On Germinal Selection as a Source of Definite Variation

This proposition seems to me to round off the whole theory of selection and to give to it that degree of inner perfection and completeness which is necessary to protect it against the many doubts which have gathered around it on all sides like so many lowering thunder-clouds. The moment variation is determined substantially though not exclusively by the adaptiveness itself, all these doubts fall to the ground, with one exception, that of the utility of the initial steps. But just this objection is the least weighty. Without doubt the theory requires that the initial steps of a variation should also have selective value; otherwise personal selection and hence germinal selection could not set in. Since, however, as I have before pointed out, in no case can we pretend to a judgment regarding the selective value of a modification, or have anyexperience thereof, therefore the assumption that in a given case where a character is transformed the original initial steps of the variation did have selective value, is not only as probable as the opposed assumption that they had none, but is infinitely more probable, for with this we can give an intelligible explanation of the mysterious fact of adaptation, while with that we cannot. Consequently, unless we are resolved to give up all attempts whatsoever at explanation, we are forced to the assumption that the initial steps of all actually affected adaptations possessed selective value.

The principal and fundamental objection that selection is unable to create the variations with which it works, is removed by the apprehension that a germinal selection exists. Natural selection is not compelled to wait until "chance" presents the favorable variations, but supposing merely that the groundwork for favorable variations is present in the transforming species, that is, supposing merely that in the constitutional basis of the part to be changed are contained components which render favorable variations possible by a change of their numerical ratio, then those variations must occur, for the reason that quantitative fluctuations are always happening, and they must also be augmented as soon as personal selection intervenes and permanently holds over them her protecting hand. Not only is the marvelous certainty and exactitude with which adaptation has operated in so many individual cases, rendered intelligible in this manner, but what is more difficult, we are able to understand the simultaneity of numerous and totally different modifications of the most diverse parts co-operant towards some collective end, such as we see so frequently occur, for example, in the simultaneous rise of instincts and protective similarities, or in the harmonious and simultaneous augmentation of two co-operant but independent organs, as of the eye and of the centre of vision, or of the nerve and its muscle, etc.

The "secret law," of which Wolff prophetically speaks in his criticism of selection, is in all likelihood naught else than germinal selection. This it is that brings it about that the necessary variations are always present, that symmetrical parts, for example, the two eyes, usually vary alike, but under circumstances may vary differently, for example, the two visual halves of soles; that homodynamic parts, (for instance, the member-pairs of Arthropoda,) have frequently varied alike, and not infrequently and in conformity with the needs of the animal, have varied differently. It brings it about also that conversely species of quite different fundamental constitutions occasionally vary alike, as instances of mimicry and numerous other cases of convergence show us. As soon as utility itself is supposed to exercise a determinative influence on the direction of variation, we get an insight into the entire process and into much else besides that has hitherto been regarded as a stumbling-block to the theory of selection, and which did indeed present difficulties that for the moment were insuperable—as, for example, the like-directed variation of a large number of already existing similar parts, seen in the origin of feathers from the scales of reptiles. The utility in the last-mentioned instance consisted, not in the transformation of one or two, but of all the scales; consequently the line of variation of all the scales must have been started simultaneously in the same direction. A large part of the objections to the theory of selection that have been recently brought forward by the acutest critics, as for example by Wigand, but particularly by Wolff,[21 - "Beiträge zur Kritik der Darwin'schen Lehre," Biologisches Centralblatt, Vol. X., p. 449. 1890.] find, as I believe, their refutation in this doctrine of germinal selection. The principle extends precisely as far as utility extends, inasmuch as it creates, not only the direction of variation for every increase or diminution demanded by the circumstances, but also every qualitative direction of variation attainable by changes of quantity, so far as that is at all possible for the organism in question.

Considering also the contrary process, the degeneration of useless parts by the cessation of selection in regard to the normal size of that part, a clear light is shed on that whole complex system of ascending and descending modifications which makes up most of the transformations of a living form, and we are led to understand how the fore extremity of a mammal can change into a fin at the same time that the hinder extremity is growing rudimentary, or how one or two toes of a hoofed animal can continue to develop more and more powerfully, whilst the others in the same degree grow weaker and weaker until finally they have disappeared entirely from the germ of most of the individuals of the species.

