Evolution Not Supported by Embryology

Evolution not Supported by Embryology BY ROBERT C. WEBB

[Continuation of the sixth of the series of articles written for the Era by Dr. Webb, on allied subjects. Each article is complete in itself, but students should read the whole series.- Editors.]

But it is equally evident that the subsequent analogies between the embryonic structure and those of lower animals have little or no "recapitulatory" significance. This may be argued from the fact, not generally understood, that, in a very real sense, the developing young of any animal is a separate individual being from the very beginning of its history; functioning with its own organs, according to the needs of its environment at any given stage, and producing only such organs as structurally and func- tionally are demanded at any such stages. Even in the mammals the connection between the circulation of the mother and the embryo is not direct, but the necessary nourishment and aeration are communicated by a process known as dialysis, consisting of a certain percolation through the tissues covered by the placenta. Indeed, the moment that we recognize the obvious fact that the whole process of maturing the embryo is one of cell-division and cell-distribution, so soon will we understand that it must, from the mere necessity of the case, proceed from a simple form of organi- zation to one more complex, which is to say more varied or elab- orated, the broad general outlines of the intended structure being first produced, and the details and special differentiations being filled in afterward. Such being the case, it is obviously reasonable that, at various times in the development of the embryo, there should be very close analogies to structures found in lower and simpler organisms. Nor, when we consider that there is a grada- tion in life-forms, just as in the light spectrum or the musical scale, is it remarkable that a representative of the "higher orders," built

up in nature's fashion, as just explained, should progressively approximate higher and higher forms of organism. But such a "recapitulation" as this bears no necessary and logical relation to any assumed "ancestral history :" such a claim is even absurd in some particulars, as already seen. According to this explanation of the matter, we find that the first step in the development of the germ is the formation of the "primitive groove," which is comparable to the keel of the ship, first laid down upon the ways. Its subsequent history also resem- bles the process of ship-building in the fact that the framework and essentials are first produced ;later, by specialization and elab- oration, all. parts are perfected together, by a development which

296 IMPROVEMENT ERA works on all at once, and does not attempt to complete one part ahead of the others. Thus, the head is formed, not from a knob, but by an actual infolding of one end of the tube-like embryo. The brain within it is at first elongated, like itself, but later ap- proaches spherical contours, and develops and enlarges in special regions, as predetermined by the rank of the individual in the grade of intelligence, entirely in step with the growth of the embryo in other characteristic particulars. This is the story of development in every other organ of the body; not necessan> because of a strange habit of "recapitulating" stages in the alic^^ process by which the race was "evolved," but because, on any — theory whatever, the growth and formation of all organs because of the process of cell-division and specialization — inevitably pro- ceeds from the simplest to the more complex forms. Because the germ is first an elongated tube-like structure, the brain begins in elongated form because the tube is predestined to fold, bud and ;

differentiate to form a definite order of mature being, the brain, and every other organ along with it, progressively approaches the destined form, as the total structure gradually elaborates. In re- spect to the gradual modification of the embryo to a nearer and nearer approach to the advanced form which it is destined to eventuate, the rule of perfection applies to it at any given stage that applies to all mature animals in the state of nature. In fact, even as to a mature animal, the principle stated by Agassiz, in the following words, applies also to the embryo "In one sense, all animals are equally perfect. Each species has its — whether more or less extended, its own definite sphere of action, peculiar office in the economy of nature; and a complete adaptation to fulfil all the purposes of its creation, beyond the possibility of im- provement. In this sense, every animal is perfect. But there is a wide difference among them, in respect to their organization. In some it is very simple, and very limited in its operation; in others, extremely

complicated, and capable of exercising a great variety of functions." Principles of Zoology.

Since our biologists, therefore, have led off with the habit of comparing the embryo with mature beings in nature, we may dare to extend the analogy, even if into a new direction. But that our new analogy is more evidently scientific cannot be denied. At any stage of its growth the adjustment between the embryo and its — environment is perfect just like that of all mature beings, simple or complex — and the adjustment is maintained by organs of such a degree of simplicity or complexity as are required by the organ- ism at that particular stage of growth, and no other. Thus, when theembryonic body is at a very simple stage of development, we one-chambered pulsating vessel, find that the heart is a simple, which becomes two-chambered, and later four-chambered, only js similar complexities in other parts of the structure are produced. A four-chambered heart, or even a highly convoluted mammalian

