wrongly defined, and had been improperly based on physiological instead of morphological grounds. The circumstance that we oppose the thumb to the other four fingers in our hand, and so can grasp things, seemed to be a special distinction of the hand in contrast to the foot, in which the corresponding great toe cannot be opposed in this way to the others. But the apes can grasp with the hind-foot as well as the fore, and so were regarded as quadrumanous. However, the inability to grasp that we find in the foot of civilised man is a consequence of the habit of clothing it with tight coverings for thousands of years. Many of the bare-footed lower races of men, especially among the negroes, use the foot very freely in the same way as the hand. As a result of early habit and continued practice, they can grasp with the foot (in climbing trees, for instance) just as well as with the hand. Even new-born infants of our own race can grasp very strongly with the great toe, and hold a spoon with it as firmly as with the hand. Hence the physiological distinction between hand and foot can neither be pressed very far, nor has it a scientific basis. We must look to morphological characters.

As a matter of fact, it is possible to draw such a sharp morphological distinction—a distinction based on anatomic structure—between the fore and hind extremity. In the formation both of the bony skeleton and of the muscles that are connected with the hand and foot before and behind there are material and constant differences; and these are found both in man and the ape. For instance, the number and arrangement of the smaller bones of the hand and foot are quite different. There are similar constant differences in the muscles. The hind extremity always has three muscles (a short flexor muscle, a short extensor muscle, and a long calf-muscle) that are not found in the fore extremity. The arrangement of the muscles also is different before and behind. These characteristic differences between the fore and hind extremities are found in man as well as the ape. There can be no doubt, therefore, that the ape’s foot deserves that name just as much as the human foot does, and that all true apes are just as “bimanous” as man. The common distinction of the apes as “quadrumanous” is altogether wrong morphologically.

But it may be asked whether, quite apart from this, we can find any other features that distinguish man more sharply from the ape than the various species of apes are distinguished from each other. Huxley gave so complete and demonstrative a reply to this question that the opposition still raised on many sides is absolutely without foundation. On the ground of careful comparative anatomical research, Huxley proved that in all morphological respects the differences between the highest and lowest apes are greater than the corresponding differences between the highest apes and man. He thus restored LinnÉ’s order of the Primates (excluding the bats), and divided it into three sub-orders, the first composed of the half-apes (LemuridÆ), the second of the true apes (SimiadÆ), the third of men (AnthropidÆ).

But, as we wish to proceed quite consistently and impartially on the laws of systematic logic, we may, on the strength of Huxley’s own law, go a good deal farther in this division. We are justified in going at least one important step farther, and assigning man his natural place within one of the sections of the order of apes. All the features that characterise this group of apes are found in man, and not found in the other apes. We do not seem to be justified, therefore, in founding for man a special order distinct from the apes.

The order of the true apes (SimiÆ or Pitheca)—excluding the lemurs—has long been divided into two principal groups, which also differ in their geographical distribution. One group (Hesperopitheca, or western apes) live in America. The other group, to which man belongs, are the Eopitheca or eastern apes; they are found in Asia and Africa, and were formerly in Europe. All the eastern apes agree with man in the features that are chiefly used in zoological classification to distinguish between the two simian groups, especially in the dentition. The objection might be raised that the teeth are too subordinate an organ physiologically for us to lay stress on them in so important a question. But there is a good reason for it; it is with perfect justice that zoologists have for more than a century paid particular attention to the teeth in the systematic division and arrangement of the orders of mammals. The number, form, and arrangement of the teeth are much more faithfully inherited in the various orders than most other characters.

Hence the form of dentition in man is very important. In the fully developed condition we have thirty-two teeth; of these eight are incisors, four canine, and twenty molars. The eight incisors, in the middle of the jaws, have certain characteristic differences above and below. In the upper jaw the inner incisors are larger than the outer; in the lower jaw the inner are the smaller. Next to these, at each side of both jaws, is a canine (or “eye tooth”), which is larger than the incisors. Sometimes it is very prominent in man, as it is in most apes and many of the other mammals, and forms a sort of tusk. Next to this there are five molars above and below on each side, the first two of which (the “pre-molars”) are small, have only one root, and are included in the change of teeth; the three back ones are much larger, have two roots, and only come with the second teeth. The apes of the Old World, or all the living or fossil apes of Asia, Africa, and Europe, have the same dentition as man.

