The Nature of Man: Studies in Optimistic Philosophy

Relationship of the human species with anthropoid apes — Analogies in- the dentition, in the organisation of the limbs and of the brain — Resemblance of the vermiform appendage of man and anthropoids — Analogy between the placenta and foetus of man and anthropoid apes — Blood relation- ship of man and monkeys shown by serums and pre- cipitates— Transmutation of species — Sudden transition from monkey to man — J. Inaudi, the calculator, as an example of the sudden appearance of characters in the human species — Rudimentary organs in man — Proportion of progressive and retrogressive organs in the organisation of man

To understand human nature it is necessary first to give an account of the origin of man. This question has pre- occupied mankind for ages, and for a long time it was believed that a solution of the problem was to be found in religious dogmas. Man was regarded as being of super- natural origin, the result of a special creation. Scientific criticism has now shown that there are no grounds for such a conclusion. Nearly half a century ago Darwin applied to man his discovery of the principle of natural selection, and of the part played by that in the origin and transmutation of species. Soon after the publication of the " Origin of Species," attention was given to the special case of man.

In 1863 Huxley * gave an admirable review of the pro- blem in his work on " Man's Place in Nature." He brought forward arguments of the highest scientific validity in support of the thesis that man is descended from animals, and that he is a mammal most nearly related to monkeys, and among these to the anthropoid apes. In spite of this masterly exposition, there are still persons of high intel- ligence and superior education who declare that science has not yet answered the question as to whence he came, and that the theory of evolution will never provide an answer.f Close examination of the structure of man has proved, in the most definite fashion, the existence of a near kinship with the higher monkeys, or anthropoids. When the chim- panzee and the ourang-outang were discovered, comparison became inevitable, and many naturalists, including the great Linnaeus, saw that the human race must find its place in classification near the anthropoids.

Now that all the details of the human organisation have been studied, and the anatomical structures of man and large monkeys without tails have been compared, bone with bone and muscle with muscle, a truly astonishing analogy between these organisms is made manifest, an analogy apparent in every detail. It is known that in the natural history of mammals the teeth play an important part as a means of determining differences and relationships. The dentition of man bears a very great resemblance to that of anthropoids. Every one knows the milk teeth and the permanent teeth of man. The anthropoid apes bear in this respect an astonishing likeness to man. The number (thirty-two in the adult), the form and general arrangement

* Republished, with other essays, as " Man's Place in Nature," Macmillan, London, 1894. of the crown, are identical in man and anthropoid apes. The differences are to be found only in minor details, such as the exact shape and relative dimensions and the number of cusps. It can be said in a general way that in the anthro- poid apes the teeth are more strongly developed than in man. The canines are much longer and the roots of the pre-molars are more complex in the gorilla than in man.

But the fact must not be lost sight of, that ail these differ- ences are less pronounced than those which exist between the dentition of anthropoid apes and that of all other monkeys. Even in the cynocephalous monkeys, those that most nearly approach the anthropoids, the teeth exhibit marked differences. Thus, the forms of the upper molars are quite different in the baboon and in the gorilla. The canines are longer, and the pre-molars and molars are still more complex in the baboon.

In the monkeys of the New World, the dentition differs still more from that of man and anthropoids. Instead of thirty-two teeth, they possess thirty-six in the adult con- dition. The number of pre-molars is twelve instead of eight. The general form and the crowns of the molars are very different from those of anthropoid apes. These considerations led Huxley to conclude that " it is obvious that, greatly as the dentition of the highest ape differs from that of man, it differs far more widely from that of the lower and lowest apes." *

Another character which shows that anthropoids are nearer man than other monkeys is furnished by the ana- tomy of the sacrum. In monkeys as a whole the sacrum is composed of three, or rarely four, vertebrae, while in anthropoid apes it contains five, that is to say just as many as in man. The whole skeleton, and particularly the skull of man, and the higher monkeys, present certainly some marked differ- ences ; but here again the differences are less than those between the anthropoid apes and other monkeys. As regards the osteology the proposition laid down by Huxley is just. " So that, for the skull, no less than for the skeleton in general, the proposition holds good, that the differences between man and the gorilla are of smaller value than those between the gorilla and some other apes." *