Possibly some of that large body of inquirers, mostly paleontologists, who till now have considered the Lamarckian principle indispensable for the explanation of these phenomena—perhaps some, I say, will not utterly close their eyes to the insight that germinal selection performs the same services for the understanding of observed transformations, particularly of the degeneration of superfluous parts, that a heredity of acquired characters would perform, without rendering necessary so violent an assumption. I have always conceded that many transformations actually do run parallel to the use and disuse of the parts,[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.] that therefore it does really look as if functional acquisitions of the individual life were hereditary. But if it be found that passively functioning parts, that is, parts which are not alterable during the individual life by function, obey the same laws and also degenerate when they become useless, then we shall scarcely be able to refuse our assent to a view which explains both cases. It certainly cannot be the physiological function which provokes modifications in the individual, which are then subsequently transmitted to the germ and in this way made hereditary, if functionless parts also change when they become useless. It is precisely this uselessness, then, from which the initial impulse emanates, and the primary modification is not in the soma but in the germ.

The Lamarckians were right when they maintained that the factor for which hitherto the name of natural selection had been exclusively reserved, viz., personal selection, was insufficient for the explanation of the phenomena. They were also right when they declared that panmixia in the form in which until recently I held the theory was also insufficient to explain the degeneration of parts that had grown useless, but they erred when they ascribed hereditary effects to the selection-processes which are enacted among the parts of the body (Wilhelm Roux) and which are rightly regarded as the results of functioning. And they did this, moreover, as they themselves admit, not because the facts of heredity directly and unmistakably required it, but because they saw no other possibility of explaining many phenomena of transformation. I am fain to relinquish myself to the hope that now after another explanation has been found, a reconciliation and unification of the hostile views is not so very distant, and that then, we can continue our work together on the newly laid foundations.

That the application of the Malthusian principle was thoroughly justified is now clear. The entire process of the development of living forms is guided by this principle. The struggle for existence, videlicet, for food and propagation, takes place at all the stages of life between all orders of living units from the biophores recently disclosed upwards to the elements that are accessible to direct observation, to the cells, and still higher up, to individuals and colonies. Consequently, in all the divers orders of biological units lying between the two extremes of biophores and colonies, the modifications must be controlled by selective processes; therefore, these govern every change of living forms no matter what its significance, and bring it about that the latter fit their conditions of life as wax does the mould; and the various stages of these processes, as enacted between the divers orders of biological units, in all organisms not absolutely simple, are involved in incessant and mutual interaction. The three principal stages of selection, that of personal selection[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.] as it was enunciated by Darwin and Wallace, that of histonal selection as it was established by Wilhelm Roux in the form of a "struggle of the parts," and finally that of germinal selection whose existence and efficacy I have endeavored to substantiate in this article—these are the factors that have co-operated to maintain the forms of life in a constant state of viability and to adapt them to their conditions of life, now modifying them pari passu with their environment, and now maintaining them on the stage attained, when that environment is not altered.

Everything is adapted in animate nature[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.] and has been from the first beginnings of life; for adaptiveness of organisation is here equivalent to the power to exist, and they alone have had the power to exist who have permanently existed. We know of only one natural principle of explanation for this fact—that of selection of the picking out of those having the power to exist from those having the power to originate. If there is any solution possible to the riddle of adaptiveness to ends,—a riddle held by former generations to be insoluble,—it can be obtained only through the assistance of this principle of the self-regulation of the originating organisms, and we should not turn our faces and flee at the sight of the first difficulties that meet its application, but should look to it whether the apparent effects of this single principle of explanation are not founded in the imperfect application that is made of it.

