In Italy independent work in the domain of the descent of man is being produced, especially by Morselli; with him are a.s.sociated, in the investigation of related problems, Sergi and Giuffrida-Ruggeri. From the ranks of American investigators we may single out in particular the eminent geologist Cope, who championed with much decision the idea of the specific difference of _h.o.m.o neandertalensis_ (_primigenius_) and maintained a more direct descent of man from the fossil Lemuridae.
In South America too, in Argentina, new life is stirring in this department of science. Ameghino in Buenos Ayres has awakened the fossil primates of the Pampas formation to new life; he even believes that in his _Tetraproth.o.m.o_, represented by a femur, he has discovered a direct ancestor of man. Lehmann-Nitsche is working at the other side of the gulf between apes and man, and he describes a remarkable first cervical vertebra (atlas) from Monte Hermoso as belonging to a form which may bear the same relation to _h.o.m.o sapiens_ in South America as _h.o.m.o primigenius_ does in the Old World. After a minute investigation he establishes a human species _h.o.m.o neogaeus_, while Ameghino ascribes this atlas vertebra to his _Tetraproth.o.m.o_.
Thus throughout the whole scientific world there is arising a new life, an eager endeavour to get nearer to Huxley"s _problema maximum_, to penetrate more deeply into the origin of the human race. There are to-day very few experts in anatomy and zoology who deny the animal descent of man in general. Religious considerations, old prejudices, the reluctance to accept man, who so far surpa.s.ses mentally all other creatures, as descended from "soulless" animals, prevent a few investigators from giving full adherence to the doctrine. But there are very few of these who still postulate a special act of creation for man. Although the majority of experts in anatomy and zoology accept unconditionally the descent of man from lower forms, there is much diversity of opinion among them in regard to the special line of descent.
In trying to establish any special hypothesis of descent, whether by the graphic method of drawing up genealogical trees or otherwise, let us always bear in mind Darwin"s words[120] and use them as a critical guiding line: "As we have no record of the lines of descent, the pedigree can be discovered only by observing the degrees of resemblance between the beings which are to be cla.s.sed." Darwin carries this further by stating "that resemblances in several unimportant structures, in useless and rudimentary organs, or not now functionally active, or in an embryological condition, are by far the most serviceable for cla.s.sification."[121] It has also to be remembered that _numerous_ separate points of agreement are of much greater importance than the amount of similarity or dissimilarity in a few points.
The hypotheses as to descent current at the present day may be divided into two main groups. The first group seeks for the roots of the human race not among any of the families of the apes--the anatomically nearest forms--nor among their very similar but less specialised ancestral forms, the fossil representatives of which we can know only in part, but, setting the monkeys on one side, it seeks for them lower down among the fossil Eocene Pseudo-lemuridae or Lemuridae (Cope), or even among the primitive pentadactylous Eocene forms, which may either have led directly to the evolution of man (Adloff), or have given rise to an ancestral form common to apes and men (Klaatsch,[122]
Giuffrida-Ruggeri). The common ancestral form, from which man and apes are thus supposed to have arisen independently, may explain the numerous resemblances which actually exist between them. That is to say, all the characters upon which the great structural resemblance between apes and man depends must have been present in their common ancestor. Let us take an example of such a common character. The bony external ear-pa.s.sage is in general as highly developed in the lower Eastern monkeys and the anthropoid apes as in man. This character must, therefore, have already been present in the common primitive form. In that case it is not easy to understand why the Western monkeys have not also inherited the character, instead of possessing only a tympanic ring. But it becomes more intelligible if we a.s.sume that forms with a primitive tympanic ring were the original type, and that from these were evolved, on the one hand, the existing New World monkeys with persistent tympanic ring, and on the other an ancestral form common to the lower Old World monkeys, the anthropoid apes and man. For man shares with these the character in question, and it is also one of the "unimportant" characters required by Darwin. Thus we have two divergent lines arising from the ancestral form, the Western monkeys (Platyrrhine) on the one hand, and an ancestral form common to the lower Eastern monkeys, the anthropoid apes, and man, on the other.