The believers in the doctrine that the human species is essentially distinct from all the known monkeys have laid great stress on the difference between the foot of man and that of anthropoid apes. This difference cannot be denied. Man assumes the direct posture habitually, while monkeys, even the highest of them, walk on two legs only occasion ally. There has followed from this a greater development of the feet in monkeys. Yet this difference ought not to be exaggerated. It has been sought to prove that monkeys are " quadrumanous," and that their hind legs terminate in " hind-hands." But it is clearly shown that in all sssen- tial respects the hinder limb of the gorilla terminates in as true a foot as that of man.f " The hind limb of the gorilla, therefore, ends in a true foot, with a very movable great toe. It is a prehensile foot, indeed, but is in no sense a hand ; it is a foot which differs from that of man not in any fundamental character, but in mere proportions, in the degree of mobility, and in the secondary arrangement of its parts." J

In all these cases the argument is confirmed, "that be the differences between the hand and foot of man and those of the gorilla what they may, the differences between those of the gorilla and those of the lower apes are much greater."* The comparison of muscles and of other internal organs leads to the same conclusion ; the differences between monkeys a;e more varied and greater than those between **>*£•'•*-* distinguished zoologists, amongst them Owen in particular, have insisted on the absence in all monkeys of certain parts of the brain peculiarly characteristic of man. Such are the posterior lobe, the posterior cornu, and the lesser hippocampus. Controversy on this topic has been animated ; but, ultimately, the opinion of Owen did not triumph, and now it is unanimously accepted that the parts of the brain in question are " precisely those structures which are the most marked cerebral characters common to man with the apes. They are among the most dis- tinctly simian peculiarities which the human organism exhibits. " f

As regards the brain, the differences between man and anthropoid apes are certainly less marked than those that exist between the higher and lower monkeys. The digestive tract affords another argument in favour of the affinity of anthropoid apes to man. The human FlG. 6. — Caecum ?nd vermiform appendage of iran (after Ewald). FlG. 7. — Caecum aiid \eriiiifonn appendage of the chimpanzee (from a preparation in the Paris Museum of Natural History).

caecum is furnished with the very remarkable and strange vermiform appendage which often is the cause of a grave and prevalent illness known as appendicitis. Now, it is quite remarkable that this organ is practically identical with the vermiform appendage of anthropoid apes. A glance at the accompany- ing figures (6 and 7) will convince the reader of this. Yet none of the other monkeys present any such resemblance with man. It is not surpris- ing, in the face of resemblances so numerous, that forty years' science has proclaimed the exist- ence of a close affinity between man and the anthropoid apes. The view has become an established doctrine, now that no single fact has been brought against it. Since the theory was enunciated we have learned much regarding the natural history of these apes. Generally, when a theory is false, a new set of facts overthrows it. Attempts may be made to trim the new facts to the existing theory, but such attempts are doomed to failure, and the theory disappears. It is of special interest, then, to confront the simian theory of the origin of man with a series of facts gathered by science since the theory was propounded.

When Huxley wrote, the embryological history of anthro- poid apes was practically unknown. Darwin, Vogt, and Haeckel, in their attempts to support the theory of the animal origin of man, had not sufficient knowledge of the embryology of monkeys. It is only recently that important work on this subject has been published. It is known that the history of development is very often an excellent guide in tracing the relationship of organisms. It is therefore interesting to examine the established facts concerning the embryology of anthropoid apes. The material for these studies is very difficult to obtain, and it is not astonishing that even our present state of know- ledge is still imperfect.

The placenta often gives information of great importance in the classification of mammals. It is sufficient to glance at the zonary placenta of dogs and seals to be convinced of the relationship of these two species, which at first sight seem so different. Now, the placentas of all the anthropoid apes examined up to the present are of the same discoid type as that of man. The arrangement of the umbilical cord of man, which was formerly considered as quite pecu- liar to him, is found in anthropoid apes, as has been established by Deniker * and Selenka.f It is striking that the anthropoids resemble man rather than the lower

monkeys in the relation of the foetus to the foetal mem- branes. With regard to the embryos themselves, the similarity between those of monkeys and of man is very great. Selenka insists on the fact that the youngest stages of human de- velopment that have been obtained can hardly be distin- guished from those of the lower monkeys either in position or in shape. More advanced stages exhibit greater differen- tiation, and the later embryos of man resemble those of

anthropoids much more closely than those of the lower monkeys. The foetus of the gibbon, figured by Selenka (Fig. 8), presents the most striking likeness to a corresponding human foetus (Fig. 9). Later on, the characters that distinguish man from even the highest of the apes become more and more pronounced. In the anthropoids the facial portion becomes more and more prominent, and betrays a bestiality absent from the human form. None the less the resemblance between the nearly mature foetus of anthropoids and human embryos of about the sixth month is evident enough. M. Deniker had the good fortune to obtain the late foetus of a gorilla — a very rare piece of fortune — and he has made an elaborate investiga- tion of its structure. The general appearance (Fig. 10) is quite enough to show the close relationship with a human foetus of a corresponding age (Fig. n). It is plain, moreover, that the young gorilla is more human-like than is the adult. Detailed anatomical investigation only confirms this con- clusion.

