Darwin, and After Darwin Volume Ii Part 14

Upon the whole, then, and with regard to the direct action of external conditions, I conclude--not only from general considerations, but also from special facts or instances quite sufficient for the purpose--that these must certainly give rise to immense numbers of somatogenetic species on the one hand, and probably to considerable numbers of blastogenetic species on the other; that in neither case is there any reason for supposing the distinctively "specific characters" to be other than "neutral" or "indifferent"; while there are the best of reasons for concluding the contrary. So that, under this division of our subject alone (B), there appears to be ample justification for the statement that "a large proportional number of specific characters" are in reality, as they are in appearance, dest.i.tute of significance from a utilitarian point of view.

(C.)

Thus far in the present chapter we have been dealing exclusively with the case of "climatic variation," or change of specific type due to changes in the external conditions of life. But it will be remembered that, in the preceding chapter, allusion was likewise made to changes of specific type due to internal causes, or to what Darwin has called "the nature of the organism." Under this division of our subject I mentioned especially s.e.xual Selection, which is supposed to arise in the aesthetic taste of animals themselves; Isolation, which is supposed to originate new types by allowing the average characters of an isolated section of an old type to develop a new history of varietal change, as we shall see more fully in the ensuing part of this treatise; and the Laws of Growth, which is a general term for the operation of unknown causes of change incidental to the living processes of organisms which present the change.

Now, under none of these divisions of our subject can there be any question touching the criterion of Heredity. For if new species--or even single specific characters of new species--are ever produced by any of these causes, they must certainly all "reproduce their like." Therefore the only question which can here obtain is as to whether or not such causes ever do originate new species, or even so much as new specific characters. Mr. Wallace, though not always consistently, answers this question in the negative; but the great majority of naturalists follow Darwin by answering it in the affirmative. And this is enough to show the only point which we need at present concern ourselves with showing--viz. that the question is, at the least, an open one. For as long as this question is an open one among believers in the theory of natural selection, it must clearly be an unwarrantable deduction from that theory, that all species, and _a fortiori_ all specific characters, are necessarily due to natural selection. The deduction cannot be legitimately drawn until the possibility of any other cause of specific modification has been excluded. But the bare fact of the question as just stated being still and at the least an open question, is enough to prove that this possibility has not been excluded. Therefore the deduction must be, again on this ground alone (C), unwarrantable.

Such are my several reasons--and it is to be observed that they are all _independent_ reasons--for concluding that it makes no practical difference to the present discussion whether or not we entertain Heredity as a criterion of specific distinction. Seeing that our species-makers have paid so little regard to this criterion, it is neither absurd nor preposterous to have adduced, in the preceding chapter, the facts of climatic variation. On the contrary, as the definition of "species" which has been practically followed by our species-makers in No. 3, and not No. 4, these facts form part and parcel of our subject. It is perfectly certain that, in the vegetable kingdom at all events, "a large proportional number" of specifically diagnostic characters would be proved by experiment to be "somatogenetic"; while there are numerous constant characters cla.s.sed as varietal, although it is well known that they are "blastogenetic." Moreover, we can scarcely doubt that many specific characters which are also hereditary characters owe their existence, not to natural selection, but to the direct action of external causes on the hereditary structure of "germ-plasm"; while, even apart from this consideration, there are at least three distinct and highly general principles of specific change, which are accepted by the great majority of Darwinists, and the only common peculiarity of which is that they produce hereditary changes of specific types without any reference to the principle of utility.

CHAPTER X.

CHARACTERS AS ADAPTIVE AND SPECIFIC (_concluded_).

Our subject is not yet exhausted. For it remains to observe the consequences which arise from the dogma of utility as the only _raison d'etre_ of species, or of specific characters, when this dogma is applied in practice by its own promoters.

Any definition of "species"--excepting Nos. 1, 2, and 5, which may here be disregarded--must needs contain some such phrase as the one with which Nos. 3 and 4 conclude. This is, that peculiar characters, in order to be recognized as of specific value, must present neither more nor less than "some certain degree of distinctness." If they present more than this degree of distinctness, the form, or forms, in question must be ranked as generic; while if they present less than this degree of distinctness, they must be regarded as varietal--and this even if they are known to be mutually sterile. What, then, is this certain degree of distinctness? What are its upper and lower limits? This question is one that cannot be answered. From the very nature of the case it is impossible to find a uniform standard of distinction whereby to draw our boundary lines between varieties and species on the one hand, or between species and genera on the other. One or two quotations will be sufficient to satisfy the general reader upon this point.