If I am not mistaken the situation is as follows: We had remained standing half way. We had applied the principle, but only to a portion of the natural units engaged in struggle. If we apply the principle throughout we reach a satisfactory explanation. Selection of persons alone is not sufficient to explain the phenomena; germinal selection must be added. Germinal selection is the last consequence of the application of the principle of Malthus to living nature. It is true it leads us into a terrain which cannot be submitted directly to observation by means of our organs of touch and by our eyes, but it shares this disadvantage in common with all other ultimate inferences in natural science, even in the domain of inorganic nature: in the end all of them lead us into hypothetical regions. If we are not disposed to follow here, nothing remains but to abandon utterly the hope of explaining the adaptive character of life—a renunciation which is not likely to gain our approval when we reflect that by the other method is actually offered at least in principle, not only a broad insight into the adaptation of the single forms of life to their conditions, but also into the mode of formation of the living world as a whole. The variety of the organised world, its transformation by adaptation to new, and by reversed adaptation to old conditions, the inequality of the systematic groups, the attainment of the same ends by different means, that is, by different organisations, and a thousand and one other things assume on this hypothesis in a certain measure an intelligible form, whilst without it they remain lifeless facts.

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.

APPENDIX

I. THE REJECTION OF SELECTION

Many years ago Semper[25 - Semper, Die natürlichen Existenzbedingungen der Thiere, Leipsic, 1880, pp. 218-219.] denied the power of selection to create an organ, declaring that the organ must have previously existed before selection could have increased and developed it. More recently Wolff[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.] has distinguished himself by the vigor with which he has attacked the "task" of "setting aside the dogma of selection." Henry B. Orr[27 - Henry B. Orr, A Theory of Development and Heredity, New York, 1893.] is also of opinion that selection is not the real cause of improved organic states; he regards it as a factor checking growth in certain directions, but not as a cause producing growth. Likewise Yves Delâge,[28 - Yves Delâge, La structure du protoplasma et les théories sur l'hérédité et les grands problèmes de la biologie générale, Paris, 1895.] in his recent voluminous but in many respects excellent work, regards natural selection solely as a subordinate principle which is devoid of all power to create species (p. 391), although he grants to it certain functions, and even characterises it as "an admirable and perfectly legitimate principle" (p. 371). A more pronounced opponent of selection, of any kind, as a principle creating species, is the Rev. Mr. Henslow,[29 - Henslow, The Origin of Species Without the Aid of Natural Selection, A Reply to Wallace. 1894.] whose views we shall discuss later, in Division VII. of this Appendix.

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 Tübingen 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.[30 - If any one should deem these words too severe, let him read the sarcastic passages in which Eimer has dispatched the late unfortunate Eric Haase who had been presumptuous enough to oppose the Tübingen Professor's deliverances on certain points. Haase, as we all know, fell a victim to the climate of the tropics, shortly after resigning the post of Director of the natural science collections in Bangkok, in order to return to Germany and to work out the fruits of his tropical sojourn. The unfortunate end of this accomplished man who had rendered important services to science had no effect in mollifying the resentment of Herr Eimer at the opposition which his views had encountered; and in twenty printed pages he takes him to task in the most personal and rancorous manner for this affront, remarking at the close: "In the meantime Herr Haase has died. Nevertheless I owe it to myself, in spite of this occurrence, to make public the foregoing facts, in order," etc. Any one who is interested in knowing the motives of Herr Eimer's excuse may find them in his book Artbildung and Verwandtschaft bei den Schmetterlingen, Part II., p. 66.]

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,[31 - "Gedanken zur Descendenz- und Vererbungstheorie." Biolog. Centralblatt, July 15, 1893.] 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!

II. CHEMICAL SELECTION

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.[32 - C. Lloyd Morgan, Animal Life and Intelligence, London, 1890-1891, p. 30-33.] 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 (muscular contractions) or the excretion of the disintegrated products, etc.

Now how is it possible that such unstable chemical combinations, answering exactly to the needs of life, could have arisen in such marvellous perfection if the useful variations had not always been presented to the ceaselessly working processes of selection? or, if the constantly increasing adaptation to the constantly augmenting delicacy of operation of physiological substances had depended in its last resort on accidental variations? Hence, not only with regard to the "form" of organs, but also with regard to the chemical and physiological composition of their materials, we are referred to the constant presence of appropriate variations.

