The most characteristic representative, however, of the modern school of unified and purified Darwinism is not Haeckel, but the Freiburg zoologist, Weismann. Through a long series of writings he has carried on the conflict against heterodox, and especially Lamarckian theories of evolution, and has developed his theories of heredity and the causes of variation, of the non-transmissibility of acquired characters, and the all-sufficiency of natural selection. In his latest great work, in two volumes, “Lectures on the Theory of Descent,”[11] he has definitely summed up and systematised his views. These will interest us when we come to inquire into the problem of the factors operative in evolution. For the moment we are only concerned with his attitude to the Theory of Descent as such. It is precisely the same as Haeckel's, although he is opposed to Haeckel in regard to the strictly Darwinian standpoint. The Theory of Descent has conquered, and it may be said with assurance, for ever. That is the firm conviction on which the whole work is based, and it is really rather treated as a self-evident axiom than as a statement to be proved. Weismann takes little trouble to [pg 104] prove it. All the well-known, usually very clear proofs from palæontology, comparative anatomy, &c., which we are accustomed to meet with in evolutionist books are wanting here, the genealogical trees of the Equidæ, with the gradually diminishing number of toes and the varying teeth, of Planorbis multiformis, of the ammonites, the graduated series of stages exhibited by individual organs, for instance, from the ganglion merely sensitive to light up to the intricate eye, or from the rayed skeleton of the paired fins in fishes up to the five-fingered hands and feet of the higher vertebrates, &c. These are only briefly touched upon in the terse “Introduction,” and the whole of the comprehensive work is then directed to showing what factors can have been operative, and to proving that they must have been “Darwinian” (selection in the struggle for existence), and not Lamarckian or any other. This is shown in regard to the coloration of animals, the phenomena of mimicry, the protective arrangements of plants, the development of instinct in animals, and the origin of flowers.
In reality Weismann only adduces one strict proof, and even that is only laying special stress on what is well known in comparative embryology; namely, the possibility of “predicting” on the basis of the theory of descent, as Leverrier “predicted” Neptune. For instance, in the lower vertebrates from amphibians upwards there is an os centrale in the skeleton of wrist, but there is none in man. Now if man be descended [pg 105] from lower vertebrates, and if the fundamental biogenetic law be true (that every form of life recapitulates in its own development, especially in its embryonic development, the evolution of its race, though with abbreviations and condensations), it may be predicted that the os centrale is to be found in the early embryonic stages of man. And Rosenberg found it. In the same way the “gill-clefts” of the fish-like ancestors have long since been discovered in the embryo of the higher vertebrates and of man. Weismann himself “predicted” that the markings of the youngest stage of the caterpillars of the Sphingidæ (hawk-moths) would be found to be not oblique but longitudinal stripes, and ten years later a fortunate observation verified the prediction. Because of the abundance of evidential facts Weismann does not go into any detailed proof of evolution. “One can hardly take up any work, large or small, on the finer or more general structural relations, or on the development of any animal, without finding in it proofs for the evolution theory.”
But assured as the doctrine of descent appears,[12] and certain as it is that it has not only maintained its hold since Darwin's day, but has strengthened it and has gained adherents, this foundation of Darwinism is [pg 106] nevertheless not the unanimous and inevitable conclusion of all scientific men in the sense and to the extent that the utterances of Weismann and others would lead us to suppose. Apart from all apologetic attempts either in religious, ethical, or æsthetic interests, apart, too, from the superior standpoint of the philosophers, who have not, so to speak, taken the theory very seriously, but regard it as a provisional theory, as a more or less necessary and useful method of grouping our ideas in regard to the organic world, there are even among the biologists themselves some who, indifferent towards religious or philosophical or naturalistic dogma, hold strictly to fact, and renounce with nonchalance any pretensions at completeness of knowledge if the data do not admit of it, and on these grounds hold themselves aloof from evolutionist generalisation. From among these come the counsels of “caution,” admissions that the theory is a scientific hypothesis and a guide to research, but not knowledge, and confessions that the Theory of Descent as a whole is verifiable rather as a general impression than in detail.
Virchow's Position.
