On the Genesis of Species Part 5

Now, every opinion or conjecture of Mr. Wallace is worthy of respectful and attentive consideration, but the explanation suggested and before referred to hardly seems a satisfactory one. What the past fauna of Celebes may have been is as yet conjectural. Mr. Wallace tells us that now there is a remarkable _scarcity_ of fly-catchers, and that their place is supplied by birds of which it can only be said that it is "highly probable" that they chase b.u.t.terflies "when other food is scarce." The quick eye of Mr. Wallace failed to detect them in the act, as also to note any unusual abundance of other insectivorous forms, which therefore, considering Mr. Wallace's zeal and powers of observation, we may conclude do not exist. Moreover, even if there ever has been an abundance of such, it is by no means certain that they would have succeeded in producing the conformation in question, for the effect of this peculiar curvature on flight is by no means clear. We have here, then, a structure hypothetically explained by an uncertain {88} property induced by a cause the presence of which is only conjectural.

Surely it is not unreasonable to cla.s.s this instance with the others before given, in which a common modification of form or colour coexists with a certain geographical distribution quite independently of the destructive agencies of animals. If physical causes connected with locality can abbreviate or annihilate the tails of certain b.u.t.terflies, why may not similar causes produce an elbow-like prominence on the wings of other b.u.t.terflies? There are many such instances of simultaneous modification.

Mr. Darwin himself[67] quotes Mr. Gould as believing that birds of the same species are more brightly coloured under a clear atmosphere, than when living on islands or near the coast. Mr. Darwin also informs us that Wollaston is convinced that residence near the sea affects the colour of insects; and finally, that Moquin-Tandon gives a list of plants which, when growing near the sea-sh.o.r.e, have their leaves in some degree fleshy, though not so elsewhere. In his work on "Animals and Plants under Domestication,"[68] Mr. Darwin refers to M. Costa as having (in _Bull. de la Soc. Imp. d'Acclimat_. tome viii. p. 351) stated "that young sh.e.l.ls taken from the sh.o.r.es of England and placed in the Mediterranean at once altered their manner of growth, and formed prominent diverging rays _like those on the sh.e.l.ls of the proper Mediterranean oyster_;" also to Mr.

Meehan, as stating (_Proc. Acad. Nat. Sc. of Philadelphia_, Jan. 28, 1862) "that twenty-nine kinds of American trees all differ from their nearest European allies in _a similar manner_, leaves less toothed, buds and seeds smaller, fewer branchlets," &c. These are striking examples indeed!

But cases of simultaneous and similar modifications abound on all sides.

Even as regards our own species there is a very generally admitted opinion that a new type has been developed in the United States, and this in about a couple of centuries only, and in a vast mult.i.tude of individuals of {89} diverse ancestry. The instances here given, however, must suffice, though more could easily be added.

[Ill.u.s.tration: THE GREAT s.h.i.+ELDED GRa.s.sHOPPER.]

It may be well now to turn to groups presenting similar variations, not through, but independently of, geographical distribution, and, as far as we know, independently of conditions other than some peculiar nature and tendency (as yet unexplained) common to members of such groups, which nature and tendency seem to induce them to vary in certain definite lines or directions which are different in different groups. Thus with regard to the group of insects, of which the walking leaf is a member, Mr. Wallace observes:[69] "The _whole family_[70] of the Phasmidae, or spectres, to which this insect belongs, is more or less imitative, and a great number of the species are called 'walking-stick insects,' from their singular {90} resemblance to twigs and branches."

[Ill.u.s.tration: THE SIX-SHAFTED BIRD OF PARADISE.]

Again, Mr. Wallace[71] tells us of no less than four kinds of orioles, which birds mimic, more or less, four species of a genus of honey-suckers, the weak orioles finding their profit in being mistaken by certain birds of prey for the strong, active, and gregarious honey-suckers. Now, many other birds would be benefited by similar mimicry, which is none the less confined, in this part of the world, to the oriole genus. It is true that the absence of mimicry in other forms may be explained by their possessing some other (as yet un.o.bserved) means of preservation. But it is nevertheless remarkable, not so much that one species should mimic, as that no less than four should do so in different ways and degrees, all these{91} four belonging to _one and the same genus_.

[Ill.u.s.tration: THE LONG-TAILED BIRD OF PARADISE.]

In other cases, however, there is not even the help of protective action to account for the phenomenon. Thus we have the wonderful birds of Paradise,[72] which agree in developing plumage unequalled in beauty, but a beauty which, as to details, is of different kinds, and produced in different ways in different species. To develop "beauty and singularity of plumage" is a character of the group, but not of any one definite kind, to be explained merely by inheritance.

{92} [Ill.u.s.tration]

Again, we have the very curious horned flies,[73] which agree indeed in a common peculiarity, but in one singularly different in detail, in different species and not known to have any protecting effect.