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or human brain at an early period would be, not only unnecessary to the needs of the total structure at that period, but also would — argue that the process had proceeded irregularly and this is not nature's — method making of the embryo precisely such a mon- strosity as would be a child with a man-size head, hands or feet. In the same manner, organs resembling the "corpora Wolffiana," mentioned by Mr. Darwin, as above, are sufficient to discharge kidney functions at an early period, for the very obvious reason that no more complicated structures are then needed. Further, in accord with the evident rule of economy holding for all natural processes, the single body canal is developed first, later the differ- entiation which produces double openings, which differentiates the birds and the monotremata from the higher mammals. This in- volves merely that the stage has not been reached in which it is consistent to have the complete structure with two external canals. The indispensable elements appear first, in general outline, then the variations, merely because the process of gestation progres- sively transforms a simple structure into more and more differ- entiated forms. We may assert, furthermore, that this is posi- tively all that science tells us on the matter for, even though we ;

may have to depend upon our zoologists for the facts in the case, we do not depend on them for our knowledge of the laws of logic, which alone enable us to sift the "evidences" which they offer for their ambitious theory. The theory of the "recapitulation" of an- cestral types is not inevitable at any stage of the process conse- ;

quently, not logical in the sense of furnishing a demonstration, as they claim. As regards the "conspicuous tail" mentioned by Romanes, we may remark that it merely indicates an apparently necessary stage in the transformation of the elongated "worm-like" embryo into the contours of its mature form. The "buds" of the lower limbs start out at points above the insertion of this "tail," an anatomical feature retained to maturity but, whereas in some animals, owing ;

to a "conditioning feature" existing, probably, from the earliest appearance of the germ-cell, the "mammalian plan" is varied by the continuous growth of the tail, along with the other organs and limbs, in man it ceases to develop, or rather does not develop at all, after the appearance of the rudimentary limbs. At no stage after the development of the limbs is there discernible a true tail in the human embryo. If the embryonal development "recapitulates" generic evolution, we should logically expect the tail to develop to a certain very advanced stage, and then to dwindle this is not :

the case, however. The limbs appear first as rounded buds, from which the rudiments of fingers start out as soon as the "arm" begins to lengthen. There is no suggestion of the alleged stages by which the fish fin passed into the hand. Why is this important process not "recapitulated?"

298 IMPROVEMENT ERA Other alleged "evidences" manifest the same contempt for logical principles. Thus, with childish glee, our would-be re- modelers of "religious thought" gravely inform us that the human embryo, at a certain stage, "is covered very thickly with wool-like hair" — therefore, our monkey ancestry is established, they suppose. It is unnecessary to comment further on this remark than to call attention to the' fact that the human animal is naturally a hairy animal, and that, in proper conditions hair may be grown on any part of the body, except, of course the palms of the hands and the soles of the feet. The atrophy of the hair follicles in most of the skin is no more remarkable, and no more "evolutionary" than the disuse of numerous muscles in the body, which should be used in a really "normal" being, precisely as the "flying muscles" of a domestic fowl are found to be much weakened, and not nourished up to the point of permitting strong flight, as in birds having no "white meat." These are all examples of variation by atrophy, which, as we have already claimed, is the larger part of all cer- tainly established variation. Similarly, most of the so-called "vestigial organs," such as the vermiform appendix, argue to de- rivation from no "lower animals" having them developed, but, precisely, to such changes in habits, diet, etc., as may be imagined in all the radical revolutions in the past history of this world, which cannot have failed to modify habits. But, of course, this is "absurd," because we say nothing about "monkey ancestry," as

is acceptable to our "revisers of religious thought."

But the utter superficiality of all alleged "analogies" and "affinities" involved in the common "evolution" arguments are more apparent in some other matters. Thus, certain so-called "scientists" have had the impudence to assert that the human embryo reproduces the "worm" stage at a certain point in its de- velopment. We find of course that this stage is suggested by the appearance of an elongated tube-like structure, which might sug- gest some low member of the Vermes or Holothuroidca, but for the plain and simple fact that the tube does not represent the alimentary canal, but the beginnings of the vertebral column. But, when we come to the consideration of the developing eye, for ex- ample, the assertion that the embryo "recapitulates" the develop- ment of ancestral types is reduced to the lowest terms of absurdity. There are no analogies worth mentioning between this process and any assumed possible stages of development in the race. This brings us to the king-argument in this entire, connection — the appearance of gill-slits and arterial arches in the third and fourth-week embryo. Before yielding, however, to the assertion that these structures may possibly have a "recapitulatory" signifi- cance, several facts associated with their appearance should be carefully investigated. In the first place, although there are no signs of branchiae, or gill structures, in the embryos of any higher