Mr. Wallace himself alludes to "the great difficulty that is felt by botanists in determining the limits of species in many large genera,"

and gives as examples well-known instances where systematic botanists of the highest eminence differ hopelessly in their respective estimates of "specific characters." Thus:--

"Mr. Baker includes under a single species, Rosa canina, no less than twenty-eight named varieties distinguished by more or less constant characters, and often confined to special localities, and to these are referred about seventy of the species of British and continental botanists. Of the genus Rubus or bramble, five British species are given in Bentham's _Handbook of British Flora_, while in the fifth edition of Babington's _Manual of British Botany_, published about the same time, no less than forty-five species are described. Of willows (Salix) the same two works enumerate fifteen and thirty-one species respectively. The hawkweeds (Hieracium) are equally puzzling, for while Mr. Bentham admits only seven British species, Professor Babington describes no less than seventy-two, besides several named varieties[125]."

[125] _Darwinism_, p. 77.

Mr. Wallace goes on to quote further instances, such as that of Draba verna, which Jordan has found to present, in the south of France alone, no less than fifty-two permanent varieties, which all "come true from seed, and thus present all the characteristics of a true species"; so that, "as the plant is very common almost all over Europe, and ranges from North America to the Himalayas, the number of similar forms over this wide area would probably have to be reckoned by hundreds, if not by thousands[126]."

[126] _Darwinism_, p. 77.

One or two further quotations may be given to the same general effect, selected from the writings of specialists in their several departments.

"There is nothing that divides systematists more than what const.i.tutes a genus. Species that resemble each other more than other species, is perhaps the best definition that can be given.

This is obviously an uncertain test, much depending on individual judgement and experience; but that, in the evolution of forms, such difficulties should arise in the limitation of genera and species was inevitable. What is a generic character in one may be only a specific character in another. As an ill.u.s.tration of the uncertain importance of characters, I may mention the weevil genus _Centrinus_ in which the leading characters in the cla.s.sification of the family to which it belongs are so mixed that systematists have been content to keep the species together in a group that cannot be defined.... No advantage or disadvantage is attached, apparently, to any of the characters. There are about 200 species, all American.

The venation of the wings of insects is another example of modifications without serving any special purpose. There is no vein in certain Thripidae, and only a rudiment or a single vein in Chalcididae. There are thousands of variations more or less marked, some of the same type with comparatively trivial variation, others presenting distinct types, even in the same family, such genera, for example, as _Polyneura_, _Tettigetra_, _Huechys_, &c. in the Cicadidae.

Individual differences have often been regarded as distinctive of species; varieties also are very deceptive, and races come very near to species. A South-American beetle, _Arescus histrio_, has varieties of yellow, red, and black, or these colours variously intermixed, and, what is very unusual, longitudinal stripes in some and transverse bars in others, and all taken in the same locality.

Mr. A. G. Butler, of the British Museum, is of opinion that 'what is generally understood by the term species (that is to say, a well-defined, distinct, and constant type, having no near allies) is non-existent in the Lepidoptera, and that the nearest approach to it in this order is a constant, though but slightly differing, rare or local form--that genera, in fact, consist wholly of a gradational series of such forms (Ann. Mag. Nat. Hist. 5, xix.

103)[127].'"

[127] Pascoe, _The Darwinian Theory of the Origin of Species_, 1891, pp. 31-33, and 46.

So much as regards entomology, and still living forms. In ill.u.s.tration of the same principles in connexion with palaeontological series, I may quote Wurtenberger, who says:--

"With respect to these fossil forms [i.e. mult.i.tudinous forms of fossil Ammonites], it is quite immaterial whether a very short or a somewhat longer part of any branch be dignified with a separate name, and regarded as a species. The p.r.i.c.kly Ammonites, cla.s.sed under the designation of Armata, are so intimately connected that it becomes impossible to separate the accepted species sharply from one another. The same remark applies to the group of which the manifold forms are distinguished by their ribbed sh.e.l.ls, and are called Planulata[128]."

[128] _Neuer Beitrag zum geologischen Beweis der Darwinischen Theorie_, 1873.

