Kitabı oku: «The Old Riddle and the Newest Answer», sayfa 14
APPENDIX
A. Evolution and the lower forms of life (p. 165)
A SINGULARLY instructive field for the study of the mutability or stability of species should be afforded by the lower forms of life, in which organization is reduced to a minimum, they being mere masses of protoplasm without even a containing envelope, while their nourishment is of the simplest. It would therefore appear that environment should be all-potent to modify them and produce specific modifications, while the extreme rapidity with which they propagate their kind, and that unisexually, ought to require no vast extent of time to make such transmutations apparent.
It is found, however, on the contrary, that nowhere in organic nature does the type remain more rigidly persistent. Professor Macbride, for example, tells us,327
"The Myxomycetæ may be regarded as the organic group in which the forces of heredity, – whatever these forces may be – are at their maximum: they have responded as little as possible to the influence of their environment."
To the same effect speaks Professor Paulesco of Bucharest, of other elementary organisms.328
What is still more remarkable, these same organisms are extremely sensitive to altered conditions of environment, which have a direct and immediate influence, gravely modifying their morphological and physiological characters, changes in respect of light, minute alterations of temperature, or the introduction of a new chemical substance, even in infinitesimal quantity, frequently causing them to assume forms very different from the specific type, and profoundly modifying their nutritive processes.
Here, it was at first thought, when Pasteur revealed their history, is clear evidence of specific transformation. But he presently convinced himself and others that it is not so, for although liable to assume such polymorphic forms according to the conditions in which they find themselves, there is no alteration of specific nature, and if the original circumstances be restored, the original forms reappear – "une élasticité functionelle de la cellule lui permettant de se plier à des conditions variées d'existence sans changer d'être." (Pasteur.)
As M. Duclaux adds:329
"La notion d'espèce ne disparait pas pour cela. La variabilité est un caractère comme un autre, bien que plus difficile à inscrire dans la classification, et une espèce est aussi bien définie par les sensibilités diverses qu'elle manifeste que par la petite liste des mots et de propriétés dans laquelle on croyait pouvoir autrefois enfermer toute son histoire… La lien de l'espèce c'est la loi qui préside à ces changements, et la variété des formes et des fonctions n'est pas du tout en contradiction avec l'unité de l'espèce."
B. Note on Chap. XV. p. 203
Since the foregoing pages have been in type there has come to hand the New York Literary Digest of January 23, 1904, containing the following article (p. 119).
"Are the Days of Darwinism Numbered?"
The recent death of Herbert Spencer lends special timeliness to the above topic, which is being actively debated just now in German theological circles. The immediate cause of the revival of interest in the present status of the Darwinian theory is found in a lengthy article by the veteran philosopher, Edward von Hartmann, which appears in Oswald's Annalen der Naturphilosophie (vol. ii. 1903), under the title 'Der Niedergang der Darwinismus' ('The Passing of Darwinism'). That the famous 'philosopher of the unconscious' is not prejudiced in favour of biblical views has been more than clear since the publication of his Selbstzersetzung der Christentums ('Disintegration of Christianity') in 1874. Hartmann in his new article has this to say —
'In the sixties of the past century the opposition of the older group of savants to the Darwinian hypothesis was still supreme. In the seventies, the new idea began to gain ground rapidly in all cultured countries. In the eighties, Darwin's influence was at its height, and exercised an almost absolute control over technical research. In the nineties, for the first time, a few timid expressions of doubt and opposition were heard, and these gradually swelled into a great chorus of voices, aiming at the overthrow of the Darwinian theory. In the first decade of the twentieth century it has become apparent that the days of Darwinism are numbered. Among its latest opponents are such savants as Eimer, Gustav Wolf, De Vries, Hoocke, von Wellstein, Fleischmann, Reinke, and many others.'
These facts, according to Hartmann's view, while they do not indicate that the Darwinian theory is doomed, undermine its most radical features:
'The theory of descent is safe, but Darwinism has been weighed and found wanting. Selection can in general not achieve any positive results, but only negative effects; the origin of species by minimal changes is possible, but has not been demonstrated. The pretensions of Darwinism as a pure mechanical explanation of results that show purpose are totally groundless.'
