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diff --git a/34077.txt b/34077.txt new file mode 100644 index 0000000..cd7c1d4 --- /dev/null +++ b/34077.txt @@ -0,0 +1,2977 @@ +The Project Gutenberg EBook of On Germinal Selection as a Source of +Definite Variation, by August Weismann + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: On Germinal Selection as a Source of Definite Variation + +Author: August Weismann + +Translator: Thomas McCormack + +Release Date: October 15, 2010 [EBook #34077] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK ON GERMINAL SELECTION *** + + + + +Produced by Bryan Ness, Keith Edkins and the Online +Distributed Proofreading Team at https://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive/American Libraries.) + + + + + + BIOLOGICAL PUBLICATIONS. + + THE PRIMARY FACTORS OF ORGANIC EVOLUTION. + By _Prof. E. D. Cope_. Cuts, 121. Pp., xvi, 547. Cl., $2.00 (10s.). + + DARWIN AND AFTER DARWIN. An Exposition of the Darwinian + Theory and a Discussion of Post-Darwinian Questions. + By _George John Romanes, LL. D., F. R. S., etc._ + + 1. THE DARWINIAN THEORY. With portrait of Darwin. + Pp., 460. Cuts, 125. Second edition. Cloth, $2.00. + + 2. POST-DARWINIAN QUESTIONS. Heredity and Utility. + With portrait of Romanes. Pp., 338. Cloth, $1.50. + + 3. POST-DARWINIAN QUESTIONS. Isolation and Physiological + Selection. With portrait of Mr. J. T. Gulick. Pp., + 181. 8vo. Cloth, $1.00. + + (_The three volumes supplied to one order for $4.00._) + + A FIRST BOOK IN ORGANIC EVOLUTION. An Introduction + to the Study of the Development Theory by _D. Kerfoot_ + _Shute, M. D._ Pages, xvi, 285, 39 illustrations--9 in natural + colors. Cloth, $2.00 net (7s. 6d. net). + + AN EXAMINATION OF WEISMANNISM. By _George John_ + _Romanes_. Pp., ix, 221. Cloth, $1.00. Paper, 40c. + + THE PSYCHIC LIFE OF MICRO-ORGANISMS. By _Dr._ + _Alfred Binet_. Pp., xii, 120. Cloth, 75c (3s. 6d.). Paper, 30c + (1s. 6d.). + + ON GERMINAL SELECTION. By _August Weismann_. Pp., + xii, 61. Paper, 30c (1s. 6d.). + + ON MEMORY, AND THE SPECIFIC ENERGIES OF THE + NERVOUS SYSTEM. By _E. Hering_. Pp., 50. Paper, 20c. + + A MECHANICO-PHYSIOLOGICAL THEORY OF ORGANIC + EVOLUTION. Summary. By _Carl von Naegeli_. + Pp., 52. Paper, 20c (9d.). + + ON ORTHOGENESIS. By _Th. Eimer_. Pp., 56. Paper, 30c. + (1s. 6d.). + + THE PRINCIPLES OF BACTERIOLOGY. By _Dr. Ferdinand_ + _Hueppe_. Woodcuts, 28. Pp., 467. $1.75 (7s. 6d.). + + THE OPEN COURT PUB. CO., CHICAGO. + + * * * * * + + +ON + +GERMINAL SELECTION + +AS A + +SOURCE OF DEFINITE VARIATION + +BY + +AUGUST WEISMANN + +TRANSLATED FROM THE GERMAN BY +THOMAS J. McCORMACK + + * * * * * + +SECOND EDITION + + * * * * * + +CHICAGO + +THE OPEN COURT PUBLISHING COMPANY. + +LONDON AGENTS: +KEGAN PAUL, TRENCH, TRUEBNER & CO., LTD. +1902. + + * * * * * + +COPYRIGHT BY +THE OPEN COURT PUBLISHING CO. +1896 + + * * * * * + + +{3} + +PREFACE. + +The present paper was read in the first general meeting of the +International Congress of Zooelogists at Leyden on September 16, 1895. +Several points, which for reasons of brevity were omitted when the paper +was read, have been re-embodied in the text, and an Appendix has been added +where a number of topics receive fuller treatment than could well be +accorded to them in a lecture. The address was first printed in _The +Monist_ for January, 1896, and afterwards in a German pamphlet. + +The basal idea of the essay--the existence of Germinal Selection--was +propounded by me some time since,[1] but it is here for the first time +fully set forth and tentatively shown to be the necessary complement of the +process of selection. Knowing this factor, we remove, it seems to me, the +patent contradiction of the assumption that the general fitness of +organisms, or the adaptations _necessary_ to their existence, are produced +by _accidental_ variations--a contradiction which formed a serious +stumbling-block to the theory of selection. Though still assuming that the +_primary_ variations are "accidental," I yet hope to have demonstrated that +an interior mechanism exists which compels them to go on increasing in a +definite direction, the moment selection intervenes. _Definitely directed +{4} variation exists_, but not predestined variation, running on +independently of the life-conditions of the organism, as Naegeli, to +mention the most extreme advocate of this doctrine, has assumed; on the +contrary, the variation is such as is elicited and controlled by those +conditions themselves, though indirectly. + +In basing my proof of the doctrine of Germinal Selection on the fundamental +conceptions of my theory of heredity, a few words of justification are +necessary, owing to the fact that the last-mentioned theory has been widely +and severely assailed since its first emergence into light and even +repudiated as absolutely futile and erroneous. + +In the first place, many critics have characterised it as a "pure creation +of the imagination." And to a certain extent it is such, as every theory +is. But is it on that account necessarily wrong? Can not its fundamental +ideas still be quite correct, and it itself therefore perfectly justified +as a means of further progress? + +Surely my critics cannot be ignorant of the prominent part which +imagination has recently played in the exactest of all natural +sciences--physics? Are they unaware that the English physicist Maxwell +"constructed from liquid vortices and friction-pulleys enclosed in cells +with elastic walls, a wonderful mechanism, which served as a mechanical +model for electromagnetism"?[2] He hoped "that further research in the +domain of theoretical electricity would be promoted rather than hindered by +such mechanical {5} fictions." And so it actually happened, for Maxwell +found by means of them "the very equations, whose singular and almost +incomprehensible power Hertz has so beautifully portrayed in his lecture on +the relations between light and electricity." "Maxwell's formulae were the +direct outcome of his mechanical models." "These ideal mechanisms"--so +relates Boltzmann in the same interesting essay--"were at first widely +ridiculed, but gradually the new ideas worked their way into all fields. +They were themselves more convenient than the old hypotheses. For the +latter could be maintained only in the event of everything's proceeding +smoothly; whereas now little inconsistencies were fraught with no peril, +for no one can take amiss a slight hitch in a mere analogy.--Ultimately +Maxwell's ideas were philosophically generalised as the theory that all +knowledge consists in the disclosure of analogies." + +But not only does it seem that there is little appreciation among +biologists for the scientific import of imagination, they also appear to +have little sense for the significance of theory. It is a favorite attitude +nowadays to look upon theory as a sort of superfluous ballast, as a +worthless survival from the epoch of decrepit "nature-philosophies." People +pronounce with pride the miscomprehended utterance of Newton, _Hypotheses +non fingo_, and place the value of the slightest new fact infinitely higher +than that of "the most beautiful theory."[3] And yet theory originally {6} +fashions science out of facts and is the indispensable precondition of +every important scientific advance. + +Heinrich Hertz,[4] the discoverer of electric undulations, had the same +thought in mind when he said: "We form inward representations or constructs +of outward objects, so constituted that the results that follow logically +and necessarily from the constructs are in turn always constructs of the +results flowing naturally and necessarily from the objects." "These +constructs or mental images copied after familiar objects possessed of +familiar properties, so constituted that from their manipulation effects +result similar to those which we observe in the objects to be explained. +Experience teaches us that the requirements here made can be fulfilled and +that consequently such 'correspondences' between reality and the supposed +images [or, as Hertz says, between nature and mind] actually exist. Having +succeeded in extracting from the accumulated experience of the past, +representative images or constructs fulfilling all these necessary +requirements, we can then reproduce by them in a short space of time, as we +might by models, results that in the outward world require a long space of +time for their actualisation or can be produced only through our personal +intervention," etc. + +{7} + +Such representative models, or constructs, now, in my theory of heredity, +are the _determinants_, which may be conceived as indefinitely fashioned +packages of units (biophores) which are set into activity by definite +impressions and put a distinctive stamp upon some small part of the +organism, on some cell or group of cells, evoking definite phenomena +somewhat as a piece of fireworks when lighted produces a brilliant sun, a +shower of sparks, or the glowing characters of a name. + +The _ids_, also, are such representative models, and may be compared to a +definitely ordered but variously compounded aggregate of fireworks, in +which the single pieces are so connected as to go off in fixed succession +and to produce a definite resultant phenomenon like a complete inscription +surrounded by a hail of fire and glowing spheres. + +Owing to the greater complexity of the phenomena in biology we can never +hope to reach the same distinctness in our constructs and models as in +physics, and the attempt to derive from them mathematical formulae by the +independent development of which research could be continued, would at +present be utterly fruitless. In the meantime it seems preferable to have +some sort of adequate model to which the imagination can always resort and +with which it can easily operate, rather than to have to revert, in +considering every special problem of heredity, to the mutual actions of the +molecules of living substance and outward agents--processes which we know +only in their roughest outlines. Or is any one presumptuous enough to +believe we can infer from our slight knowledge of the chemical and physical +constitution of the germs of a trout and a salmon the real cause {8} of the +one's becoming a trout and of the other's becoming a salmon? + +The fact is, we can make no show of accounting for the complex phenomena of +heredity with mere _material_ units; we can never reach these phenomena +from below, but must begin farther up and make the assumption of _vital_ +units and _hereditary_ units, if there is to be any advance in this field. + +It is undoubtedly a splendid aim which the newly founded science of +developmental mechanics has set itself of laying bare the entire causal +line leading from the egg to the finished organism; yet, however much we +may wish to see the success of this plan realised, we cannot disguise the +fact that little or nothing is to be accomplished by it in the settlement +of the problems of heredity. It is impossible to suspend the study of +heredity until this mechanics is completed, and even if we could it would +help us little, for the riddles of heredity are not concealed in the +ontogenesis of types, or, to give an example, in the developmental history +of man _as a race_, but in the ontogenesis of _individuals_, in that of a +_definite and particular_ man. This last ontogenesis exhibits the phenomena +of variation, of reversion, of the predominance of the one or the other +parent, etc., and no one is likely to believe that inductive evolutional +inquiry alone will ever afford us knowledge of these minute and delicate +processes, which, in their bearing on the total resultant development, +phylogenesis, are after all the most important of all. + +There is, accordingly, no choice left. If we are really bent on +scientifically investigating the question of heredity, we are obliged +perforce to form from the observed facts of heredity a highly detailed and +{9} elaborate theory, on the basis of which we can propound new questions, +which will give rise in turn to new facts, and thus will exercise a +retroactive influence on the theory, improving and transforming it. + +This is precisely what I have sought to accomplish by my theory of +Germ-plasm, as I stated in the Preface to the book bearing that name. It +was never intended as a theory of life, nor, indeed, primarily, as a theory +of evolution, but first and above all as a theory of heredity. I cannot +understand, therefore, the animadversion, that my theory in no way furthers +our insight into the mechanics of development. That is not its purpose; in +fact, it takes the ultimate physical and chemical processes which make up +the vital processes for granted; and inevitably it is constrained to do so. +Its aim is to put into our hands a serviceable formula by means of which we +can go on working in the field of heredity at any rate, and, if I am not +mistaken, also in that of evolution. To me, at least, the newest results of +developmental mechanics do not seem so