Amongst plants, also, we meet with the same peculiarity. The great group of Orchids presents a number of species which offer strange and bizarre {93} approximations to different animal forms, and which have often the appearance of cases of mimicry, as it were in an incipient stage.

[Ill.u.s.tration: HORNED FLIES.]

[Ill.u.s.tration: THE MAGNIFICENT BIRD OF PARADISE.]

The number of similar instances which could be brought forward from amongst animals and plants is very great, but the examples given are, it is {94} hoped, amply sufficient to point towards the conclusion which other facts will, it is thought, establish, viz. that there are causes operating (in the evocation of these harmonious diverging resemblances) other than "Natural Selection," or heredity, and other even than merely geographical, climatal, or any simply external conditions.

Many cases have been adduced of striking likenesses between different animals, not due to inheritance; but this should be the less surprising, in that the very same individual presents us with likenesses between different parts of its body (_e.g._, between the several joints of the backbone), which are certainly not so explicable. This, however, leads to a rather large subject, which will be spoken of in the eighth chapter of the present work. Here it will be enough to affirm (leaving the proof of the a.s.sertion till later) that parts are often h.o.m.ologous which have no direct genetic relations.h.i.+p,--a fact which harmonizes well with the other facts here given, but which "Natural Selection," pure and simple, seems unable to explain.

But surely the independent appearance of similar organic forms is what we might expect, _a priori_, from the independent appearance of similar inorganic ones. As Mr. G. H. Lewes well observes,[74] "We do not suppose the carbonates and phosphates found in various parts of the globe--we do not suppose that the families of alkaloids and salts have any nearer kins.h.i.+p than that which consists in the similarity of their elements, and the conditions of their combination. Hence, in organisms, as in salts, morphological ident.i.ty may be due to a community of causal connexion, rather than community of descent.

"Mr. Darwin justly holds it to be incredible that individuals identically the same should have been produced through Natural Selection from parents _specifically distinct_, but he will not deny that identical forms may issue from parents _genetically distinct_, when these parent forms and {95} the conditions of production are identical. To deny this would be to deny the law of causation."

Professor Huxley has, however, suggested[75] that such mineral ident.i.ty may be explained by applying also to minerals a law of descent; that is, by considering such similar forms as the descendants of atoms which inhabited one special part of the primitive nebular cosmos, each considerable s.p.a.ce of which may be supposed to have been under the influence of somewhat different conditions.

Surely, however, there can be no real parity between the relations.h.i.+p of existing minerals to nebular atoms, and the relations.h.i.+p of existing animals and plants to the earliest organisms. In the first place, the latter have produced others by generative multiplication, which mineral atoms never did. In the second, existing animals and plants spring from the living tissues of preceding animals and plants, while existing minerals spring from the chemical affinity of separate elements. Carbonate of soda is not formed, by a process of reproduction, from other carbonate of soda, but directly by the suitable juxtaposition of carbon, oxygen, and sodium.

Instead of approximating animals and minerals in the mode suggested, it may be that they are to be approximated in quite a contrary fas.h.i.+on; namely, by attributing to mineral species an internal innate power. For, as we must attribute to each elementary atom an innate power and tendency to form (under the requisite external conditions) certain unions with other atoms, so we may attribute to certain mineral species--as crystals--an innate power and tendency to exhibit (the proper conditions being supplied) a definite and symmetrical external form. The distinction between animals and vegetables on the one hand, and minerals on the other, is that, while in the organic world close similarity is the result sometimes of inheritance, sometimes of direct production independently of parental action, in the{96} inorganic world the latter is the constant and only mode in which such similarity is produced.

When we come to consider the relations of species to s.p.a.ce--in other words, the geographical distribution of organisms--it will be necessary to return somewhat to the subject of the independent origin of closely similar forms, in regard to which some additional remarks will be found towards the end of the seventh chapter.

In this third chapter an effort has been made to show that while on the Darwinian theory concordant variations are extremely improbable, yet Nature presents us with abundant examples of such; the most striking of which are, perhaps, the higher organs of sense. Also that an important influence is exercised by conditions connected with geographical distribution, but that a deeper-seated influence is at work, which is hinted at by those special tendencies in definite directions, which are the properties of certain groups. Finally, that these facts, when taken together, afford strong evidence that "Natural Selection" has not been the exclusive or predominant cause of the various organic structural peculiarities. This conclusion has also been re-enforced by the consideration of phenomena presented to us by the inorganic world. [Page 97]

CHAPTER IV.

MINUTE AND GRADUAL MODIFICATIONS.

There are difficulties as to minute modifications, even if not fortuitous.--Examples of sudden and considerable modifications of different kinds.--Professor Owen's view.--Mr. Wallace.--Professor Huxley.--Objections to sudden changes.--Labyrinthodont.--Potto.--Cetacea.--As to origin of bird's wing.--Tendrils of climbing plants.--Animals once supposed to be connecting links.--Early specialization of structure.--Macrauchenia.--Glyptodon.--Sabre-toothed tiger.--Conclusion.

