22. Stage of Simiæ. Orbit completely separated from the temporal fossa by an inward extension of the frontal and malar bones meeting the alisphenoid. Placenta consolidated into a disc, and with a maternal deciduous portion. Mammæ pectoral only. The dental formula is 2.1.3.3. All the fingers and toes are protected by flat nails. The tail is long. The American prehensile-tailed monkeys are a lower side-branch.
23. Stage of Catarrhinæ Cercopithecidæ. The dental formula is 2.1.2.3, owing to the loss of one pair of premolars in each jaw. The frontal and alisphenoid bones are in contact, separating the parietal from the malar bone; this feature is correlated with the enlarged brain. The internarial septum is narrow, and the nostrils look forwards and downwards instead of sidewards—hence the term 'Catarrhinæ.' The external auditory meatus is long and bony. The tail is long, with the exception of Macacus inuus. The body is covered with a thick coat of furry hair. Catarrhine monkeys have existed, we know with certainty, since the Miocene.
24. Stage of Catarrhinæ Anthropoidæ, or Apes. Now represented by the large apes—namely, the Hylobates or gibbon of South-Eastern Asia, Simia satyrus, the orang-utan of Sumatra and Borneo, Troglodytes gorilla, T. niger and T. calvus, the gorilla and the chimpanzees from Western Equatorial Africa. Of fossils are to be mentioned Pliopithecus and Dryopithecus from European Miocene, and Troglodytes sivalensis from the Pliocene of the Punjaub. The tail is reduced to a few caudal vertebræ, which are transformed into a coccyx, not visible externally; but in the embryos of apes and man the tail is still a conspicuous feature. The walk is semierect; in adaptation to the prevailing arboreal life, the arms are longer than the legs. The hair of the body is considerably more scanty than in the tailed monkeys. Troglodytes calvus, a species or variety of chimpanzee, is bald-headed. None of the recent genera of apes can lay claim to a place in the ancestry of mankind.
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,[23] 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.
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.[24] 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.
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.