Part 3

It must, however, be admitted that this opinion is still strongly combated by some distinguished authorities. At the Leyden Congress it was attacked by the illustrious pathologist Rudolf Virchow. He, however, is one of the minority of leading men of science who set themselves to refute the theory of Evolution in every possible way. For thirty years he has defended the thesis: 'It is quite certain that man is not a descendant of apes.' He declares any intermediate form to be unimaginable save in a dream.

See Notes, p. 93.

Virchow went to the Leyden Congress with the set purpose of disproving that the bones found by Dubois belonged to a creature which linked together apes and man. First, he maintained that the skull was that of an ape, while the thigh belonged to man. This insinuation was at once refuted by the expert palæontologists, who declared that without the slightest doubt the bones belonged to one and the same individual. Next, Virchow explained that certain exostoses or growths observable on the thigh proved its human nature, since only under careful treatment the patient could have healed the original injury. Thereupon Professor Marsh, the celebrated palæontologist, exhibited a number of thigh-bones of wild monkeys which showed similar exostoses and had healed without hospital treatment. As a last argument the Berlin pathologist declared that the deep constriction behind the upper margin of the orbits proved that the skull was that of an ape, as such never occurred in man. It so happened that a few weeks later Professor Nehring of Berlin demonstrated exactly the same formation on a human prehistoric skull received by him from Santos, in Brazil.

Virchow was, in fact, just as unlucky in Leyden in his fight with our pliocene ancestor as he had been unfortunate in his opinion on the famous skulls of Neanderthal, Spy, La Naulette, etc., every one of which he explained as a pathological abnormality. It would be a very curious coincidence indeed if all these and other fossil human remains were those of idiots or otherwise abnormal individuals, provided they are old and low enough in their organization to be of phylogenetic value to the unbiassed zoologist.

As the sworn adversary of Evolution, transformism, and Darwinism in particular, but a believer in the constancy of species, the great and renowned pathologist has been driven to the incredible contention that all variations of organic forms are pathological.

Four years ago, as honorary president of the Anthropological Congress at Vienna, he attacked Darwinism in the severest manner, and declared that 'man may be as well descended from the elephant or from the sheep as from the ape.' Such attacks on the theory of transformism indicate a failure to understand the principles of the theory of Evolution and to appreciate the significance of palæontology, comparative anatomy, and ontogeny.

The thousands of other objections which have been made during the last forty years (chiefly by outsiders) may be passed over in silence. They do not require serious refutation. In spite of, or perhaps because of, these attacks, the theory of Evolution stands established more firmly than ever.

It is easy for the outsider to exult over the difficulties which our problem implies--difficulties which we who have given our lives to the study understand likewise, and try our best not only to bridge over, but also to point out. Anyhow, we do not conceal them; while those who reject the explanation offered by Evolution make the most of the gaps, and pass silently over the far more numerous points favourable to our theory.

How fruitful during the last thirty years the astonishing progress in our palæontological knowledge has been for our Pithecometra-thesis is best shown by a short glance at the growth of our knowledge of fossil Primates. Cuvier, the founder of palæontology, continued up to the time of his death, in 1832, to assert that fossil remains of monkeys and lemurs did not exist. The only skull of a fossil lemuroid which he described (namely, Adapis) he declared to be that of an ungulate. Not until 1836 were the first fragments of extinct monkeys found in India; it was two years later, near Athens, that the skeleton of Mesopithecus penthelicus was discovered. Other remains of lemurs were found in 1862. But during the last twenty years the number of fossil Primates has been augmented by the remarkable discoveries of Gaudry, Filhol, Milne Edwards, Seeley, Schlosser, and others in Europe; of Marsh, Cope, Osborn, Leidy, Ameghino, in South America; and Forsyth Major in Madagascar. These tertiary remains, chiefly of Eocene and Miocene date, fill many gaps between existing genera of Primates, and afford us quite a clear insight into the phyletic development of this order during the millions of years of the Cænozoic age.

See notes, p. 87.

F. AMEGHINO: 'Contribucion al conocimiento de los mamíferos de la república Argentina.' In Actas de la Academia nacional de Sciencias en Cordoba, 1889.--Another article in Revista Argentina de Historia natural. Buenos Aires, 1891.

A. GAUDRY: 'Animaux fossiles et géologie de l'Attique.' 1862.--'Le Dryopithèque.' Mém. Soc. géol. de France: 'Paléontologie.' 1890.

O. MARSH: 'Introduction and Succession of Vertebrate Life in America.' Address, Amer. Assoc. Adv. Sci., Nashville, 1887.

H. F. OSBORN: 'The Rise of the Mammalia in North America.' Address, Amer. Assoc. Adv. Sci., Madison, 1893.

L. RUETIMEYER: 'Ueber die Herkunft unserer Thierwelt,' Basel, 1867.

C. S. FORSYTH MAJOR: 'Fossil Monkeys from Madagascar.' Geological Magazine, 1896.

M. SCHLOSSER: 'Ueber die Beziehungen der ausgestorbenen Saeugethierfaunen und ihr Verhaeltniss zur Saeugethierfauna der Gegenwart.' Biolog. Centralblatt, 1888.