III. VARIATION AND MUTATION

I have still to add a few remarks on the subject touched on in the[33 - 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.] at page 31 (#x1_x_1_i126). The view there referred to was discussed by Professor Scott before in an article published in the American Journal of Science, Vol. XLVIII., for November, 1894, entitled "On Variations and Mutations." Following the precedent of Waagen and Neumayr, Scott sharply discriminates between the inconstant vacillating variations which it is supposed [?] produce simultaneously occurring "varieties," and "mutations," or the successively evolved time-variations of a phylum, which constitute the stages of phyletic development. The facts on which this view is based are those already adduced in the text—the Zielstrebigkeit (to use K. E. von Bär's phraseology) displayed in the visible paleontological development, the directness of advance of the modifications to a final "goal." "The direct, unswerving way in which development proceeds, however slowly, is not suggestive of many trials and failures in all directions save one." And again, "The march of transformation is the resultant of forces both internal and external which operate in a definite manner upon a changeable organism and similarly affect large numbers of individuals."

The two points which I have here italicised are actually the facts which separate phylogenetic from common individual variation: the definite manner of the change, repeated again and again without modification, and its occurrence in a large number of individuals.

Still the two are not solely a result of observation, deduced from paleontological data; they are also a consequence of the theory of selection, as was shown in the text. If the theory in its previous form was unable to fulfil this requirement, it is certainly now able to do so after germinal selection has been added, and it is not in any sense necessary to assume a difference of character between phylogenetic and ontogenetic variations. Bateson and Scott are wrong in imagining that I ask them "to abrogate reason" in pronouncing the "omnipotence of natural selection." On the contrary, the theory seems to me to accord so perfectly with the facts that we might, by reversing the process, actually construct the facts from the theory. What other than the actual conditions could be expected, if it is a fact that selection favors only the useful variations and singles them out from the rest by producing them in increasing distinctness and volume with every generation, and also in an increasing number of individuals? The mere displacement of the zero-point of useful variations alone must produce this effect, especially when it is supported by germinal selection. It is impossible, indeed, to see how considerable, that is perceptible, deviations could arise at all on the path of phyletic development if in each generation a large number of individuals always possessed the useful, that is, the phyletic variations? In fact, by the assumption itself, the difference between useful and less useful variations is merely one of degree, and that a slight one.

Hence, as I before remarked at page 31, I see no reason for assuming two kinds of hereditary variations, distinct as to their origin, such as Scott and the other palæontologists mentioned have been led to adopt, although with the utmost caution. I believe there is only one kind of variation proceeding from the germ, and that these germinal variations play quite different rôles according as they lie or do not lie on the path of adaptive transformation of the species, and consequently are or are not favored by germinal selection. To repeat what I have said in the footnote to page 31 only a relatively small portion of the numberless individual variations lie on the path of phyletic advancement and so mark out under the guidance of germinal selection the way of further development; and hence it would be quite possible to distinguish continuous, definitely directed variations from such as fluctuate hither and thither with no uniformity in the course of generations. The origin of the two is the same; they bear in them nothing that distinguishes the one from the other, and their success alone, that is, the actual resultant phyletic modification, permits their being known as phyletic or as vacillating variations. Uncertain fluctuations along the path of evolution are what the geologists would be naturally led to expect from the theory of selection, but which they were unable to discover in the facts; it is evident, however, that these fluctuations are not a logical consequence of the theory of selection as that is perfected by germinal selection, and there seems to me to be no reason now for attributing "variations" to the union of changing hereditary tendencies, while "mutations" are ascribed to the effect "of dynamical agencies acting long in a uniform way, and the results controlled by natural selection."

