Part 7

F. Mueller'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. Mueller 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.

The second naturalist who has approached the fundamental idea of my doctrine of germinal selection, is a more recent writer. I refer to the English botanist Thiselton-Dyer, a scientist whose occasional utterances on the general questions of biology have more than once evoked my sympathetic approval. In an article, "Variation and Specific Stability," which appeared in {79} Nature for March 14, 1895, this author enunciates twenty theses touching this subject, many of which appear to me apposite and correct, particularly the following: In every species there is a mean specific form round which the variations are symmetrically grouped like shots around the bull's eye of a target. As soon as natural selection comes into play and favors one of these variations it must shift the centre of density. Variations arise by a change in the outward conditions of life and can be useful or indifferent; only in the first case will natural selection obtain control of them and "the new variation will get the upper hand and the centre of density will be shifted."

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 Mueller, 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 {80} 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? (Spencer.) 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.

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V. HISTORICAL REMARKS CONCERNING THE ULTIMATE VITAL UNITS.

(For this Appendix which is marked "Appendix V." in the German edition of Germinal Selection see the footnote at page 40.)

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VI. THE INITIAL STAGES OF USEFUL MODIFICATIONS.

In characterising as "least" weighty the old objection that the variations are too small at the start to be useful and to be selected, I find myself diametrically opposed to many writers of the present day, who have taken up with renewed vigor this old stumbling block to the principle of selection. Bateson regards the deficient proof of the utility of initial stages as the most serious objection that can be made to natural selection. New organs must in the necessity of the case have first been imperfect; how, then, could they have been selected since imperfect organs cannot be useful? Answers from various quarters have already been {81} made to this and to similar objections, and Darwin himself has referred to the fact that even the smallest variations may have selective value; Dohrn, too, has urged his principle of change of functions, which with regard to this question of the utility of initial stages has certainly a wide significance. Still, every transformation and new structure in the narrow sense of the word does not rest on change of function, and neither Darwin nor Wallace, nor any other more recent champion of the principle of selection, can ever succeed in demonstrating in every case the selective value of an initial stage. One reason why this cannot be done is because in no case of morphological variation do we really know what these initial stages are. To say that "new organs were at first necessarily imperfect" appears obvious enough, but it is at bottom a meaningless assertion, for it is not only possible but certain, that "imperfect" organs may still have selective value, and in by far the most cases have had selective value. The fact that we see to-day a long graduated line of forest-butterflies which possess resemblance to leaves and by this means are able in a measure to conceal themselves from prying eyes, yet that this resemblance in many species is very imperfect, in others more perfect, and in a very small number very perfect, simply proves that even "imperfect" formations may be of utility. The word "imperfect" in this connexion is itself very imperfect, for it is utterly anthropomorphic and estimates the biological value of a structure by our own peculiar artistic notions of its faithfulness to a leaf-copy, whilst we are really concerned here only with its protective value for the species in question, which is by no means dependent merely on the faithfulness of the copying, on the {82} faithfulness of the imitation, but on numerous other factors, such as the frequency and sharp-sightedness of the enemies of the species, the fertility of the species, their frequency and persecution in earlier developmental stages, and so forth, in brief, on their need of protection on the one hand and on their other means of protection on the other.

Now all this cannot be exactly calculated in any given case, and it will be better, instead of haggling about individual cases concerning which we can never judge with certainty, to take the position adopted in the text and say: Since the utility of the initial stages must be assumed unless we are to renounce forever the explanation of adaptation, let us then take it for granted. No contradiction of facts is involved in this assumption; in fact, even individual variations exist whose eventual utility can be demonstrated, for example, the invisible differences enabling Europeans of certain constitutions to resist the attacks of tropical malarial fevers,--or the differences of structure, likewise not directly visible, which enable palms from the summits of the Cordilleras to withstand our winter climate better than palms of the same species from along the base-line of the mountains; and so on.

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VII. THE ASSUMPTION OF INTERNAL EVOLUTIONARY FORCES

Definite variation was not only postulated in the last decade by Naegeli and Askenasy, but has also been repeatedly set up in recent years by various other authors. The Rev. George Henslow, in his book The Origin of Species Without the Aid of Natural Selection, 1894, regards the variations occurring in the state {83} of nature as always definite and not with Darwin as indefinite, and meets the objection that modification but not adaptation to outward conditions of life can be inferred from this fact, by the bold assumption that it is precisely the outward conditions of life or the environment which "induces the best fitted to arise." He further concludes that natural selection has nothing to do with the origin of species. At the basis of his conviction lies the naturally correct view that the summation of accidental variations is insufficient for transforming the species, but that definitely directed variation is necessary to this end. But concerning the way in which external conditions are always able to produce the fit variations, he can give us no information--if I am not mistaken, for the simple reason that such is not the fact, that the outward conditions only apparently determine the direction of variations whilst in truth it is the adaptive requirement itself that produces the useful direction of variation by means of selectional processes within the germ.

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 {84} "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 (disadvantages of position) 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.

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{85}

INDEX.

Accidental variations, 3, 83. Acquired variations, 33. Acracids, 19. Acraea, 52. Active selection, 38. Adaptations, 3, 10, 22, 61, 82. Adaptiveness, 66 footnote, 67, 74 et seq. Ageronia, 19. Anaea, 22. Anlagen, 35, 47, 53. Arthropoda, 32, 62. Articulata, 30. Artificial selection, 33. Askenasy, 24, 60, 82. Atoms, 57, 58.

Baer, 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. Bruecke, 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. Delage, 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. {86} 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.