The most important difference between the two groups of existing monkeys is indicated by their dentition. Adult man possesses, like all the other Catarrhine Simiæ, thirty-two teeth, whilst the American monkeys (the Platyrrhinæ) have thirty-six teeth--namely, one pair of premolars more in the upper and lower jaws. Comparative odontology leads us to the phylogenetic conclusion that this number has been produced by reduction from a still older form with forty-four teeth. This typical dental formula (three incisors, one canine, four premolars, and three molars, in each half-jaw) is common to all those most important older mammals which in the beginning of the Eocene period constituted the four large groups of Lemuravida, Condylarthra, Esthonychida, and Ictopsida. These are the four ancestral groups of the four main orders of Placentalia--namely, of the Primates, Ungulata, Rodentia, and Carnassia. They seem to be so closely related by their primitive organization that they may be united in one common super-order, Prochoriata.

With a considerable degree of probability, we are led to formulate the further hypothesis that all the orders of Placentalia--from the lowest Prochoriata upwards to man--have descended from some unknown common ancestor living in the Cretaceous period, and that this oldest placental form originated from some Jurassic group of marsupials.

Among these numerous fossil Lemures which have been discovered within the last twenty years, there exist, indeed, all the connecting forms of the older series of Primates, all the 'missing links' sought for by comparative odontology.

The oldest Lemures of the tertiary age are the Eocene Pachylemures, or Hyopsodina. They possess the complete dentition of the Prochoriata--namely, forty-four teeth (3.1.4.3/3.1.4.3). Then follow the Eocene Palæolemures, or Adapida, with forty teeth, they having lost one pair of incisors in each jaw. To these are attached the younger Autolemures, or Stenopida, with thirty-six teeth, they thus possessing already the same dentition as the Platyrrhinæ. The characteristic dentition of the Catarrhinæ is derived from this formula by the loss of another premolar.

These relations are so clear and so closely connected with a gradual transformation of the whole skull, and with the progressive differentiation of the Primate-form, that we are justified in saying that the pedigree of the Primates, from the oldest Eocene Lemures upwards to man, is now so well known, its principal features so firmly fixed within the Tertiary age, that there is no missing link whatever.

Quite different, and much more incomplete, is the palæontological evidence, if we go further back into the Secondary or Mesozoic age, and look there for the older ancestors of the mammalian series. There we meet everywhere with wide gaps, and the scarce fragments of fossil Mesozoic mammals (excessively rare in the Cretaceous formation) are too poor to permit definite conclusions as to their systematic position. Indeed, comparative anatomy and ontogeny lead us to the hypothesis that the oldest Cretaceous Mammalia--the Prochoriata--are descended from Jurassic marsupials, and these again from Monotremes. We may also suppose with high probability that among the unknown Cretaceous Prochoriata there have been Lemuravida and forms intermediate between these and the Jurassic Amphitheriidæ, and that these marsupials in their turn are descendants of Pantotheria or similar monotreme-like creatures of the Triassic age. Any certain evidence for these hypotheses is at present still wanting. One important fact, however, is established--namely, that these interesting and oldest Mammalia--the Pantotheria of Marsh, the Triassic Dromatheriidæ, and the Jurassic Triconodontidæ of Osborn--were small insectivorous mammals with a very primitive organization. Probably they were Monotremes, and may be derived directly from Permian Sauromammalia, an ill-defined mixture of Mammalia and Reptilia.

This generalized characteristic supports our view that the whole class of Mammalia is monophyletic, and that all its members, from the oldest Monotremes upwards to man, have descended from one common ancestor living in the older Triassic, or perhaps in the Permian, age. To acquire full conviction of this important conception, we have only to think of the hair and the glands of our human skin, of our diaphragm, the heart and the blood corpuscles without a nucleus, our skull with its squamoso-mandibular articulation. All these singular and striking modifications of the vertebrate organization are common to mammals, and distinguish them clearly from the other Craniota. This characteristic combination and correlation proves that they have been developed only once in the history of the vertebrate stem, and that they have been transferred by heredity from one common ancestor to all the members of the class of Mammalia.

The next step, as we trace our human phylogeny to its origin, leads us further back into the lower Vertebrata, into that obscure Palæozoic age the immeasurable length of which (much greater than that of the Mesozoic) may, according to one of the newest geological calculations, have comprised about one thousand millions of years.

See note, 'Geological Time and Evolution' p. 134.

The first important fact we have to face here is the complete absence of mammalian remains. Instead of these we find in the later Palæozoic period, the Permian, air-breathing reptiles as the earliest representatives of Amniota. They belong to the most primitive order of that class, the Tocosauria; and besides them there were the Theromorpha, which approach the Mammalia in a remarkable manner. These reptiles in turn were preceded, in the Carboniferous period, by true Amphibia, most of them belonging to the armour-clad Stegocephali. These interesting Progonamphibia were the oldest Tetrapoda, the first vertebrates which had adapted themselves to the terrestrial mode of life; in them the swimming fin of fishes and Dipneusta was transformed into the pentadactyle extremities characteristic of quadrupeds.

To appreciate the high importance of this metamorphosis, we need only compare the skeleton of our own human limbs with that of the living Amphibia. We find in the latter the same characteristic composition as in man: the same shoulder and pelvic girdle; the same single bone, the humerus or the femur, followed by the same pair of bones in the forearm and leg; then the same skeletal elements composing the wrist and the ankle regions; and, lastly, the same five fingers and toes.