On the other hand, all the American apes have an additional pre-molar in each half of the jaw. They have six molars above and below on each side, or thirty-six teeth altogether. This characteristic difference between the eastern and western apes has been so faithfully inherited that it is very instructive for us. It is true that there seems to be an exception in the case of a small family of South American apes. The small silky apes (Arctopitheca or HapalidÆ), which include the tamarin (Midas) and the brush-monkey (Jacchus), have only five molars in each half of the jaw (instead of six), and so seem to be nearer to the eastern apes. But it is found, on closer examination, that they have three premolars, like all the western apes, and that only the last molar has been lost. Hence the apparent exception really confirms the above distinction.

Of the other features in which the two groups of apes differ, the structure of the nose is particularly instructive and conspicuous. All the eastern apes have the same type of nose as man—a comparatively narrow partition between the two halves, so that the nostrils run downwards. In some of them the nose protrudes as far as in man, and has the same characteristic structure. We have already alluded to the curious long-nosed apes, which have a long, finely-curved nose. Most of the eastern apes have, it is true, rather flat noses, like, for instance, the white-nosed monkey (Fig. 276); but the nasal partition is thin and narrow in them all. The American apes have a different type of nose. The partition is very broad and thick at the bottom, and the wings of the nostrils are not developed, so that they point outwards instead of downwards. This difference in the form of the nose is so constantly inherited in both groups that the apes of the New World are called “flat-nosed” (PlatyrrhinÆ), and those of the Old World “narrow-nosed” (CatarrhinÆ). The bony passage of the ear (at the bottom of which is the tympanum) is short and wide in all the Platyrrhines, but long and narrow in all the Catarrhines; and in man this difference also is significant.

This division of the apes into Platyrrhines and Catarrhines, on the ground of the above hereditary features, is now generally admitted in zoology, and receives strong support from the geographical distribution of the two groups in the east and west. It follows at once, as regards the phylogeny of the apes, that two divergent lines proceeded from the common stem-form of the ape-order in the early Tertiary period, one of which spread over the Old, the other over the New, World. It is certain that all the Platyrrhines come of one stock, and also all the Catarrhines; but the former are phylogenetically older, and must be regarded as the stem-group of the latter.

What can we deduce from this with regard to our own genealogy? Man has just the same characters, the same form of dentition, auditory passage, and nose, as all the Catarrhines; in this he radically differs from the Platyrrhines. We are thus forced to assign him a position among the eastern apes in the order of Primates, or at least place him alongside of them. But it follows that man is a direct blood relative of the apes of the Old World, and can be traced to a common stem-form together with all the Catarrhines. In his whole organisation and in his origin man is a true Catarrhine; he originated in the Old World from an unknown, extinct group of the eastern apes. The apes of the New World, or the Platyrrhines, form a divergent branch of our genealogical tree, and this is only distantly related at its root to the human race. We must assume, of course, that the earliest Eocene apes had the full dentition of the Platyrrhines; hence we may regard this stem-group as a special stage (the twenty-sixth) in our ancestry, and deduce from it (as the twenty-seventh stage) the earliest Catarrhines.

We have now reduced the circle of our nearest relatives to the small and comparatively scanty group that is represented by the sub-order of the Catarrhines; and we are in a position to answer the question of man’s place in this sub-order, and say whether we can deduce anything further from this position as to our immediate ancestors. In answering this question the comprehensive and able studies that Huxley gives of the comparative anatomy of man and the various Catarrhines in his Man’s Place in Nature are of great assistance to us. It is quite clear from these that the differences between man and the highest Catarrhines (gorilla, chimpanzee, and orang) are in every respect slighter than the corresponding differences between the highest and the lowest Catarrhines (white-nosed monkey, macaco, baboon, etc.). In fact, within the small group of the tail-less anthropoid apes the differences between the various genera are not less than the differences between them and man. This is seen by a glance at the skeletons that Huxley has put together (Figs. 278–282). Whether we take the skull or the vertebral column or the ribs or the fore or hind limbs, or whether we extend the comparison to the muscles, blood-vessels, brain, placenta, etc., we always reach the same result on impartial examination—that man is not more different from the other Catarrhines than the extreme forms of them (for instance, the gorilla and baboon) differ from each other. We may now, therefore, complete the Huxleian law we have already quoted with the following thesis: “Whatever system of organs we take, a comparison of their modifications in the series of Catarrhines always leads to the same conclusion; the anatomic differences that separate man from the most advanced Catarrhines (orang, gorilla, chimpanzee) are not as great as those that separate the latter from the lowest Catarrhines (white-nosed monkey, macaco, baboon).”

