Part 6

25. Stage of Pithecanthropi. Hitherto the only known representative is Pithecanthropus erectus, from the Upper Pliocene of Java. In adaptation to a more erect gait, the legs have become stronger and the hind-hand has been turned into a flat-soled walking 'foot.' The brain is considerably enlarged. Presumably it is still devoid of so-called articulate speech; this is indicated by the fact that children have to learn the language of their parents, and by the circumstance that comparative philology declares it impossible to reduce the chief human languages to anything like one common origin.

26. Man. Known with certainty to have existed as an implement-using creature in the last Glacial epoch. His probable origin cannot, therefore, have been later than the beginning of the Plistocene. The place of origin was probably somewhere in Southern Asia.

Whilst we have to admit that there are great defects in the older (invertebrate) portion of our pedigree, we have all the more reason to be satisfied with the positive results of our investigation of the more recent (vertebrate) part of it. All modern researches have confirmed the views of Lamarck, Darwin, and Huxley, and they allow of no doubt that the nearest vertebrate ancestors of mankind were a series of Tertiary Primates.

Particularly valuable are the admirable attempts of the two zoologists, Paul and Fritz Sarasin, to throw light upon the human phylogeny by painstaking comparison of all the skeletal parts of man with those of the anthropoid apes. They have shown that among the lower races of man the primitive Veddahs of Ceylon approach the apes most nearly, and that among the latter the chimpanzee stands nearest to man.

'Ergebnisse naturwissenschaftlicher Forschungen auf Ceylon,' vols. 4 and 5. (With an atlas of 84 plates; 1893.)

The direct descent of man from some extinct ape-like form is now beyond doubt, and admits of being traced much more clearly than the origin of many another mammalian order. The pedigrees of the Elephants, the Sirenia, the Cetacea, and, above all, of the Edentata, for example, are much more obscure and difficult to explain. In many parts of their organization--for example, in the number and structure of his five digits and toes--man and monkeys have remained much more primitive than most of the Ungulata.

The immense significance of this positive knowledge of the origin of man from some Primate does not require to be enforced. Its bearing upon the highest questions of philosophy cannot be exaggerated. Among modern philosophers no one has perceived this more deeply than Herbert Spencer. He is one of those older thinkers who before Darwin were convinced that the theory of development is the only way to solve the 'enigma of the world.' Spencer is also the champion of those evolutionists who lay the greatest weight upon progressive heredity, or the much combated heredity of acquired characters. From the first he has severely attacked and criticised the theories of Weismann, who denies this most important factor of phylogeny, and would explain the whole of transformism by the 'all-sufficiency of selection.' In England the theories of Weismann were received with enthusiastic acclamation, much more so than on the Continent, and they were called 'Neo-Darwinism,' in opposition to the older conception of Evolution, or 'Neo-Lamarckism.' Neither of those expressions is correct. Darwin himself was convinced of the fundamental importance of progressive heredity quite as much as his great predecessor Lamarck; as were also Huxley and Spencer.

'Principles of Biology': 'The Factors of Organic Evolution'; 'The Inadequacy of Natural Selection.'

Three times I had the good fortune to visit Darwin at Down, and on each occasion we discussed this fundamental question in complete harmony. I agree with Spencer in the conviction that progressive heredity is an indispensable factor in every true monistic theory of Evolution, and that it is one of its most important elements. If one denies with Weismann the heredity of acquired characters, then it becomes necessary to have recourse to purely mystical qualities of germ-plasm. I am of the opinion of Spencer, that in that case it would be better to accept a mysterious creation of all the various species as described in the Mosaic account.

If we look at the results of modern anthropogeny from the highest point of view, and compare all its empirical arguments, we are justified in affirming that the descent of man from an extinct Tertiary series of Primates is not a vague hypothesis, but an historical fact.

Of course, this fact cannot be proved exactly. We cannot explain all the innumerable physical and chemical processes, all the physiological mutations, which have led during untold millions of years from the simplest Monera and from the unicellular Protista upwards to the chimpanzee and to man. But the same consideration applies to all historical facts. We all believe that Aristotle, Cæsar, and King Alfred did live; but it is impossible to give a proof within the meaning of modern exact science. We believe firmly in the former existence of these and other great heroes of thought, because we know well the works they have left behind them, and we see their effects in the history of human culture. These indirect arguments do not furnish stronger evidence than those of our history as vertebrates. We know of many Jurassic mammals only a single bone, the under jaw. We all believe that these mammals possessed also an upper jaw, a skull, and other bones. But the so-called 'exact school,' which regards the transformation of species as a hypothesis not proven, must suppose that the mandibula was the only bone in the body of these curious animals.

Looking forward to the twentieth century, I am convinced that it will universally accept our theory of descent, and that future science will regard it as the greatest advance made in our time. I have no doubt that the influence of the study of anthropogeny upon all other branches of science will be fruitful and auspicious. The work done in the present century by Lamarck and Darwin will in all future times be considered one of the greatest conquests made by thinking man.

EVOLUTIONARY STAGES OF THE PRINCIPAL GROUPS OF VERTEBRATA.

STAGES OF THE CLASSES. STAGES OF THE HEART. PAIRED LIMBS.

