But here is an illustration of another class of cases. Mr. Tomes has shown that the molar teeth of the Orang present an extraordinary and altogether superfluous amount of attachment in their sockets—the fangs being not only exceedingly long, and therefore deeply buried in the jaw-bone, but also curving round one another, so as still further to strengthen the whole[133]. In the allied genera of anthropoid apes there is no such abnormal amount of attachment. Now, the question is, of what conceivable use can it ever have been, either to the existing genus, or to its parent species, that such an abnormal amount of attachment should obtain? It certainly is not required to prevent dislocation of the teeth, seeing that in all allied genera, and even in man himself, the amount of attachment is already so great that teeth will break before they can be drawn by anything short of a dentist's forceps. Therefore I conclude that this peculiarity in the dentition of the genus must have arisen in its parent species by way of what Darwin calls a "fluctuating variation," without utilitarian significance. And I adduce it in the present connexion because the peculiarity is one which is equally unamenable to a utilitarian explanation, whether it happens to occur as a generic or a specific character.
Numberless similar cases might be quoted; but probably enough has now been said to prove the inconsistency of the distinction which our opponents draw between specific and all higher characters in respect of utility. In point of fact, a very little thought is enough to show that no such distinction admits of being drawn; and, therefore, that any one who maintains the doctrine of utility as universal in the case of specific characters, must in consistency hold to the same doctrine in the case of generic and all higher characters. And the fact that our opponents are unable to do this becomes a virtual confession on their part of the futility of the generalization which they have propounded[134].
On what then do Mr. Wallace and his followers rely for their great distinction between specific and all other characters in respect of utility? This is the final and fundamental question which I must leave these naturalists themselves to answer; for my whole contention is, that it is unanswerable. But although I am satisfied that they have nothing on which to base their generalization, it seems worth while to conclude by showing yet one further point. And this is, that these naturalists themselves, as soon as they quit merely abstract assertions and come to deal with actual facts, contradict their own generalization. It is worth while to show this by means of a few quotations, that we may perceive how impossible it is for them to sustain their generalization in the domain of fact.
As it is desirable to be brief, I will confine myself to quoting from Mr. Wallace.
"Colour may be looked upon as a necessary result of the highly complex chemical constitution of animal tissues and fluids. The blood, the bile, the bones, the fat, and other tissues have characteristic, and often brilliant colours, which we cannot suppose to have been determined for any special purpose as colours, since they are usually concealed. The external organs and integuments, would, by the same general laws, naturally give rise to a greater variety of colour[135]."
Surely comment is needless. Have the colour of external organs and integuments nothing to do with the determining of specific distinctions by systematists? Or, may we not rather ask, are there any other "characters" which have had more to do with their delineation of animal species? Therefore, if "the external organs and integuments naturally give rise to a greater variety of colours," for non-utilitarian reasons, than is the case with internal organs and tissues; while even the latter present, for similarly non-utilitarian reasons, such variety and intensity of colours as they do; must it not follow that, on the ground of the "Laws of Growth" alone, Mr. Wallace has conceded the entire case as regards "a large proportional number of specific characters" being non-adaptive—"spontaneous" in their occurrence, and "meaningless" in their persistence?
Once more:—
"The enormously lengthened plumes of the bird of paradise and of the peacock, can, however, have no such use [i.e. for purposes of defence], but must be rather injurious than beneficial in the birds' ordinary life. The fact that they have been developed to so great an extent in a few species is an indication of such perfect adaptation to the conditions of existence, such complete success in the battle for life, that there is, in the adult male at all events, a surplus of strength, vitality, and growth-power, which is able to expend itself in this way without injury. That such is the case is shown by the great abundance of most of the species which possess these wonderful superfluities of plumage.... Why, in allied species, the development of accessory plumes has taken different forms, we are unable to say, except that it may be due to that individual variability which has served as a starting-point for so much of what seems to us strange in form, or fantastic in colour, both in the animal and vegetable world[136]."
Here, again, one need only ask, How can such statements be reconciled with the great dogma, "which is indeed a necessary deduction from the theory of Natural Selection, namely, that none of the definite facts of organic nature, no special organ, no characteristic form or marking can exist, but which must now be, or once have been, useful"? Can it be said that the plumes of a bird of paradise present "no characteristic form," or the tail of a peacock "no characteristic marking"? Can it be held that all the "fantastic colours," which Darwin attributes to sexual selection, and all the "strange forms" in the vegetable world which present no conceivable reference to adaptation, are to be ascribed to "individual variability" without reference to utility, while at the same time it is held, "as a necessary deduction from the theory of Natural Selection," that all specific characters must be "useful"? Or must we not conclude that we have here a contradiction as direct as a contradiction can well be[137]?
Nor is it any more possible to reconcile these contradictory statements by an indefinite extension of the term "correlation," than we found it to be in the cases previously quoted. It might indeed be logically possible, howsoever biologically absurd, to attribute the tail of a peacock—with all its elaboration of structure and pattern of colour, with all the drain that its large size and weight makes upon the vital resources of the bird, with all the increased danger to which it exposes the bird by rendering it more conspicuous, more easy of capture, &c.—to correlation with some useful character peculiar to peacocks. But to say that it is due to correlation with general "vitality," is merely to discharge the doctrine of correlation of any assignable meaning. Vitality, or "perfect adaptation to the conditions of existence," is obviously a prime condition to the occurrence of a peacock's tail, as it is to the occurrence of a peacock itself; but this is quite a different thing from saying that the specific characters which are presented by a peacock's tail, although useless in themselves, are correlated with some other and useful specific characters of the same bird—as we saw in a previous chapter with reference to secondary sexual characters in general. Therefore, when Mr. Wallace comes to the obvious question why it is that even in "allied species," which must be in equally "perfect adaptation to the conditions of existence," there are no such "wonderful superfluities of plumage," he falls back—as he previously fell back—on whatever unknown causes it may have been which produced the peacock's tail, when the primary condition to their operation has been furnished by "complete success in the battle for life."