We must, therefore, consider the descent of man from other Catarrhines to be fully proved. Whatever further information on the comparative anatomy and ontogeny of the living Catarrhines we may obtain in the future, it cannot possibly disturb this conclusion. Naturally, our Catarrhine ancestors must have passed through a long series of different forms before the human type was produced. The chief advances that effected this “creation of man,” or his differentiation from the nearest related Catarrhines, were: the adoption of the erect posture and the consequent greater differentiation of the fore and hind limbs, the evolution of articulate speech and its organ, the larynx, and the further development of the brain and its function, the soul; sexual selection had a great influence in this, as Darwin showed in his famous work.

With an eye to these advances we can distinguish at least four important stages in our simian ancestry, which represent prominent points in the historical process of the making of man. We may take, after the Lemurs, the earliest and lowest Platyrrhines of South America, with thirty-six teeth, as the twenty-sixth stage of our genealogy; they were developed from the Lemurs by a peculiar modification of the brain, teeth, nose, and fingers. From these Eocene stem-apes were formed the earliest Catarrhines or eastern apes, with the human dentition (thirty-two teeth), by modification of the nose, lengthening of the bony channel of the ear, and the loss of four pre-molars. These oldest stem-forms of the whole Catarrhine group were still thickly coated with hair, and had long tails—baboons (Cynopitheca) or tailed apes (Menocerca, Fig. 276). They lived during the Tertiary period, and are found fossilised in the Miocene. Of the actual tailed apes perhaps the nearest to them are the Semnopitheci.

If we take these Semnopitheci as the twenty-seventh stage in our ancestry, we may put next to them, as the twenty-eighth, the tail-less anthropoid apes. This name is given to the most advanced and man-like of the existing Catarrhines. They were developed from the other Catarrhines by losing the tail and part of the hair, and by a higher development of the brain, which found expression in the enormous growth of the skull. Of this remarkable family there are only a few genera to-day, and we have already dealt with them (Chapter XV)—the gibbon (Hylobates, Fig. 203) and orang (Satyrus, Figs. 204, 205) in South-Eastern Asia and the Archipelago; and the chimpanzee (Anthropithecus, Figs. 206, 207) and gorilla (Gorilla, Fig. 208) in Equatorial Africa.

The great interest that every thoughtful man takes in these nearest relatives of ours has found expression recently in a fairly large literature. The most distinguished of these works for impartial treatment of the question of affinity is Robert Hartmann’s little work on The Anthropoid Apes. Hartmann divides the primate order into two families: (1) Primarii (man and the anthropoid apes); and (2) SimianÆ (true apes, Catarrhines and Platyrrhines). Professor Klaatsch, of Heidelberg, has advanced a different view in his interesting and richly illustrated work on The Origin and Development of the Human Race. This is a substantial supplement to my Anthropogeny, in so far as it gives the chief results of modern research on the early history of man and civilisation. But when Klaatsch declares the descent of man from the apes to be “irrational, narrow-minded, and false,” in the belief that we are thinking of some living species of ape, we must remind him that no competent scientist has ever held so narrow a view. All of us look merely—in the sense of Lamarck and Darwin—to the original unity (admitted by Klaatsch) of the primate stem. This common descent of all the Primates (men, apes, and lemurs) from one primitive stem-form, from which the most far-reaching conclusions follow for the whole of anthropology and philosophy, is admitted by Klaatsch as well as by myself and all other competent zoologists who accept the theory of evolution in general. He says explicitly (p. 172): “The three anthropoid apes—gorilla, chimpanzee, and orang—seem to be branches from a common root, and this was not far from that of the gibbon and man.” That is in the main the opinion that I have maintained (especially against Virchow) in a number of works ever since 1866. The hypothetical common ancestor of all the Primates, which must have lived in the earliest Tertiary period (more probably in the Cretaceous), was called by me Archiprimus; Klaatsch now calls it Primatoid. Dubois has proposed the appropriate name of Prothylobates for the common and much younger stem-form of the anthropomorpha (man and the anthropoid apes). The actual Hylobates is nearer to it than the other three existing anthropoids. None of these can be said to be absolutely the most man-like. The gorilla comes next to man in the structure of the hand and foot, the chimpanzee in the chief features of the skull, the orang in brain development, and the gibbon in the formation of the chest. None of these existing anthropoid apes is among the direct ancestors of our race; they are scattered survivors of an ancient branch of the Catarrhines, from which the human race developed in a particular direction.