The idea which the Grecian philosophers evolved of the thousands of non-adaptive formations that nature brings forth by the side of adaptive ones, and which must subsequently all perish as being unfit to live, is certainly correct in its ultimate foundations. But it is in need of far more radical refinement than it underwent in the hands of Empedocles, or than it seems likely to undergo at the hands of many contemporary inquirers. We know now that nature did not produce isolated eyes, ears, arms, legs, and trunks, and afterwards permit them to be joined together just as the play of the fundamental forces of love and hatred directed, leaving the monsters to perish and granting permanent existence only to harmonious products. Yet there is a weak echo of this conception, although infinitely far removed from its prototype, in the question as to where all the non-adaptive individuals are preserved that have perished in the struggle for existence and been eliminated from development by selection? Where, for example, are the fossil remains of the rejected individuals in the line of the Horses? Certainly they should be forthcoming in far larger numbers than the individuals lying directly in the path of development, for by our very assumption the latter were greatly in the minority in every generation. Doubtless the question would be a proper one if our eyes were sufficiently keen-sighted to assign the life-value of the various minute differences that distinguish the "better" from the "worse" individuals of every generation. But this is a task which we can accomplish at best only with selective processes which are artificially directed by ourselves, as in the case of doves and chickens, and even there only with the utmost difficulty and only with reference to a single characteristic and not with any species which to-day exists in the state of nature. Picture, then, the difficulties attending such a task as applied to the meagre fossilic bones of prehistoric species, touching which the richest discoveries never so much as remotely approach to the actual number of individuals that have lived together for a single generation in the same habitat. If the differences between good and bad in a single generation were striking enough to be immediately remarked as such in fossil bones, the development of species would take place so rapidly that we could directly witness it in living species.

IV. REMARKS ON THE HISTORY OF DEFINITELY DIRECTED VARIATIONS

As to the attempt here made to apply the selective process to the elements of the germinal substance (the idioplasm) 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.

Allusions to a connexion between the direction of variation and the selective processes are to be found, but they remained unnoticed or undeveloped. I have been able to find at least two such observations, but would not wish to assert that there are not more of them hidden somewhere in the literature of the subject. One of them is old and comes from Fritz Müller. It was appended by his brother Hermann as a "Supplementary Remark" to his book Die Befruchtung der Blumen durch Insecten (1873) and is dated November 24, 1872. We read there: "My brother Fritz Müller communicates to me in a letter which reached my hands only after the bulk of the present work had passed through the press, the following law discovered by him, which materially facilitates the explanation by natural selection of the pronounced characters of sharply distinguished species: 'The moment a choice in a definite direction is made in a variable species, progressive modification from generation to generation in the same direction will set in as the result of this choice, wholly apart from the influence of external conditions. Transformation into new forms is thus greatly facilitated and accelerated.'"

The facts on which F. Müller based the enunciation of his law, are the results of several experiments with plants, the numbers of whose grains (maize), 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. Müller'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. Müller 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 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 Müller, 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? (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.

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[34 - 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.] at page 40 (#x1_x_1_i142).)

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[35 - Materials for the Study of Variation with Especial Regard to Discontinuity in the Origin of Species, London, 1895, p. 16.] 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 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 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.

VII. THE ASSUMPTION OF INTERNAL EVOLUTIONARY FORCES

Definite variation was not only postulated in the last decade by Nägeli 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 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[36 - "Gedanken zur Descendenz- and Vererbungstheorie," Biolog. Centralblatt, 1893, Vol. XIII., p. 397.] 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 (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.

notes

1

Neue Gedanken zur Vererbungsfrage, eine Antwort an Herbert Spencer. Jena. 1895.

2

See Boltzmann, Methoden der theor. Physik, Munich, 1892. (In the Catalogue of the Mathematical Exhibit.)

3

Of late this saying of Newton's is frequently quoted as if Newton were a downright contemner of scientific hypotheses. But if we read the passage in question in its original context, we shall discover that his renunciation of hypotheses referred solely to a definite case, viz., to that of universal gravitation, of whose character Newton could form no conception and hence was unwilling to construct hypotheses concerning it. Indeed, such a wholesale repudiation of hypotheses is antecedently incredible on the part of the inventor of the emission-theory of light, in which, to speak of only one daring conjecture, "fits" were ascribed to the luminous particles. Compare Newton, Philosophiae Naturalis Principia Mathematica, second edition, 1714, page 484.

4

H. Hertz, Die Principien der Mechanik.