I have quoted the above passages, not so much for the sake of exposing fundamental inconsistencies on the part of an adversary, as for the sake of observing that they constitute a much truer exposition of "Darwinism" than do the contradictory views expressed in some other parts of the work bearing that title. For even if characters of so much size and elaboration as the tail of a peacock, the plumes of a bird of paradise &c., are admitted to be due to non-utilitarian causes, much more must innumerable other characters of incomparably less size and elaboration be mere "superfluities." Without being actually deleterious, "a large proportional number of specific characters," whose utility is not apparent, must a fortiori have been due to "individual variation," to "general laws which determine the production" of such characters—or, in short, to some causes other than natural selection. And this, I say, is a doctrine much more in harmony with "Darwinism" than is the contradictory doctrine which I am endeavouring to resist.
But once again, and still more generally, after saying of "the delicate tints of spring foliage, and the intense hues of autumn," that "as colours they are unadaptive, and appear to have no more relation to the well-being of plants themselves than do the colours of gems and minerals," Mr. Wallace proceeds thus:—
"We may also include in the same category those algae and fungi which have bright colours—the red snow of the Arctic regions, the red, green, or purple seaweeds, the brilliant scarlet, yellow, white or black agarics, and other fungi. All these colours are probably the direct results of chemical composition or molecular structure, and being thus normal products of the vegetable organism, need no special explanation from our present point of view; and the same remark will apply to the varied tints of the bark of trunks, branches and twigs, which are often of various shades of brown and green, or even vivid reds and yellows[138]."
Here, as Mr. Gulick has already observed, "Mr. Wallace seems to admit that instead of useless specific characters being unknown, they are so common and so easily explained by 'the chemical constitution of the organism' that they claim no special attention[139]." And whatever answer Mr. Wallace may make to this criticism, I do not see how he is to meet the point at present before us—namely, that, upon his own showing, there are in nature numberless instances of "characters which are useless without being hurtful," and which nevertheless present absolute "constancy." If, in order to explain the contradiction, he should fall back upon the principle of correlation, the case would not be in any way improved. For, here again, if the term correlation were extended so as to include "the chemical constitution or the molecular structure of the organism," it would thereby be extended so as to discharge all Darwinian significance from the term.
I will conclude this discussion of the Utility question by recapitulating the main points in an order somewhat different from that in which they have been presented in the foregoing chapters. Such a variation may render their mutual connexions more apparent. But it is only to the main points that allusion will here be made, and, in order the better to show their independent character, I will separately number them.
1. The doctrine of utility as universal, whether with respect to species only or likewise with respect to specific characters, is confessedly an a priori doctrine, deduced by way of general reasoning from the theory of natural selection.
2. Being thus founded exclusively on grounds of deduction, the doctrine cannot be combated by any appeal to facts. For this question is not one of fact: it is a question of reasoning. The treatment of our subject matter is logical: not biological.
3. The doctrine is both universal and absolute. According to one form of it all species, and according to another form of it all specific characters, must necessarily be due to the principle of utility.
4. The doctrine in both its forms is deduced from a definition of the theory of natural selection as a theory, and the sole theory, of the origin of species; but, as Professor Huxley has already shown, it does not really follow, even from this definition, that all specific characters must be "necessarily useful." Hence the two forms of the doctrine, although coincident with regard to species, are at variance with one another in respect of specific characters. Thus far, of course, I agree with Professor Huxley; but if I have been successful in showing that the above definition of the theory of natural selection is logically fallacious, it follows that the doctrine in both its forms is radically erroneous. The theory of natural selection is not, accurately speaking, a theory of the origin of species: it is a theory of the origin and cumulative development of adaptations, to whatever order of taxonomic division these may happen to belong. Thus the premisses of the deduction which we are considering collapse: the principle of utility is shown not to have any other or further reference to species, or to specific characters, than it has to fixed varieties, genera, families, &c., or to the characters severally distinctive of each.
5. But, quitting all such antecedent considerations, we next proceeded to examine the doctrine a posteriori, taking the arguments which have been advanced in favour of the doctrine, other than those which rest upon the fallacious definition. These arguments, as presented by Mr. Wallace, are two in number.
First, it is represented that natural selection must occupy the whole field, because no other principle of change can be allowed to operate in the presence of natural selection. Now I fully agree that this statement holds as regards any principle of change which is deleterious, but I cannot agree that it does so as regards any such principle which is merely neutral. No reason has ever been shown why natural selection should interfere with "indifferent" characters—to adopt Professor Huxley's term—supposing such to have been produced by any of the agencies which we shall presently have to name. Therefore this argument—or rather assertion—goes for nothing.
Mr. Wallace's second argument is, that utility is the only principle which can endow specific characters with their characteristic stability. But this again is mere assertion. Moreover, it is assertion opposed alike to common sense and to observable fact. It is opposed to common sense, because it is obvious that any other principle would equally confer stability on characters due to it, provided that its action is constant, as Darwin expressly held. Again, this argument is opposed to fact, because we know of thousands of cases where peculiar characters are stable, which, nevertheless, cannot possibly be due to natural selection. Of such are the Porto Santo rabbits, the niata cattle, the ducks in St. James' Park, turkeys, dogs, horses, &c., and, in the case of plants, wheat, cabbage, maize, &c., as well as all the hosts of climatic varieties, both of animals and plants, in a state of nature. Indeed, on taking a wide survey of the facts, we do not find that the principle of utility is any better able to confer stability of character than are many other principles, both known and unknown. Nay, it is positively less able to do so than are some of these other principles. Darwin gives two very probable reasons for this fact; but I need not quote them a second time. It is enough to have seen that this argument from stability or constancy is no less worthless than the previous one. Yet these are the only two arguments of a corroborative kind which Mr. Wallace adduces whereby to sustain his "necessary deduction."
6. At this point, therefore, it may well seem that we need not have troubled ourselves any further with a generalization which does not appear to have anything to support it. And to this view of the case I should myself agree, were it not that many naturalists now entertain the doctrine as an essential article of their Darwinian creed. Hence, I proceeded to adduce considerations per contra.