Other scholars think that Hartmann does not do full justice to the reaction that has set in, particularly in Germany, against Darwinism. This sentiment is voiced by Professor Zoeckler, of the University of Greifswald, in the Beweis des Glaubens (No. xi.), a journal which recently published a collection of anti-Darwinian views from German naturalists. He calls the article of Hartmann 'the tombstone-inscription [Grabschrift] for Darwinism,' and goes on to say:
'The claim that the hypothesis of descent is secured scientifically must most decidedly be denied. Neither Hartmann's exposition nor the authorities he cites have the force of moral conviction for the claim for purely mechanical descent. The descent of organisms is not a scientifically demonstrated proposition, although descent in an ideal sense can be made to harmonize with the biblical account of creation.'
Views of a similar kind are voiced in many quarters. The Hamburg savant, Edward Hoppe, has written a brochure, Ist mit der Descendenz-Theorie eine religiöse Vorstellung vereinbar? [Is the Theory of Evolution reconcilable with the Religious Idea?] in which he takes issue, in the name of religion, with the purely naturalistic type of Darwinian thought. The most pronounced convert to anti-Darwinian views is Professor Fleischmann, of Erlangen, who has not only discarded the mechanical conception of the origin of being, but the whole Darwinian theory. He recently delivered a course of lectures, entitled 'Die Darwin'sche Theorie,' which have appeared in book form in Leipsic. He comes to this conclusion: 'The Darwinian theory of descent has not a single fact to confirm it in the realm of nature. It is not the result of scientific research, but purely the product of the imagination.'
From another article in the same journal (p. 116), entitled 'A Study of Creation,' the following paragraphs may be cited:
"The French have never been enthusiastic Darwinians. It is, perhaps, not surprising, therefore, to find a French geologist, M. Stanislas Meunier, arguing in the Revue Scientifique (December 19) against all schools of transformism and stoutly maintaining what is practically a doctrine of special creation. He admits that living beings form a connected series; but the connexion, he believes, is not one of physical descent, but inheres in something outside of and pre-existent to the earth. He does not name it, but he would probably not object to the inference that it is the mind of a creator.
"M. Meunier gives at some length his reasons for rejecting Darwin's, Lamarck's, and all other theories of transformism. All we can be sure of, he thinks, is that, as in the case of the various kinds of pottery, we have to do with an orderly development, although he thinks it is not a development by descent. He closes, thus:
"'Doubtless we cannot usefully risk any hypothesis on the mechanism of the production of living things; but it is, perhaps, a step in advance only to come to the conclusion that the cause of life and its manifestations on the earth is exterior to the earth; that it is anterior to our world, just as are doubtless the laws of physics and chemistry, which govern the relations of matter and force throughout space.
"'The philosophy of science can lose nothing by the admission of points of view that, far from narrowing our subjects of study, enlarge them beyond all limits; and this is, perhaps, the occasion to show once more to persons who are turning toward metaphysics in their thirst for mystery, that they will find in pure science that wherewith they may satisfy their legitimate aspirations.'"
C. Succession of Plant forms p. 220
Recent investigations have led to the remarkable discovery that many fern-like plants of the Carboniferous rocks, hitherto classed as Cryptogams, were in reality seed-bearers, and thus intermediate between Cryptogams and Cycads, the most primitive of existing seed-plants. They have accordingly been placed in a special group "Cycadofilices," or "Fern-Cycads," and regarded as transitional types, the view that they are the remains of a natural bridge connecting the Ferns with the Gymnosperms having received wide support,330 and at first sight this conclusion would appear natural and obvious. But here, as in other cases, the difficulty is that the seeds which have been found are all fully developed; there are none in the intermediate stages between true spores and true seeds; we have the finished article, but no trace of seeds in the making; which upon any theory of evolution must have been exceedingly numerous. Hence Dr. Scott tells us:331
"The important discoveries of the seeds of the Pteridosperms scarcely touch the question of descent, for these organs are of too advanced a type to throw light on the probable derivation of the group."
In this instance, therefore, as in others, it remains true that in no case is any trace found of rudimentary character in the earliest fossil specimens of any class.
It is undoubtedly a further puzzle that some of the Carboniferous cryptogams which did not bear real seeds, yet simulated them, a habit not easily explained on evolutionary principles.
D. The Course of Evolution
The evidence of Professor Vines quoted in the text (pp. 202, 237) receives a remarkable confirmation from that of Dr. Smith Woodward, Keeper of Geology in the National Museum of Natural History. Speaking before the International Congress of Arts and Science, St. Louis, U.S.A., September 22nd, 1904, he thus touched upon the same question, which he illustrated especially from the history of fossil fishes, which he has made his special study.332
"It must be confessed that repeated discoveries have now left faint hope that exact and gradual links will ever be forthcoming between most of the families and genera. The 'imperfection of the record,' of course, may still render some of the negative evidence untrustworthy; but even approximate links would be much commoner in collections than they actually are if the doctrine of gradual evolution were correct. Palæontology, indeed, is clearly in favour of the theory of discontinuous mutation, or advance by sudden changes, which has lately received so much support from the botanical experiments of H. de Vries.
