On Germinal Selection as a Source of Definite Variation Part 3

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 a.s.sume a difference of _character_ between phylogenetic and ontogenetic variations. Bateson and Scott are wrong in imagining that I ask them "to abrogate reason" in p.r.o.nouncing 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 {74} 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 a.s.sumption 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 a.s.suming two kinds of hereditary variations, _distinct as to their origin_, such as Scott and the other palaeontologists 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 roles 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 {75} 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 {76} 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 a.s.sumption 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 a.s.sign 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 {77} 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 a.s.sert that there are not more of them hidden somewhere in the literature of the subject. One of them is old and comes from Fritz Muller. 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 Muller communicates to me in a letter which reached my hands only after the bulk of the present work had pa.s.sed through the press, the following law discovered by him, which materially facilitates the explanation by natural selection of the p.r.o.nounced 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. Muller 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 {78} example, that of the long-tailed j.a.panese c.o.c.k 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. Muller'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 s.h.i.+fted 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. Muller 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 s.h.i.+ft 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 s.h.i.+fted."

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 s.h.i.+fting of the zero-point of variation. Neither Fritz Muller, whose utterances Thiselton-Dyer was obviously ignorant of, nor Thiselton-Dyer himself pushed his inquiries beyond the thought that the s.h.i.+fting 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 ma.s.s 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 ma.s.s 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 footnote at page 40.)

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[33] 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 a.s.sertion, 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-b.u.t.terflies 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 a.s.sumed 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 a.s.sumption; in fact, even individual variations exist whose eventual utility can be demonstrated, for example, the invisible differences enabling Europeans of certain const.i.tutions 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 a.s.sUMPTION OF INTERNAL EVOLUTIONARY FORCES

Definite variation was not only postulated in the last decade by Nageli 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 a.s.sumption 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 a.s.signing 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[34] 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 a.s.sumption 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 const.i.tutional 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.