Seeing that the doctrine in question can only rest on the assumption that there is no cause other than natural selection which is capable of originating any single species—if not even so much as any single specific character—I began by examining this assumption. It was shown first that, on merely antecedent grounds, the assumption is "infinitely precarious." There is absolutely no justification for the statement that in all the varied and complex processes of organic nature natural selection is the only possible cause of specific change. But, apart altogether from this a priori refutation of the dogma, our analysis went on to show that, in point of actual fact, there are not a few well-known causes of high generality, which, while having no connexion with the principle of utility, are demonstrably capable of originating species and specific characters—if by "species" and "specific characters" we are to understand organic types which are ranked as species, and characters which are described as diagnostic of species. Such causes I grouped under five different headings, viz. Climate, Food, Sexual Selection, Isolation, and Laws of Growth. Sexual Selection and Isolation are, indeed, repudiated by Mr. Wallace; but, in common I believe with all biologists, he accepts the other three groups of causes as fully adequate to produce such kinds and degrees of modification as are taken to constitute specific distinction. And this is amply sufficient for our present purposes. Besides, under the head of Sexual Selection, it does not signify in the present connexion whether or not we accept Darwin's theory on this subject. For, in any case, the facts of secondary sexual characters are indisputable: these characters are, for the most part, specific characters: and they cannot be explained by the principle of utility. Even Mr. Wallace does not attempt to do so; and the explanation which he does give is clearly incompatible with his doctrine touching the necessarily life-serving value of all specific characters. Lastly, the same has to be said of the Laws of Growth. For we have just seen that on the grounds of this principle likewise Mr. Wallace abandons the doctrine in question. As regards Isolation, much more remains to be said in the ensuing portion of this work, while, as regards Climatic Variation, there are literally innumerable cases where changes of specific type are known to have been caused by this means.
7. To the latter class of cases, however, it will be objected that these changes of specific type, although no doubt sufficiently "stable" so long as the changed conditions remain constant, are found by experiment not to be hereditary; and this clearly makes all the difference between a true specific change and a merely fictitious appearance of it.
Well, in the first place, this objection can have reference only to the first two of the five principles above stated. It can have no reference to the last three, because of these heredity constitutes the very foundation. This consideration ought to be borne in mind throughout. But now, in the second place, even as regards changes produced by climate and food, the reply is nugatory. And this for three reasons, as follows.
(a) No one is thus far entitled to conclude against the possible transmission of acquired characters; and, so long as there is even so much as a possibility of climatic (or any other admittedly non-utilitarian) variations becoming in this way hereditary, the reply before us merely begs the question.
(b) Even supposing, for the sake of argument, that acquired characters can never in any case become congenital, there remains the strong probability—sanctioned as such even by Weismann—that changed conditions of life may not unfrequently act upon the material of heredity itself, thus giving rise to specific changes which are from the first congenital, though not utilitarian. Indeed, there are not a few facts (Hoffmann's plants, Weismann's butterflies, &c.), which can only be explained either in this way, or as above (a). And in the present connexion it is immaterial which of these alternative explanations we choose to adopt, seeing that they equally refute our opponents' objection. And not only do these considerations—(a) and (b)—refute this particular objection; they overturn on new and independent grounds the whole of our opponents' generalization. For the generalization is, that the principle of utility, acting through natural selection, is "necessarily" the sole principle which can be concerned in hereditary changes of specific type. But here we perceive both a possibility (a) and a probability (b), if not indeed a certainty, that quite other principles have been largely concerned in the production of such changes.
(c) Altogether apart from these considerations, there remains a much more important one. For the objection that fixed—or "stable"—climatic varieties differ from true species in not being subject to heredity, raises the question—What are we to understand by a "species"? This question, which was thus far purposely left in abeyance, had now to be dealt with seriously. For it would clearly be irrational in our opponents to make this highly important generalization with regard to species and specific characters, unless they are prepared to tell us what they mean by species, and therefore by characters as specific. In as far as there is any ambiguity on this point it makes entirely for our side in the debate, because even any small degree of uncertainty with regard to it would render the generalization in question proportionally unsound. Yet it is notorious that no word in existence is more vague, or more impossible to define, than the word "species." The very same men who at one time pronounce their great generalization with regard to species, at another time asseverate that "a species is not a definite entity," but a merely abstract term, serving to denote this that and the other organic type, which this that and the other systematist regards as deserving such a title. Moreover it is acknowledged that systematists differ among themselves to a wide extent as to the kinds and degrees of peculiarity which entitle a given form to a specific rank. Even in the same department of systematic work much depends on merely individual taste, while in different departments widely different standards of delimination are in vogue. Hence, our reductio ad absurdum consists in this—that whether a given form is to be regarded as necessarily due to natural selection, and whether all its distinctive characters are to be regarded as necessarily utilitarian characters, will often depend on whether it has been described by naturalist A or by naturalist B. There is no one criterion—there is not even any one set of criteria—agreed upon by naturalists for the construction of specific types. In particular, as regards the principle of heredity, it is not known of one named species in twenty—probably not in a hundred—whether its diagnostic characters are hereditary characters; while, on the other hand, even in cases where experiment has proved "constant varieties" to be hereditary—and even also cross-sterile with allied varieties—it is only some three or four living botanists who for these reasons advocate the elevation of such varieties to the rank of species. In short, as we are not engaged on any abstract question touching the principles on which species ought to have been constituted by their makers, but upon the actual manner in which they have been, the criterion of heredity must needs be disregarded in the present discussion, as it has been in the work of systematists. And the result of this is, that any objection to our introducing the facts of climatic variation in the present discussion is excluded. In particular, so far as any question of heredity is concerned, all these facts are as assuredly as they are cogently relevant. It is perfectly certain that there is "a large proportional number" of named species—particularly of plants—which further investigation would resolve into climatic varieties. With the advance of knowledge, "bad species" are always increasing at the expense of "good species," so that we are now justified in concluding with Kerner, Häckel, and other naturalists best qualified to speak on this subject, that if we could know as much about the past history and present relations of the remaining good species as we do about the bad, all the former, without exception, would become resolved into the latter. In point of fact, and apart altogether from the inductive experience on which this conclusion is based, the conclusion follows "as a necessary deduction" from the general theory of descent. For this theory essentially consists in supposing either the past or the present existence of intermediate varietal forms in all cases, with the consequence that "good species" serve merely to mark lacunae in our knowledge of what is everywhere a finely graduated process of transmutation. Hence, if we place this unquestionably "necessary deduction" from the general theory of descent side by side with the alleged "necessary deduction" from the theory of natural selection, we cannot avoid the following absurdity—Whether or not a given form is to be regarded as necessarily due to natural selection, and all its characters necessarily utilitarian, is to be determined, and determined solely, by the mere accident of our having found, or not having found, either in a living or in a fossil state, its varietal ancestry.