I had here supplied a number of similar quotations from writers in various other departments of systematic work, but afterwards struck them out as superfluous. For it is not to be antic.i.p.ated that any competent naturalist will nowadays dispute that the terms "variety," "species,"

and "genus" stand for merely conventional divisions, and that whether a given form shall be ranked under one or the other of them is often no more than a matter of individual taste. From the nature of the case there can be no objective, and therefore no common, standards of delimitation. This is true even as regards any one given department of systematic work; but when we compare the standards of delimitation which prevail in one department with those which prevail in another, it becomes evident that there is not so much as any attempt at agreeing upon a common measure of specific distinction.

But what, it may well be asked, is the use of thus insisting upon well-known facts, which n.o.body will dispute? Well, in the first place, we have already seen, in the last chapter, that it is inc.u.mbent on those who maintain that all species, or even all specific characters, must be due to natural selection, to tell us what they mean by a species, or by characters as specific. If I am told to believe that the definite quality A is a necessary attribute of B, and yet that B is "not a distinct ent.i.ty," but an undefinable abstraction, I can only marvel that any one should expect me to be so simple. But, without recurring to this point, the use of insisting on the facts above stated is, in the second place, that otherwise I cannot suppose any general reader could believe them in view of what is to follow. For he cannot but feel that the cost of believing them is to render inexplicable the mental processes of those naturalists who, in the face of such facts, have deduced the following conclusions.

The school of naturalists against which I am contending maintains, as a generalization deduced from the theory of natural selection, that all species, or even all specific characters, must necessarily owe their origin to the principle of utility. Yet this same school does not maintain any such generalization, either with regard to varietal characters on the one hand, or to generic characters on the other. On the contrary, Professor Huxley, Mr. Wallace, and all other naturalists who agree with them in refusing to entertain so much as the abstract possibility of any cause other than natural selection having been productive of species, fully accept the fact of other causes having been largely concerned in the production of varieties, genera, families, and all higher groups, or of the characters severally distinctive of each.

Indeed, Mr. Wallace does not question what appears to me the extravagant estimate of Professor Cope, that the non-adaptive characters distinctive of those higher groups are fully equal, in point of numbers, to the adaptive. But, surely, if the theory of evolution by natural selection is, as we all agree, a true theory of the origin of species, it must likewise be a true theory of the origin of genera; and if it be supposed essential to the integrity of the theory in its former aspect that all specific characters should be held to be useful, I fail to see how, in regard to its latter aspect, we are so readily to surrender the necessary usefulness of all generic characters. And exactly the same remark applies to the case of constant "varieties," where again the doctrine of utility as universal is not maintained. Yet, according to the general theory of evolution, constant varieties are what Darwin termed "incipient species," while species are what may be termed "incipient genera." Therefore, if the doctrine of utility as universal be conceded to fail in the case of varieties on the one hand and of genera on the other, where is the consistency in maintaining that it must "necessarily" hold as regards the intermediate division, species?

Truly the shade of Darwin may exclaim, "Save me from my friends." And truly against logic of this description a follower of Darwin must find it difficult to argue. If one's opponents were believers in special creation, and therefore stood upon some definite ground while maintaining this difference between species and all other taxonomic divisions, there would at least be some issue to argue about. But when on the one hand it is conceded that species are merely arbitrary divisions, which differ in no respect as to the process of their evolution from either varieties or genera, while on the other hand it is affirmed that there is thus so great a difference in the result, all we can say is that our opponents are entangling themselves in the meshes of a sheer contradiction.

Or, otherwise stated, specific characters differ from varietal characters in being, as a rule, more p.r.o.nounced and more constant: on this account advocates of utility as universal apply the doctrine to species, while they do not feel the "necessity" of applying it to varieties. But now, generic and all higher characters are even more constant and more p.r.o.nounced than specific characters--not to say, in many cases, more generally diffused over a larger number of organisms usually occupying larger areas. Therefore, _a fortiori_, if for the reasons above stated evolutionists regard it as a necessary deduction from the theory of natural selection that all specific characters must be useful, much more ought it to be a necessary deduction from this theory that all generic, and still more all higher, characters must be useful. But, as we have seen, this is not maintained by our opponents.

On the contrary, they draw the sharpest distinction between specific and all other characters in this respect, freely conceding that both those below and those above them need not--and very often do not--present any utilitarian significance.

Although it appears to me that this doctrine is self-contradictory, and on this ground alone might be summarily dismissed, as it is now held in one or other of its forms by many naturalists, I will give it a more detailed consideration in both its parts--namely, first with respect to the distinction between varieties and species, and next with respect to the distinction between species and genera.