widely at variance with the theory +of determinants as might appear at first sight; so far as I can see, they +can be quite readily made to harmonise with the theory, provided only the +initial stage of the disintegration of the germ-plasm in the determinant +groups be not invariably placed at the beginning of the process of +segmentation, but be transferred according to circumstances to a subsequent +period. The exact state of things cannot as yet be determined, so long as +the mass of facts is still in constant flux. + +In any event I still hold fast to the hope which I expressed in the Preface +to my _Germ-plasm_, that despite the unavoidable uncertainties in its +foundation my theory would yet prove more than a mere work {10} of +imagination, and that the future would find in it some durable points which +would outlive the mutations of opinion. It is possible that one of these +durable gains is my much impugned idea of determinants, and in fact not +only will the present essay be made to rest on this idea, but it will also +defend it on new grounds, although primarily only as a representation of +something which we do not as yet exactly know, but which still exists and +on which we can reckon, leaving it to the future to decide the greater or +less resemblance of our hypothetical construct to nature. + +The real aim of the present essay is to rehabilitate the principle of +selection. If I should succeed in reinstating this principle in its +emperilled rights, it would be a source of extreme satisfaction to me; for +I am so thoroughly convinced of its indispensability as to believe that its +demolition would be synonymous with the renunciation of all inquiry +concerning the causal relation of vital phenomena. If we could understand +the adaptations of nature, whose number is infinite, only upon the +assumption of a teleological principle, then, I think, there would be +little inducement to trouble ourselves about the causal connexion of the +stages of ontogenesis, for no good reason would exist for excluding +teleological principles from this field. Their introduction, however, means +the ruin of science. + + AUGUST WEISMANN. + + FREIBURG, Nov. 18, 1895. + + * * * * * + + +{11} + +GERMINAL SELECTION. + + * * * * * + +Numerous and varied are the objections that have been advanced against the +theory of selection since it was first enunciated by Darwin and +Wallace--from the unreasoning strictures of Richard Owen and the acute and +thoughtful criticisms of Albert Wigand and Naegeli to the opposition of our +own day, which contends that selection cannot create but only reject, and +which fails to see that precisely through this rejection its creative +efficacy is asserted. The champions of this view are for discovering the +motive forces of evolution in the _laws_ that govern organisms--as if the +norm according to which an event happens were the event itself, as if the +rails which determine the direction of a train could supplant the +locomotive. Of course, from every form of life there proceeds only a +definite, though extremely large, number of tracks, _the possible +variations_, whilst between them lie stretches without tracks, _the +impossible variations_, on which locomotion is impossible. But the actual +travelling of a track is not performed by the track, but by the locomotive, +and on the other hand, the choice of a track, the decision whether the +destination of the train shall be Berlin or Paris, is not made by the +locomotive, the cause of the variation, but by the driver of the +locomotive, who directs the engine on the right track. In the theory of +selection the engine-driver is represented by utility, for with utility +rests the decision {12} as to what particular variational track shall be +travelled. The cogency, the irresistible cogency, as I take it, of the +principle of selection is precisely its capacity of explaining why fit +structures always arise, and that certainly is the great problem of life. +Not the fact of change, but the _manner_ of the change, whereby all things +are maintained capable of life and existence, is the pressing question. + +It is, therefore, a very remarkable fact, and one deserving of +consideration, that to-day (1895), after science has been in possession of +this principle for something over thirty years and during this time has +steadily and zealously busied itself with its critical elaboration and with +the exact determination of its scope, that now the estimation in which it +is held should apparently be on the decrease. It would be easy to enumerate +a long list of living writers who assign to it a subordinate part only in +evolution, or none at all. One of our youngest biologists speaks without +ado of the "pretensions of the refuted Darwinian theory, so called,"[5] and +one of the oldest and most talented inquirers of our time, a pioneer in the +theory of evolution, who, unfortunately, is now gone to his rest, Thomas +Huxley, implicitly yet distinctly intimated a doubt regarding the principle +of selection when he said: "Even if the Darwinian hypothesis were swept +away, evolution would still stand where it is." Therefore, he, too, +regarded it as not impossible that this hypothesis should disappear from +among {13} the great explanatory principles by which we seek to approach +nearer to the secrets of nature. + +I am not of that opinion. I see in the growth of doubts regarding the +principle of selection and in the pronounced and frequently bitter +opposition which it encounters, a transient depression only of the wave of +opinion, in which every scientific theory must descend after having been +exalted, here perhaps with undue swiftness, to the highest pitch of +recognition. It is the natural reaction from its overestimation, which is +now followed by an equally exaggerated underestimation. The principle of +selection was not overrated in the sense of ascribing to it too much +explanatory efficacy, or of extending too far its sphere of operation, but +in the sense that naturalists imagined that they perfectly understood its +ways of working and had a distinct comprehension of its factors, which was +not so. On the contrary, the deeper they penetrated into its workings the +clearer it appeared that something was lacking, that the action of the +principle, though upon the whole clear and representable, yet when +carefully looked into encountered numerous difficulties, which were +formidable, for the reason that we were unsuccessful in tracing out the +actual details of the individual process, and, therefore, in _fixing_ the +phenomenon as it actually occurred. We can state in no single case how +great a variation must be to have selective value, nor how frequently it +must occur to acquire stability. We do not know when and whether a desired +useful variation really occurs, nor on what its appearance depends; and we +have no means of ascertaining the space of time required for the fulfilment +of the selective processes of nature, and hence cannot calculate the exact +number of such {14} processes that do and can take place at the same time +in the same species. Yet all this is necessary if we wish to follow out the +precise details of a given case. + +But perhaps the most discouraging circumstance of all is, that in scarcely +a single actual instance in nature can we assert whether an observed +variation is useful or not--a drawback that I distinctly pointed out some +time ago.[6] Nor is there much hope of betterment in this respect, for +think how impossible it would be for us to observe all the individuals of a +species in all their acts of life, be their habitat ever so limited--and to +observe all this with a precision enabling us to say that this or that +variation possessed selective value, that is, was a decisive factor in +determining the existence of the species. + +In many cases we can reach at least a probable inference, and say, for +example, that the great fecundity of the frog is a property having +selective value, basing our inference on the observation that in spite of +this fertility the frogs of a given district do not increase. + +But even such inferences offer only a modicum of certainty. For who can say +precisely how large this number is? Or whether it is on the increase or on +the decrease? And besides, the exact degree of the fecundity of these +animals is far from being known. Rigorously viewed, we can only say that +great fecundity must be advantageous to a much-persecuted animal. + +And thus it is everywhere. Even in the most indubitable cases of +adaptation, as, for instance, in that of the striking protective coloring +of many butterflies, {15} the sole ground of inference that the species +upon the whole is adequately adapted to its conditions of life, is the +simple fact that the species is, to all appearances, preserved +undiminished, and the inference is not at all permissible that just this +protective coloring has selective value for the species, that is, that if +it were lacking, the species would necessarily have perished. + +It is not inconceivable that in many species today these colorings are +actually unnecessary for the preservation of the species, that they +formerly were, but that now the enemies which preyed on the resting +butterflies have grown scarce or have died out entirely, and that the +protective coloring will continue to exist by the law of inertia[7] only +for a short while till panmixia or new adaptations shall modify it. + +Discouraging, therefore, as it may be, that the control of nature in her +minutest details is here gainsaid us, yet it were equivalent to sacrificing +the gold to the dross, if simply from our inability to follow out the +details of the individual case we should renounce altogether the principle +of selection, or should proclaim it as only subsidiary, on the ground that +we believe the protective coloring of the butterfly is not a protective +coloring, but a combination of colors inevitably resulting from internal +causes. The protective coloring remains a protective coloring whether at +the time in question it is or is not necessary for the species; and it +arose as protective coloring--arose not because it was a constitutional +necessity of the animal's organism that here a red and there a white, +black, or yellow spot should be produced, but because it was {16} +advantageous, because it was necessary for the animal. There is only one +explanation possible for such patent adaptations and that is selection. +What is more, no other natural way of their originating is conceivable, for +we have no right to assume teleological forces in the domain of natural +phenomena. + +I have selected the example of the butterfly's wing, not solely because it +is so widely known, but because it is so exceedingly instructive, because +we are still able to learn so much from it. It has been frequently asserted +that the color-patterns of the butterfly's wings have originated from +internal causes, independently of selection and conformably to inward laws +of evolution. Eimer has attempted to prove this assertion by establishing +in a division of the genus Papilio the fact that the species there admit of +arrangement in series according to affinity of design. But is a proof that +the markings are modified in definite directions during the course of the +species's development equivalent to a definite statement as to the _causes_ +that have produced these gradual transformations? Or, is our present +inability to determine with exactness the biological significance of these +markings and their modifications, a proof that the same have no +significance whatever? On the contrary, I believe it can be clearly proved +that the wing of the butterfly is a tablet on which nature has inscribed +everything she has deemed advantageous to the preservation and welfare of +her creatures, and nothing else; or, to abandon the simile, that these +color-patterns have not proceeded from inward evolutional forces, but are +the result of selection. At least in all places where we do understand +their biological significance these patterns are constituted and +distributed over the wing exactly as utility would require. {17} + +I do not pledge myself, of course, to give an explanation of every spot and +every line on a wing. The inscription is often a very complicated one, +dating from remote and widely separated ages; for every single existing +species has inherited the patterns of its ancestral species and that again +the patterns of a still older species. Even at its origin, therefore, the +wing was far from being a _tabula rasa_, but was a closely written and +fully covered sheet, on which there was no room for new writing until a +portion of the old had been effaced. But other parts were preserved, or +only slightly modified, and thus in many cases gradually arose designs of +almost undecipherable complexity. + +I should be far from maintaining that the markings arose unconformably to +law. Here, as elsewhere, the dominance of law is certain. But I take it, +that the laws involved