Read Ebook: On Germinal Selection as a Source of Definite Variation by Weismann August McCormack Thomas J Thomas Joseph Translator

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That the foregoing process has actually taken place is evidenced not only by the presence of the beginnings of such transformations, as found for example in some greenish-tinted specimens of Kallima, but mainly by certain species of the South American genus Catonephele, all of which are forest-butterflies, and which, with many species having dark-brown under surfaces, present some also with bright green under surfaces--a green that is not like the fresh green of our beech and oak trees, but resembles the bright under surface of the cherry-laurel leaf, and is the color of the under surfaces of the thick, leathery leaves, colored dark-green above, borne by many trees in the tropics.

The difference between this and the old conception of the selection-process consists not only in the fact that a large number of individuals with the initial stages of the desired variation is present from the beginning, for always innumerable plus and minus variations exist, but principally in the circumstance that the constant uninterrupted progress of the process after it is once begun is assured, that there can never be a lack of progressively advantageous variations in a large number of individuals. Selection, therefore, is now not compelled to wait for accidental variations but produces such itself, whenever the required elements for the purpose are present. Now, where it is a question simply of the enlargement or diminution of a part, or of a part of a part, these variations are always present, and in modifications of quality they are at least present in many cases.

All value has been denied my doctrine of determinants on the ground that it only shifts the riddles of evolution to an invisible terrain where it is impossible for research to gain a foothold.

And so in this case, I may say, that again doubt is the parent of all progress. For the idea of germinal selection has its roots in the necessity of putting something else in the place of the Lamarckian principle, after that had been recognised as inadequate. That principle did, indeed, seem to offer an easy explanation of many phenomena, but others stood in open contradiction to it, and consequently that was the point at which the lever had to be applied if we were to penetrate deeper into the phenomena in question. For it is at the places where previous views are at variance with facts that the divining rod of the well-seekers must thrice nod. There lie the hidden waters of knowledge, and they will leap forth as from an artesian well if he who bores will only drive undaunted his drill into their depths.

Finally, must be mentioned the name of Th. Eimer, as that of a pronounced and bitter enemy of the theory of selection. I shall leave it to others to decide whether he can properly be called an "opponent" of the principle, in the scientific acceptance of the word. I can see in the blind railings of the T?bingen Professor nothing but a reiteration of the same unproved assertions, mingled with loud praises of his own doughty performances and captious onslaughts on every one who does not value them as highly as their originator.

The lack of confidence latterly placed in the theory of selection even by professed adherents of the doctrine, is well shown by such remarks as the following from Emery, who says: "Some pupils of Darwin have gone beyond their master and discovered in natural selection the sole and universal factor controlling variations. Thus there has arisen in the natural course of things a reaction, especially on the part of those who, while they accept evolution, will have naught to do with natural selection or Darwinism as they call it." Emery then professes himself a Darwinian, although not in the sense of Wallace and "other co-workers and pupils of Darwin." For him "natural selection is a very important factor in evolution, and in determining the direction of variation plays the highest part; but it is far from being the only factor and is probably also not the most efficient factor." Not the most efficient factor but plays the highest part!

If we refer adaptation to selection, we have also to trace back to this source the origin of the organic combinations which make up the various tissues of the body and which go by the collective name of muscular, nervous, glandular substance, etc. Lloyd Morgan has prettily likened the vital processes to the periodic formation and discharge of explosive substances. Unstable combinations are upon the application of a stimulus suddenly disintegrated into simpler and more stable compounds; through this disintegration they evoke what is called the function of the disintegrating part--for example, certain changes of form or the excretion of the disintegrated products, etc.

As to the attempt here made to apply the selective process to the elements of the germinal substance and thus to acquire a foothold for definitely directed variation not blind in its tendency but proceeding in the direction of adaptive growth, it is remarkable that the same was not made long ago by some one or other of the many who have thought and written on selection and evolution.

The facts on which F. M?ller based the enunciation of his law, are the results of several experiments with plants, the numbers of whose grains , or styles, or flowering leaves, were, by the exercise of choice in the cultivation, made to change in definite directions. Accurately viewed their significance is the same as that of numerous other cases of artificial selection, for example, that of the long-tailed Japanese cock which was laid at the foundation of the theory in the text, although the numerical form of the observation gives more precision and distinctness to the reasoning based on them, than is to be observed in cases where we speak of characters as being simply "longer" or "shorter."

F. M?ller's opinion regarding the increase of characters by selection is expressed as follows: "The simplest explanation of these facts appears to be that every species possesses the faculty of varying within certain limits; the crossing of different individuals, so long as no choice is effected in a definite direction, maintains the mean round which the oscillations take place at the same points, and consequently the extremes also remain unaltered. If, however, one side is preferred by natural or artificial selection, the mean is shifted in the direction of this side and accordingly the extreme forms are also displaced towards that side, going now beyond the original limit. However, this explanation does not satisfy me in all cases."

It is not known to me that F. M?ller ever returned to this conception subsequently to the year 1872 or gave further developments of the same, nor have I been able to discover that it has been mentioned by other writers or incorporated in previous notions regarding selection.