But considerations similar to those which showed it to be impossible that man should have developed from an ancestor common to him and the monkeys, yet outside of and parallel with these, may be urged also against the likelihood of a parallel evolution of the lower Eastern monkeys, the anthropoid apes, and man. The anthropoid apes have in common with man many characters which are not present in the lower Old World monkeys. These characters must therefore have been present in the ancestral form common to the three groups. But here, again, it is difficult to understand why the lower Eastern monkeys should not also have inherited these characters. As this is not the case, there remains no alternative but to a.s.sume divergent evolution from an indifferent form. The lower Eastern monkeys are carrying on the evolution in one direction--I might almost say towards a blind alley--while anthropoids and men have struck out a progressive path, at first in common, which explains the many points of resemblance between them, without regarding man as derived directly from the anthropoids. Their many striking points of agreement indicate a common descent, and cannot be explained as phenomena of convergence.
I believe I have shown in the above sketch that a theory which derives man directly from lower forms without regarding apes as transition-types leads _ad absurdum_. The close structural relationship between man and monkeys can only be understood if both are brought into the same line of evolution. To trace man"s line of descent directly back to the old Eocene mammals, alongside of, but with no relation to these very similar forms, is to abandon the method of exact comparison, which, as Darwin rightly recognised, alone justifies us in drawing up genealogical trees on the basis of resemblances and differences. The farther down we go the more does the ground slip from beneath our feet. Even the Lemuridae show very numerous divergent conditions, much more so the Eocene mammals (Creodonta, Condylarthra), the chief resemblance of which to man consists in the possession of pentadactylous hands and feet! Thus the farther course of the line of descent disappears in the darkness of the ancestry of the mammals. With just as much reason we might pa.s.s by the Vertebrates altogether, and go back to the lower Invertebrates, but in that case it would be much easier to say that man has arisen independently, and has evolved, without relation to any animals, from the lowest primitive form to his present isolated and dominant position. But this would be to deny all value to cla.s.sification, which must after all be the ultimate basis of a genealogical tree. We can, as Darwin rightly observed, only infer the line of descent from the degree of resemblance between single forms. If we regard man as directly derived from primitive forms very far back, we have no way of explaining the many points of agreement between him and the monkeys in general, and the anthropoid apes in particular. These must remain an inexplicable marvel.
I have thus, I trust, shown that the first cla.s.s of special theories of descent, which a.s.sumes that man has developed, parallel with the monkeys, but without relation to them, from very low primitive forms cannot be upheld, because it fails to take into account the close structural affinity of man and monkeys. I cannot but regard this hypothesis as lamentably retrograde, for it makes impossible any application of the facts that have been discovered in the course of the anatomical and embryological study of man and monkeys, and indeed prejudges investigations of that cla.s.s as pointless. The whole method is perverted; an unjustifiable theory of descent is first formulated with the aid of the imagination, and then we are asked to declare that all structural relations between man and monkeys, and between the different groups of the latter, are valueless,--the fact being that they are the only true basis on which a genealogical tree can be constructed.
So much for this most modern method of cla.s.sification, which has probably found adherents because it would deliver us from the relationship to apes which many people so much dislike. In contrast to it we have the second cla.s.s of special hypotheses of descent, which keeps strictly to the nearest structural relationship. This is the only basis that justifies the drawing up of a special hypothesis of descent. If this fundamental proposition be recognised, it will be admitted that the doctrine of special descent upheld by Haeckel, and set forth in Darwin"s _Descent of Man_, is still valid to-day. In the genealogical tree, man"s place is quite close to the anthropoid apes; these again have as their nearest relatives the lower Old World monkeys, and their progenitors must be sought among the less differentiated Platyrrhine monkeys, whose most important characters have been handed on to the present day New World monkeys. How the different genera are to be arranged within the general scheme indicated depends in the main on the cla.s.sificatory value attributed to individual characters. This is particularly true in regard to _Pithecanthropus_, which I consider as the root of a branch which has sprung from the anthropoid ape root and has led up to man; the latter I have designated the family of the Hominidae.
