Popular Science Monthly/Volume 45/June 1894/Weismann's Concessions
NEARLY three years ago, and before the appearance of the second volume of Weismann's Essays, in a Critique of Weismann, based entirely on statements contained in the first volume, I intimated that in my judgment he had already admitted enough to invalidate his doctrine of the non-transmissibility of acquired characters where these are of a functional nature. After showing from his own language that, according to his theory, no variation would be possible later than the Protozoan stage of development, which was a reductio ad absurdum, I proceeded to point out that, apparently from a sense of this position, he had actually admitted the possibility that external influences may affect the germ. One of the passages embodying such an admission is the following:
"I believe, however, that they [hereditary variations] can be referred to the various external influences to which the germ is exposed before the commencement of embryonic development. Hence we may fairly attribute to the adult organism influences which determine the phyletic development of its descendants. For the germ cells are contained in the organism, and the external influences which affect them are intimately connected with the state of the organism in which they lie hid. If it be well nourished, the germ cells will have abundant nutriment; and, conversely, if it be weak and sickly, the germ cells will be arrested in their growth. It is even possible that the effects of these influences may be more specialized; that is to say, they may act only upon certain parts of the germ cells."
In the same essay, speaking of the influence of climate, he also uses language that has a decidedly Lamarckian sound:
"It is difficult to say whether the changed climate may not have first changed the germ, and if this were the case the accumulation of effects through the action of heredity would present no difficulty."
Upon this, my comment was:
"I can not see why this is not conceding the whole issue. Of course, all modifications must first affect the germ, otherwise there could be no hereditary transmission. The only question is: Can the climate or the environment impress changes upon the germ? If yes, the Neo-Lamarckian asks no more. All that he contends for is conceded."
In his later work on the Germ-Plasm, Prof. Weismann says that I am in error if I suppose that "the proof that climatic influences are capable of modifying the germ-plasm contains all that is required by the Neo-Lamarckian school." It is true that climatic influences in the restricted sense are not the only ones that Neo-Lamarckians suppose to act directly upon the germ. They maintain that functional variations are heritable to a greater or less degree, and make the chief distinction between these and accidental variations, such as mutilations and other injuries. The principal stress has hitherto been and still continues to be laid, by both Prof. Weismann and his followers, upon the latter class, which is therefore a waste of words and a mere show of argument calculated to deceive those who have little acquaintance with the subject. But when it comes to modifications of form which are brought about by the efforts and struggles of the creature to obtain its sustenance or accomplish desired ends, the case is wholly different. Such modifications are necessarily complex and involve a harmonious adjustment of all the parts that are brought into exercise, which, when transmitted, secures the complete and systematic variation which species are believed to undergo. Climatic influences are among the most important ones against which the creature thus reacts, but the entire environment may be regarded as constantly impinging, so as to bring about perpetual modifications.
In the second volume of his Essays there are further concessions in this same general direction. In his reply to Prof. Vines, he is compelled to admit that variation may take place in different forms of asexual reproduction, which is a practical abandonment of his theory of the continuity—i. e., of the unalterable nature—of the germ-plasm. He is apparently willing to "concede that some amount of individual variability can be called forth by direct influences on the germ-plasm." Surely a discussion as to the "amount" of such variation is a radically different thing from a discussion as to whether it can take place at all. The principle at issue is shifted when such an admission is made.
But this was only a beginning of the almost complete retreat that he has now made in his last work on the Germ-Plasm. As before, it seems to have been the phenomena which the vegetable kingdom presents that most obstinately refuse to adapt themselves to the mechanical theory of heredity of which he is the author. Before these facts his fundamental distinction between the blastogenic and the somatogenic idioplasm breaks down completely, and here at least he is "compelled to assume that most, if not all, of the cells contain all the primary constituents of the species in a latent condition." After carefully considering such cases as those of Bryophyllum and Begonia, almost any part of which may be made to grow if properly situated, he admits that such observations "apparently prove that 'every small fragment of the members of a plant contains the elements from which the whole complex body can be built up, when this fragment is isolated under suitable external conditions.'"
