Evolution Not Supported by Embryology

Evolution Not Supported by Embryology

BY ROBERT C. WEBB

[Sixth of a 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.] The so-called "argument from embryology" for the hypoth- esis of organic evolution is nearly the most famous of all the sup- posed "evidences" in its behalf. In considering the embryo as, in some sense, an epitome or "recapitulation" of its generic his- tory, it is also nearly the oldest formal argument for the hypoth- esis representing, in fact, the point at which the word "evolution" ;

was first introduced into the vocabulary of biology. As far back as the time of Harvey — he who "discovered" the circulation of the — blood the- study of embryology was well under way toward a scientific formulation ; although it suffered the retarding influence of several fantastic theories, before it was finally established. Among these was the theory, fathered probably by Albrecht von Haller (1708-77), that the germ in ovo is a perfect "miniature model" of the adult individual, and that, furthermore, the fertile ovum contains, not only this "animalcule," as they termed it, but also, germ within germ, ad infinitum, the simulacra, potential but complete, each in itself, of the individuals to be begotten by the "outermost," or first of the "models," which is supposed to repre- sent the individual emerging into life at the completion of any given process of gestation. The successive appearances (births) of these "models," generation after generation, was supposed to constitute a vital succession, which was termed "evolution," or the "unfolding" of the destinies which had been "preformed" from the beginning of time. Although, in its formal statement, any such theory as this one would be ridiculed by biologists of the present day, the same idea is involved in the current popular un- derstanding of evolution as the racial working-out of an involved potentiality of development, which is latent in every germ, through the process describable as "cosmic gestation." Tt certainly accords

with Professor Le Conte's definition of evolution as a "continuous progressive change * * * * by means of resident forces." In modern evolution literature the ascribed significance of the developing embryo is the reverse of that mentioned above. Now, it is not so clearly the preformed epitome of all coming genera-

tions, but rather the "recapitulation" of the past. Thus, the mod- ern evolutionist sees in its growth a very definitely marked "re- enactment" of the main features of the process by which, sup- posedly, the race represented by the embryo was first originated. This idea is frequently expressed in some such statements as that "the embryonic life of man is almost an epitome of the animal

248 IMPROVEMENT ERA kingdom, beginning with characters common to the moneys and worms, and ending with the vertebrates." (Packard.) The be- ginnings of this theory are presented in Chambers' "Vestiges of Creation," which outlines the development of the human brain, through all the various stages in which it resembles the brains of lower animals, from the "avertebrate" type to the human, during the period of gestation. It has since been much elaborated ln- such enthusiasts as Haeckel and Le Conte, who do not hesitate to represent it as in the highest sense significant and established. The same analogies are extended to every part of the developing organism. Thus Haeckel is quoted as "identifying" no less than twenty-two separate types of organism exemplified by stages in the growth of the embryo. Prominent among these are "struc- tureless protoplasm, (moner), egg, morula, planula, gastrula (sac stage), ascidian (exhibiting what some regard as the homologue of a spinal marrow), amphioxus, low shark, amphibian, mono- treme, marsupial, lemurid, tailed monkey, tailless ape, Papuan (Anthropogenic)." Such statements are made with a confidence and naivete that might lead the general unbiological reader to suppose that the resemblances referred to were somewhat other than of a rather vague and general character, which is not the case. Professor Le Conte gives the following estimate of the de- velopment of the human brain, which is worthy quotation, not only for sake of fairness, but also in way of exhibiting the quality of his logical analysis, and the temper of dogmatic certainty which he assumes. He says "Now, why should this peculiar order be observed in the building of the individual brain? We find the answer, the only conceivable scientific answer to this question, in the fact that this is the order of the building of the vertebrate brain by evolution throughout geological history. We have already seen that fishes were the only vertebrates living in Devonian times. The first form of brain, therefore, was that characteristic of that class. Then reptiles were introduced; then birds and marsupials; then true mammals; and lastly man. The different styles of brains characteristic of these classes were, therefore, suc- cessively made by evolution from earlier and simpler forms. In phylogeny* this order was observed because these successive forms were necessary for perfect adaptation to the environment at each step. In taxonomy* we find the same order, because, as already explained, every stage in advance in phylogeny is still represented in existing forms. In ontogeny* we have still the same order, because ancestral

*Phylogeny, the history of the evolution of a species or group; tribal history; ancestral development. Taxonomy, the department of science that embodies the principles of classification: * * * * especially the branch of biology that treats of the systematic classification of organisms or of morphological facts. Ontogeny, the history of the evolution of the individual: germ- history; the development of the individual. From Ar f70 Standard Dictionary, (1913).

EVOLUTION AM) EMBRYOLOGY 249

characteristics arc inherited, and family history recapitulated in the individual history." Evolution and Its Relation to Religious Thought.