8. But this leads us to consider the final and crowning incongruities which have been dealt with in the present chapter. For here we have seen, not only that our opponents thus draw a hard and fast line between "varieties" and "species" in regard to "necessary origin" and "necessary utility," but that they further draw a similar line between "species" and "genera" in the same respects. Yet, in accordance with the general theory of evolution, it is plainly as impossible to draw any such line in the one case as it is to do so in the other. Just as fixed varieties are what Darwin called "incipient species," so are species incipient genera, genera incipient families, and so on. Evolutionists must believe that the process of evolution is everywhere the same. Nevertheless, while admitting all this, the school of Huxley contradicts itself by alleging some unintelligible exception in the case of "species," while the school of Wallace presses this exception so as to embrace "specific characters." Indeed Mr. Wallace, while maintaining that all specific characters must necessarily be useful, maintains at the same time that any number of varietal characters on the one hand, and a good half of generic characters on the other, are probably useless. Thus he contradicts his argument from the "constancy of specific characters" (seeing that generic characters are still more constant), as later on we saw that he contradicts his deductive generalization touching their necessary utility, by giving a non-utilitarian explanation of whole multitudes of specific characters. I need not, however, again go over the ground so recently traversed; but will conclude by once more recurring to the only explanation which I have been able to devise of the otherwise inexplicable fact, that in regard to this subject so many naturalists still continue to entangle themselves in the meshes of absurdity and contradiction.
The only conceivable explanation is, that these naturalists have not yet wholly divested themselves of the special creation theory. Although professing to have discarded the belief that "species" are "definite entities," differing in kind from "varieties" on the one hand and from "genera" on the other, these writers are still imbued with a vague survival of that belief. They well know it to belong to the very essence of their new theory that "species" are but "pronounced varieties," or, should we prefer it, "incipient genera"; but still they cannot altogether escape the pre-Darwinian conception of species as organic units, whose single mode of origin need not extend to other taxonomic groups, and whose characters therefore present some exceptional significance to the scientific naturalist. So to speak, such divinity doth still hedge a species, that even in the very act of declaring it but an idol of their own creation, these naturalists bow before their fetish as something that is unique—differing alike in its origin and in its characters from the varieties beneath and the genera above. The consequence is that they have endeavoured to reconcile these incompatible ideas by substituting the principle of natural selection for that of super-natural creation, where the particular case of "species" is concerned. In this way, it vaguely seems to them, they are able to save the doctrine of some one mode of origin as appertaining to species, which need not "necessarily" appertain to any other taxonomic division. All other such divisions they regard, with their pre-Darwinian forefathers, as merely artificial constructions; but, likewise with these forefathers, they look upon species as natural divisions, proved to be such by a single and necessary mode of origin. Hence, Mr. Wallace expressly defines a species with reference to this single and necessary mode of origin (see above, p. 235), although he must be well aware that there is no better, or more frequent, proof of it in the case of species, than there is in that of somewhat less pronounced types on the one hand (fixed varieties), or of more pronounced types on the other (genera, families, &c.). Hence, also, the theory of natural selection is defined as par excellence a theory of the origin of species; it is taken as applying to the particular case of the origin of species in a peculiarly stringent manner, or in a manner which does not apply to the origin of any other groups. And I believe that an important accessory reason of the continuance of this view for more than thirty years after the publication of the Origin of Species by means of Natural Selection, is to be found in the title of that work. "Natural Selection" has thus become verbally associated with "Origin of Species," till it is thoughtlessly felt that, in some way or another, natural selection must have a peculiar reference to those artificially delineated forms which stand anywhere between a fixed variety and a so-called genus. This verbal association has no doubt had the effect of still further preserving the traditional halo of mystery which clings to the idea of a "species." Hence it comes that the title which Darwin chose—and, looking to the circumstances of the time, wisely chose—for his great work, has subsequently had the effect of fostering the very idea which it was the object of that work to dissipate, namely, that species are peculiar entities, which differ more or less in origin or kind from all other taxonomic groups. The full title of this work is—The Origin of Species by means of Natural Selection: or the Preservation of Favoured Races in the Struggle for Life. Now, supposing that instead of this its author had chosen some such title as the following:—The Origin of Organic Types by means of Adaptive Evolution: or Survival of the Fittest Forms in the Struggle for Life. Of course this would have been a bad substitute from various points of view; but could any objection have been urged against it from our present point of view? I do not see that there could. Yet, if such had been the title, I have little doubt that we should never have heard of those great generalizations with regard to species and specific characters, the futility of which it has been the object of these chapters to expose.
In conclusion, it only remains to reiterate that in thus combating what appears to me plainly erroneous deductions from the theory of natural selection, I am in no wise combating that theory itself. On the contrary, I hope that I am rendering it no unimportant service by endeavouring to relieve it of a parasitic growth—an accretion of false logic. Regarding as I do the theory of natural selection as, primarily, a theory of the origin (or cumulative development) of adaptations, I see in merely non-adaptive characters—be they "specific" or other—a comparatively insignificant class of phenomena, which may be due to a great variety of incidental causes, without any further reference to the master-principle of natural selection than that in the presence of this principle none of these non-adaptive characters can be actively deleterious. But that there may be "any number of indifferent characters" it is no part of the theory of natural selection to deny; and all attempts to foist upon it a priori "deductions" opposed alike to the facts of nature and to the logic of the case, can only act to the detriment of the great generalization which was expressly guarded from such fallacies by the ever-careful judgement of Darwin.