The skulls of the young stages of anthropoids are much more human in their character than the adult skulls. S^ljnka states that such young skulls of different anthropoids not only resemble one another more closely, but are more human. As soon as the teeth begin to appear, the indi- vidual characters are assumed so rapidly, and become so marked, that, in the absence of the intermediate stages, it would be difficult to establish the kinships. • The data derived from embryology do not point to any ane of the existing genera of monkeys as the ancestor of man. They lead us to infer, rather, that man and the anthropoid apes had a common origin, and pakeontological evidence must be scanned to find this ancestor. The greatest importance has been attached to a discovery in Java, made

in 1894 by Eugene Dubois. The remains, consisting of the crown of a skull, two teeth and a femur, belonging to a creature for which the name Pithecanthropus erectus * has been invented, have been interpreted by several anatomists as those of a form intermediate between man and the anthropoid apes. However, as the facts about this creature are meagre and have been interpreted differently, I shall not make use of them in my argument. Even apart from them, the simian origin of man may be taken as proved.

The series of facts that I have been employing as evidence of the relationship between men and anthropoid apes has been drawn from the observations of anatomists and embryo - legists. Darwin, seeking to broaden the basis of the argu- ment, called attention to the resemblances of the parasites of men and apes, as evidence of a close similarity of physio- logical processes in the creatures. In the last few years, investigations in a very different field seem capable of throwing a novel light on the question.

When the blood of one mammal is injected into the body of another, the latter shows remarkable modifications. When there is added to a serum, prepared from the blood of a rabbit and consisting of a colourless transparent liquid, a few drops of blood drawn from another rodent (for instance a guinea-pig), nothing unusual happens. The blood of the guinea-pig preserves its normal colour, and its corpuscles remain practically unaltered. If, instead of adding guinea- pig's blood to the serum of rabbit's blood, we add a serum drawn from the blood of the guinea-pig, still no special change occurs.

If, however, a serum be prepared from the blood of a rabbit into which there 'had first been injected the blood * A summary of this question is to be found in a new volume by M. Alsberg, " Die Abstammung des Menschen," chap, iii., 1902. ot a guinea-pig, the serum shows new and striking qualities. The addition to it of some drops of guinea-pig's blood brings about, in a ver} short time, a changed appearance. The red liquid, at first opaque, becomes transparent. The

mixture of the prepared serum of the rabbit with the blood of the guinea-pig will assume the colour of claret mixed with water. The change is due to solution of the red corpuscles of the guinea-pig in the blood-serum of the rabbit. This serum has still another property not less worthy of attention. If there is added to it not pure blood but only blood serum of the guinea-pig, a disturbance in the mixture occurs almost at once, and leads to the forming of a precipi- tate more or less abundant.

The injection of the blood of the guinea-pig into a rabbit has therefore changed the serum of the latter by intro- ducing new properties : that of dissolving the red corpuscles of the guinea-pig and of giving a precipitate with the blood serum of the same animal. Frequently the blood serum of animals prepared by pre- vious injections of the blood of other species of animals is strictly specific. In such cases the serum only gives a precipitate with the serum of the species which has furnished the blood for the injections, and only dissolves the red corpuscles of this same species. But there are some instances in which a serum of a prepared animal dissolves, not only the red corpuscles of the species which has furnished the injected blood, but those of allied species. Thus the blood serum of the rabbit, after some injections of blood of the chicken, becomes capable of dissolving not only the red corpuscles of the chicken but also those of the pigeon, although in a less degree.

It has been suggested that assistance could be ren- dered to forensic medicine by making use of this property of serums, to discover the origin of a certain blood. As is well known, it is often very important to decide whether a stain was caused by the blood of man or of another animal. Until quite recently it was not known how to distinguish human blood from that of other mammals. Experiments have been made to discover if the red corpuscles found in the blood stain could be dissolved by the serum of animals which had previously been injected with the blood of man.