here, that is, the physiological conditions of the +variation, are without exception subservient to the ends of a higher +power--utility; and that it is utility primarily that determines the kind +of colors, spots, streaks and bands that shall originate, as also their +place and mode of disposition. The laws come into consideration only to the +extent of conditioning the quality of the constructive materials--the +variations, out of which selection fashions the designs in question. And +this also is subject to important restrictions, as will appear in the +sequel. + +The meaning of formative laws here is that definite spots on the surfaces +of the wings are linked together in such a manner by inner, invisible +bonds, as to represent the same spots or streaks, so that we can predict +from the appearance of a point at one spot the appearance of another +similar point at another, and {18} so on. It is an undoubted fact that such +relations exist, that the markings frequently exhibit a certain symmetry, +that--to use the words of the most recent observer on this subject, +Bateson[8]--a meristic representation of equivalent design-elements occurs. +But I believe we should be very cautious in deducing laws from these facts, +because all the rules traceable in the markings apply only to small groups +of forms and are never comprehensive nor decisive for the entire class or +even for the single sub-class of diurnal butterflies, in fact, often not so +for a whole genus. All this points to special causes operative only within +this group. + +If internal laws controlled the marking on butterflies' wings, we should +expect that some general rule could be established, requiring that the +upper and under surfaces of the wings should be alike, or that they should +be different, or that the fore wings should be colored the same as or +differently from the hind wings, etc. But in reality all possible kinds of +combinations occur simultaneously, and no rule holds throughout. Or, it +might be supposed that bright colors should occur only on the upper surface +or only on the under surface, or on the fore wings or only on the hind +wings. But the fact is, they occur indiscriminately, now here, now there, +and no one method of appearance is uniform throughout all the species. But +the fitness of the various distributions of colors is apparent, and the +moment we apply the principle of utility we know why in the diurnal +butterflies the upper surface alone is usually variegated and the under +surface protectively colored, or why in the nocturnal {19} butterflies the +fore wings have the appearance of bark, of old wood, or of a leaf, whilst +the hind wings, which are covered while resting, alone are brilliantly +colored. On this theory we also understand the exceptions to these rules. +We comprehend why Danaids, Heliconids, Euploids, and Acracids, in fact all +diurnal butterflies, offensive to the taste and smell, are mostly brightly +marked and equally so on both surfaces, whilst all species not thus exempt +from persecution have the protective coloring on the under surface and are +frequently quite differently colored there from what they are on the upper. + +In any event, the supposed formative laws are not obligatory. Dispensations +from them can be issued and are issued _whenever utility requires it_. +Indeed, so far may these transgressions of the law extend, that in the very +midst of the diurnal butterflies is found a genus, the South American +Ageronia, which, like the nocturnal butterfly, shows on the entire _upper_ +surface of both wings a pronounced bark-coloration, and concerning which we +also know (and in this respect it is an isolated genus and differs from +almost all other diurnal butterflies), that it spreads out its wings when +at rest like the nocturnal butterfly, and does not close them above it as +its relatives do. Therefore, entirely apart from cases of mimicry, which +after all constitute the strongest proof, the facts here cited are alone +sufficient to remove all doubt that not inner necessities or so-called +formative laws have painted the surface of the butterflies' wings, but that +the conditions of life have wielded the brush. + +This becomes more apparent on considering the details. I have remarked that +the usually striking colorations of exempt butterflies, as of the +Heliconids, {20} are the same on both the upper and the lower surfaces of +the wings. Possibly the expression of a law might be seen in this fact, and +it might be said, the coloration of the Heliconids _runs through_ from the +upper to the under surface. But among numerous imitators of the Heliconids +is the genus Protogonius, which has the coloration of the Heliconids on its +upper surface, but on its lower exhibits a magnificent leaf-design. During +flight it appears to be a Heliconid and at rest a leaf. How is it possible +that two such totally different types of coloration should be combined in a +single species, if any sort of _inner_ rigorous necessity existed, +regulating the coloration of the two wing-surfaces? Now, although we are +unable to prove that the Protogonius species would have perished unless +they possessed this duplex coloration, yet it would be nothing less than +intellectual blindness to deny that the butterflies in question are +effectively protected, both at rest and during flight, _that their +colorations are adaptive_. We do not know their primitive history, but we +shall hardly go astray if we assume that the ancestors of the Protogonius +species were forest-butterflies and already possessed an under surface +resembling a leaf. By this device they were protected when at rest. +Afterwards, when this protection was no longer sufficient, they acquired on +their upper surface the coloration of the exempt species with which they +most harmonised in abode, habits of life, and outward appearance. + +At the same time it is explained why these butterflies did not acquire the +coloration of the Heliconids on the under surface. The reason is, that in +the attitude of repose they were already protected, and that in an +admirable manner. {21} + +That _exempt_ diurnal butterflies should be colored on the upper and under +surfaces alike, and should never resemble in the attitude of repose their +ordinary surroundings, is intelligible when we reflect that it is a much +greater protection to be despised when discovered than to be well, or very +well, but never absolutely, protected from discovery. + +It has been so often reiterated that diurnal butterflies, as a rule, are +protectively colored on the under surfaces, that one has some misgivings in +stating the fact again. And yet the least of those who hold this to be a +trivial commonplace know how strongly its implications militate against the +inner motive and formative forces of the organism, which are ever and anon +appealed to. No less than sixty-two genera are counted today in the family +of diurnal butterflies known as the Nymphalidae. Of these by far the +largest majority are sympathetically colored underneath, that is, they show +in the posture of rest the colorings of their usual environment. In a large +number of the species belonging to this group the entire surface of the +hind wings possesses such a sympathetic coloration, as does also the +distant apex of the fore wings. Why? The reason is obvious. This part only +of the fore wing is visible in the attitude of repose. Here, then,--as a +zealous opponent of the theory of selection once exclaimed,--there is +undoubted "correlation" between the coloring of the surface of the hind +wing and of the apex of the fore wing. Correlation is unquestionably a fine +word, but in the present instance it contributes nothing to the +understanding of the problem, for there are near relatives and often +species of the same genera in which this correlation is not restricted to +the apex of the {22} fore wings, but extends to a third or even more of +their wings, and these species are also in the habit of drawing back their +wings less completely in the state of rest, thus rendering a larger portion +of them visible. There are species, too, like the forest-butterflies of +South America just mentioned, the Protogonius, Anaea, Kallima species, +etc., which have nearly the _whole_ of the under surfaces of their fore +wings marked according to the same pattern with their hind wings, and these +butterflies when at rest hold their fore wings free and uncovered by their +hind wings. Where are the formative laws in such cases? + +Or, perhaps some one will say: "The covering by the hind wings hinders the +formation of scales on the wing, or impedes the formation of the colors in +the scales." Such a person should examine one of these species. He will +find that the scales are just as dense on the covered as on the uncovered +surface of the wing, and in many species, for example, in Katagramma, the +scales of the covered surface are colored most brilliantly of all. + +But the facts are still more irresistible, when we consider _special +adaptations_; for example, the imitation of leaves, which is so often +cited. It is to be noted, first, that this sort of imitation is by no means +restricted to a few genera, still less to a few species. All the numerous +species of the genus Anaea, which are distributed over the forests of +tropical South America, exhibit this imitation in pronounced and varied +forms, as do likewise the American genera Hypna and Siderone, the Asiatic +Symphaedra, the African Salamis, Eurypheme, etc. I have observed +fifty-three genera in which it is present in one, several, or in many +species, but there are many others. {23} + +These genera, now, are by no means all so nearly allied that they could +have inherited the leaf-markings from a common ancestral form. They belong +to different continents and have probably for the most part acquired their +protective colorings themselves. But one resemblance they have in +common--they are all _forest-butterflies_. Now what is it that has put so +many genera of forest-butterflies and no others into positions where they +could acquire this resemblance to leaves? Was it directive formative laws? +If we closely examine the markings by which the similarity of the leaf is +determined, we shall find, for example, in Kallima Inachis, and Parallecta, +the Indian leaf-butterflies, that the leaf-markings are executed _in +absolute independence of the other uniformities governing the wing_. + +From the tail of the wing to the apex of the fore wings runs with a +beautiful curvature a thick, doubly-contoured dark line accompanied by a +brighter one, representing the midrib of the leaf. This line cuts the +"veins" and the "cells" of the wing in the most disregardful fashion, here +in acute and here in obtuse angles, and in absolute independence of the +regular system of divisions of the wing, which should assuredly be the +expression of the "formative law of the wing," if that were the product of +an internal directive principle. But leaving this last question aside, this +much is certain with regard to the markings, that they are dependent, not +on an _internal_, but on an _external_ directive power. + +Should any one be still unconvinced by the evidence we have adduced, let +him give the leaf-markings a closer inspection. He will find that the +midrib is composed of two pieces of which the one belongs to the {24} hind +wing and the other to the fore wing, and that the two fit each other +exactly when the butterfly is in the attitude of repose, but not otherwise. +Now these two pieces of the leaf-rib do not begin on corresponding spots of +the two wings, but on absolutely non-identical spots. And the same is also +true of the lines which represent the lateral ribs of the leaf. These lines +proceed in acute angles from the rib; to the right and to the left in the +same angle, those of the same side parallel with each other. Here, too, no +relation is noticeable between the parts of the wings over which the lines +pass. The venation of the wing is utterly ignored by the leaf-markings, and +its surface is treated as a _tabula rasa_ upon which anything conceivable +can be drawn. In other words, we are presented here with a _bilaterally +symmetrical_ figure engraved on a surface which is essentially _radially +symmetrical_ in its divisions. + +I lay unusual stress upon this point because it shows that we are dealing +here with one of those cases which cannot be explained by mechanical, that +is, by natural means, unless natural selection actually exists and is +actually competent to create new properties; for the Lamarckian principle +is excluded here _ab initio_, seeing that we are dealing with a formation +which is only passive in its effects; the leaf-markings are effectual +simply by their existence and not by any function which they perform; they +are present in flight as well as at rest, during the absence of danger, as +well as during the approach of an enemy. + +Nor are we helped here by the assumption of _purely internal motive +forces_, which