A determinant must be composed of heterogeneous bioph.o.r.es, 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 bioph.o.r.es as well as between the species of the determinants. But changes in the quant.i.tative ratios of the bioph.o.r.es 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 a.s.suming 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 _quant.i.tative_ 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 b.u.t.terfly'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 ill.u.s.trate my views regarding the color-transformations of b.u.t.terflies'

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-b.u.t.terfly habitually reposed on branches which hung near the ground and were covered with dry or rotten leaves; such a species would a.s.sume 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 a.s.sumption that such shades were possible by a displacement in the quant.i.tative proportions of the different kinds of bioph.o.r.es 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 bioph.o.r.es 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 s.e.xual 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-b.u.t.terflies, 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 princ.i.p.ally in the circ.u.mstance that the constant uninterrupted progress of the process after it is once begun is a.s.sured, 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 cla.s.s 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 b.u.t.terflies, 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 b.u.t.terflies, are produced, a.s.suredly such a result cannot rest on accidental, but must be the outcome of a _definitely directed_, variation, produced by utility. We cannot a.s.sume 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 a.s.sumption 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 t.i.tle 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 const.i.tuents here a.s.sumed.

But I regard its existence as a.s.sured, although I by no means underrate the fact that eminent thinkers, like Herbert Spencer, contest its validity and believe they are warranted in a.s.suming 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 const.i.tutional 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 const.i.tute 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 const.i.tute 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 princ.i.p.ally 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 c.o.c.k, 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 b.u.t.terfly 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 s.e.x 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 a.s.sumption, 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 a.s.sumption is the _simpler_ one? Quite the contrary, its simplicity is merely apparent. Whilst my theory needs for each modification only a modification of _one_ const.i.tutional 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 a.s.sumption of my const.i.tutional 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 const.i.tutional elements are reduced to the molecules and atoms--a view which in my judgment is inadmissible. A _real_ {58} epigenesis from absolutely _h.o.m.ogeneous_ 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 a.s.sumption of invisible ent.i.ties--ent.i.ties that have not always proved unfruitful for science by reason of that defect, in proof whereof we may instance the familiar a.s.sumptions of atoms and molecules. Probably the bioph.o.r.es also will be included under that head if the determinants should be adjudged utterly unproductive. But so far I have always held that a.s.sumptions 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 circ.u.mstances 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 const.i.tuents 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 a.s.sumptions of a "definitely directed variation" such as Nageli 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 a.s.sumption 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 a.s.sumption 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 a.s.sumption that the initial steps of all actually affected adaptations possessed selective value.

The princ.i.p.al 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 const.i.tutional 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 quant.i.tative 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 exact.i.tude_ 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 circ.u.mstances may vary differently, for example, the two visual halves of soles; that h.o.m.odynamic 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 const.i.tutions 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. .h.i.therto 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 circ.u.mstances, but also every qualitative direction of variation attainable by changes of quant.i.ty, 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 a.s.sumption. 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 _pa.s.sively 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 a.s.sent 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 bioph.o.r.es 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 bioph.o.r.es 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 princ.i.p.al 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 pa.s.su_ 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 a.s.sistance 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 a.s.sume 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 p.r.o.nounced 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 p.r.o.nounced 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 Tubingen Professor nothing but a reiteration of the same unproved a.s.sertions, 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, ent.i.tled "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 const.i.tute 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 Bar'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_."