Although man is directly connected with this anthropoid family and originates from it, we may assign an important intermediate form between the Prothylobates and him (the twenty-ninth stage in our ancestry), the ape-men (Pithecanthropi). I gave this name in the History of Creation to the “speechless primitive men” (Alali), which were men in the ordinary sense as far as the general structure is concerned (especially in the differentiation of the limbs), but lacked one of the chief human characteristics, articulate speech and the higher intelligence that goes with it, and so had a less developed brain. The phylogenetic hypothesis of the organisation of this “ape-man” which I then advanced was brilliantly confirmed twenty-four years afterwards by the famous discovery of the fossil Pithecanthropus erectus by Eugen Dubois (then military surgeon in Java, afterwards professor at Amsterdam). In 1892 he found at Trinil, in the residency of Madiun in Java, in Pliocene deposits, certain remains of a large and very man-like ape (roof of the skull, femur, and teeth), which he described as “an erect ape-man” and a survivor of a “stem-form of man” (Fig. 283). Naturally, the Pithecanthropus excited the liveliest interest, as the long-sought transitional form between man and the ape: we seemed to have found “the missing link.” There were very interesting scientific discussions of it at the last three International Congresses of Zoology (Leyden, 1895, Cambridge, 1898, and Berlin, 1901). I took an active part in the discussion at Cambridge, and may refer the reader to the paper I read there on “The Present Position of Our Knowledge of the Origin of Man” (translated by Dr. Gadow with the title of The Last Link).

An extensive and valuable literature has grown up in the last ten years on the Pithecanthropus and the pithecoid theory connected with it. A number of distinguished anthropologists, anatomists, paleontologists, and phylogenists have taken part in the controversy, and made use of the important data furnished by the new science of pre-historic research. Hermann Klaatsch has given a good summary of them, with many fine illustrations, in the above-mentioned work. I refer the reader to it as a valuable supplement to the present work, especially as I cannot go any further here into these anthropological and pre-historic questions. I will only repeat that I think he is wrong in the attitude of hostility that he affects to take up with regard to my own views on the descent of man from the apes.

The most powerful opponent of the pithecoid theory—and the theory of evolution in general—during the last thirty years (until his death in September, 1902) was the famous Berlin anatomist, Rudolf Virchow. In the speeches which he delivered every year at various congresses and meetings on this question, he was never tired of attacking the hated “ape theory.” His constant categorical position was: “It is quite certain that man does not descend from the ape or any other animal.” This has been repeated incessantly by opponents of the theory, especially theologians and philosophers. In the inaugural speech that he delivered in 1894 at the Anthropological Congress at Vienna, he said that “man might just as well have descended from a sheep or an elephant as from an ape.” Absurd expressions like this only show that the famous pathological anatomist, who did so much for medicine in the establishment of cellular pathology, had not the requisite attainments in comparative anatomy and ontogeny, systematic zoology and paleontology, for sound judgment in the province of anthropology. The Strassburg anatomist, Gustav Schwalbe, deserved great praise for having the moral courage to oppose this dogmatic and ungrounded teaching of Virchow, and showing its untenability. The recent admirable works of Schwalbe on the Pithecanthropus, the earliest races of men, and the Neanderthal skull (1897–1901) will supply any candid and judicious reader with the empirical material with which he can convince himself of the baselessness of the erroneous dogmas of Virchow and his clerical friends (J. Ranke, J. BumÜller, etc.).

As the Pithecanthropus walked erect, and his brain (judging from the capacity of his skull, Fig. 283) was midway between the lowest men and the anthropoid apes, we must assume that the next great step in the advance from the Pithecanthropus to man was the further development of human speech and reason.

Comparative philology has recently shown that human speech is polyphyletic in origin; that we must distinguish several (probably many) different primitive tongues that were developed independently. The evolution of language also teaches us (both from its ontogeny in the child and its phylogeny in the race) that human speech proper was only gradually developed after the rest of the body had attained its characteristic form. It is probable that language was not evolved until after the dispersal of the various species and races of men, and this probably took place at the commencement of the Quaternary or Diluvial period. The speechless ape-men or Alali certainly existed towards the end of the Tertiary period, during the Pliocene, possibly even the Miocene, period.