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mammals, and although, as some authorities have asserted, the slits themselves are — not fully perforated they seem, as is asserted, to be closed by membranes — the fact remains, unless all published drawings of these features are quite misleading, that the arteries circulate the foetal blood through the gill-arches, precisely as if true "water-breathing" were taking place. Secondly, these appar- ent gill-slits persist for less than three — — probably not for more than two weeks of the entire period of embryonic development, and disappear with the complete establishment of umbilical circu- lation and aeration. These facts would seem to argue strongly that these gill-slits and arterial arches are not "vestigial structures" in any sense, but that they actually subserve some present use very closely analogous to breathing and the "aeration" of the blood by osmosis in mature animals of the water-breathing types. When we consider the further fact that the embryo itself floats in the liquid filling the amnionic sac, the concurrent presence of a very well developed water-breathing structure seems to furnish con- firmatory evidence of our supposition. Indeed, this conclusion has actually been reached by several competent anatomists, not under obligation to weave arguments for the support of an indi- gent hypothesis. Thus, Agassiz directly states that, in the embryo of a fowl in the egg shell, "there exist true gills upon the sides of the neck, and a branchial respiration goes on." (Principles of Zoology.) At this stage the human embryo is less than a quarter inch in total length, and the functions are probably very slow, so that such air as may be in the amnionic water may be sufficient for its needs. At any rate the facts enforce our conclusion that, pre- vious to the development of more efficient apparatus for maintain- ing the normal equilibrium of conditions required by nature, a simple temporary structure is improvised to serve present need, and is eliminated with the completion of other organs. In per- fectly analogous fashion, the young mammal, unlike the young bird, unable to begin life by taking food like his parents, continues his "parasitic existence," as we might call it, by the curious habit of absorbing its mother's milk. This temporary function persists until, with the growth of its teeth, it is able to eat like a normal adult. That the mammalian young is not born with fully de- veloped teeth merely exemplifies the fact that nature requires further time, and new conditions for their development, meantime using* a temporary, and rather rudimentary expedient, until the more perfect structures appear. The explanation of a temporary structure to supply a temporary need also explains the gills on the unborn terrestrial "salamanders" mentioned, as above, by Romanes. If, however, the stages of development, and the temporary forms, found in the course of up-building the mammalian, or vertebrate, embryo, argue "ancestral vestiges" and "recapitula-

300 IMPROVEMENT ERA tions," the rule of analogy should be observable throughout the entire world of living' forms. In this test, however, it is found sadly and absurdly deficient. Thus, in the development of those six-legged arthropods, known as insects, whose structure is, in many points, quite as advanced and complicated as that of verte- brates — — although along different lines we find the curious process of "metamorphosis," instead of the direct production of the young from the egg-cell. Without mentioning the wings of these crea- tures, which, like those of birds, as already explained, may be held to offer grave difficulties in the way of the evolution theory, we may assert positively that the larval (*. c, the grub or caterpillar) stage of no insect bears any resemblance whatever to its mature, or "imago" form, and presents no parallels or analogies to any assumed "ancestral types." The insect larva differs from the vertebrate embryo in the fact that it is a complete and independent being, so far as the requirements of its environment demand com- pleteness. When, however, it shrivels into the pupa, or chrysalis, stage, resuming a form of embryonic life, in course of which it is radically transformed, we discern a stage of development which would be difficult by "ancestral analogies." On the to explain other hand, the process by which the legs and "pro-legs" of the caterpillar are eliminated, and the six-jointed limbs of the mature insect appear, is only another proof that temporary structures, in- tended to serve temporary uses, are formed and used, and dis- appear in due time. The transformation of the larva into the chrysalis is not typical of slow development in ancestral forms, as assumed, but a metamorphosis almost Circean in its suddenness and completeness. Such facts as these have been utterly ignored by advocates of the evolution hypothesis. Nor are these the only ones. The few facts supposed to prove it, or to create a presumption of its truth, have been treated very much in the same manner as the facts of astronomy were handled by the wise men of old, in their efforts to demonstrate the Ptolemaic theory of the universe, and prove that this earth was the centre around which all the stars revolve. However favorable the few facts collated by "scientists" may appear to the hypothesis, or dogma, of organic evolution, there are myriads more that fatally oppose it. It may be, as they claim, that all the innumerable types, organs, functions and structures found through organic nature were really produced by some sort of variation on more primitive forms, but it may be asserted posi- vitely that they are not to be explained by the evolution hypoth- esis, which would have to be radically modified in almost every particular before it could possibly be accepted as a clear explana- tion of even the smallest fraction of the appallingly numerous variants of form to be found in nature.