This is not germinal selection, but it is the same as what I have referred to in this and in the preceding essay as displacement of the zero-point of variation. Thiselton-Dyer did not draw the conclusion that a definitely directed variation answering to utility resulted from this process, which variation alone must cause the disappearance of useless parts, for the reason that he never attempted to penetrate to the causes of the shifting of the zero-point of variation. Neither Fritz M?ller, whose utterances Thiselton-Dyer was obviously ignorant of, nor Thiselton-Dyer himself pushed his inquiries beyond the thought that the shifting in question resulted entirely in consequence of personal selection. There is no gainsaying that the degeneration of useless organs cannot be explained by personal selection alone, seeing that though the minus variations may possibly have a selective value at the beginning of a degenerative process, they certainly cannot have such in the subsequent course of the same, when the organ has dwindled down to a really minimal mass of substance as compared with the whole body. Of what advantage would it be to the whale if his hinder leg, now concealed in a mass of flesh and no longer protruding beyond the skin, should still be reduced one or several centimetres in size? If the minus variations have no selective value, how can the upper limit of the variational field be constantly displaced downwards, as actually happens? It is unquestionable but something different from personal selection must come here co-determinatively into play.

C. Lloyd Morgan also has recently expressed himself in favor of the necessity of definite variation, though likewise without assigning a basis for its action, and without being able to show how its efficacy is compatible with the plain fact of adaptation to the conditions of life. He seeks to find the origin of variation in "mechanical stresses and chemical or physical influences," but this conception is too general to be of much help. He has, in fact, not been able to abandon completely the heredity of acquired characters.

Emery likewise sees only the alternative of a "definitely directed variation" from internal causes and of a summation of "accidental" variations. He says: "A summation of entirely accidental variations in a given direction is extremely difficult," because "natural selection thus always awaits its fortune at the hands of accident whereby it is possible that the little good thereby produced will be swept away by other accidents or obliterated in the following generations by unfortunate crossings." We can, therefore, continues Emery, well conceive "how many scientists look upon the whole theory of selection as a fable, or else throw themselves into the arms of Lamarckism." Unquestionably Emery has here singled out the insufficient points in the assumption of a selection of "accidental" variations; he has recognised the necessity of operating, not with single variations, but with "directions of variation." He has not, however, attempted the derivation of directed tendencies of variation from known factors; he apparently thinks of them as of something which has sprung from unknown constitutional factors and consequently ascribes to them the capacity of shooting beyond their mark, so to speak, that is, of acting beyond and ahead of utility, and so of producing modifications which may lead to the destruction of the species.

B?r, K. E. von, 73. Bateson, 18, 73, 80. "Better" individuals, 76. Biology, character of research in, 7. Biophores, 40, 47, 58. Boltzmann, 4, 5. Bonnet, 53. Bourne, footnote, 54. Br?cke, 40. Butterflies, 14 et seq., 18 et seq., 81.

Catonephele, 50. Chance, 61. Chemical selection, 71. Chitons, 28. Coadaptation, 30. Colorings, protective, 14 et seq. Constancy of species, 46. Constructs, 8. Cormi, 66 footnote. Correlation, 21.

Danaids, 19. Darwin, 11, 25, 29, 36, 38, 66, 81, 83. Definite variation, 3, 4, 60, 76-79, 82. Degeneration, 30 et seq., 39 et seq. 55, 63, 64, 79. Del?ge, Yves, 40, 69. Determinants, 6 et seq., 10, 36 et seq. 42, 54, 58. Developmental mechanics, 8, 9. De Vries, 40. Dimorphism, 58. Directions of variations, 83. Directive forces, 23, 24. Dixey, 51 footnote. Dohrn, 81. Driesch, Hans, 12. Dyer, Thiselton, 78-79.

Eimer, 16, 70. Emery, 71, 83-84. Empedocles, 75. Epigenesis, 53 footnote, 58, 59. Euploids, 19. Europeans, exempt from malarial fevers, 82. Eurypheme, 22. Evolution, 53 footnote, 59.

Fireworks, determinants and ids compared to, 7. "Fits," 6 footnote. Fluctuations of development, 74-75. Formative laws, 17 et seq., 23. Frog, 14. Functional adaptation, 29. Functionless parts, 64.

Galton, 36. Germs, 7 et seq., 40 et seq. Germinal selection, 3, 39, 44, 50-53, 59, 63, 66-68. Germinal substance, 55 et seq. Germ-plasm, 9, 44, 57.

Haase, Eric, 70. Heliconids, 19, 20, 51 footnote. Henslow, G., 70, 82. Heredity, 4 et seq. Hertwig, O., 54 footnote, 58, 59. Hertz, 5, 6. Histonal selection, 66. Huxley, Thomas, 12. Hypna, 22. Hypotheses, nature of, 5 et seq.

Ids, their theoretical character, 7. Imagination, its function in science, 4. "Imperfect" formations, 81. Individual variations, 73 et seq. Inertia, law of organic, 15. Internal forces of evolution, 16, 23, 24, 31, 60, 82-4. Intrabiontic selection, 29. Ishikawa, Professor, 34.

Japanese cocks, long-tailed, 34, 44, 78.