"Further results obtained from the study of fossils have a bearing even on the deepest problems of Biology, namely, those connected with the nature of life itself. For instance, it is allowable to infer, from the statements already made, that the main factor in the evolution of organisms is some inherent impulse – the 'bathmic force' of Cope – which acts with unerring certainty whatever be the conditions of the moment."
E. Pedigree of the Horse
Some recent evidence on this subject certainly does not clear away the difficulties set forth in the text.
From Nature, Sept. 8, 1904, p. 474.
"Professor Osborn (in a lecture before the British Association) mentioned that more than a hundred more or less complete skeletons of horses and horse-like animals had been found in North America. He thought he had established the fact that horses were polyphyletic, there being four or five contemporary series in the Miocene, but that the direct origin of the genus Equus in North America was not established with certainty."
Professor Sedgwick, Student's Text Book of Zoology, p. 599.
"Much has been written on the ancestry of the horse. It has been maintained by many authors that a continuous series of forms connecting it with the four-toed, brachyodont Hyracothoridæ of the Eocene has been discovered, and that here if anywhere a demonstrative historical proof has been obtained of the doctrine of organic evolution. Without desiring in the smallest degree to impugn that doctrine, it may be permitted us here to examine rather closely the view that the series of forms which recent palæontological research has undoubtedly brought to light constitute that historical proof which has been claimed for them."
[After an examination of the structural characters of these intermediate forms, viz., Pliohippus, Protohippus, Desmathippus, Miohippus, Mesohippus, Orohippus, and Hyracotherium, the author proceeds]:
"So far as the characters mentioned are concerned, we have here a very remarkable series of forms which at first sight seem to constitute a linear series with no cross-connections. Whether, however, they really do this is a difficult point to decide. There are flaws in the chain of evidence, which require careful and detailed consideration. For instance, the genus Equus appears in the Upper Siwalik beds, which have been ascribed to the Miocene age. It has, however, been maintained that these beds are in reality Lower Pliocene, or even Upper Pliocene. It is clear that the decision of this question is of the utmost importance. If Equus really existed in the Upper Miocene, it was antecedent to some of its supposed ancestors. Again in the series of equine forms, Mesohippus, Miohippus, Desmathippus, Protohippus, which are generally regarded as coming into the direct line of equine descent, Scott333 points out that each genus is, in some respect or other, less modified than its predecessor. In other words, it would appear that in this succession of North American forms the earlier genera show, in some points, closer resemblance to the modern Equus than to their immediate successors. It is possible that these difficulties and others of the same kind will be overcome with the growth of knowledge, but it is necessary to take note of them, for in the search after truth nothing is gained by ignoring such apparent discrepancies between theory and fact."
Besides the structure of limbs and teeth, another argument for the descent of the horse has been drawn from certain phenomena of colouration. Stripings are found not unfrequently to occur in the legs and withers, which Darwin took for a reversion to the character of a very remote ancestor, the common parent, in fact, of horses and asses, which he supposed to have been striped all over like a zebra. Like other such common ancestors, this hypothetical animal had never been seen, but was thought to be most nearly represented by the Kathiwar horse, with stripes on a dun ground, a specimen of which is exhibited as illustrating the hypothesis in the National Museum of Zoology.
Recently, however, Professor Ridgeway, who has devoted special attention to the problem, has satisfied himself that there is no sufficient foundation for these suppositions. He thus sums up the evidence which he has been able to collect:334
"Darwin's view that the original ancestor of the Equidæ was a dun-coloured animal, striped all over, was based, not merely on the occurrence of stripes in horses, but on his belief that such stripes were common in dun horses, and that there was a tendency in horses to revert to dun colour. But it must be confessed that the facts do not warrant his conclusion… It is clear that stripes are at least as often a concomitant of dark as of dun colour. Moreover, if Darwin's hypothesis of a dun-coloured ancestor with stripes is sound, dark colours such as bay and brown must be of more recent origin, and accordingly there ought to be a great readiness on the part of a progeny of a light-coloured animal when mated with a dark to revert to the light. But Professor Ewart's zebra stallion has never been able to stamp his own peculiar pattern or his own colours on his hybrid offspring. The ground colour has been determined by the dams of the hybrids."