Naegeli, Askenasy, and others have put forward as supplying +a _mechanical_ force of evolution. It is impossible to regard the {25} +coincidence of an Indian butterfly with the leaf of a tree now growing in +an Indian forest as fortuitous, as a _lusus naturae_. Assuming this +seemingly mechanical force, therefore, we should be led back inevitably to +a teleological principle which produces adaptive characters and which must +have deposited the directive principle in the very first germ of +terrestrial organisms, so that after untold ages at a definite time and +place the illusive leaf-markings should be developed. The assumption of +pre-established harmony between the evolution of the ancestral line of the +tree with its pre-figurative leaf, and that of the butterfly with its +imitating wing, is absolutely necessary here--a fact which I pointed out +many years ago,[9] but which is constantly forgotten by the promulgators of +the theory of internal evolutionary forces. + +For the present I leave out of consideration altogether the question as to +the conceivable extent of the sphere of operation of natural selection; I +am primarily concerned only with elucidating the process of selection +itself, wholly irrespective of the comprehensiveness or limitedness of its +sphere of action. For this purpose it is sufficient to show, as I have just +done, _that cases exist wherein all natural explanations except that of +selection fail us_. But let us now see how far the principle of selection +will carry us in the explanation of such cases--natural selection, I mean, +as it was formulated by Darwin and Wallace. + +There can be no doubt but the leaf-markings readily admit of production in +this manner, slowly and with a gradual but constant increase of fidelity, +provided a single condition is fulfilled: _the occurrence of the {26} right +variations at the right place_. But just here, it would seem, is the +insurmountable barrier to the explanatory power of our principle, for who, +or what, is to be our guarantee that dark scales shall appear at the exact +spots on the wing where the midrib of the leaf must grow? And that later +dark scales shall appear at the exact spots to which the midrib must be +prolonged? And that still later such dark spots shall appear at the places +whence the lateral ribs start, and that here also a definite acute angle +shall be accurately preserved, and the mutual distances of the lateral ribs +shall be alike and their courses parallel? And that the prolongation of the +median rib from the hind wing to the fore wing shall be extended exactly to +that spot where the fore wing is not covered by the hind wing in the +attitude of repose? And so on. + +If I could go more minutely into this matter, I should attempt to prove +that the markings, as I have just assumed, have not arisen suddenly, but +were perfected very, very gradually; that in one species they began on the +fore wing and in another on the hind wing; and that in many they never +until recently proceeded beyond one wing, in other species they went only a +little way, and in only a few did they spread over the entire surface of +both wings. + +That these markings advanced slowly and gradually, but with marvelous +accuracy, is no mere conjecture. But it follows that the right variations +at the right places must never have been wanting, or, as I expressed it +before: _the useful variations were always present_. But how is that +possible in such long extensive lines of dissimilar variations as have +gradually come to constitute markings of the complexity here presented? +Suppose that the useful colors had not {27} appeared at all, or had not +appeared at the right places? It is a fact that in constant species, that +is, in such as are not in process of transformation, the variations of the +markings are by no means frequent or abundant. Or, suppose that they had +really appeared, but occurred only in individuals, or in a small percentage +of individuals? + +Such are the objections raised against the theory of selection by its +opponents, and put forward as insurmountable obstacles to the process. Nor +are such objections relevant only in the case of protective colorings; they +are applicable in all cases where the process of selection is concerned. +Take the case of instincts that are called into action only once in life, +as, for example, the pupal performances of insects, the artificial +fabrication of cocoons, etc. How is it that the useful variations were +always present here? And yet they must have been present, if such +complicated spinning instincts could have taken their rise as are +observable in the silk-worm, or in the emperor-moth. And they have been +developed, and that in whole families, in forms varying in all species, and +in every case adapted to the special wants of the species. + +Particularly striking is the proof afforded of this constant presence of +the useful variations by cases where we meet with the development of highly +special adaptations that are uncommon even for the group of organisms +concerned. Such a case, for example, is the apparatus designed for the +capture of small animals and their digestion, found in widely different +plants and widely separated families. On the other hand, very common +adaptations, such as the eyes of animals, show distinctly that in all cases +where it was necessary, the useful variations for the formation of {28} an +eye were presented, and were presented further exactly at spots at which +organs of vision could perform their best work: thus, in Turbellaria and +many other worms that live in the light, at the anterior extremity of the +body and on the dorsal surface; in certain mussels, on the edge of the +mantle; in terrestrial snails, on the antennae; in certain tropical marine +snails inhabiting shallow waters, on the back; and in the chitons even on +the dorsal surface of the shell! + +But even taking the very simplest cases of selection, it is impossible to +do without this assumption, that the useful variations are always present, +or that _they always exist in a sufficiently large number of individuals +for the selective process_. You know the thickness and power of resistance +of the egg-shells of round-worms. The eggs of the round-worms of horses +have been known to continue their course of development undisturbed even +after they had been thrown into strong alcohol and all other kinds of +injurious liquids--much to the vexation of the embryologists, who wished to +preserve a definite stage of development and sought to kill the embryo at +that stage. Indeed, think of the result, if in the course of their +phylogenesis stout and resistant variations of egg-shells had not been +presented in these worms, or had not always been presented, or had not been +presented in every generation and not in sufficient quantities. + +The cogency of the facts is absolutely overpowering when we consider that +practically no modification occurs _alone_, that every primary modification +brings in its train secondary ones, and that these induce forced +modifications in many parts of the body, frequently of the most +diversified, or even self-contradictory, forms. Recently Herbert Spencer +has drawn {29} fresh attention to these secondary modifications, which must +always occur in harmony with the primary one, and has, as he thinks, +advanced in this set of facts, a convincing disproof of the contention that +such coadaptive modifications of numerous cofunctioning parts can rest on +natural selection. Now, although I deem his conclusion precipitate, yet the +very fact of a simultaneous, functionally concordant, yet essentially +diversified modification of numerous parts, points conclusively to the +circumstance that _something is still wanting to the selection of Darwin +and Wallace, which it is obligatory on us to discover, if we possibly can_, +and without which selection as yet offers no complete explanation of the +phyletic processes of transformation. There is a hidden secret to be +unriddled here before we can obtain a satisfactory insight into the +phenomena in question. _We must seek to discover why it happens that the +useful variations are always present._ + +Herbert Spencer appealed to Lamarck's principle for the explanation of +coadaptation, and it is certain that functional adaptation is operative +during the individual life, and that it compensates in a certain measure +the inequalities of the inherited constitutions. I shall not repeat what I +have said before on this subject, nor maintain, in refutation of Spencer's +contention, that functional adaptation is itself nothing more than the +efflux of _intra-biontic_ selective processes, as Spencer himself once +suggested in a prophetic moment, but which it was left for Wilhelm Roux to +introduce into science as "the struggle of the parts" of organisms.[10] I +shall only remark that if functional adaptations were themselves +inheritable, this would still be insufficient {30} for the explanation of +coadaptation, for the reason that precisely similar coadaptive +modifications occur in _purely passively_ functioning parts, in which, +consequently, modification _by_ function is excluded. This is the case with +the skeletal parts of Articulata; e. g., it is true of their articular +surfaces with their complex adaptations to the most varied forms of +locomotion. In all these cases the ready-made, hard, unalterable, chitinous +part is _first_ set into activity; consequently its adaptation to the +function must have been _previously_ effected, independently of that +function. These joints, and divers other parts, accordingly, have been +developed in the precisest manner for the function, and the latter could +have had no direct share in their formation. When we consider, now, that it +is impossible that every one of the numerous surfaces, ridges, furrows, and +corners found in a single such articulation, let alone in all the +articulations of the body, should hold in its hands the power of life and +death over individuals for untold successions of generations, the fact is +again unmistakably impressed upon our attention that the conception of the +selective processes which has hitherto obtained is insufficient, that the +root of the process in fact lies deeper, that it is to be found in the +place where it is determined what variations of the parts of the organism +shall appear--namely _in the germ_. + +The phenomena observed in the _stunting_, or _degeneration_, _of parts +rendered useless_, point to the same conclusion. They show distinctly that +ordinary selection which operates by the removal of entire persons, +_personal selection_, as I prefer to call it, cannot be the only cause of +degeneration; for in most cases of degeneration it cannot be assumed that +slight individual {31} vacillations in the size of the organ in question +have possessed selective value. On the contrary, we see such retrogressions +affected apparently _in the shape of a continuous evolutionary process +determined by internal causes_, in the case of which there can be no +question whatever of selection of persons or of a survival of the fittest, +that is, of individuals with the smallest rudiments. + +It is this consideration principally that has won so many adherents for the +Lamarckian principle in recent times, particularly among the +paleontologists. They see the outer toes of hoofed animals constantly and +steadily degenerating through long successions of generations and species, +concurrently with the re-enforcement of one or two middle toes, which are +preferred or are afterwards used exclusively for stepping, and they believe +correctly enough that these results should not be ascribed to the effects +of personal selection alone. They demand a principle which shall effect the +degeneration by internal forces, and believe that they have found it in +functional adaptation.[11] {32} On this last point, now, I believe, they +are mistaken, be they ever so strongly convinced of the correctness of +their view and ever so aggressive and embittered in their defence of it. + +Recently, an inquirer of great caution and calmness of judgment, Prof. C. +Lloyd Morgan, has expressed the opinion that the Lamarckian principle must +at least be admitted as a working hypothesis. But with this I cannot agree, +at least as things stand at present. A working hypothesis may be false, and +yet lead to further progress; that is, it may constitute an advance to the +extent of being useful in formulating the problem and in illuminating paths +that are likely to lead to results. But it seems to me that a hypothesis of +this kind has performed its services and must be discarded the moment it is +found to be at hopeless variance with the facts. If it can be proved that +precisely the same degenerative processes also take place in such +superfluous parts as have only _passive_ and not active functions, as is +the case with the _chitinous parts of the skeleton of Arthropoda_, then it +is a demonstrated fact, that the cessation of functional action is not the +efficient cause of the process of degeneration. At once your legitimate +working hypothesis is transformed into an illegitimate dogma--illegitimate +because it no longer serves as a guide on the path to knowledge but {33} +blocks that path. For the person who is convinced he has found the right +explanation is not going to seek for it. + +I can understand perfectly well the hesitation that has prevailed on this +point in many minds, from their having seen _one_ aspect of the facts more +distinctly than the other. From this sceptical point of view Osborn has +drawn the following perfectly correct conclusion: "If acquired variations +are transmitted, there must be some unknown principle in heredity; if they +are not transmitted, there must be some unknown factor in evolution."