Kallima, 22, 23, 50. Katagramma, 22. Knowledge, its character, 5.

Lamarckian principles, 24, 29 et seq., 31 et seq., 38, 63-64, 68, 84. Leaves, imitated by butterflies, 20 et seq. Locomotive, simile of, 11.

Malthusian principle, 65, 67. Markings, butterflies', 16 et seq. Maxwell, 4, 5. Mean of variation, 78-79. Meristic, 18. Mimicry, 19, 51 et seq. Minot, S., 54 footnote. Models, mental, 4 et seq. Molecules, 58. Morgan, Prof. C. Lloyd, 32, 71, 83. M?ller, Fritz, 77-79. M?ller, Hermann, 77. Mussels, 28. Mutations, 31 footnote, 72-76.

N?geli, 4, 11, 24, 60, 82. Neumayr, 72. Newton, 5. Nutrition of determinants, 36, 37, 41, 47. Nymphalidae, 21.

Ontogenesis, 8. Orr, Henry B., 69. Osborn, Prof. H. F., 33. Owen, Richard, 11.

Paleontology, 31, 73, 75, 76. Palms from Cordilleras, 82. Pangenes, 40. Panmixia, 15, 39, 42, 43, 64. Papilio, 16, 52. Parallecta, 23. Parts, struggling of the, 29, 39, 66-67. Passively functioning parts, 30 et seq., 64. Personal selection, 30, 41, 42, 45, 52, 64-86, 80. Phyletic variation, 31-32 footnote. Phylogenesis, 8. Phylogenetic variations, 31-32, 73. Plasomes, 40. Plus and minus variations, 35, 42, 46, 50, 79-80. Polymorphism, 58. Poulton, 64 footnote. Predestined variation, 4. Pre-established harmony, 25. Preformation, 53. Protective colorings, 14 et seq. Protogonius, 22. Pseudocraea, 52.

Qualitative modifications, 46. Quantitative changes, 46-47.

Retrogressive development, 38. Round-worms, eggs of, 28. Roux, Wilhelm, 29, 39, 65, 66.

Salamis, 22. Scott, Prof. W. B., 31 footnote, 72-74. Segmentation, 10. Selection, natural, 10, 25 et seq., 50, 51, 67, 69-73, 81, 82. Selective value of variations, 60. Semper, 69. Siderone, 22. Snails, 28. Spencer, 14, 28, 29, 40, 53, 56, 80. Struggle for existence, 65. Survival of the fit, 52. Symphaedra, 22.

Units, vital, biological, physiological, etc., 8, 40, 41, 53, 56, 65, 80. Useful modifications, value of initial stages of, 80-82. Utility, 11, 18, 33, 45, 48, 62, 63, 82.

Variations, necessary, their constant presence, 26 et seq., 31 et seq., 61; generally, 3, 11-14, 61, 71 et seq.

Waagen, 72. Wallace, 11, 25, 29, 51, 66, 81. Weldon, 36. Whale, hind leg of, 42, 56, 80. Whitman, C. O., 53. Wiesner, 40. Wigand, Albert, 11, 63. Wings of butterflies, 14 et seq., 47-52, 56. Wolff, K. F., 53, 62, 63, 69. "Worse" individuals, 76.

Zero-point of variation, 36 et seq., 45, 74, 79.

Notes

That is, by the law of exceedingly slow retrogression of superfluous characters, which may be designated the law of organic inertia.

I speak here of determinants, not of groups of determinants, which is the more correct expression, merely for the sake of brevity. It is a matter of course that a whole extremity, such as we have here chosen, cannot be represented in the germ by a single determinant only, but requires a large group of determinants.

Nor will those, who demand a demonstration of "how the biophores and determinants are constituted in every case, and must be arranged in the architecture of the germ-plasm." . As if any living being could have the temerity even so much as to guess at the actual ultimate phenomena in evolution and heredity! The whole question is a matter of symbols only, just as it is in the matter of "forces," "atoms," "ether undulations," etc., the only difference being that in biology we stumble much earlier upon the unknown than in physics.

As the highest stage of selective processes must be regarded that between the highest biological units, the colonies or cormi--a stage, however, which is not essentially different from personal selection. In this stage the persons enact the part that the organs play in personal selection. Like their prototypes they also battle with one another for food and in this way maintain harmony in the colony. But the result of the struggle endures only during the life of the individual colony and can be transmitted through the germ-cells to the following generation as little as can histological changes provoked by use in the individual person. Only that which issues from the germ has duration.

This statement has often been declared extravagant, and it is so if it is taken in its strict literalness. On the other hand, it would also seem, by a more liberal interpretation, as if there existed non-adaptive characters, for example, rudimentary organs. Adaptiveness, however, is never absolute but always conditioned, that is, is never greater than outward and inward circumstances permit. Moreover, an organ can only disappear gradually and slowly when it has become superfluous; yet this does not prevent our recognising every stage of its degeneration as adapted when compared with its precursor. Further, it does not militate against the correctness of the above proposition that there are also characters whose fitness consists in their being the necessary accompaniments of other directly adapted features, as, for instance, the red color of the blood.

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