Until it can be shown that species are something more than merely arbitrary divisions, due to the disappearance of intermediate varietal links; that in some way or another they _are_ "definite ent.i.ties," which admit of being delineated by the application of some uniform or general principles of definition; that, in short, species have only then been cla.s.sified as such when it has been shown that the origin of each has been due to the operation of causes which have not been concerned in the production of varieties;--until these things are shown, it clearly remains a gratuitous dogma to maintain that forms which have been called species differ from forms which have been called varieties in the important respect, that they (let alone each of all their distinctive characters) must necessarily have been due to the principle of utility.

Yet, as we have seen, even Mr. Wallace allows that a species is "not a distinct ent.i.ty," but "an a.s.semblage of individuals which have become somewhat modified in structure, form, and const.i.tution"; while estimates of the kinds and degrees of modification which are to be taken as of specific value are conceded to be undefinable, fluctuating, and in not a few cases almost ludicrously divergent.

Perhaps one cannot more forcibly present the rational value of this position than by noting the following consequences of it. Mr. Gulick writes me that while studying the land-sh.e.l.ls of the Sandwich Islands, and finding there a rich profusion of unique varieties, in cases where the intermediate varieties were rare he could himself have created a number of species by simply throwing these intermediate varieties into his fire. Now it follows from the dogma which we are considering, that, by so doing, not only would he have created new species, but at the same time he would have proved them due to natural selection, and endowed the diagnostic characters of each with a "necessarily" adaptive meaning, which previously it was not necessary that they should present. Before his destruction of these intermediate varieties, he need have felt himself under no obligation to a.s.sume that any given character at either end of the series was of utilitarian significance: but, after his destruction of the intermediate forms, he could no longer entertain any question upon the matter, under pain of being denounced as a Darwinian heretic.

Now the application is self-evident. It is a general fact, which admits of no denial, that the more our knowledge of any flora or fauna increases, the greater is the number of intermediate forms which are brought to light, either as still existing or as having once existed.

Consequently, the more that such knowledge increases, the more does our catalogue of "species" diminish. As Kerner says, "bad species" are always multiplying at the expense of "good species"; or, as Oscar Schmidt (following Hackel) similarly remarks, if we could know as much about the latter as we do about the former, "all species, without any exception, would become what species-makers understand by 'bad species'[129]." Hence we see that, just as Mr. Gulick could have created good species by secretly destroying his intermediate varieties, so has Nature produced her "good species" for the delectation of systematists.

And just as Mr. Gulick, by first hiding and afterwards revealing his intermediate forms, could have made the self-same characters in the first instance necessarily useful, but ever afterwards presumably useless, so has Nature caused the utility of diagnostic characters to vary with our knowledge of her intermediate forms. It belongs to the essence of our theory of descent, that in _all_ cases these intermediate forms must either be now existing or have once existed; and, therefore, that the work of species-makers consists in nothing more than marking out the _lacunae_ in our knowledge of them. Yet we are bound to believe that wherever these _lacunae_ in our knowledge occur, there occurs also the objective necessity of causation as utilitarian--a necessity, however, which vanishes so soon as our advancing information supplies the intermediate forms in question. It may indeed appear strange that the utility or non-utility of organic structures should thus depend on the accidents of human knowledge; but this is the Darwinian faith, and he who doubts the dogma is to be anathema.

[129] _The Doctrine of Descent and Darwinism_, Eng. Trans. p. 102.

Turning next to the similar distinction which it is sought to draw between species and genera, here it will probably be urged, as I understand it to be urged by Mr. Wallace, that generic characters (and still more characters of families, orders, &c.) refer back to so remote a state of things that utility may have been present at their birth which has disappeared in their maturity. In other words, it is held that all generic characters were originally specific characters; that as such they were all originally of use; but that, after having been rendered stable by heredity, many of them may have ceased to be of service to the descendants of those species in which they originated, and whose extinction has now made it impossible to divine what that service may have been.

Now, in the first place; this is not the interpretation adopted by Darwin. For instance, he expressly contrasts such cases with those of vestigial or "rudimentary" structures, pointing out that they differ from vestigial structures in respect of their permanence. One quotation will be sufficient to establish the present point.