Before passing to the major admissions of Weismann it may be well to mention a few of the "doubtful phenomena of heredity" which, in case they really occur, form such a stumbling block to his system. On this side of the water one is amused at the statement that "blue grains occasionally occur among the yellow ones in cobs of the yellow-grained maize (Zea) after fertilization with the pollen of a blue-grained species." There is probably only one "species" of Indian corn, but the cultivated varieties are endless, and every farmer's boy knows that it is of the greatest importance to keep these apart, so that the ears will "fill" with the same kind of kernels. Few American farmers would hesitate to stake their farms on the much more than "occasional" occurrence of different kinds of kernels on the same cob in a field where different varieties are planted together.
As regards the numerous cases of the alleged transmission of characters derived from one sire to the offspring of a subsequent sire, though disposed to discredit the evidence, he nevertheless admits their possibility to a limited extent. For he says of them: "We may, however, at any rate suppose that this so-called 'infection,' if not altogether deceptive, only occurs in rare instances, and by no means regularly, or at most only in some cases."
Here we have again, as in the general case above considered, a characteristic Weismannian argument, shifting the point from the qualitative to the quantitative, from the principle to the degree, which reminds one very forcibly of Jack Easy's wet nurse Sarah, who sought to excuse the illegitimacy of her child by the plea that "it was a very little one." In his reply to Mr. Herbert Spencer's articles he has made matters worse by explaining it on the supposition that "spermatozoa occasionally reach the ovary, and there enter into some of the immature eggs. Amphimixis can not proceed, as the germ-plasm of the egg is not ripe, but the nucleus of the sperm cell continues to live in certain circumstances, and so remains till the time of a subsequent coitus with another mate."
It is obvious that in such a case the "subsequent coitus" need have nothing to do with the matter; whenever the egg was ripe there would be nothing to prevent amphimixis taking place, followed by all the stages of ontogeny, and we should have a case of parthenogenesis in the mammalia. If this were possible in the human race it would create something of a ripple in the social world.
Prof. Weismann does not deny that certain diseases, especially germ diseases, are hereditary and directly transmissible in the first instance, and he admits that this has "definitely been proved to occur in the case of syphilis. The father, as well as the mother, is capable of transmitting this disease to the embryo, and the only possible explanation of this fact is, therefore, that the specific bacteria of syphilis can be transmitted by the spermatozoön." But he will not admit that this constitutes a case of the transmission of acquired characters, undertakes to connect it with the adaptation of the parasite to the host, and concludes:
"It will, I think, at any rate be conceded that a 'constitutional' disease can not be taken as a proof that the processes of heredity are therein concerned until we can determine wdiether we are actually dealing with heredity—i. e., the transmission of a constitution and not only with a transference of microbes."
This all seems very absurd to the average reader, and conveys the impression that the scientific discussion of these questions has, after all, no interest for the public, and only amounts to a useless hair-splitting on the part of the doctors. For what matters it to the consumptive whether his case is one of "the transmission of a constitution" or "the transference of microbes"? Mr. Spencer, in the articles above referred to, has sufficiently characterized the reasoning which allows a microscopically visible microbe to penetrate tissues through which even biophors can not pass; and Prof. Weismann, in showing that the latter must break out of jail, should also explain how the former are able to break into jail. Taking all these things into account, I am constrained to repeat a former remark, that "if the term 'acquired' is to be any further refined away, then discussion is useless, for it is not a mere dispute about a word that interests us, but the fundamental question whether external conditions do or do not permanently and progressively influence the development of organic beings."
Reverting, then, to the main question as to the influence of external conditions on the germ, I would remind the reader that in his essay on amphimixis, originally published in 1891, Prof. Weismann held that "a belief m the inheritance of acquired characters by the highly differentiated Protozoa, as ivell as by Metazoa, must be opposed," and imagined that "the phyletic modifications of Protozoa arise from the germ-plasm, that is from the idioplasm of the nucleus"; and he further says:
"My earlier views on unicellular organisms as the source of individual differences, in the sense that each change called forth in them by external influences, or by use and disuse, was supposed to be hereditary, must therefore be dismissed to some stage less distant from the origin of life."