There are several points of considerable theoretical importance connected with Panmixia, which were omitted from the text, in order to avoid distracting attention from the main issue which is there under consideration. These side issues may now be appropriately presented in the form in which they were published in Nature, March 13, 1890[140]. After stating, in almost the same words, what has already been said in Chapter X, this paper proceeds, with the exception of a few verbal alterations, as follows.
"There is, however, one respect in which Professor Weismann's statement of the principle of panmixia differs from that which was considered by Mr. Darwin; and it is this difference of statement—which amounts to an important difference of theory—that I now wish to discuss.
"The difference in question is, that while Professor Weismann believes the cessation of selection to be capable of inducing degeneration down to the almost complete disappearance of a rudimentary organ, I have argued that, unless assisted by some other principle, it can at most only reduce the degenerating organ to considerably above one-half its original size—or probably not through so much as one-quarter. The ground of this argument (which is given in detail in the Nature articles of 1873-1874) is, that panmixia depends for its action upon fortuitous variations round an ever-diminishing average—the average thus diminishing because it is no longer sustained by natural selection. But although no longer sustained by natural selection, it does continue to be sustained by heredity; and therefore, as long as the force of heredity persists unimpaired, fortuitous variations alone—or variation which is no longer controlled by natural selection—cannot reduce the dwindling organ to so much as one-half of its original size; indeed, as above foreshadowed, the balance between the positive force of heredity and the negative effects of promiscuous variability will most likely be arrived at above the middle line thus indicated. Only if for any reason the force of heredity begins to fail can the average round which the cessation of selection works become a progressively diminishing average. In other words, so long as the original force of heredity as regards the useless organ remains unimpaired, the mere withdrawal of selection cannot reduce the organ much below the level of efficiency above which it was previously maintained by the presence of selection. If we take this level to be 80 or 90 per cent. of the original size, cessation of selection will reduce the organ through the 10 or 20 per cent., and there leave it fluctuating about this average, unless for any reason the force of heredity begins to fail—in which case, of course, the average will progressively fall in proportion to the progressive weakening of this force.
"Now, according to my views, the force of heredity under such circumstances is always bound to fail, and this for two reasons. In the first place, it must usually happen that when an organ becomes useless, natural selection as regards that organ will not only cease, but become reversed. For the organ is now absorbing nutriment, causing weight, occupying space, and so on, uselessly. Hence, even if it be not also a source of actual danger, 'economy of growth' will determine a reversal of selection against an organ which is now not merely useless, but deleterious. And this degenerating influence of the reversal of selection will throughout be assisted by the cessation of selection, which will now be always acting round a continuously sinking average. Nevertheless, a point of balance will eventually be reached in this case, just as it was in the previous case where the cessation of selection was supposed to be working alone. For, where the reversal of selection has reduced the diminishing organ to so minute a size that its presence is no longer a source of detriment to the organism, the cessation of selection will carry the reduction a small degree further; and then the organ will remain as a 'rudiment.' And so it will remain permanently, unless there be some further reason why the still remaining force of heredity should be abolished. This further (or second) reason I found in the consideration that, however enduring we may suppose the force of heredity to be, we cannot suppose that it is actually everlasting; and, therefore, that we may reasonably attribute the eventual disappearance of rudimentary organs to the eventual failure of heredity itself. In support of this view there is the fact that rudimentary organs, although very persistent, are not everlasting. That they should be very persistent is what we should expect, if the hold which heredity has upon them is great in proportion to the time during which they were originally useful, and thus firmly stamped upon the organization by natural selection causing them to be strongly inherited in the first instance. For example, we might expect that it would be more difficult finally to eradicate the rudiment of a wing than the rudiment of a feather; and accordingly we find it a general rule that long-enduring rudiments are rudiments of organs distinctive of the higher taxonomic divisions—i.e. of organs which were longest in building up, and therefore longest sustained in a state of working efficiency.
"Thus, upon the whole, my view of the facts of degeneration remains the same as it was when first published in these columns seventeen years ago, and may be summarized as follows.
"The cessation of selection when working alone (as it probably does during the first centuries of its action upon structures or colours which do not entail any danger to, or perceptible drain upon, the nutritive resources of the organism) cannot cause degeneration below, probably, some 10 to 20 per cent. But if from the first the cessation of selection has been assisted by the reversal of selection (on account of the degenerating structure having originally been of a size sufficient to entail a perceptible drain on the nutritive resources of the organism, having now become a source of danger, and so forth), the two principles acting together will continue to reduce the ever-diminishing structure down to the point at which its presence is no longer a perceptible disadvantage to the species. When that point is reached, the reversal of selection will terminate, and the cessation of selection will not then be able of itself to reduce the organ through more than at most a very few further percentages of its original size. But, after this point has been reached, the now total absence of selection, either for or against the organ, will sooner or later entail this further and most important consequence, a failure of heredity as regards the organ. So long as the organ was of use, its efficiency was constantly maintained by the presence of selection—which is merely another way of saying that selection was constantly maintaining the force of heredity as regards that organ. But as soon as the organ ceased to be of use, selection ceased to maintain the force of heredity; and thus, sooner or later, that force began to waver or fade. Now it is this wavering or fading of the force of heredity, thus originally due to the cessation of selection, that in turn co-operates with the still continued cessation of selection in reducing the structure below the level where its reduction was left by the actual reversal of selection. So that from that level downwards the cessation of selection, and the consequent failing of heredity, act and react in their common work of causing obsolescence. In the case of newly added characters, the force of heredity will be less than in that of more anciently added characters; and thus we can understand the long endurance of 'vestiges' characteristic of the higher taxonomic divisions, as compared with those characteristic of the lower. But in all cases, if time enough be allowed under the cessation of selection, the force of heredity will eventually fall to zero, when the hitherto obsolescent structure will finally become obsolete. In cases of newly added and comparatively trivial characters, with regard to which reversal of selection is not likely to take place (e.g. slight differences of colour between allied species), cessation of selection is likely to be very soon assisted by a failure in the force of heredity; seeing that such newly added characters will not be so strongly inherited as are the more ancient characters distinctive of higher taxonomic groups.