As a preparation for his invasion of the field of "religious thought," Professor Le Conte evidently assumes the seat of au- thority of the "new dogmatism," making a series of utterly inde- fensible statements, to be accepted, apparently, "because he knows the facts"— of biology. We may judge of his qualifications as a philosopher by his method of handling his facts. Thus, as we shall argue, the "order observed in the building of the individual brain" is not explained only by his "only conceivable scientific answer:" there are other answers quite as conceivable and quite as scientific. His assumption that "fishes were the only verte- brates living in Devonian times" is an unmitigated dogma, and one in which he is contradicted by Huxley's theories, as already seen. As for his jumble of learned terms, we might excuse his pedantry, but for the fact that the type of "religion" which he, and his school, would foist upon the world has no other excuse than to afford a pretense of piety to people who lack courage to acknowledge that they are really atheists. But this is the role of our evolution "theologies." In addition to the indicated similarities to be observed in the process of developing the individual vertebrate and human brain, quite analogous stages are to be observed in the progressive up- building of the heart, and have been suggested in connection with several other organs. The most triumphantly used argument, how- ever, is that which urges the fact that the embryo, at a certain stage, shows true gill slits, like a fish or other water-breather and the statement of this fact is frequently made in italic type which is urged as a certain evidence of the persistence of "ances- tral structures," supplanted by quite different organs in the adult animal. Dr. Romanes sums the general points of the argument, as follows

"Now this progressive inheritance by higher types of embryo- logical characteristics common to lower types is a fact which tells greatly in favor of the theory of descent, whilst it seems almost fatal to the theory of design. For instance, to take a specific case, Mr. Lewes remarks of a species of salamander— which differs from most — salamanders in being exclusively terrestrial that, although its young ones can never require gills, yet, * * * * when placed in the water the young ones swim about like the tadpoles of the water newt. Now, to suppose that these utterly useless gills were specially de- signed, is to suppose design without any assignable purpose; for even the far-fetched assumption that a unity of ideal is the cause of organic affinities, becomes positively ridiculous when applied to the case of embryonic structures, which are destined to disappear before the animal is born. Who, for instance, would have the courage to affirm that the Deity had any such motive in providing, not only the unborn young of specially created salamanders, but also the unborn young of specially created man, with the essential anatomical feature of gills? 1

"But this remark leads us to consider a little more attentively the anatomical features presented by the human embryo. The gill-slits

250 [MPROVEMENT ERA just mentioned occur on each side of the neck, and to them the arteries run in branching arches as in a fish. This, in fact, is the stage through which the branchiae of a fish are developed, and, therefore, in fishes the slits remain open during life, while the so-called 'visceral arches' throw out filaments which receive the arterial branches coming from the aortic arches, and so become the organs of respiration, or bran- chiae. But in all other vcrtebrata (/. c, except fishes and amphibia) the gill-slits do not develop branchiae, become closed (with the fre- quent exception of the first), and so never subserve the function of respiration. Or, as Mr. Darwin states it, 'At this period the arteries run in arch-like branches, as if to carry the blood to the branchiae, which are not present in the higher vertebrata, though the slits on the sides of the neck still remain, marking their former position.' * * "At a later period the human embryo is provided with a very con- spicuous tail, which is considerably longer than the rudimentary legs occurring at that period of development, and which Professor Turner — has found to be provided with muscles the extensor, which is so largely developed in many animals, being especially well marked. "Again, as Mr. Darwin says, 'In the embryos of all air-breathing vertebrates, certain glands, called the corpora Wolffiana, correspond with and act like the kidneys of mature fishes;' and during the sixth month the whole body is covered very thickly with wool-like hair even the forehead and ears being closely coated; but it is, as Mr. Darwin observes, 'a significant fact that the palms of the hands and the soles of the feet are quite naked, like the inferior surfaces of all four extremities in most of the lower animals,' including monkeys." Scientific Evidence of Organic Evolution.

The average evolutionist discussion of embryology might read- ily lead the casual and superficial reader to suppose that the devel- opment of the embryo of any species of animal is one long series of protean changes, or kaleidoscopic rearrangements of elements, in which it masquerades, first in one semblance, then in another, be- fore settling down to the sober business of life. Such a person might even conceive the notion that a developing embryo, taken at any "typical period," and placed in a favorable environment, might be expected to begin its independent existence, there and then, as an "ascidian, amphioxus, low shark, amphibian," or even a "tailed monkey," and grow old and die in that form, without further development, precisely like the gill-breathing young of the land-dwelling "salamanders" mentioned by Romanes. That such is not the case, however, scarcely needs be said. The embryo of any higher animal is essentially and unalterably an embryo merely, an incomplete being in process of forming, and, if removed prem- aturely from its natural environment, before a definite very ad- vanced period, will infallibly perish. Furthermore, the specified structural and functional analogies to certain lower animals, shown, as stated, by vertebrate embryos, are of the most superficial and empirical character, mere casual resemblances, in fact, which would lead no one to suspect a "recapitulatory" significance, apart from the desire to discover fresh "evidence" for a preassumed theory. Because the effort of theorists is to accumulate as large a number as possible of facts in supposed support of their hypoth-