He then ascribed all variations above this early stage to amphimixis and sexual reproduction. In the new work he indeed reiterates this view, and says that these processes furnish "an inexhaustible supply of fresh combinations of individual variations which are indispensable to the process of selection." But he now introduces the following important qualification:
"Although the process of amphimixis is an essential condition for the further development of the species, and for its adaptation to new conditions of existence among the higher and more complicated organisms, it is not the primary cause of hereditary variation."
He then proceeds to explain the change that has taken place in his mind, obviously while writing this book, admits that he had overestimated the power of sexual reproduction to modify species, and shows that though the general result might be changed there could be no variation in the determinants themselves, "which alone could gradually lead to a transformation of the species." Not only is amphimixis incapable of modifying the determinants, but it is also, and for the same reason, incapable of increasing the number of kinds, yet on his general theory these must be enormously increased with the development of every species. A new principle must therefore be found to explain the observed fact. Strangely enough, he finds this principle to be none other than the Lamarckian law of the effect of external conditions in modifying the hereditary elements!
"Amphimixis alone could never produce a multiplication of the determinants. The cause of hereditary variation must lie deeper than this; it must he due to the direct effect of external influences on the biophors and determinants."
It is easy to see that this is a complete abandonment of his fundamental doctrine of the immutability of the germ-plasm, and here again he shifts the point of the argument to the quantitative* and would have us believe that it was the same thing to say that it possesses "great power of remaining constant." But he adds:
"We can none the less avoid assuming that the elements of the germ-plasm—i.e., the biophors and determinants—are subject to continual changes of composition during their almost uninterrupted growth, and that these very minute fluctuations, which are imperceptible to us, are the primary cause of the greater deviations in the determinants, which we finally observe in the form of individual variations."
These variations that take place in the hereditary elements he ascribes to "the impossibility of a complete uniformity as regards nutrition existing during growth," or to "the modifying influence of nutrition." The following passage is as complete an admission of the Lamarckian principle as any one need wish, while at the same time it illustrates over again his characteristic tendency to evade the issue by maintaining that its influence is small compared to that of some other principle:
"Even though it can no longer be doubted that climatic and other external influences are capable of producing permanent variations in a species, owing to the fact that, after acting uniformly for a long period, they cause the first slight modifications of certain determinants to increase, and gradually affect the less changeable variants of the determinants also, the countless majority of modifications is not due to this cause, but to the processes of selection."
In this passage there is a curious psychological implication in the expresssion "no longer," which obviously refers to the changes in his own mind, that are by him projected to the world at large, which, as a matter of fact, has from the first intuitively arrived at the conclusion which has cost him such a great cycle of elaborate reasoning. This new theory of his as to the origin of variations is summed up in the following paragraph:
"The origin of a variation is equally independent of selection and of amphimixis, and is due to the constant recurrence of slight inequalities of nutrition in the germ-plasm which affect every determinant in one way or another, and differ even in the same germ-plasm—not only in different individuals but also in different regions. These variations are at first infinitesimal, hut may accumulate; and, in fact, they must do so when the modified conditions of nutrition which gave rise to them have lasted for several generations. In this way deviations may occur in the structure of single determinants or of groups of them—never, perhaps, in all ids at once, but at any rate in several or even many of them. A doubling of certain determinants of the germ-plasm may originate in the same way. The process of amphimixis has an important share in the accumulation of these modified determinants, for it may raise the minority previously existing in the two parents to a majority by combining their halved germ-plasms. Then, and then only, does selection begin to take place."