"Let us now turn to Weismann's view of degeneration. First of all, he has omitted to perceive that 'panmixia' alone (if unassisted either by reversed selection or an inherent diminishing of the force of heredity) cannot reduce a functionless organ to the condition of a rudiment. Therefore he everywhere represents panmixia (or the mere cessation of selection) as of itself sufficient to cause degeneration, say from 100 to 5, instead of from 100 to 90 or 80, which, for the reasons above given, appeared (and still appears) to me about the most that this principle can accomplish, so long as the original force of heredity continues unimpaired. No doubt we have here what must be regarded as a mere oversight on the part of Professor Weismann; but the oversight is rendered remarkable by the fact that he does invoke the aid of reversed selection in order to explain the final disappearance of a rudiment. Yet it is self-evident that the reversal of selection must be much more active during the initial than during the final stages of degeneration, seeing that, ex hypothesi, the greater the degree of reduction which has been attained the less must be the detriment arising from any useless expenditure of nutrition, &c.
"And this leads me to a second oversight in Professor Weismann's statement, which is of more importance than the first. For the place at which he does invoke the assistance of reversed selection is exactly the place at which reversed selection must necessarily have ceased to act. This place, as already explained, is where an obsolescent organ has become rudimentary, or, as above supposed, reduced to 5 per cent. of its original size; and the reason why he invokes the aid of reversed selection at this place is in order to save his doctrine of 'the stability of germ-plasm.' That the force of heredity should finally become exhausted if no longer maintained by the presence of selection, is what Darwin's theory of perishable gemmules would lead us to expect, while such a fact would be fatal to Weismann's theory of an imperishable germ-plasm. Therefore he seeks to explain the eventual failure of heredity (which is certainly a fact) by supposing that after the point at which the cessation of selection alone can no longer act (and which his first oversight has placed some 80 per cent. too low), the reversal of selection will begin to act directly against the force of heredity as regards the diminishing organ, until such direct action of reversed selection will have removed the organ altogether. Or, in his own words, 'The complete disappearance of a rudimentary organ can only take place by the operation of natural selection; this principle will lead to its diminution, inasmuch as the disappearing structure takes the place and the nutriment of other useful and important organs.' That is to say, the rudimentary organ finally disappears, not because the force of heredity is finally exhausted, but because natural selection has begun to utilize this force against the continuance of the organ—always picking out those congenital variations of the organ which are of smallest size, and thus, by its now reversed action, reversing the force of heredity as regards the organ.
"Now the oversight here is in not perceiving that the smaller the disappearing structure becomes, the less hold must 'this principle' of reversed selection retain upon it. As above observed, during the earlier stages of reduction (or while co-operating with the cessation of selection) the reversal of selection will be at its maximum of efficiency; and, as the process of diminution continues, a point must eventually be reached at which the reversal of selection can no longer act. Take the original mass of a now obsolescent organ in relation to that of the entire organism of which it then formed a part to be represented by the ratio 1:100. For the sake of argument we may assume that the mass of the organism has throughout remained constant, and that by 'mass' in both cases is meant capacity for absorbing nutriment, causing weight, occupying space, and so forth. Now, we may further assume that when the mass of the organ stood to that of its organism in the ratio of 1:100, natural selection was strongly reversed with respect to the organ. But when this ratio fell to 1:1000, the activity of such reversal must have become enormously diminished, even if it still continued to exercise any influence at all. For we must remember, on the one hand, that the reversal of selection can only act as long as the presence of a diminishing organ continues to be so injurious that variations in its size are matters of life and death in the struggle for existence; and, on the other hand, that natural selection in the case of the diminishing organ does not have reference to the presence and the absence of the organ, but only to such variations in its mass as any given generation may supply. Now, the process of reduction does not end even at 1:1000. It goes on to 1:10,000, and eventually 1:∞. Consequently, however great our faith in natural selection may be, a point must eventually come for all of us at which we can no longer believe that the reduction of an obsolescent organ is due to reversed selection. And I cannot doubt that if Professor Weismann had sufficiently considered the matter, he would not have committed himself to the statement that 'the complete disappearance of a rudimentary organ can only take place by the operation of natural selection.'
"According to my view, the complete disappearance of a rudimentary organ can only take place by the cessation of natural selection, which permits the eventual exhaustion of heredity, when heredity is thus simply left to itself. During all the earlier stages of reduction, the cessation of selection was assisted in its work by the reversal of selection; but when the rudiment became too small for such assistance any longer to be supplied, the rudiment persisted in that greatly reduced condition until the force of heredity with regard to it was eventually worn out. This appears to me, as it appeared in 1873, the only reasonable conclusion that can be drawn from the facts. And it is because this conclusion is fatal to Professor Weismann's doctrine of the permanent 'stability' of germ-plasm, while quite in accordance with all theories which belong to the family of pangenesis, that I deem the facts of degeneration of great importance as tests between these rival interpretations of the facts of heredity. It is on this account that I have occupied so much space with the foregoing discussion; and I shall be glad to ascertain whether any of the followers of Professor Weismann are able to controvert these views.
"George J. Romanes."
