The many and thorough investigations made during the last few decades into the ancestral history of the mammals have convinced all zoologists who were engaged in them that they may be traced to a common root. All the mammals, from the lowest monotremes and marsupials to the ape and man, have a large number of striking characteristics in common, and these distinguish them from all other vertebrates: the hair and glands of the skin, the feeding of the young with the mother's milk, the peculiar formation of the lower jaw and the ear-bones connected therewith, and other features in the structure of the skull; also, the possession of a knee-cap (patella), and the loss of the nucleus in the red blood-cells. Further, the complete diaphragm, which entirely separates the pectoral cavity from the abdominal, is only found in the mammals; in all the other vertebrates there is still an open communication between the two cavities. The monophyletic (or single) origin of the whole mammalian class is therefore now regarded by all competent experts as an established fact.
In the face of this important fact, what is called the "ape-question" loses a good deal of the importance that was formerly ascribed to it. All the momentous consequences that follow from it in regard to our human nature, our past and future, and our bodily and psychic life, remain undisturbed whether we derive man directly from one of the primates, an ape or lemur, or from some other branch, some unknown lower form, of the mammalian stem. It is important to point this out, because certain dangerous attempts have been made lately by Jesuitical zoologists and zoological Jesuits to cause fresh confusion on the matter.
In a richly illustrated and widely read work that Hans Kraemer published a few years ago, under the title, The Universe and Man, an able and learned anthropologist, Professor Klaatsch of Heidelberg, deals with "the origin and development of the human race," and admirably describes the primitive history of man and his civilisation. However, he denounces the idea of man's descent from the ape as "irrational, narrow-minded, and false"; he grounds this severe censure on the fact that none of the living apes can be the ancestor of humanity. But no competent scientist had ever said anything so foolish. If we look closer into this fight with windmills, we find that Klaatsch holds substantially the same view of the pithecoid theory as I have done since 1866. He says expressly: "The three anthropoid apes, the gorilla, chimpanzee, and orang, seem to diverge from a common root, which was near to that of the gibbon and man." I had long ago given the name of archiprimas to this single hypothetical root-form of the primates, which he calls the "primatoid." It lived in the earliest part of the Tertiary period, and had probably been developed in the Cretaceous from older mammals. The very forced and unnatural hypothesis by means of which Klaatsch goes on to make the primates depart very widely from the other mammals, seems to me to be quite untenable, like the similar hypothesis that Alsberg, Wilser, and other anthropologists who deny our pithecoid descent, have lately advanced.
All these attempts have a common object—to save man's privileged position in Nature, to widen as much as possible the gulf between him and the rest of the mammals, and to conceal his real origin. It is the familiar tendency of the parvenu, which we so often notice in the aristocratic sons of energetic men who have won a high position by their own exertions. This sort of vanity is acceptable enough to the ruling powers and the Churches, because it tends to support their own fossilised pretensions to a "Divine image" in man and a special "Divine grace" in princes. The zoologist or anthropologist who studies our genealogy in a strictly scientific spirit takes no more notice of these tendencies than of the Almanach de Gotha. He seeks to discover the naked truth, as it is yielded by the great results of modern science, in which there is no longer any doubt that man is really a descendant of the ape—that is to say, of a long extinct anthropoid ape. As has been pointed out over and over again by distinguished supporters of this opinion, the proofs of it are exceptionally clear and simple—much clearer and simpler than they are in regard to many other mammals. Thus, for instance, the origin of the elephants, the armadilloes, the sirena, or the whales, is a much more difficult problem than the origin of man.
When Huxley published his powerful essay on "Man's Place in Nature" in 1863, he gave it a frontispiece showing the skeletons of man and the four living anthropoid apes, the Asiatic orang and gibbon, and the African chimpanzee and gorilla. Plate II. in the present work differs from this in giving two young specimens of the orang and the chimpanzee, and raising their size to correspond with the other three skeletons. Candid comparison of these five skeletons shows that they are not only very like each other generally, but are identical in the structure, arrangement, and connection of all the parts. The same 200 bones compose the skeleton in man and in the four tailless anthropoid apes, our nearest relatives. The same 300 muscles serve to move the various parts of the skeleton. The same hair covers the skin; the same mammary glands provide food for the young. The same four-chambered heart acts as central pump of the circulation; the same 32 teeth are found in our jaws; the same reproductive organs maintain the species; the same groups of neurona or ganglionic cells compose the wondrous structure of the brain, and accomplish that highest function of the plasm which we call the soul, and many still believe to be an immortal entity. Huxley has thoroughly established this profound truth, and by further comparison with the lower apes and lemurs he came to formulate his important pithecometra principle: "Whatever organ we take, the differences between man and the anthropoid apes are slighter than the corresponding differences between the latter and the lower apes." If we make a superficial comparison of our skeletons of the anthropomorpha, we certainly notice a few salient differences in the size of the various parts; but these are purely quantitative, and are due to differences in growth, which in turn are caused by adaptation to different environments. There are, as is well known, similar differences between human beings; their arms are sometimes long, sometimes short; the forehead may be high or low, the hair thick or thin, and so on.