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 acc.u.mulation 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.[123] 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[124] inclines towards the a.s.sumption 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 _h.o.m.o primigenius_ must have arisen in a secondary and degenerative manner.
But this is not the place, nor have I the s.p.a.ce 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 (_Tetraproth.o.m.o_), from which a South American primitive man, _h.o.m.o 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 _h.o.m.o pampaeus_.[125] The fossil forms discovered by Ameghino deserve the most minute investigation, as does also the fossil man from South America of which Lehmann-Nitsche[126]
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 fossile 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 cla.s.sification, 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 surpa.s.sed; 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 ma.s.s of material in the acc.u.mulation 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.
FOOTNOTES:
[Footnote 75: _Life and Letters of Thomas Henry Huxley_, Vol. I. p.
171, London, 1900.]
[Footnote 76: _Ibid._, p. 363.]
[Footnote 77: No italics in original.]
[Footnote 78: _Life and Letters of Charles Darwin_, Vol. I. p. 93.]
[Footnote 79: _Ibid._ Vol. II. p. 263.]
[Footnote 80: _Ibid._ Vol. I. p. 94.]
[Footnote 81: _Life and Letters_, Vol. III. p. 175.]
[Footnote 82: _Ibid._ Vol. II. p. 109.]
[Footnote 83: _Ibid._ Vol. III. p. 112.]
[Footnote 84: _Ibid._ Vol. I. pp. 304-317.]
[Footnote 85: _Life and Letters_, Vol. I. p. 309.]
[Footnote 86: _Loc. cit._ p. 313.]
[Footnote 87: _Ibid._ Vol. II. p. 310.]
[Footnote 88: _Ibid._ Vol. III. p. 236. ["C. Ridley," Mr. Francis Darwin points out to me, should be H. N. Ridley. A.C.S.]]
[Footnote 89: _Descent of Man_ (Popular Edit., 1901), fig. 1, p. 14.]
[Footnote 90: G. Schwalbe, "Das Darwin"sche Spitzohr beim menschlichen Embryo," _Anatom. Anzeiger_, 1889, pp. 176-189, and other papers.]
[Footnote 91: _Descent of Man_, fig. 3, p. 24.]
[Footnote 92: _Descent of man_, p. 6.]
[Footnote 93: _Ibid._ p. 54.]
[Footnote 94: _Descent of Man_, p. 92.]
[Footnote 95: _Ibid._ p. 100.]
[Footnote 96: _Life and letters_, Vol. II. p. 161, June 22, 1859.]
[Footnote 97: _Ibid._ Vol. III. p. 15, March 17, 1863.]
[Footnote 98: _Descent of Man_, p. 132.]
[Footnote 99: _Ibid._ pp. 136, 137.]
[Footnote 100: _Ibid._ p. 143.]
[Footnote 101: _Ibid._ p. 193.]
[Footnote 102: _Descent of Man_, p. 231.]
[Footnote 103: _Descent of Man_, p. 308.]
[Footnote 104: _Life and Letters_, Vol. II. p. 23.]
[Footnote 105: _Loc. cit._ p. 39.]
[Footnote 106: _Loc. cit._ (1856), p. 82.]
[Footnote 107: _Ibid._ Vol. III p. 159.]
[Footnote 108: _Descent of Man_, p. 924.]
[Footnote 109: "Die Hautfarbe des Menschen," _Mitteilungen der Anthropologischen Gessellschaft in Wien_, Vol. x.x.xIV. pp. 331-352.]
[Footnote 110: _Ibid._ p. 947.]