"P.S.—Since the above article was sent in, Professor Weismann has published in these columns (February 6) his reply to a criticism by Professor Vines (October 24, 1889). In this reply he appears to have considerably modified his views on the theory of degeneration; for while in his Essays he says (as in the passage above quoted) that 'the complete disappearance of a rudimentary organ can only take place by the operation of natural selection'—i.e. only by the reversal of selection,—in his reply to Professor Vines he says, 'I believe that I have proved that organs no longer in use become rudimentary, and must finally disappear, solely by 'panmixia'; not through the direct action of disuse, but because natural selection no longer sustains their standard structure'—i.e. solely by the cessation of selection. Obviously, there is here a flat contradiction. If Professor Weismann now believes that a rudimentary organ 'must finally disappear solely' through the withdrawal of selection, he has abandoned his previous belief that 'the complete disappearance of a rudimentary organ can only take place by the operation of selection.' And this change of belief on his part is a matter of the highest importance to his system of theories as a whole, since it betokens a surrender of his doctrine of the 'stability' of germ-plasm—or of the virtually everlasting persistence of the force of heredity, and the consequent necessity for a reversal of this force itself (by natural selection placing its premium on minus instead of on plus variations), in order that a rudimentary organ should finally disappear. In other words, it now seems he no longer believes that the force of heredity in one direction (that of sustaining a rudimentary organ) can only be abolished by the active influence of natural selection determining this force in the opposite direction (that of removing a rudimentary organ). It seems he now believes that the force of heredity, if merely left to itself by the withdrawal of natural selection altogether, will sooner or later become exhausted through the mere lapse of time. This, of course, is my own theory of the matter as originally published in these columns; but I do not see how it is to be reconciled with Professor Weismann's doctrine of so high a degree of stability on the part of germ-plasm, that we must look to the Protozoa and the Protophyta for the original source of congenital variations as now exhibited by the Metazoa and Metaphyta. Nevertheless, and so far as the philosophy of degeneration is concerned, I shall be very glad if (as it now appears) Professor Weismann's more recent contemplation has brought his principle of panmixia into exact coincidence with that of my cessation of selection."
Before passing on it may here be noted that, to any one who believes in the inheritance of acquired characters, there is open yet another hypothetical cause of degeneration, and one to which the final disappearance of vestigial organs may be attributed. Roux has shown in his work on The Struggle for Existence between Parts of an Organism that the principle of selection must operate in every constituent tissue, and as between every constituent cell of which an organism is composed. Now, if an organ falls into disuse, its constituent cells become worsted in their struggles with other cells in the organism. Hence, degeneration of the disused organ may progressively increase, quite independently of any struggle for existence on the part of the organism as a whole. Consequently, degeneration may proceed without any reference to the principle of "economized nutrition"; and, if it does so, and if the effects of its doing so are transmitted from generation to generation, the disused organ will finally disappear by means of Roux's principle.
The long communication above quoted led to a still longer correspondence in the pages of Nature. For Professor Ray Lankester wrote[141] to impugn the doctrine of panmixia, or cessation of selection, in toto, arguing with much insistence that "cessation of selection must be supplemented by economy of growth in order to produce the results attributed to panmixia." In other words, he denied that panmixia alone can cause degeneration in any degree at all; at most, he said, it can be but "a condition," or "a state," which occurs when an organ or part ceases to be useful, and therefore falls under the degenerating influence of active causes, such as economy of nutrition. Or, in yet other words, he refused to recognize that any degenerative process can be due to natural selection as merely withdrawn: only when, besides being withdrawn, natural selection is reversed, did he regard a degenerative process as possible. As a result of the correspondence, however, he eventually[142] agreed that, if the "birth-mean" of an organ, in respect either of size or complexity of structure, be lower than the "selection-mean" while the organ is useful (a fact which he does not dispute); then, if the organ ceases to be useful, it will degenerate by the withdrawal of selection alone. Which, of course, is merely a re-statement of the doctrine of panmixia, or cessation of selection, in somewhat varied terminology—provided that the birth-mean be taken over a number of generations, or not only over a few following the selection-mean of the structure while still in its highest state of efficiency. For the sake of brevity I will hereafter speak of these "few following" generations by the term of "first generations."
It remains to consider the views of Professor Lloyd Morgan upon the subject. In my opinion he is the shrewdest, as well as the most logical critic that we have in the field of Darwinian speculation; therefore, if possible, I should like to arrive at a full agreement with him upon this matter. His latest utterance with regard to it is as follows:—
"To account for the diminution of organs or structures no longer of use, apart from any inherited effects of disuse, Mr. Romanes has invoked the Cessation of Selection; and Mr. Francis Galton has, in another connexion, summarized the effects of this cessation of selection in the convenient phrase 'Regression to Mediocrity.' This is the Panmixia of Professor Weismann and his followers; but the phrase regression to mediocrity through the cessation of selection appears to me preferable. It is clear that so long as any organ or structure is subject to natural selection through elimination, it is, if not actually undergoing improvement, kept at a high standard of efficiency through the elimination of all those individuals in which the organ in question falls below the required standard. But if, from change in the environment or any other cause, the character in question ceases to be subject to selection, elimination no longer takes place, and the high standard will no longer be maintained. There will be reversion to mediocrity. The probable amount of this reversion is at present a matter under discussion[143]."
So far, then, Professor Lloyd Morgan is in complete agreement with previous writers upon the subject. He does not doubt that the cessation of selection must always be a cause of degeneration: the only question is as to the potency of this cause, or the amount of degeneration which it is capable of effecting.
Taking, first, the case of bulk or size of an organ, as distinguished from its organization or complexity, we have seen that Weismann represents the cessation of selection—even if working quite alone, or without any assistance from the reversal of selection—to be capable of reducing a fully developed organ to the state of a rudiment, or even, if we take his most recent view, of abolishing the organ in toto.
Professor Lloyd Morgan, on the other hand, does not think that the cessation of selection alone can cause reduction further than the level of "mediocrity" in the first generations—or, which is much the same thing, further than the difference between the "birth-mean" and the "selection-mean" of the first generations. This amount of reduction he puts at 5 per cent., as "a very liberal estimate."
Here, then, we have three estimates of the amount of degeneration which can be produced by panmixia alone, where mere size or bulk of an organ is concerned—say, 3 to 5 per cent., 10 to 20 per cent., and 95 per cent. to 0. At first sight, these differences appear simply ludicrous; but on seeking for the reasons of them, we find that they are due to different views touching the manner in which panmixia operates. The oversights which have led to Weismann's extremely high estimate have already been stated. The reason of the difference between the extremely low estimate of Professor Lloyd Morgan, as compared with my own intermediate one, is, that he supposes the power of panmixia to become exhausted as soon as the level of mediocrity of the first generations has become the general level in succeeding generations. In my view, however, the level of mediocrity is itself a sinking level in successive generations, with the result that there is no reason why the reducing power of panmixia should ever become exhausted, save that the more reduction it effects the greater is the force of heredity which remains to be overcome, as previously explained. Thus the only question between Professor Lloyd Morgan and myself is—Does the level of mediocrity fall in successive generations under the cessation of selection, or does it remain permanently where it used to be under the presence of selection? Does the "birth-mean" remain constant throughout any number of generations, notwithstanding that the sustaining influence of selection has been withdrawn; or does it progressively sink as a consequence of such withdrawal?