"A structure which has been developed through long-continued selection, when it ceases to be of service to a species, generally becomes variable, as we see with rudimentary organs, for it will no longer be regulated by this same power of selection. But when, from the nature of the organism and of the conditions, modifications have been induced which are unimportant for the welfare of the species, they may be, and apparently often have been, transmitted in nearly the same state to numerous, otherwise modified, descendants[130]."

[130] _Origin of Species_, p. 175.

Here, and in the context, we have a sufficiently clear statement of Darwin's view--first, that unadaptive characters may arise in _species_ as "fluctuating variations, which sooner or later become _constant_ through the nature of the organism and of surrounding conditions, as well as through the intercrossing of distinct individuals, but _not_ through natural selection"[131]; second, that such unadaptive characters may then be transmitted in this their stable condition to species-progeny, so as to become distinctive of genera, families, &c.; third, that, on account of such characters not being afterwards liable to diverse adaptive modifications in different branches of the species-progeny, they are of more value as indicating lines of pedigree than are characters which from the first have been useful; and, lastly, they are therefore now empirically recognized by systematists as of most value in guiding the work of cla.s.sification. To me it appears that this view is not only perfectly rational in itself, but likewise fully compatible with the theory of natural selection--which, as I have previously shown, is _primarily_ a theory of adaptive characters, and therefore not necessarily a theory of _all_ specific characters. But to those who think otherwise, it must appear--and does appear--that there is something wrong about such a view of the case--that it was not consistent in the author of the _Origin of Species_ thus to refer non-adaptive generic characters to a parentage of non-adaptive specific characters. Nevertheless, as a matter of fact, Darwin was perfectly consistent in putting forth this view, because, unlike Wallace, he was not under the sway of any antecedent dogma erroneously deduced from the theory of natural selection.

[131] _Ibid._ p. 176: italics mine.

Next without reference to Darwin's authority, let us see for ourselves where the inconsistency really lies. To allow that generic characters may be useless, while denying that specific characters can ever be so (unless correlated with others that are useful), involves an appeal to the argument from ignorance touching the ancestral habits, life-conditions, &c., of a parent species now extinct. Well, even upon this a.s.sumption of utility as obsolete, there remains to be explained the "stability" of useless characters now distinctive of genera, families, orders, and the rest. We know that specific characters which have owed their origin to utility and have afterwards ceased to present utility, degenerate, become variable, inconstant, "rudimentary," and finally disappear. Why, then, should these things not happen with regard to useless generic distinctions? Still more, why should they not happen with regard to family, ordinal, and cla.s.s distinctions? On the lines against which I am arguing it would appear impossible that any answer to this question can be suggested. For what explanation can be given of the contrast thus presented between the obsolescence of specific characters where previous utility is demonstrable, and the permanence of higher characters whose previous utility is a.s.sumed? As we have already seen, Mr. Wallace himself employs this consideration of permanence and constancy against the view that any cause other than natural selection can have been concerned in the origin and maintenance of _specific_ characters. But he does not seem to see that the consideration cuts two ways--and much more forcibly against his views than in favour of them.

For while, as already shown in the chapter before last, it is sufficiently easy to dispose of the consideration as Wallace uses it (by simply pointing out with Darwin that any causes other than natural selection which may have been concerned in the genesis of _specific_ characters, must, if equally uniform in their operation, equally give rise to permanence and constancy in their results); on the other hand, it becomes impossible to explain the stability of useless _generic_ characters, if, as Wallace's use of the argument requires, natural selection is the only possible cause of stability. The argument is one that cannot be played with fast and loose. Either utility is the sole condition to the stability of _any_ diagnostic character (in which case it is not open to Mr. Wallace to a.s.sume that all _generic_ or higher characters which are now useless have owed their origin to a past utility); or else utility is not the sole condition to stability (in which case his use of the present argument in relation to _specific_ characters collapses). We have seen, indeed, in the chapter before last, that his use of the argument collapses anyhow, or quite irrespective of his inconsistent att.i.tude towards generic characters, with which we were not then concerned. But the point now is that, as a mere matter of logic, the argument from stability as Wallace applies it to the case of specific characters, is incompatible with his argument that useless generic characters may originally have been useful specific characters.

It can scarcely be questioned that the trans.m.u.tation of a species into a genus must, as a rule, have allowed time enough for a newly acquired--i.e. peculiar specific-character--to show some signs of undergoing degeneration, if, as supposed, the original cause of its development and maintenance was withdrawn when the parent species began to ramify into its species-progeny. Yet, as Darwin says, "it is notorious that specific characters are more variable than generic[132]."