The third, and last, stage of our animal ancestry is the true or speaking man (Homo), who was gradually evolved from the preceding stage by the advance of animal language into articulate human speech. As to the time and place of this real “creation of man” we can only express tentative opinions. It was probably during the Diluvial period in the hotter zone of the Old World, either on the mainland in tropical Africa or Asia or on an earlier continent (Lemuria—now sunk below the waves of the Indian Ocean), which stretched from East Africa (Madagascar, Abyssinia) to East Asia (Sunda Islands, Further India). I have given fully in my History of Creation, (chapter xxviii) the weighty reasons for claiming this descent of man from the anthropoid eastern apes, and shown how we may conceive the spread of the various races from this “Paradise” over the whole earth. I have also dealt fully with the relations of the various races and species of men to each other.

SYNOPSIS OF THE CHIEF SECTIONS OF OUR STEM-HISTORY

First Stage: The Protists

Man’s ancestors are unicellular protozoa, originally unnucleated Monera like the Chromacea, structureless green particles of plasm; afterwards real nucleated cells (first plasmodomous Protophyta, like the Palmella; then plasmophagous Protozoa, like the Amoeba).

Second Stage: The BlastÆads

Man’s ancestors are round coenobia or colonies of Protozoa; they consist of a close association of many homogeneous cells, and thus are individuals of the second order. They resemble the round cell-communities of the MagospherÆ and Volvocina, equivalent to the ontogenetic blastula: hollow globules, the wall of which consists of a single layer of ciliated cells (blastoderm).

Third Stage: The GastrÆads

Man’s ancestors are GastrÆads, like the simplest of the actual Metazoa (Prophysema, Olynthus, Hydra, Pemmatodiscus). Their body consists merely of a primitive gut, the wall of which is made up of the two primary germinal layers.

Fourth Stage: The Platodes

Man’s ancestors have substantially the organisation of simple Platodes (at first like the cryptocoelic Platodaria, later like the rhabdocoelic Turbellaria). The leaf-shaped bilateral-symmetrical body has only one gut-opening, and develops the first trace of a nervous centre from the ectoderm in the middle line of the back (Figs. 239, 240).

Fifth Stage: The Vermalia

Man’s ancestors have substantially the organisation of unarticulated Vermalia, at first Gastrotricha (Ichthydina), afterwards Frontonia (Nemertina, Enteropneusta). Four secondary germinal layers develop, two middle layers arising between the limiting layers (coeloma). The dorsal ectoderm forms the vertical plate, acroganglion (Fig. 243).

Sixth Stage: The Prochordonia

Man’s ancestors have substantially the organisation of a simple unarticulated Chordonium (Copelata and Ascidia-larvÆ). The unsegmented chorda develops between the dorsal medullary tube and the ventral gut-tube. The simple coelom-pouches divide by a frontal septum into two on each side; the dorsal pouch (episomite) forms a muscle-plate; the ventral pouch (hyposomite) forms a gonad. Head-gut with gill-clefts.

Seventh Stage: The Acrania

Man’s ancestors are skull-less Vertebrates, like the Amphioxus. The body is a series of metamera, as several of the primitive segments are developed. The head contains in the ventral half the branchial gut, the trunk the hepatic gut. The medullary tube is still simple. No skull, jaws, or limbs.

Eighth Stage: The Cyclostoma

Man’s ancestors are jaw-less Craniotes (like the Myxinoida and Petromyzonta). The number of metamera increases. The fore-end of the medullary tube expands into a vesicle and forms the brain, which soon divides into five cerebral vesicles. In the sides of it appear the three higher sense-organs: nose, eyes, and auditory vesicles. No jaws, limbs, or floating bladder.

Ninth Stage: The Ichthyoda

Man’s ancestors are fish-like Craniotes: (1) Primitive fishes (Selachii); (2) plated fishes (Ganoida); (3) amphibian fishes (Dipneusta); (4) mailed amphibia (Stegocephala). The ancestors of this series develop two pairs of limbs: a pair of fore (breast-fins) and of hind (belly-fins) legs. The gill-arches are formed between the gill-clefts: the first pair form the maxillary arches (the upper and lower jaws). The floating bladder (lung) and pancreas grow out of the gut.

Tenth Stage: The Amniotes

Man’s ancestors are Amniotes or gill-less Vertebrates: (1) Primitive Amniotes (Proreptilia); (2) Sauromammals; (3) Primitive Mammals (Monotremes); (4) Marsupials; (5) Lemurs (ProsimiÆ); (6) Western apes (PlatyrrhinÆ); (7) Eastern apes (CatarrhinÆ): at first tailed Cynopitheca; then tail-less anthropoids; later speechless ape-men (Alali); finally speaking man. The ancestors of these Amniotes develop an amnion and allantois, and gradually assume the mammal, and finally the specifically human, form.