On Germinal Selection as a Source of Definite Variation

5

Hans Driesch, Die Biologie als selbstständige Grundwissenschaft, Leipsic, 1893, p. 31, footnote. The sentence reads: "An examination of the pretensions of the refuted Darwinian theory, so called, would be an affront to our readers."

6

Die Allmacht der Naturzüchtung. A Reply to Herbert Spencer. Jena, 1893, p. 27 et seq. [Also in the Contemporary Review for September, 1893.]

7

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

8

Materials for the Study of Variation with Especial Regard to Discontinuity in the Origin of Species. London, 1895.

9

Studien zur Descendenztheorie, Leipsic, 1876. Vol. II. pp. 295 and 322.

10

Compare my essay, Neue Gedanken zur Vererbungsfrage, Jena, 1895, p. 10, second footnote.

11

On the same day on which the present address was delivered at the International Congress of Zoölogists in Leyden, and on the same occasion, Dr. W. B. Scott, Professor of Geology in Princeton College, New Jersey, read a very interesting paper on the tertiary mammalian fauna of North America, in which, without a knowledge of my paper, he took his stand precisely on this argument and arrived at the opinion that it could not possibly be the ordinary individual variations which accomplished phyletic evolution, but that it was necessary to assume in addition phyletic variations. I believe our views are not as widely remote as might be supposed. Of course, I see no reason for assuming two kinds of hereditary variations, different in origin. Still it is likely that only a relatively small portion of the numberless individual variations lie on the path of phyletic advancement and so under the guidance of germinal selection mark out the way of further development; and hence it would be quite possible in this sense to distinguish continuous, definitely directed individual variations from such as fluctuate hither and thither with no uniformity in the course of generations. The root of the two is of course the same, and they admit of being distinguished from each other only by their success, phyletic modification, or by their failure.

12

H. F. Osborn, "The Hereditary Mechanism and the Search for the Unknown Factors of Evolution," in Biological Lectures delivered at the Marine Biolog. Lab. at Wood's Holl in the Summer Session of 1894. Boston, 1895.

13

In 1886. See my paper on "Retrogression in Nature," published in English in Nos. 105, 107, 108, and 109 of The Open Court, and also in my essays on Heredity, Jena, 1892.

14

Neue Gedanken zur Vererbungsfrage, Jena, 1895.

15

Delâge, in La structure du protoplasma et les théories sur l'hérédité, etc., Paris, 1895, is mistaken in attributing to Herbert Spencer the merit of having first pointed out the necessity of the assumption of biological units ranking between the molecule and the cell. Brücke set forth this idea three years previously to Spencer and established it exhaustively in a paper which in Germany at least is famous ("Elementarorganismen," Wiener Sitzungsberichte, October 10, 1861, Vol. XLIV., II., p. 381). Spencer's Principles of Biology appeared between 1864 and 1868; consequently there can be no dispute touching the priority of the idea. Strangely enough Delâge cites Brücke's essay in the Bibliographical Index at the end of his book correctly, although Brücke's name and views are nowhere mentioned in the book itself. It is to be observed, however, that the elementary organisms of Brücke are not merely the precursors of Spencer's "physiological units," but repose on much firmer foundations than the latter, which, as Delâge himself remarks, are at bottom nothing more than magnified molecules and not combinations of different molecules of such character as to produce necessarily phenomena of life. He aptly remarks on this point: "the physiological units of Spencer are only chemical molecules of greater complexity than the rest, and as he defines them they would be regarded as such by every chemist. He attributes to them no property essentially different from those of chemical molecules." Assimilation, growth, propagation, in short the attributes of life, are not attributed by Spencer to his units, while Brücke by his very designation "elementary organisms" expresses the idea of "ultimate living units," to use Wiesner's phrase. Of course this particular aspect of the vital units was not emphasised by Brücke with the same distinctness and sharpness as by recent inquirers, who took up Brücke's ideas thirty years after. I refer to the conception that the union of a definite combination of heterogeneous molecules into an invisibly small unit, forms the cradle or focus of the vital phenomena. This was first done and apparently on independent considerations by De Vries, and soon after by Wiesner, and subsequently by myself (De Vries, Intracelluläre Pangenesis, Jena, 1889; Wiesner, Die Elementarstructur and das Wachsthum der lebenden Substanz, Vienna, 1892; Weismann, Das Keimplasma, Jena, 1892). Let me say at the close of this note that it is not my intention in thus defending the rights of a great physiologist, to censure in the least the distinguished author of L'hérédité who has set himself a remarkably high standard of exactitude in such matters. Certainly, when we consider the enormous extent of the literature that had to be mastered to produce his book, embracing as it did all the various theories of recent times, such an oversight is quite excusable.