These anatomic proofs of the pithecoid theory are most happily supplemented and confirmed by certain recent brilliant discoveries in physiology. Chief amongst these are the famous experiments of Dr. Hans Friedenthal at Berlin. He showed that the human blood acts poisonously on and decomposes the blood of the lower apes and other mammals, but has not that effect on the blood of the anthropoid apes.[8]
From previous transfusion experiments it had been learned that the affinity of mammals is connected to a certain extent with their chemical blood-relationship. If the living blood of two nearly related animals of the same family, such as the dog and the fox, or the rabbit and the hare, is mixed together, the living blood-cells of each species remain uninfluenced. But if we mix the blood of the dog and the rabbit, or the fox and the hare, a struggle for life immediately takes place between the two kinds of blood-cells. The watery fluid or serum destroys the blood-cells of the rodent, and vice versâ. It is the same with specimens of the blood of the various primates. The blood of the lower apes and lemurs, which are close to the common root of the primate stem, has a destructive effect on the blood of the anthropoid apes and man, and vice versâ. On the other hand, the human blood has no injurious effect when it is mixed with that of the anthropoid apes.
In recent years these interesting experiments have been continued by other physiologists and physicians, such as Professor Uhlenhuth at Greifswald and Nuttall at London, and they have proved directly the blood-relationship of various mammals. Nuttall studied them carefully in 900 different kinds of blood, which he tested by 16,000 reactions. He traced the gradation of affinity to the lowest apes of the New World; and Uhlenhuth continued as far as the lemurs. By these results the affinity of man and the anthropoid apes, long established by anatomy, has now been proved physiologically to be in real "blood-relationship."[9]
Not less important are the embryological discoveries of the deceased zoologist, Emil Selenka. He made two long journeys to the East Indies, in order to study on the spot the embryology of the Asiatic anthropoid apes, the orang and gibbon. By means of a number of embryos that he collected he showed that certain remarkable peculiarities in the formation of the placenta, that had up to that time been considered as exclusively human, and regarded as a special distinction of our species, were found in just the same way in the closely related anthropoid apes, though not in the rest of the apes. On the ground of these and other facts, I maintain that the descent of man from extinct Tertiary anthropoid apes is proved just as plainly as the descent of birds from reptiles, or the descent of reptiles from amphibians, which no zoologist hesitates to admit to-day. The relationship is as close as was claimed by my former fellow-student, the Berlin anatomist, Robert Hartmann (with whom I sat at the feet of Johannes Müller fifty years ago), in his admirable work on the anthropoid apes (1883). He proposed to divide the order of primates into two families, the primarii (man and the anthropoid apes), and simianæ (the real apes, the catarrhine or eastern, and the platyrrhine or western apes).
Since the Dutch physician, Eugen Dubois, discovered the famous remains of the fossil ape-man (pithecanthropus erectus) eleven years ago in Java, and thus brought to light "the missing link," a large number of works have been published on this very interesting group of the primates. In this connection we may particularly note the demonstration by the Strassburg anatomist, Gustav Schwalbe, that the previously discovered Neanderthal skull belongs to an extinct species of man, which was midway between the pithecanthropus and the true human being—the homo primigenus. After a very careful examination, Schwalbe at the same time refuted all the biassed objections that Virchow had made to these and other fossil discoveries, trying to represent them as pathological abnormalities. In all the important relics of fossil men that prove our descent from anthropoid apes Virchow saw pathological modifications, due to unsound habits, gout, rickets, or other diseases of the dwellers in the diluvial caves. He tried in every way to impair the force of the arguments for our primate affinity. So in the controversy over the pithecanthropus he raised the most improbable conjectures, merely for the purpose of destroying its significance as a real link between the anthropoid apes and man.