[12] + +Such in fact is the case and I shall attempt to point out to you what this +factor is. My inference is a very simple one: if we are forced by the facts +on all hands to the assumption that the useful variations which render +selection possible are always present, then _some profound connection must +exist between the utility of a variation and its actual appearance_, or, in +other words, _the direction of the variation of a part must be determined +by utility_, and we shall have to see whether facts exist that confirm our +conjecture. + +The facts do indeed exist and lie before our very eyes, despite their not +having been recognised as such before. All _artificial selection_ practised +by man rests on the fact that by means of the selection of individuals +having a given character slightly more pronounced than usual, there is +gradually produced a general augmentation of this character, which +subsequently reaches a point never before attained by any individual {34} +of this species. I shall choose an example which seems to me especially +clear and simple because only one character has been substantially modified +here. The long-tailed variety of domestic cock, now bred in Japan and +Corea, owes its existence to skilful selection and not at all to the +circumstance that at some period of the race's history a cock with +tail-feathers six feet in length suddenly and spasmodically appeared. At +the present day even, as Professor Ishikawa of Tokio writes me, the +breeders still make extraordinary efforts to increase the length of the +tail, and every inch gained adds considerably to the value of the bird. Now +nothing has been done here whatever except always to select for purposes of +breeding the cocks with the longest feathers; and in this way alone were +these feathers, after the lapse of many generations, prolonged to a length +far exceeding every previous variation. + +I once asked a famous dove-fancier, Mr. W. B. Tegetmeier of London, whether +it was his opinion that by artificial selection alone a character could be +augmented. He thought a long time and finally said: "It is without our +power to do anything if the variation which we seek is not presented, but +once that variation is given, then I think the augmentation can be +effected." And that in fact is the case. If cocks had never existed whose +tail-feathers were a little longer than usual the Japanese breed could +never have originated; but as the facts are, always the cocks with the +longest feathers were chosen from each generation, and these only were +bred, and thus a hereditary augmentation of the character in question was +effected, which would hardly have been deemed possible. + +Now what does this mean? Simply that the {35} hereditary diathesis, the +constitutional predisposition (_Anlage_) of the breed was changed in the +respect in question, and our conclusion from this and numerous similar +facts of artificial selection runs as follows: _by the selection alone of +the plus or minus variations of a character is the constant modification of +that character in the plus or minus direction determined._ Obviously the +hereditary _diminution_ of a part is also effected by the simple selection +of the individuals in each generation possessing the smallest parts, as is +proved, for example, by the tiny bills and feet of numerous breeds of +doves. We may assert, therefore, in general terms: a definitely directed +progressive variation of a given part is produced by continued selection in +that definite direction. This is no hypothesis, but a direct inference from +the facts and may also be expressed as follows: _By a selection of the kind +referred to the germ is progressively modified in a manner corresponding +with the production of a definitely directed progressive variation of the +part._ + +In this general form the proposition is not likely to encounter opposition, +as certainly no one is prepared to uphold the view that the germ remains +unchanged whilst the products proceeding from it, its descendants, are +modified. On the contrary, all will agree when I say that the germ in this +case must have undergone modifications, and that their character must +correspond with the modifications undergone by its products. Thus far, +then, we find ourselves, not on the ground of the hypothesis that has been +lately so much maligned, but on the ground of facts and of direct +inferences from facts. But if we attempt to pierce deeper into the problem, +we are in need of the hypothesis. {36} + +The first and most natural explanation will be this--that through selection +the zero-point, about which, figuratively speaking, the organ may be said +to oscillate in its plus and minus variations, is displaced upwards or +downwards. Darwin himself assumed that the variations oscillated about a +mean point, and the statistical researches of Galton, Weldon, and others +have furnished a proof of the assumption. If selection, now, always picks +out the plus variations for imitation, perforce, then, the mean or +zero-point will be displaced in the upward direction, and the variations of +the following generation will oscillate about a higher mean than before. +This elevation of the zero-point of a variation would be continued in this +manner until the total equilibrium of the organism was in danger of being +disturbed. + +There is involved here, however, an assumption which is by no means +self-evident, that every advancement gained by the variation in question +constitutes a new centre for the variations occurring in the following +generation. _That this is a fact_, is proved by such actual results of +selection as are obtained in the case of the Japanese cock. But the +question remains, Why is this the fact? + +Now here, I think, my theory of determinants gives a satisfactory answer. +According to that theory every independently and hereditarily variable part +is represented in the germ by a _determinant_, that is by a determinative +group of vital units, whose size and power of assimilation correspond to +the size and vigor of the part. These determinants multiply, as do all +vital units, by growth and division, and necessarily they increase rapidly +in every individual, and the more rapidly the greater the quantity of the +germinal cells {37} the individual produces. And since there is no more +reason for excluding irregularities of passive nutrition, and of the supply +of nutriment in these minute, microscopically invisible parts, than there +is in the larger visible parts of the cells, tissues, and organs, +consequently the descendants of a determinant can never all be exactly +alike in size and capacity of assimilation, but they will oscillate in this +respect to and fro about the maternal determinant as about their +zero-point, and will be partly greater, partly smaller, and partly of the +same size as that. In these oscillations, now, the material for further +selection is presented, and in the inevitable fluctuations of the nutrient +supply I see the reason why every stage attained becomes immediately the +zero-point of new fluctuations, and consequently why the size of a part can +be augmented or diminished by selection without limit, solely by the +displacement of the zero-point of variation as the result of selection. + +We should err, however, if we believed that we had penetrated to the root +of the phenomenon by this insight. There is certainly some other and +mightier factor involved here than the simple selection of persons and the +consequent displacement of the zero-point of variation. It would seem, +indeed, as if in one case, _videlicet_, in that of the Japanese cock, the +augmentation of the character in question were completely explained by this +factor _alone_. In fact, in this and similar cases we cannot penetrate +deeper into the processes of variation, and therefore cannot say _a priori_ +whether other factors have or have not been involved in the augmentation of +the character in question--other characters, that is, than the simple +displacement of the zero-point. There is, however, another class of +phyletic modifications, which point {38} unmistakably to the conclusion +that the displacement of the zero-point of variation by personal selection +is not and cannot be the only factor in the determination and +accomplishment of the direction of variation. I refer to _retrogressive +development_, the gradual degeneration of parts or characters that have +grown useless, the gradual disappearance of the eye in cave-animals, of the +legs in snakes and whales, of the wings in certain female butterflies, in +short, to that entire enormous mass of facts comprehended under the +designation of "rudimentary organs." + +I have endeavored on a previous occasion to point out the significance of +the part played in the great process of animate evolution by these +retrogressive growths, and I made at the time the statement that "the +phenomena of retrogressive growth enabled us in a greater measure almost +than those of progressive growth to penetrate to the causes which produce +the transformations of animate nature." Although at that time[13] I had no +inkling of certain processes which today I shall seek to prove the +existence of, yet my statement receives a fresh confirmation from these +facts. + +For, in most retrogressive processes _active_ selection in Darwin's sense +plays no part, and advocates of the Lamarckian principle, as above +remarked, have rightly denied that active selection, that is, the selection +of individuals possessing the useless organ in its most reduced state, is +sufficient to explain the process of degeneration. I, for my part, have +never assumed this, {39} and I enunciated precisely on this account the +_principle of panmixia_. Now, although this, as I still have no reason for +doubting, is a perfectly correct principle, which really does have an +essential and indispensable share in the process of retrogression, still it +is not _alone_ sufficient for a full explanation of the phenomena. My +opponents, in advancing this objection, were right, to the extent indicated +and as I expressly acknowledge, although they were unable to substitute +anything positive in its stead or to render my explanation complete. The +very fact of the cessation of control over the organ is sufficient to +explain its _degeneration_, that is, its deterioration, the disharmony of +its parts, but not the fact which actually and always occurs where an organ +has become useless--viz., _its gradual and unceasing diminution continuing +for thousands and thousands of years culminating in its final and absolute +effacement._ + +If, now, neither the selection of persons nor the cessation of personal +selection can explain this phenomenon, assuredly some other principle must +be the efficient cause here, and this cause I believe I have indicated in +an essay written at the close of last year and only recently published.