After all this it is certainly surprising that he should still cling to his former declaration that acquired characters are not transmissible. After abandoning all his premises he still adheres to his conclusion. Dr. J. G. Romanes, who has been one of his most liberal critics, after characterizing the latter part of the Germ-Plasm as "a right-about-face manœuvre," says that his first impulse "was to cancel all the criticisms which I had written of the Weismannian theory," and it really seems as though it were time to drop this prolonged discussion. Its further continuance must certainly be chargeable to his own course as pursued in Chapter XIII of his Germ-Plasm, and in his reply to Mr. Spencer in the face of these concessions. It is somewhat difficult to understand how he is able to reconcile these apparently conflicting views. That he does not limit the influence of external conditions to the germ-plasm proper, or fertilized germ cell, is apparent from his cheerful acceptance of Nägeli's "opinion that all variations are slowly prepared in the idioplasm in the course of generations before they become apparent," and we must suppose him to admit that it is the hereditary units themselves that are undergoing these transformations. In my address before the Biological Society I had referred to this in the following language:
"You will understand that I am speaking of variations which take place in the germ cells and sperm cells of parental organisms before they blend in the fertilized ovum. Most of Weismann's argument is directed to show that the fertilized ovum itself can not be affected by any transforming influence acting upon the mother during the growth of the embryo. This may be true, but it is unimportant. The time required to develop the embryo is too short for the environment to produce any material change however strong the tendency might be at the time in the direction of such change. It is chiefly the uncombined sexual elements which are admitted by all to be undergoing specific transformation."
This is the main issue, and if admitted, the Neo-Lamarckian asks no more. How then does Weismann evade this issue? He says:
"It is self-evident from the theory of heredity here propounded, that only those characters are transmissible which have been controlled—i. e., produced—by determinants of the germ, and that consequently only those variations are hereditary which result from the modification of several or many determinants in the germ-plasm, and not those which have arisen subsequently in consequence of some influence exerted upon the cells of the body. In other words, it follows from this theory that somatogenic or acquired characters can not he transmitted."
From these and other statements we are obliged to infer that while he admits the power of external influences to affect the somatic cells at all points where they impinge, adapting the organs of the body to the environment, and also admits that inequalities of nutrition (which at bottom are the same thing) modify the germ cells, he denies that these two facts have any connection with each other. Obvious as it is that the species becomes modified to suit the changing environment just as does the individual, he attributes the former wholly to natural selection and the latter wholly to direct adaptation. All, therefore, that is gained by this latter process is necessarily lost, and we have a strong indictment against Nature, "who," he says, "always manages with economy." It seems far more logical to argue from the economy of Nature and the parallelism of these two processes for a causal connection between them.
But it must not be forgotten that he now makes natural selection itself entirely dependent upon "inequalities of nutrition" in the germ-plasm as its universal antecedent. Is this then so widely different from the direct adaptation that takes place in the somatic cells? Let us see how narrow the distinction grows with careful analysis. He admits that alcohol affects the germ and sperm cells by debilitating them and makes weakly children. He would admit the same of any deleterious drug. He would not deny that any disease that debilitates the parents would have a similar effect. These agencies may he regarded as the opposites of nutrition—i, e., as constituting part of the "inequalities of nutrition" that affect the germ and cause it to vary. Variations in the germ-plasm are necessarily quantitative, more or less, according as nutrition is abundant or deficient, and all qualitative differences must be due to the external influences affecting certain constituents more strongly than the rest. How, then, does this differ from pure Lamarckism?
When we say that an organ is strengthened by use, there is obviously an ellipsis. What we mean is that exercise increases nutrition and nutrition strengthens the organ. We may be even more explicit and say that exercise causes increased circulation to the part exercised, causing more tissue to be deposited, thus enlarging and strengthening the organ. Lamarck, of course, understood all this, but did not think it necessary to explain these elementary principles. It is the same with the influence of climate and of the environment in general. All these agencies produce variation by affecting nutrition. If defective nutrition can affect the germ-plasm, why can not abundant nutrition affect it? How does the germ get its nutrition except in the same way that all the other cells of the body get theirs, through the food supply? Is the germ "immortal" in the sense that, like spirit, it can subsist indefinitely upon nothing? If it depends upon sustenance from the body, it must receive its nutrition from the body, and the quantity and quality of that nutrition will vary as those of the body vary. That they do vary he admits, and makes this the very fons et origo of hereditary variation.