In a certain case the human origin of the stain in question was shown. But it was soon discovered that this method was not infallible. It is now found that the method of precipitates gives much more conclusive results. It is done in this way : Human blood is injected several times into any animal (rabbit, dog, sheep, horse). Some time after- wards the animal is bled, and a clear and limpid serum, quite devoid of corpuscles, is prepared. When there is added to this serum one or several drops of human serum, it forms immediately a precipitate which falls to the bottom. In this way it is discovered whether the prepared serum is sufficiently active. It then becomes possible to recognise even dried human blood. A little of such blood is dissolved in normal salt solution, and placed in a tube containing the serum of an animal prepared by means of the injections of human blood. If a precipitate forms in the liquid in a short time, the fact indicates that the stain is really human blood. This method is being practised in forensic medicine. This reaction is. of great interest to us because it is of assistance in revealing the relationship between species. The serum of an animal prepared with the blood of the fowl gives a precipitate, not only with the serum of the fowl itself, but also with that of the pigeon ; on the other hand, it remains undisturbed when the serum of mammals is added. The reaction indicates then that there is a suffi- ciently marked degree of relationship between the fowl and the pigeon. Here is another example : the serum of an animal prepared with the blood of an ox gives an abundant precipitate when there is added to it a little blood serum of the ox, but it does not produce this reaction with the serum of any of the other mammals, not even with that of the sheep, stag and deer.* The relationship between * Uhlenhuth, "Deutsche Medecin.

Wochenschrift," p. 82, 1901. the Bovidcs and these other ruminants is then not so close as that between the fowl and the pigeon. How does the serum of animals which has been injected with human blood behave ? The serum capable of giving a precipitate with human serum does not produce the same reaction except with the serum of some monkeys (the small Papio)* Gruenbaum, of Liverpool, f has been fortunate enough to procure a considerable quantity of the blood of three large anthropoid apes — the gorilla, chimpanzee, and ourang- outang. He has been able to prove that the serum of animals injected with man's blood gives a precipitate not only with this blood but also with that of the above-men- tioned apes. It was impossible for him " to distinguish this precipitate as regards quality and quantity from that which is obtained with human blood."

To verify this result, Gruenbaum prepared the serum of animals injected with the blood of the gorilla, chimpanzee, and ourang-outang. These three kinds cf serum gave pre- cipitates with the blood of these three apes, and to the same extent with the blood of man. It is therefore evident that there exists between the human species and the anthro- poid apes not only a superficial analogy of body and of the principal organs, but a close blood-relationship.

Facts of this kind could not be foreseen when the theory of the simian origin of man was put forward. In spite of this they have arisen to confirm it in a truly astonishing way. It is therefore impossible to doubt that man is a member of the group of primates having a close connection with the * Wassermann and Schuetze, " Berliner klinische Wochenschrift/ p. 7, 1901. higher monkeys of the present time. This result is of great importance in all questions relating to human nature.

It would certainly be of considerable interest to know more exactly what steps were followed in this simian descent of man. On this question our knowledge is still very imper- fect. In his researches on anthropoid apes, Selenka insists on a more intimate relationship between the chimpanzee and man. " The great resemblance of the premolars and of the molars in the permanent dentition of the chimpanzee with human teeth appears to indicate that the chimpanzee and man have a common origin, and descend from extinct forms like Dryopithecus. This conclusion, however, is con- tradicted by the fact that the milk teeth of the chimpanzee are much nearer those of the ourang-outang than those of man." *

It is evident that to clear up this question it would be necessary to have a greater knowledge of fossil anthropoids such as Dryopithecus and its allies. In the present state of knowledge only a very general hypothesis can be formu- ated as to the exact mode of human descent. We have already shown that the foetus of man and of the anthropoid monkeys resemble each other much more than the adult forms, and that the young of these apes also bear a greater likeness to man than do the adults. The great development of the skull as compared with the face is characteristic of young monkeys and of man young or old. The jaws continue to develop in the anthropoids, while in man there occurs in this respect a certain arrest of develop- ment. The hairs, so small in man, also show a similar arrest. Generally they remain during the whole life in a state oi incomplete development. It is especially on the back of man that this feeble development of hairs occurs. * Selenka, loc. cit. p. 157.