[14] +I call it _germinal selection_. + +The principle in question reposes on the application, made some fifteen +years ago by Wilhelm Roux, of the principle of selection to the _parts_ of +organisms--on the _struggle of the parts_, as he called it. If such a +struggle obtains among organs, tissues, and cells, it must also obtain +between the smallest and for us invisible vital particles, not only between +those of the body-cells, strictly so called, but also between those of the +{40} germinal cells. Roux himself spoke of the struggle of the molecules, +by which he presumably understood the smallest ultimate units of vital +phenomena--elements which De Vries designated pangenes, Wiesner plasomes, +and I _biophores_, after Bruecke's ingenious conception[15] of these +invisible entities had been almost totally forgotten, or at least had lain +unnoticed for thirty years. No struggle, as that is understood in the +theory of selection, could take place between real {41} molecules, for +molecules are neither nourished, subject to growth, nor propagated. + +The gradual degeneration of organs grown useless may be explained, now, by +the theory of determinants very simply and without any co-operation on the +part of active personal selection, as follows. + +Nutrition, it is known, is not merely a passive process. A part is not only +_nourished_ but also actively _nourishes_ itself, and the more vigorously, +the more powerful and capable of assimilation it is. Hence powerful +determinants in the germ will absorb nutriment more rapidly than weaker +determinants. The latter, accordingly, will grow more slowly and will +produce weaker descendants than the former. + +Let us assume, now, that a part of the body, say the hinder extremities of +the quadruped ancestors of {42} our common whales, are rendered useless. +Panmixia steps in, _i. e._, selection ceases to influence these organs. +Individuals with large and individuals with small hind legs are equally +favored in the struggle for existence. + +From this fact alone would result a degradation of the organ, but of course +it would not be very marked in extent, seeing that the minus variations +which occur are no longer removed. According to our assumption, however, +such minus variations repose on the weaker determinants of the germ, that +is, on such as absorb nutriment less powerfully than the rest. And since +every determinant battles stoutly with its neighbors for food, that is, +takes to itself as much of it as it can, consonantly with its power of +assimilation and proportionately to the nutrient supply, therefore the +unimpoverished neighbors of this minus determinant will deprive it of its +nutriment more rapidly than was the case with its more robust ancestors; +hence, it will be unable to obtain the full quantum of food corresponding +even to its weakened capacity of assimilation, and the result will be that +its ancestors will be weakened still more. Inasmuch, now, as no weeding out +of the weaker determinants of the hind leg by personal selection takes +place on our hypothesis, inevitably the average strength of this +determinant must slowly but constantly diminish, that is, the leg must grow +smaller and smaller until finally it disappears altogether. The +determinants[16] of the useless organ are constantly at {43} a disadvantage +as compared with the determinants of their environment in the germinal +tenement, because no assistance is offered to them by personal selection +after they have once been weakened by a decrease of the passive nutrient +influx. Nor is the degeneration stopped by the uninterrupted crossing of +individuals in sexual propagation, but only slightly retarded. The number +of individuals with weaker determinants must, despite this fact, go on +increasing from generation to generation, so that soon every determinant +that still happens to be endowed with exceptional vigor will be confronted +by a decided overplus of weaker determinants, and by continued crossing +therefore will become more and more impoverished. Panmixia is the +indispensable precondition of the whole process; for owing to the fact that +persons with weak determinants are just as capable of life as those with +strong, owing to the fact that they cannot now, as formerly, when the organ +was still useful, be removed by personal selection, solely by this means is +a further weakening effected in the following generations--in short, only +by this means are the determinants of the useless organ brought upon the +inclined plane, down which they are destined slowly but incessantly to +slide towards their completed extinction. + +The foregoing explanation will be probably accepted as satisfactory _in a +purely formal regard_, but it will be objected that, even granting this, it +has not yet been proved to be the correct one. In answer I can of course +adduce nothing except that it is at present the only one that can be given. +It may be that the actual state of things in nature is different, but if it +can be shown that a self-direction of variation merely from the need of it +is at all conceivable by mechanical means, {44} that in itself, it seems to +me, is a decided gain. It must also not be forgotten that some process or +other _must_ take place in the germ-plasm when an organ becomes +rudimentary, and that as the result of it this organ, and only this organ, +must disappear. Now in what shall this process consist, if not in a +modification of the constitution of the germ? And how could the effect of +such a modification be limited only to _one_ organ which was becoming +rudimentary if the modification itself were not a local one? These are +questions which it is incumbent on those to answer who conceive the +germinal substance to be composed of like units. + +Applying, now, the explanation derived from the disappearance of organs to +the opposed transformation, namely, to the _enlargement_ of a part, the +presumption lies close at hand that the production of the long +tail-feathers of the Japanese cock does not repose solely on the +displacement directly effected by personal selection, of the zero-point of +variation upwards, but that _it is also fostered and strengthened by +germinal selection_. Were that not so, the phenomena of the transmutation +of species, in so far as fresh growth and the enlargement and complication +of organs already present are concerned, _would not be a whit more +intelligible than they were before_. We should know probably how it comes +to pass that the constitutional predisposition (group of determinants) of a +_single_ organ is intensified by selection, but the flood of objections +against the theory of selection touching its inability to modify _many_ +parts at once would not be repressed by such knowledge. The initial impulse +conditioning the independent maintenance of the useful direction of +variation in the germ-plasm must rather be sought {45} in the utility of +the modification itself, and this also seems to me intelligible from the +side of the theory. For as soon as personal selection favors the more +powerful variations of a determinant, the moment that these come to +predominate in the germ-plasm of the species, at once the tendency must +arise for them to vary _still more strongly_ in the plus direction, not +solely because the zero-point has been pushed farther upwards, but because +they themselves now oppose a relatively more powerful front to their +neighbors, that is, actively absorb more nutriment, and upon the whole +increase in vigor and produce more robust descendants. From the relative +vigor or dynamic status of the particles of the germ-plasm, thus, will +issue spontaneously an ascending line of variation, precisely as the facts +of evolution require. For, as I have already said, it is not sufficient +that the augmentation of a character should be brought about by +uninterrupted personal selection, even supposing that the displacement of +the zero-point were possible without germinal selection. + +Thus, I think, may be explained how personal selection imparts the initial +impulse to processes in the germ-plasm, which, when they are once set +agoing, persist of themselves in the same direction, and are, therefore, in +no need of the continued supplementary help of personal selection, _as +directed exclusively to a definite part_. If but from time to time, that +is, if upon the average the poorest individuals, the bearers of the weakest +determinants, are eliminated, the variational direction of the part in +question, now reposing on germinal selection, must persist, and it will +very slowly but very surely increase until further development is impeded +by its inutility and personal selection {46} arrests the process, that is, +ceases to eliminate the weaker individuals. + +In this manner it becomes intelligible how a large number of modifications +varying in kind and far more so in degree can be guided _simultaneously_ by +personal selection; how in strict conformity with its adaptive wants every +part is modified, or preserved unmodified; how a given articulation can +undergo modifications, causing it to disappear on one side, to grow in +volume on another, and to continue unaltered on a third. For every part +that is perfectly adapted, although it can fluctuate slightly, yet can +never undergo a permanent alteration in the ascending or descending +direction because every plus and every minus variation which has attained +selective value would be eliminated by personal selection in the course of +time. Therefore, a definite direction of variation cannot arise in such +cases and we have also reached, as it seems to me, a satisfactory +explanation of the _constancy_ of well-adapted species and characters. + +Hitherto I have spoken only of plus and minus variation. But there exist, +as we know, not only variations of size but also variations of _kind_; and +the coloration of the wings of butterflies, which we chose above as our +example, would fall, according to the ordinary usage of speech, under just +this head of variations of quality. The question arises, therefore, Have +the principles just developed any claim to validity in the explanation of +_qualitative_ modifications? + +In considering this question it should be carefully borne in mind that by +far the largest part of the qualitative modifications falling under this +head rest on _quantitative_ changes. Of course, chemical transformations, +which usually also involve quantitative {47} alterations, cannot be reduced +to the processes of augmentation described, inasmuch as these, by their +very nature, can be effected only in living elements capable of increase by +propagation; but the interference of selection does not begin originally +with the constitutional predisposition (_Anlagen_) of the germ, i. e. with +the determinants, but with the ultimate units of life, the _biophores_. + +A determinant must be composed of heterogeneous biophores, and on their +numerical proportion reposes, according to our hypothesis, their specific +nature. If that proportion is altered, so also is the character of the +determinant. But disturbances of this numerical proportion must result at +once on proof of their usefulness, or as soon as the modifications +determined thereby in the inward character of the determinant turn out to +be of utility. For fluctuations of nutriment and the struggle for +nutriment, with its sequent preference of the strongest, must take place +between the various species of the biophores as well as between the species +of the determinants. But changes in the quantitative ratios of the +biophores appear to us qualitative changes in the corresponding +determinants, somewhat as a simple augmentation of a determinant, for +example, that of a hair, may on its development appear to us as a +qualitative change, a spot on the skin where previously only isolated hairs +stood being now densely crowded with them, and assuming thus the character +of a downy piece of fur. The single hair need not have changed in this +process, and yet the spot has virtually undergone a qualitative +modification. The majority of the changes that appear to us qualitative +rest on invisible _quantitative_ changes, and such can be produced at all +times and _at all stages_ {48} _of the vital units_ by germinal selection. +In a similar manner are induced the most varied qualitative changes of the +corresponding determinants and of the characters conditioned thereby, just +as changes in the numerical proportions of atoms produce essential changes +in the properties of a chemical molecule. + +In this way we acquire an approximate conception of the possible mechanical +_modus operandi_ of actual events--namely, of the manner in which the +useful variations required by the conditions of life _can_ always, that is, +very frequently, make their appearance. This possibility is the sole +condition of our being able to understand how different parts of the body, +absolutely undefined in extent, can appear as variational units and vary in +the same or in different directions, according to the special needs of the +case, or as the conditions of life prescribe. Thus, for example, in the +case of the butterfly's wings it rests entirely with utility to decide the +size and the shape of the spots that shall vary simultaneously in the same +direction. At one time the whole under surface of the wing appears as the +variational unit and has the same color; at another the inside half, which +is dark, is contrasted with the outside half which is bright; or the same +contrast will exist between the anterior and posterior halves; or, finally, +narrow stripes or line-shaped streaks will behave as variational units and +form contrasts with manifold kinds of spots or with the broader intervals +between them, with the result that the picture of a leaf or of another +protected species is produced. + +I must refrain from entering into the details of such cases and shall +illustrate my views regarding the color-transformations of butterflies' +wings by the simplest {49} conceivable example--viz. that of the uniform +change of color on the entire under surface of the wing. + +Suppose, for example, that the ancestral species of a certain +forest-butterfly habitually reposed on branches which hung near the ground +and were covered with dry or rotten leaves; such a species would assume on +its