16

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.

17

That this is not so in all cases has recently been shown by Dixey from observations on certain white butterflies of South America which mimic the Heliconids and in which a small, yellowish red streak on the under surface of the hind wing has served as the point of departure and groundwork of the development of a protective resemblance to quite differently colored Heliconids. "On the Relation of Mimetic Characters to the Original Form," in the Report of the British Association for 1894.

18

Oscar Hertwig, Zeit-und Streitfragen der Biologie, Jena, 1894. It is customary now to look upon the preformation-theory of Bonnet as a discarded monstrosity, and on the epigenesis of K. F. Wolff as the only legitimate view, and to draw a parallel between these two and what might be called to-day "evolution" [i. e. unfoldment] and epigenesis. The evolution, or unfoldment, of Bonnet and Harvey, however, was something totally different from modern doctrines of evolution, and Whitman is quite right when he says that even my theory of determinants would have appeared to the inquirers of the last century as "extravagant epigenesis." Biologists in that day were concerned with quite different questions from what they are at present, and although now we probably all share the conviction of Wolff that new characters do arise in the course of evolution, yet the acceptance of this view is far from settling the question as to how these new characters are established in the germ-substance—for in this substance they certainly must have their foundation. When, therefore, O. Hertwig laments over my regarding evolution and not epigenesis as the correct foundation of the theory of development, his sorrow is almost as naïve as is the statement of Bourne that epigenesis is a fact and not a theory "a statement of morphological fact," Science Progress, April, 1894, page 108), or, as is the latter's unconsciousness that facts originally receive their scientific significance from thought, i. e. from their interpretation and combination, and that thought is theory. And when S. Minot, as the leader of the embryologists, carries his zeal to the pitch of issuing a general pronunciamento against me as a corruptor of youth, in which he declares it to be a "scientific duty to protest in the most positive manner against Weismann's theory," I wonder greatly that he does not suggest the casting of a general ballot in the matter. (See the Biologisches Centralblatt of August 1, 1895.) We see how with these gentlemen the wisdom of the recitation-room regarding the infallibility of epigenesis has grown into a dogma, and whoever ventures to disturb its foundations must be burnt as a heretic.

19

Oscar Hertwig, Zeit- und Streitfragen der Biologie, Jena, 1894.

20

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." (O. Hertwig, loc. cit., p. 137). 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.

21

"Beiträge zur Kritik der Darwin'schen Lehre," Biologisches Centralblatt, Vol. X., p. 449. 1890.

22

Poulton has adverted to the fact that this is nevertheless not always the case; for example, it is not so with the teeth, whose shape it had also been sought to reduce to the mechanical effects of pressure and friction. See "The Theory of Selection" in The Proceedings of the Boston Society of Natural History, Vol. XX., page 389. 1894.

23

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.

24

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.

25

Semper, Die natürlichen Existenzbedingungen der Thiere, Leipsic, 1880, pp. 218-219.

26

Wolff, "Beiträge zur Kritik der Darwin'schen Lehre," Biolog. Centralblatt, Vol. X., Sept. 15, 1890, and "Bemerkungen zum Darwinismus mit einem experimentellen Beitrag zur Physiologie der Entwicklung," Biolog. Centralblatt, Vol. XIV., Sept. 1, 1894.

27

Henry B. Orr, A Theory of Development and Heredity, New York, 1893.

28

Yves Delâge, La structure du protoplasma et les théories sur l'hérédité et les grands problèmes de la biologie générale, Paris, 1895.

29

Henslow, The Origin of Species Without the Aid of Natural Selection, A Reply to Wallace. 1894.