EVOLUTION AND EMBRYOLOGY 251

esis,we find such writers as Haeckel mentioning anion-- recapit- ulated "ancestral types," the "morula, planula, astrula," mere stages of inevitable cell-division all, to be observed in the process of developing any many-celled individual from the one-cell ovum. Why this process includes the several stages found, we cannot, of course, undertake to determine. That such stages surely indicate "ancestral types," rather than the simple rule of all cell-work whatever, ancestral or not, is a statement utterly gratuitous and unsupported and that in spite of the fact that some of the lowest ;

orders of life do actually show the "gastrula," and other forms of many-cell structure as permanent life-forms. Such "animals" as the one-celled amoeba, for example, reproduce by "division ;" a process in which the original cell and its nucleus both give out a portion of the substance forming the original individual, thus forming a new one, which performs the same function over and over again, thus continuing the "species." The difference between this order of being and those consisting of many cells is that, in the latter case, the numerous consecutive cell-divisions — one into — two, two into four, four into eight, etc., are made for the definite purpose of beginning the building-up of tissues and organs, in the structure of which all the individual cells co-operate to form an active unit, and, under normal conditions, attempt no semblance of separate existence, either singly or in groups. One fact which writers like Haeckel neglect to mention in the "recapitulation" connection is the actual "difference in kind" be- tween the behavior of amoeba and the development of Coclcntcrata of the gastrula type, in the formation of which a hollow sphere, composed of numerous distinct, but closely-associated cells, be- comes turned in upon itself, as it were, so as to form a double- walled sac. Nor, even admitting that the gastrula type of creature may have resulted from an "acquired habit" in numerous separate one-cell individuals of associating to form sphere or gastrula "col- onies," which later became true many-celled individuals, is there any certain explanation of further assumed development into the "higher" and more complex forms of creature certainly and as- ;

suredly of nothing in any way resembling the processes occurring in the course of developing a vertebrate, or other higher animal by ordinary ovulation or gestation. The life-story of the developing embryo indicates surely that the one object involved in the several stages of cell-division, by which the one original cell subdivides to form an association of numerous smaller cells, is to afford the vehicle for the embryo itself, which, as we may state here, does not result from further — transformations of the total mass of cells by which, for example, the gastrula passes into a "bi-gastrula," and that into something still more differentiated, by any number of stages that might be

— imagined but is formed from a select few of them, in a definite locality, and is protected and nourished by the remainder. Nor is

252 IMPROVEMENT ERA there any very evident analogy between this process and the "dele- gation" of functions to separate sets of cells or organisms, as seen in the colony-forming zoophytes. In order to support our contention that the early stages, at least, of cell-division and combination in the process Of developing and nourishing the embryo, argue to no "ancestral references" whatever, we may outline these stages. After the formation of the cell-cluster known as "morula" —this is the Latin word for — mulberry, and is used because of the resemblance we find that in the central cavity, formed' by the numerous associated cells, a special form of cell-combination begins, in a definite area known as the "embryonal disc," and quickly spreads, giving rise to the three-layered "blastoderm" (i. e., "germ-skin"). The next stage is the appearance, on the "embryonal disc" of a definite thicken- ing, upon which appears the so-called "primitive groove," the first rudiments of the "longitudinal axis" of the vertebrate animal. At a similar stage in the development of arthropods, for example, we find, instead of such a groove, a series of segments, characteristic of the transverse divisions of the mature body structure, which is suggestive of the fact that the difference between vertebrate and invertebrate life-forms is to be discerned upon the first definite appearance of the germ. This vertebrate "primitive groove" be- comes closed at both ends, by the meeting and fusing of its ends, thus forming an outline resembling a flattened ring, or a very much elongated letter "o." Its edges then close longitudinally, transforming it into a tube. At one end of this closed "groove" is begun the development of the head, and at the other, of the

lower extremities of the trunk. The embryo, thus laid down in the bare outline of the creature to develop from it, is now enclosed in the folds of the decidua, formed from the inner layer of the blastoderm, known as the "hypoblast," which thus produces its enveloping sac, known thereafter as the "amnion." Thus, as is evident, the embryo arises, not from a recombina- tion of all the cells of the "morula," or of the derived "blasto- derm," but from a selected few of them, gathered at a definite region on its wall. In other words, the process of germ-develop- ment seems to begin as a substitution, rather than a metamorphosis, in course of which the part absorbs the whole, and a new type of life-form builds itself up from the material of the old. It may be admissible to compare the process to the growth of a parasitic organism, which begins by involving certain few cells in a definite locality, and aims to absorb into itself the entire cell-structure, for its own use and nourishment. In view of such facts, we may understand that Haeckel's first five "recapitulatory stages" are very imperfectly obvious. (This subject in the series of articles will be concluded in the Feb- ruary number.)