under surface a protective coloring which by its dark, brown, yellow, +or red tints would tend toward similarity with such leaves. If, however, +the descendants of this species should be subsequently compelled, no matter +from what cause, to adopt the habit of resting on the green-leafed branches +higher up, then from that period on the brown coloring would act less +protectively than the shades verging towards green. And a process of +selection will have set in which consisted first in giving preference only +to such persons whose brown and yellow tints showed a tendency to green. +Only on the assumption that such shades were possible by a displacement in +the quantitative proportions of the different kinds of biophores composing +the determinants of the scales affected, was a further development in the +direction of green possible. Such being the case, however, that development +_had to_ result; because fluctuations in the numerical proportions of the +biophores are always taking place, and consequently the material for +germinal selection is always at hand. At present it is impossible to +determine exactly the magnitude of the initial stages of the deviations +thus brought about and promoted by the sexual blending of characters; but +it may perhaps be ascertained in the future, with exceptionally favorable +material. Pending such special observations, however, it can only be said +_a priori_ that slight changes in the composition of a determinant do not +necessarily {50} condition similar slight deviations of the corresponding +character,--in this case the color,--just as slight changes in the atomic +composition of a molecule may result in bestowing upon the latter widely +different properties. As soon, however, as the beginning has been made and +a definite direction has been imparted to the variation, as the result of +this or that primary variation's being preferred, the selective process +must continue until the highest degree of faithfulness required by the +species in the imitation of fresh leaves has been attained. + +That the foregoing process has actually taken place is evidenced not only +by the presence of the beginnings of such transformations, as found for +example in some greenish-tinted specimens of Kallima, but mainly by certain +species of the South American genus Catonephele, all of which are +forest-butterflies, and which, with many species having dark-brown under +surfaces, present some also with bright green under surfaces--a green that +is not like the fresh green of our beech and oak trees, but resembles the +bright under surface of the cherry-laurel leaf, and is the color of the +under surfaces of the thick, leathery leaves, colored dark-green above, +borne by many trees in the tropics. + +The difference between this and the old conception of the selection-process +consists not only in the fact that a large number of individuals with the +initial stages of the desired variation is present from the beginning, for +always innumerable plus and minus variations exist, but principally in the +circumstance that the constant uninterrupted progress of the process after +it is once begun is assured, that there can never be a lack of +progressively advantageous variations in a large number of individuals. +Selection, {51} therefore, is now not compelled to wait for accidental +variations but produces such itself, whenever the required elements for the +purpose are present. Now, where it is a question simply of the enlargement +or diminution of a part, or of a part of a part, these variations are +always present, and in modifications of quality they are at least present +in many cases. + +This is the only way in which I can see a possibility of explaining +phenomena of _mimicry_--the imitation of one species by another. The useful +variations must be produced in the germ itself by internal +selection-processes if this class of facts is to be rendered intelligible. +I refer to the mimicry of an exempt species by two or three other species, +or, the aping of _different_ exempt patterns by _one_ species in need of +protection. It must be conceded to Darwin and Wallace that some degree of +similarity between the copy and the imitation was present from the start, +at least in very many cases;[17] but in no case would this have been +sufficient had not slight shades of coloring afforded some hold for +personal selection, and in this way furnished a basis for independent +germinal selection acting only in the direction indicated. It would have +been impossible for such a minute similarity in the design, and +particularly in the shades of the coloration, ever to have arisen, if the +process of adaptation rested entirely {52} on personal selection. Were this +so, a complete scale of the most varied shades of color must have been +continually presented as variations in every species, which certainly is +not the case. For example, when the exempt species _Acraea Egina_, whose +coloration is a brick-red, a color common only in the genus Acraea, is +mimicked by two other butterflies, a Papilio and a Pseudacraea, so +deceptively that not only the cut of the wings and the pattern of their +markings, but also that precise shade of brick-red, which is scarcely ever +met with in diurnal butterflies, are produced, assuredly such a result +cannot rest on accidental, but must be the outcome of a _definitely +directed_, variation, produced by utility. We cannot assume that such a +coloration has appeared as an _accidental_ variation in just and in only +these two species, which fly together with the _Acraea_ in the same +localities of the same country and same part of the world--the Gold Coast +of Africa. It is conceivable, indeed, that non-directed variation should +have accidentally produced this brick-red _in a single case_, but that it +should have done so three times and in three species, which live together +but are otherwise not related, is a far more violent and improbable +assumption than that of a causal connexion of this coincidence. Now +hundreds of cases of such mimicry exist in which the color-tints of the +copy are met with again in more or less precise and sometimes in +exceedingly exact imitations, and there are thousands of cases in which the +color-tint of a bark, of a definite leaf, of a definite blossom, is +repeated _exactly_ in the protectively colored insect. In such cases there +can be no question of accident, but _the variations presented to personal +selection must themselves have been produced by the principle of the +survival of the_ {53} _fit!_ And this is effected, as I am inclined to +believe, through such profound processes of selection in the interior of +the germ-plasm as I have endeavored to sketch to you to-day under the title +of germinal selection. + +I am perfectly well aware how schematic my presentation of this process is, +and must be at present, owing mainly to our inability to gain exact +knowledge concerning the fundamental germinal constituents here assumed. +But I regard its existence as assured, although I by no means underrate the +fact that eminent thinkers, like Herbert Spencer, contest its validity and +believe they are warranted in assuming a germ which is composed of _similar +units_. I strongly doubt whether even so much as a _formal_ explanation of +the phenomena can be arrived at in this manner. So far as direct +observation is concerned, the two theories stand on an equal footing, for +neither my dissimilar, nor Spencer's similar, units of germinal substance +can be _seen_ directly. + +The attempt has been recently made to discredit my _Anlagen_, or +constitutional germ-elements, on the ground that they are simply a +subtilised reproduction of Bonnet's old theory of preformation.[18] This +{54} impression is very likely based upon ignorance of the real character +of Bonnet's theory. I will not go into further details here, particularly +as Whitman, in several excellently written and finely conceived essays, has +recently afforded opportunity for every one to inform himself on the +subject. My determinants and groups of determinants have nothing to do with +the preformations of Bonnet; in a sense they are the exact opposites of +them; they are simply _those living parts of the germ whose presence +determines the appearance of a definite organ of a definite character in +{55} the course of normal evolution_. In this form they appear to me to be +an absolutely necessary and unavoidable inference from the facts. There +_must_ be contained in the germ parts that correspond to definite parts of +the complete organism, that is, parts that constitute the reason why such +other parts are formed. + +It is conceded even by my opponents that the reason why one egg produces a +chicken and another a duck is not to be sought in external conditions, but +lies in a difference of the germinal substance. Nor can they deny that a +difference of germinal substance must also constitute the reason why a +slight _hereditary_ difference should exist between two filial organisms. +Should there now, in a possible instance, be present between them a second, +a third, a fourth, or a hundredth difference of hereditary character, each +of which could vary from the germ, then, certainly, some second, third, +fourth, or hundredth part of the germ must have been different; for whence, +otherwise, should the heredity of the differences be derived, seeing that +external influences affecting the organism in the course of evolution +induce only non-transmissible and transient deviations? But the fact that +every complex organism is actually composed of a very large number of parts +independently alterable from the germ, follows not only from the comparison +of allied species, but also and principally from the experiments long +conducted by man in artificial selection, and by the consequent and not +infrequent change of only a single part which happens to claim his +interest; for example, the tail-feathers of the cock, the fruit of the +gooseberry, the color of a single feather or group of feathers, and so on. +But a still more cogent proof is furnished by the degeneration of parts +grown {56} useless, for this process can be carried on to almost any extent +without the rest of the body necessarily becoming involved in sympathetic +alteration. Whole members may become rudimentary, like the hind limbs of +the whale, or it may be only single toes or parts of toes; the whole wing +may degenerate in the females of a butterfly species, or only a small +circular group of wing-scales, in the place of which a so-called "window" +arises. A single vein of the wing also may degenerate and disappear, or the +process may affect only a part of it, and this may happen in one sex only +of a species. In such cases the rest of the body may remain absolutely +unaltered; only a stone is taken out of the mosaic. + +The assumption, thus, appears to me irresistible, that every such +hereditary and likewise independent and very slight change of the body +rests on some alteration of a _single_ definite particle of the germinal +substance, and not as Spencer and his followers would have it, on a change +of _all_ the units of the germ. If the germinal substance consisted wholly +of like units, then in every change, were it only of a single character, +_each_ of these units would have to undergo exactly the same modification. +Now I do not see how this is possible. + +But it may be that Spencer's assumption is the _simpler_ one? Quite the +contrary, its simplicity is merely apparent. Whilst my theory needs for +each modification only a modification of _one_ constitutional element of +the germ, that is, of _one_ particle of the germinal substance, according +to Spencer _every_ particle of that substance must change, for they are all +supposed to be and to remain alike. But seeing that all hereditary +differences, be they of individuals, races, {57} or species, must be +contained in the germ, the obligation rests on these similar units, or +rather the capacity is required of them, to produce in themselves a truly +enormous number of differences. But this is possible only provided their +composition is an exceedingly complex one, or only on the condition that in +every one of them are contained as many alterable particles as according to +my view there are contained determinants in the whole germ. _The +differences that I put into the whole germ, Spencer and his followers are +obliged to put into every single unit of the germinal substance._ My +position on this point appears to me incontrovertible so long as it is +certain that the single characters can vary hereditarily; for, if a thing +can vary independently, that is, _of its own accord_, and _from the germ_, +then that thing must be represented in the germ by some particle of the +substance, _and be represented there in such wise that a change of the +representative particle produces no other change in the organism developing +from the germ than such as are connected with the part which depends on +it_. I conceive that even on the