For the rest, there are, as we have said, various possible ways of constructing the narrower genealogy within the limits of this branch including men and apes, and these methods will probably continue to change with the accumulation of new facts. Haeckel himself has modified his genealogical tree of the Primates in certain details since the publication of his "Generelle Morphologie" in 1866, but its general basis remains the same. (Haeckel's latest genealogical tree is to be found in his most recent work, "Unsere Ahnenreihe". Jena, 1908.) All the special genealogical trees drawn up on the lines laid down by Haeckel and Darwin--and that of Dubois may be specially mentioned--are based, in general, on the close relationship of monkeys and men, although they may vary in detail. Various hypotheses have been formulated on these lines, with special reference to the evolution of man. "Pithecanthropus" is regarded by some authorities as the direct ancestor of man, by others as a side-track failure in the attempt at the evolution of man. The problem of the monophyletic or polyphyletic origin of the human race has also been much discussed. Sergi (Sergi G. "Europa", 1908.) inclines towards the assumption of a polyphyletic origin of the three main races of man, the African primitive form of which has given rise also to the gorilla and chimpanzee, the Asiatic to the Orang, the Gibbon, and Pithecanthropus.
Kollmann regards existing human races as derived from small primitive races (pigmies), and considers that Homo primigenius must have arisen in a secondary and degenerative manner.
But this is not the place, nor have I the space to criticise the various special theories of descent. One, however, must receive particular notice.
According to Ameghino, the South American monkeys (Pitheculites) from the oldest Tertiary of the Pampas are the forms from which have arisen the existing American monkeys on the one hand, and on the other, the extinct South American Homunculidae, which are also small forms. From these last, anthropoid apes and man have, he believes, been evolved. Among the progenitors of man, Ameghino reckons the form discovered by him (Tetraprothomo), from which a South American primitive man, Homo pampaeus, might be directly evolved, while on the other hand all the lower Old World monkeys may have arisen from older fossil South American forms (Clenialitidae), the distribution of which may be explained by the bridge formerly existing between South America and Africa, as may be the derivation of all existing human races from Homo pampaeus. (See Ameghino's latest paper, "Notas preliminares sobre el Tetraprothomo argentinus", etc.
"Anales del Museo nacional de Buenos Aires", XVI. pages 107-242, 1907.)The fossil forms discovered by Ameghino deserve the most minute investigation, as does also the fossil man from South America of which Lehmann-Nitsche ("Nouvelles recherches sur la formation pampeenne et l'homme fossile de la Republique Argentine". "Rivista del Museo de la Plata", T. XIV. pages 193-488.) has made a thorough study.
It is obvious that, notwithstanding the necessity for fitting man's line of descent into the genealogical tree of the Primates, especially the apes, opinions in regard to it differ greatly in detail. This could not be otherwise, since the different Primate forms, especially the fossil forms, are still far from being exhaustively known. But one thing remains certain,--the idea of the close relationship between man and monkeys set forth in Darwin's "Descent of Man". Only those who deny the many points of agreement, the sole basis of classification, and thus of a natural genealogical tree, can look upon the position of Darwin and Haeckel as antiquated, or as standing on an insufficient foundation. For such a genealogical tree is nothing more than a summarised representation of what is known in regard to the degree of resemblance between the different forms.
Darwin's work in regard to the descent of man has not been surpassed; the more we immerse ourselves in the study of the structural relationships between apes and man, the more is our path illumined by the clear light radiating from him, and through his calm and deliberate investigation, based on a mass of material in the accumulation of which he has never had an equal. Darwin's fame will be bound up for all time with the unprejudiced investigation of the question of all questions, the descent of the human race.