In order to answer this question we had better begin by considering now the case of organization of structure, as distinguished from mere size of structure. Take any case where a complex organ—such as a compound eye—has been slowly elaborated by natural selection, and is it not self-evident that, when natural selection is withdrawn, the complex structure will deteriorate? In other words, the level of mediocrity, say in the hundred thousandth generation after the sustaining influence of natural selection has been withdrawn, will not be so high as it was in the first generations. For, by hypothesis, there is now no longer any elimination of unfavourable variations, which may therefore perpetuate themselves as regards any of the parts of this highly complex mechanism; so that it is only a matter of time when the mechanism must become disintegrated. I can scarcely suppose that any one who considers the subject will question this statement, and therefore I will not say anything that might be said in the way of substantiating it. But, if the statement be assented to, it follows that there is no need to look for any cause of deterioration, further than the withdrawal of selection—or cessation of the principle which (as we are supposing) had hitherto been the sole means of maintaining efficient harmony among all the independently variable parts of the highly complex structure.
Now, I hold that the same thing is true, though in a lesser degree, as regards degeneration of size. That there is no difference in kind between the two cases, Professor Lloyd Morgan implicitly allows; for what he says is—
"In any long-established character, such as wing-power in birds, brain-development, the eyes of crustacea, &c., no shortcomer in these respects would have been permitted by natural selection to transmit his shortcomings for hundreds of generations. All tendency to such shortcomings would, one would suppose, have been bred out of the race. If after this long process of selection there still remains a strong tendency to deterioration, this tendency demands an explanation[144]."
Here, then, deterioration as to size of structure (wings of birds), and deterioration as to complexity of structure (brain and eyes) are expressly put upon the same footing. Therefore, if in the latter case the "tendency to deterioration" does not "demand an explanation," beyond the fact that the hitherto maintaining influence has been withdrawn, neither is any such further explanation demanded in the former case. Which is exactly my own view of the matter. It is also Mr. Galton's view. For although, in the passage formerly quoted, Professor Lloyd Morgan appears to think that by the phrase "Regression to Mediocrity" Mr. Galton means to indicate that panmixia can cause degeneration only as far as the mediocrity level of the first generations, this, in point of fact, is not what Galton means, nor is it what he says. The phrase in question occurs "in another connexion," and, indeed, in a different publication. But where he expressly alludes to the cessation of selection, this is what he says. The italics are mine.
"A special cause may be assigned for the effects of use in causing hereditary atrophy of disused parts. It has already been shown that all exceptionally developed organs tend to deteriorate: consequently, those that are not protected by selection will dwindle. The level of muscular efficiency in the wing of a strongly flying bird [curiously enough, the same case that is chosen by Professor Lloyd Morgan to illustrate his opposite view], is like the level of water in the leaky vessel of a Danaid, only secured to the race by constant effort, so to speak. Let the effort be relaxed ever so little, and the level immediately falls[145]."
I take it, then, that the burden of proof lies with Professor Lloyd Morgan to show why the withdrawal of selection is not sufficient to account for degeneration any further than the mediocrity-level in the former presence of selection. Why does "the strong tendency[146] to deterioration demand an explanation," further than the fact that when all variations below the average in every generation are allowed to survive, they must gradually lower the average itself through a series of generations? To answer that any such tendency "would have been bred out of the race" by the previous action of selection, is to suppose that the function of selection is at an end when once it has built up a structure to the highest point of working efficiency,—that the presence of selection is no longer required to maintain the structure at that point. But it is enough to ask in reply—Why, under the cessation of selection, does complexity of structure degenerate so much more rapidly than size of structure? Why is it, for instance, that "the eyes of crustacea" in dark caves have entirely disappeared, while their foot-stalks (when originally present) still remain? Can it be maintained that "for hundreds of generations" natural selection was more intent on developing the foot-stalks than the eyes which were mounted upon them—so that while the latter were left by selection with "a strong tendency to deterioration," the former have had this tendency "bred out in the race"[147]?
To sum up. There is now no question in any quarter touching the fact that panmixia, or the cessation of selection, is a true cause of degeneration. The only question is as to the amount of degeneration which it is able to effect when not assisted by the reversal of selection, or any other cause of degeneration. Moreover, even with regard to this question of amount, there is no doubt on any side that panmixia alone causes degeneration more rapidly where it has to do with complexity of organization, than it does where it is concerned with a mere reduction of mass.
The question as to the amount of degeneration that is caused by the cessation of selection alone is without any practical importance where species in a state of nature are concerned, because here the cessation of selection is probably always associated more or less with the reversal of it; and it is as impossible as it is immaterial to determine the relative shares which these two co-operating principles take in bringing about the observed results. But where organisms in a state of domestication are concerned, the importance of the question before us is very great. For if the cessation of selection alone is capable of reducing an organ through 10 or 12 per cent. of its original size, nearly all the direct evidence on which Darwin relied in favour of use-inheritance is destroyed. On the other hand, if reduction through 5 per cent. be deemed a "very liberal estimate" of what this principle can accomplish, the whole body of Darwin's direct evidence remains as he left it. I have now given my reasons for rejecting this lower estimate on the one band, and what seems to me the extravagant estimate of Weismann on the other. But my own intermediate estimate is enough to destroy the apparent proof of use-inheritance that was given by Darwin. Therefore it remains for those who deny Lamarckian principles, either to accept some such estimate, or else to acknowledge the incompatibility of any lower one with the opinion that there is no evidence in favour of these principles.