But it does not seem possible to Prof. Weismann that a specific variation of some organ or part of the body can influence the reproductive products in precisely the same way so as to perpetuate that variation in the progeny. That we can not understand this may be freely admitted. It is the essence of the mystery of heredity. We know that like produces like. If we abandon that principle, there will be no stopping short of the opposite one, that like produces unlike. It is the same in principle to say that horses may produce cattle as to say that robust horses may produce feeble ones, although the robust ones may have acquired their robustness, not formerly possessed, through proper food, care, and treatment. And there is still no difference in the principle if, instead of robustness, the character be some specific one, such as a "racking" gait, which might be acquired during the life of a single individual. Such qualities are often transmitted. So, too, are the colors of flowers, which can be changed by adding certain ingredients to the soil, as are also certain artificially enforced habits in plants, such as are engendered by "layering," etc. But these are characters only feebly impressed and can not be expected to persist unless carefully aided by artificial selection, yet they must have commenced as acquired characters. Well-broken horses and well-trained dogs transmit these qualities to their offspring, and all domestication and cultivation of animals and plants, all changes wrought in them by man, must have been first acquired to some degree, and then, by intelligent selection, the degree can easily be increased. Like produces like, and if we can not explain why, it is because we have not yet solved the problem of heredity. The elaborate theory offered by Prof. Weismann in his Germ-Plasm, plausible as it sometimes seems, true as it doubtless is in many of its details, utterly fails to solve this problem. It is altogether too rigid, too mechanical, to explain such subtle phenomena. Nature is more flexible, more self-adjusting, more delicate than his system contemplates, and is constantly doing just those things which he insists can not be done.
I trust that it has been sufficiently shown, chiefly from his own words, that in elaborating this complicated theory Prof. Weismann, guided, as he always seems to be, by the highest regard for truth, has, greatly to his credit, conceded all the essential points in the long controversy as to the inheritance of acquired characters. The discussion may therefore be regarded as narrowed down, not so much to the relative importance of the direct and indirect factors, as to the degree to which in any given case the one or the other has operated in determining the observed result.
- Essays upon Heredity and Kindred Biological Problems. By Dr. August Weismann. Authorized Translation. Oxford: At the Clarendon Press. Vol. i, 1889; vol. ii, 1892.
- Neo Darwinism and Neo-Lamarckism. Annual Address of the President of the Biological Society of Washington, delivered January 24, 1891. Proceedings, vol. vi, Washington, 1891, pp. 45-50.
- Essays, vol. i, pp. 103-104.
- Ibid., p. 98.
- Neo-Darwinism, etc., p. 58.
- The Germ-Plasm: A Theory of Heredity. By August Weismann. Translated by W. Newton Parker and Harriet Rönnfeldt. New York: Charles Scribner's Sons, 1893. Contemporary Science Series. See p. 408.
- Essays, vol. ii, p. 95.
- The Germ-Plasm, p. 206. The Italics are his in this and all subsequent passages.
- Ibid., p. 212. The words quoted by Prof. Weismann appear to be taken from De Vries.
- Ibid., p. 383.
- Ibid., p. 385.
- The Inadequacy of "Natural Selection." Contemporary Review for February, March, and May, 1893; reprint, London, Williams & Norgate; New York, D. Appleton & Co., 1893, p. 69.
- The All-sufficiency of Natural Selection. A Reply to Herbert Spencer. Contemporary Review for September and October, 1893, p. 609.
- The Germ-Plasm, p. 388.
- Ibid., p. 891.
- Neo-Darwinism and Neo-Lamarckism, etc., p. 59.
- Essays, vol. ii, p. 192.
- Ibid., p. 193
- The Germ-Plasm, p. 413.
- Ibid., p. 414.
- The Germ-Plasm, p. 415.
- Ibid., p. 417.
- Ibid., p. 422.
- The Germ-Plasm, p. 431.
- The Open Court, vol. vii. Chicago, September 14, 1893. Supplement, p. iii.
- Neo-Darwinism and Neo-Lamarckism, etc., p. 49.
- Germ-Plasm, p. 462,
- Ibid., p. 63.