Warnings of this kind have come occasionally from Du Bois-Reymond, but the true type of this group, and its mode of thought, is Virchow. It will repay us and suffice us to make acquaintance with it through him. His opposition to Darwinism and the theory of descent was directed at its most salient point: the [pg 107] descent of man from the apes. In lectures and treatises, at zoological and anthropological congresses, especially at the meetings of his own Anthropological-Ethnological Society in Berlin, from his “Vorträge über Menschen-und Affen-Schädel” (Lectures on the Skulls of Man and Apes, 1869), to the disputes over Dubois' Pithecanthropus erectus in the middle of the nineties, he threw the whole weight of his immense learning—ethnological and anthropological, osteological, and above all “craniological”—into the scale against the Theory of Descent and its supporters. Virchow has therefore been reckoned often enough among the anti-Darwinians, and has been quoted by apologists and others as against Darwinism, and he has given reason for this, since he has often taken the field against “the Darwinists” or has scoffed at their “longing for a pro-anthropos.”[13] Sometimes even it has been suggested that he was actuated by religious motives, as when he occasionally championed not only freedom for science, but, incidentally, the right of existence for “the churches,” leaving, for instance, in his theory of psychical life, gaps in knowledge which faith might occupy in moderation and modesty. But this last proves nothing. With Virchow's altogether unemotional nature it is unlikely that religious or spiritual motives had any rôle in the establishment of his convictions, and in Haeckel's naïve blustering at religion, there is, so to speak, more [pg 108] religion than in the cold-blooded connivance with which Virchow leaves a few openings in otherwise frozen ponds for the ducks of faith to swim in! And he has nothing of the pathos of Du Bois-Reymond's “ignorabimus.” He is the neutral, prosaic scientist, who will let nothing “tempt him to a transcendental consideration,”[14] either theological or naturalistic, who holds tenaciously to matters of fact, who, without absolutely rejecting a general theory, will not concern himself about it, except to point out every difficulty in the way of it; in short, he is the representative of a mood that is the ideal of every investigator and the despair of every theoriser.
His lecture of 1869 already indicates his subsequent attitude. “Considered logically and speculatively” the Theory of Descent seems to him “excellent,”[15] indeed a logical moral(!) hypothesis, but unproved in itself, and erroneous in many of its particular propositions. As far back as 1858, before the publication of Darwin's great work, he stated at the Naturalists' Congress in Carlsruhe, that the origin of one species out of another appeared to him a necessary scientific inference, but——And throughout the whole lecture he alternates between favourable recognition of the theory in general, and emphasis of the difficulties which confront it in detail. The skull, which, according to Goethe's theory, has [pg 109] evolved from three modified vertebræ, is fundamentally different in man and monkeys, both in regard to its externals, crests, ridges and shape, and especially in regard to the nature of the cavity which it forms for the brain. Specifically distinctive differences in the development and structure of the rest of the body must also be taken into account. The so-called ape-like structures in the skull and the rest of the body, which occasionally occur in man (idiots, microcephaloids, &c.) cannot be regarded as atavisms and therefore as proofs of the Theory of Descent; they are of a pathological nature, entirely facts sui generis, and “not to be placed in a series with the normal results of evolution.” A man modified by disease “is still thoroughly a man, not a monkey.”
Virchow continued to maintain this attitude and persisted in this kind of argument. He energetically rejected all attempts to find “pithecoid” characters in the prehistoric remains of man. He declared the narrow and less arched forehead, the elliptical form, and the unusually large frontal cavities of the “Neanderthal skull” found in the Wupperthal in 1856, to be simply pathological features, which occur as such in certain examples of homo sapiens.[16] He explained the abnormal appearance of the jaw from the Moravian cave of Schipka as a result of the retention of teeth,[17] accompanied by directly “antipithecoid” characters.
The proceedings at the meetings of the Ethnological Society in 1895, at which Dubois was present, had an almost dramatic character.[18] In the diverse opinions of Dubois, Virchow, Nehring, Kollmann, Krause and others, we have almost an epitome of the present state of the Darwinian question. Virchow doubted whether the parts put together by Dubois (the head of a femur, two molar teeth, and the top of a skull) belonged to the same individual at all, disputed the calculations as to the large capacity of the skull, placed against Dubois' very striking and clever drawing of the curves of the skull-outline, which illustrated, with the help of the Pithecanthropus, the gradual transition from the skull of a monkey to that of man, his own drawing, according to which the Pithecanthropus curve simply coincides with that of a gibbon (Hylobates), and asserted that the remains discovered were those of a species of gibbon, refusing even to admit that they represented a new genus of monkeys. He held fast to his ceterum censeo: “As yet no diluvial discovery has been made which can be referred to a man of a pithecoid type.” Indeed, his polemic or “caution” in regard to the Theory of Descent went even further. He not only refused to admit the proof of the descent of man from monkey, he would not even allow that the descent of one race from another has been demonstrated.[19] [pg 111] In spite of all the plausible hypotheses it remains “so far only a pium desiderium.” The race obstinately maintains its specific distinctness, and resists variation, or gradual transformation into another. The negro remains a negro in America, and the European colonist of Australia remains a European.
Yet all Virchow's opposition may be summed up in the characteristic words, which might almost be called his motto, “I warn you of the need for caution,” and it is not a seriously-meant rejection of the Theory of Descent. In reality he holds the evolution-idea as an axiom, and in the last-named treatise he shows distinctly how he conceives of the process. He starts with variation (presumably “kaleidoscopic”), which comes about as a “pathological” phenomenon, that is to say, not spontaneously, but as the result of environmental stimulus, as the organism's reaction to climatic and other conditions of life. The result is an alteration of previous characteristics, and a new stable race is established by an “acquired anomaly.”[20]