{ 1. Acrania. I. Leptocardia. I. Adactylia { Cold-blooded; heart s. Impinnata. { with one chamber; Without jaws { without lungs. and limbs. { { 2. Cyclostomata. } II. Ichthyocardia. } Cold-blooded; heart } two-chambered, with } one atrium and one } ventricle; heart } containing venous } blood only; without II. Polydactylia { 3. Pisces. } lungs. s. Pinnata. { With two { } III. Amphicardia. pairs of fins. { 4. Dipnoi. } Cold-blooded; heart } with three complete } chambers, namely, with } two atria and one } ventricle, or (Reptilia) { 5. Amphibia. } two ventricles with still { } incomplete septum; heart { } containing mixed venous { } and arterialized III. Pentadactylia { 6. Reptilia. } blood; with lungs. s. Tetrapoda. { With two pairs { { IV. Thermocardia. of pentadactyle { { Warm-blooded; heart limbs (unless { 7. Aves. { with four complete they have { { chambers, namely, two been lost by { { auricles and two reduction). { { ventricles; right half { { of the heart with venous, { { left half with { { arterialized, blood; with { 8. Mammalia. { lungs.

Abridged from Haeckel's 'Systematische Phylogenie der Vertebraten,' § 14.

BIOGRAPHICAL SKETCHES

JEAN BAPTISTE DE MONET, CHEVALIER DE LAMARCK, was born on August 1, 1744, in Picardy, where his father owned land. Originally educated for the Church, he soon enlisted, and distinguished himself in active service. Owing to an accident affecting his health, the young Lieutenant gave up the military career, and, without means, studied medicine and natural sciences at Paris. In 1778 appeared his 'Flore française.' In 1793 he was appointed to a Chair of Zoology at the newly-formed Musée d'Histoire Naturelle. He had the misfortune to become gradually blind, and the last years of his life were spent amid straitened circumstances. He died in 1829.

In 1794 Lamarck divided the whole animal kingdom into vertebrate and invertebrate animals, and founded successively the groups of Crustacea, Arachnida, Annelida, and Radiata. Between 1816 and 1822 he published his celebrated 'Histoire naturelle des Animaux sans Vertèbres.'

His most famous work is the 'Philosophie zoologique,' 1809.

Assuming the spontaneous origin of life, he propounded the doctrine that all animals and plants have arisen from low forms through incessant modifications and changes. In this respect he was in absolute opposition to Cuvier, who upheld the immutability of species, and did his best by absolute silence to suppress the spread of the new doctrine.

Lamarck has explained his views of transformism chiefly in the seventh chapter of the first volume of his 'Philosophie zoologique.'

Organisms strive to accommodate or adapt themselves to new circumstances, or to satisfy new requirements--e.g., climate, mode of procuring food, escape from enemies. The continued function of parts of an organism changes the old and produces new organs. The acquirements are inherited by the offspring, and thus are produced the more complicated from simpler organisms. Continued disuse brings about degeneration and ultimate loss of an organ.

Lamarck consequently sees in the adaptability, or power of adaptation, which he assumes for all living matter the ultimate cause of variation; and, as he was certainly the first to point out that acquired characters are inherited by the progeny, he has given a working explanation of Evolution.

But his doctrine did not spread--partly because he was misunderstood. His theory, that a new want, by making itself felt, exacts from the animal new exertions, perhaps from parts hitherto not used, until the want is satisfied--this way of putting it sounds too teleological to explain the yearned-for change in a mechanical or natural way. Moreover, many of his examples lacked the exact basis of experiment and observation necessary for their acceptance. Witness that of the neck of the giraffe,--a never-failing source of ridicule to men who cannot see the deeper purpose underlying the well-meant attempt at an explanation, which failed from want of complete knowledge of the intricate circumstances.

However, the theory of transformism was, so to speak, in the air; and various authors have written on the subject, filling the gap between Lamarck and Darwin, especially Goethe, Treviranus, Leopold von Buch, and Herbert Spencer. But it is Darwin's immortal merit to have opened our eyes by his theory of natural selection, which is, at least, the first attempt to explain some of the causes and incidents of organic Evolution in a natural mechanical way. Moreover, he was the first clearly to express the fundamental principles of the theory of descent, to elaborate what had been at best a general sketch of an ill-defined problem, and to enter into detail, supported by a host of painstaking observations, the making of which had taken him half a lifetime. Darwin, without going further than cursorily into the causes of variation, argued as follows: We know that variations do occur in every kind of living creatures. Some of these variations lead to something, while others do not. An enormously greater number of animals and plants are born than reach maturity and can in their turn continue the race. What is the regulating factor? His answer is, The struggle for existence--in other words, the weeding out of the less fit, or rather of the owners of those variations which are not so well adapted to their surroundings.

For 'adapted' we had better read 'adaptable,' because a variation which does not answer, which cannot be made use of, or, still more notably, is a hindrance or disadvantage, does not become an adapted feature. There is often a confusion between adaptation as an accomplished fact, a feature, or resultant condition, and adaptation as the mode of fitting the organism to, or making the best of, the prevailing surroundings or circumstances.

ÉTIENNE GEOFFROY SAINT-HILAIRE was born in 1772 at Étampes, Seine-et-Oise. He was originally brought up for the Church; but when already ordained he attended lectures on natural science and medicine in Paris. He managed to get the place of assistant in the Musée d'Histoire Naturelle; he became Professor of Zoology in 1793, and took the opportunity of encouraging young Cuvier. Later he became Professor of Zoology of the Faculté des Sciences, and in 1818 he published his remarkable 'Philosophie anatomique.' He died in 1844.