assumption of my constitutional elements +(_Anlagen_) the germ-plasm is complex enough, and that there is no need of +increasing its complexity to a fabulous extent. Be that as it may, the +person who fancies he can produce a complex organism from a _really_ simple +germinal substance is mistaken: he has not yet thoroughly pondered the +problem. The so-called "epigenetic" theory with its _similar_ germinal +units is therefore naught else than an evolution-theory where the primary +constitutional elements are reduced to the molecules and atoms--a view +which in my judgment is inadmissible. A _real_ {58} epigenesis from +absolutely _homogeneous_ and not merely _like_ units is not thinkable. + +All value has been denied my doctrine of determinants[19] on the ground +that it only shifts the riddles of evolution to an invisible terrain where +it is impossible for research to gain a foothold. + +Now I have indeed to admit that no information can be gained concerning my +determinants, either with the aided or with the unaided eye. But +fortunately there exists in man another organ which may be of use in +fathoming the riddles of nature and this organ which is called the brain +has in times past often borne him out in the assumption of invisible +entities--entities that have not always proved unfruitful for science by +reason of that defect, in proof whereof we may instance the familiar +assumptions of atoms and molecules. Probably the biophores also will be +included under that head if the determinants should be adjudged utterly +unproductive. But so far I have always held that assumptions of this kind +_are_ really productive, if they are only capable of being used, so to +speak, as a _formula_, whereby to perform our computations, unconcerned for +the time being as to what shall be its subsequent fate. Now, as I take it, +the determinants have had fruitful results, as their application to various +biological problems shows. Is it no advance that we are able to reduce the +scission of a form of life into two or several forms subject to separately +continued but recurrent changes,--I refer to dimorphism and +polymorphism,--that we are able to reduce such phenomena to the formula of +male, female, and worker determinants? It has been, I think, {59} rendered +conceivable how these diverse and extremely minute adaptations could have +developed side by side in the same germ-plasm, under the guidance of +selection; how sterile forms could be _hereditarily_ established and +transformed in just that manner which best suits with their special duties; +and how they themselves under the right circumstances could subsequently +split up into two or even into three new forms. Surely at least the unclear +conception of an _adaptively_ transformative influence of food must be +discarded. It is true, we cannot penetrate by this hypothesis to the last +root of the phenomena. The hotspurs of biology, who clamor to know +forthwith how the molecules behave, will scarcely repress their +dissatisfaction[20] with such provisional knowledge--forgetful that _all +our knowledge is and remains throughout provisional_. + +But I shall not enter more minutely into the question whether epigenesis or +evolution is the right foundation of the theory of development, but shall +content myself with having shown, first, that it is illusory to imagine +that epigenesis admits of a simpler structure of the germ, (the precise +opposite is true,) and secondly, that there are phenomena that can be +understood only by an evolution-theory. Such a phenomenon is {60} the +_guidance of variation by utility_, which we have considered to-day. For +without primary constituents of the germ, whether they are called as I call +them, determinants, or something else, _germinal selection_, or guidance of +variation by personal selection, is impossible; for where all units are +alike there can be no struggle, no preference of the best. And yet such a +guidance of variation exists and demands its explanation, and the early +assumptions of a "definitely directed variation" such as Naegeli and +Askenasy made are insufficient, for the reason that they posit only +_internal_ forces as the foundations thereof, and because, as I have +attempted to show, the harmony of the direction of variation with the +requirements of the conditions of life subsists and represents the riddle +to be solved. _The degree of adaptiveness which a part possesses itself +evokes the direction of variation of that part._ + +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 any_ {61} _experience 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, {62} 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 {63} that have been recently brought +forward by the acutest critics, as for example by Wigand, but particularly +by Wolff,[21] 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 +{64} 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] 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 {65} +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 {66} _personal_ selection[23] +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] 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 {67} 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 {68} 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. + + * * * * * + + +{69} + +APPENDIX. + + * * * * * + +I. THE REJECTION OF SELECTION. + +Many years ago Semper[25] 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] has +distinguished himself by the vigor with which he has attacked the "task" of +"setting aside the dogma of selection." Henry B. Orr[27] 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 Delage,[28] 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 +{70} 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] 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 Tuebingen 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] + +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 {71} from Emery,[31] 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] Unstable combinations are upon the application of a {72} +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 footnote +at page 31. 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 {73} adduced in the text--the _Zielstrebigkeit_ (to use K. E. +von Baer'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 {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 +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 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 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 {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 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 +Mueller. 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 Mueller 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. Mueller 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 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. 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. + + * * * * * + +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 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. + + * * * * * + +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[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 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. + + * * * * * + + +{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. + + Japanese cocks, long-tailed, 34, 44, 78. + + Kallima, 22, 23, 50. + Katagramma, 22. + Knowledge, its character, 5. + + Lamarckian principles, 24, 29 et seq., 31 et seq., 38, 63-64, 68, 84. + Leaves, imitated by butterflies, 20 et seq. + Locomotive, simile of, 11. + + Malthusian principle, 65, 67. + Markings, butterflies', 16 et seq. + Maxwell, 4, 5. + Mean of variation, 78-79. + Meristic, 18. + Mimicry, 19, 51 et seq. + Minot, S., 54 footnote. + Models, mental, 4 et seq. + Molecules, 58. + Morgan, Prof. C. Lloyd, 32, 71, 83. + Mueller, Fritz, 77-79. + Mueller, Hermann, 77. + Mussels, 28. + Mutations, 31 footnote, 72-76. + + Naegeli, 4, 11, 24, 60, 82. + Neumayr, 72. + Newton, 5. + Nutrition of determinants, 36, 37, 41, 47. + Nymphalidae, 21. + + Ontogenesis, 8. + Orr, Henry B., 69. + Osborn, Prof. H. F., 33. + Owen, Richard, 11. + + Paleontology, 31, 73, 75, 76. + Palms from Cordilleras, 82. + Pangenes, 40. + Panmixia, 15, 39, 42, 43, 64. + Papilio, 16, 52. + Parallecta, 23. + Parts, struggling of the, 29, 39, 66-67. + Passively functioning parts, 30 et seq., 64. + Personal selection, 30, 41, 42, 45, 52, 64-86, 80. + Phyletic variation, 31-32 footnote. + Phylogenesis, 8. + Phylogenetic variations, 31-32, 73. + Plasomes, 40. + Plus and minus variations, 35, 42, 46, 50, 79-80. + Polymorphism, 58. + Poulton, 64 footnote. + Predestined variation, 4. + Pre-established harmony, 25. + Preformation, 53. + Protective colorings, 14 et seq. + Protogonius, 22. + Pseudocraea, 52. + + Qualitative modifications, 46. + Quantitative changes, 46-47. + + Retrogressive development, 38. + Round-worms, eggs of, 28. + Roux, Wilhelm, 29, 39, 65, 66. + + Salamis, 22. + Scott, Prof. W. B., 31 footnote, 72-74. + Segmentation, 10. + {87} + Selection, natural, 10, 25 et seq., 50, 51, 67, 69-73, 81, 82. + Selective value of variations, 60. + Semper, 69. + Siderone, 22. + Snails, 28. + Spencer, 14, 28, 29, 40, 53, 56, 80. + Struggle for existence, 65. + Survival of the fit, 52. + Symphaedra, 22. + + _Tabula rasa_, 27, 24. + Tegetmeier, W. B., 34. + Teleological principles, 10, 16, 25. + Theories, nature of, 5 et seq. + Turbellaria, 28. + + Units, vital, biological, physiological, etc., 8, 40, 41, 53, 56, 65, 80. + Useful modifications, value of initial stages of, 80-82. + Utility, 11, 18, 33, 45, 48, 62, 63, 82. + + Variations, necessary, their constant presence, 26 et seq., 31 et seq., + 61; + generally, 3, 11-14, 61, 71 et seq. + + Waagen, 72. + Wallace, 11, 25, 29, 51, 66, 81. + Weldon, 36. + Whale, hind leg of, 42, 56, 80. + Whitman, C. O., 53. + Wiesner, 40. + Wigand, Albert, 11, 63. + Wings of butterflies, 14 et seq., 47-52, 56. + Wolff, K. F., 53, 62, 63, 69. + "Worse" individuals, 76. + + Zero-point of variation, 36 et seq., 45, 74, 79. + + * * * * * + + +Notes + +[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_. + +[5] Hans Driesch, _Die Biologie als selbststaendige 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 Naturzuechtung._ 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 Zooelogists 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] Delage, in _La structure du protoplasma et les theories sur +l'heredite_, 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. +Bruecke 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 Delage cites Bruecke's essay in the +Bibliographical Index at the end of his book correctly, although Bruecke's +name and views are nowhere mentioned in the book itself. It is to be +observed, however, that the elementary organisms of Bruecke are not merely +the precursors of Spencer's "physiological units," but repose on much +firmer foundations than the latter, which, as Delage 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 +Bruecke 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 Bruecke with the +same distinctness and sharpness as by recent inquirers, who took up +Bruecke'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, +_Intracellulaere 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'heredite_ 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 naive 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] "Beitraege 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 natuerlichen Existenzbedingungen der Thiere_, Leipsic, +1880, pp. 218-219. + +[26] Wolff, "Beitraege 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 Delage, _La structure du protoplasma et les theories sur +l'heredite et les grands problemes de la biologie generale_, Paris, 1895. + +[29] Henslow, _The Origin of Species Without the Aid of Natural Selection, +A Reply to Wallace_. 1894. + +[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 Tuebingen 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. + +[31] "Gedanken zur Descendenz- und Vererbungstheorie." _Biolog. +Centralblatt_, July 15, 1893. + +[32] C. Lloyd Morgan, _Animal Life and Intelligence_, London, 1890-1891, p. +30-33. + +[33] _Materials for the Study of Variation with Especial Regard to +Discontinuity in the Origin of Species_, London, 1895, p. 16. + +[34] "Gedanken zur Descendenz- and Vererbungstheorie," _Biolog. +Centralblatt_, 1893, Vol. XIII., p. 397. + + + + + + +End of the Project Gutenberg EBook of On Germinal Selection as a Source of +Definite Variation, by August Weismann + +*** END OF THIS PROJECT GUTENBERG EBOOK ON GERMINAL SELECTION *** + +***** This file should be named 34077.txt or 34077.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/4/0/7/34077/ + +Produced by Bryan Ness, Keith Edkins and the Online +Distributed Proofreading Team at https://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive/American Libraries.) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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