Not only are there good reasons against the acceptance of the exclusive operation of "Natural Selection" as the one means of specific origination, but there are difficulties in the way of accounting for such origination by the sole action of modifications which are infinitesimal and minute, whether fortuitous or not.

Arguments may yet be advanced in favour of the view that new species have from time to time manifested themselves with suddenness, and by modifications appearing at once (as great in degree as are those which separate _Hipparion_ from _Equus_), the species remaining stable in the intervals of such modifications: by stable being meant that their variations only extend for a certain degree in various directions, like oscillations in a stable equilibrium. This is the conception of Mr.

Galton,[76] who compares the development of species with a many {98} facetted spheroid tumbling over from one facet, or stable equilibrium, to another. The existence of internal conditions in animals corresponding with such facets is denied by pure Darwinians, but it is contended in this work, though not in this chapter, that something may also be said for their existence.

The considerations brought forward in the last two chapters, namely, the difficulties with regard to incipient and closely similar structures respectively, together with palaeontological considerations to be noticed later, appear to point strongly in the direction of sudden and considerable changes. This is notably the case as regards the young oysters already mentioned, which were taken from the sh.o.r.es of England and placed in the Mediterranean, and at once altered their mode of growth and formed prominent diverging rays, _like those of the proper Mediterranean oyster_; as also the twenty-nine kinds of American trees, all differing from their nearest European allies _similarly_--"leaves less toothed, buds and seeds smaller, fewer branchlets," &c. To these may be added other facts given by Mr. Darwin. Thus he says, "that climate, to a certain extent, directly modifies the form of dogs."[77]

The Rev. R. Everett found that setters at Delhi, though most carefully paired, yet had young with "nostrils more contracted, noses more pointed, size inferior, and limbs more slender." Again, cats at Mombas, on the coast of Africa, have short stiff hairs instead of fur, and a cat at Algoa Bay, when left only eight weeks at Mombas, "underwent a complete metamorphosis, having parted with its sandy-coloured fur."[78] The conditions of life seem to produce a considerable effect on horses, and instances are given by Mr.

Darwin of pony breeds[79] having independently arisen in different parts of the world, possessing a certain similarity in their physical {99} conditions. Also changes due to climate may be brought about at once in a second generation, though no appreciable modification is shown by the first. Thus "Sir Charles Lyell mentions that some Englishmen, engaged in conducting the operations of the Real del Monte Company in Mexico, carried out with them some greyhounds of the best breed to hunt the hares which abound in that country. It was found that the greyhounds could not support the fatigues of a long chase in this attenuated atmosphere, and before they could come up with their prey they lay down gasping for breath; but these same animals have produced whelps, which have grown up, and are not in the least degree incommoded by the want of density in the air, but run down the hares with as much ease as do the fleetest of their race in this country."[80]

We have here no action of "Natural Selection;" it was not that certain puppies happened accidentally to be capable of enduring more rarefied air, and so survived, but the offspring were directly modified by the action of surrounding conditions. Neither was the change elaborated by minute modifications in many successive generations, but appeared at once in the second.

With regard once more to sudden alterations of form, Nathusius is said to state positively as to pigs,[81] that the result of common experience and of his experiments was that rich and abundant food, given during youth, tends by some direct action to make the head broader and shorter. Curious jaw appendages often characterize Normandy pigs, according to M. Eudes Deslongchamps. Richardson figures these appendages on the old "Irish greyhound pig," and they are said by Nathusius to appear occasionally in all the long-eared races. Mr. Darwin observes,[82] "As no wild pigs are known to have a.n.a.logous appendages, we have at present no reason to {100} suppose that their appearance is due to reversion; and if this be so, we are forced to admit that somewhat complex, though apparently useless structures may be suddenly developed without the aid of selection." Again, "Climate directly affects the thickness of the skin and hair" of cattle.[83] In the English climate an individual Porto Santo rabbit[84]

recovered the proper colour of its fur in rather less than four years. The effect of the climate of India on the turkey is considerable. Mr. Blyth[85]

describes it as being much degenerated in size, "utterly incapable of rising on the wing," of a black colour, and "with long pendulous appendages over the beak enormously developed." Mr. Darwin again tells us that there has suddenly appeared in a bed of common broccoli a peculiar variety, faithfully transmitting its newly acquired and remarkable characters;[86]

also that there have been a rapid transformation and transplantation of American varieties of maize with a European variety;[87] that certainly "the Ancon and Manchamp breeds of sheep," and that (all but certainly) Niata cattle, turnspit and pug dogs, jumper and frizzled fowls, short-faced tumbler pigeons, hook-billed ducks, &c., and a mult.i.tude of vegetable varieties, have suddenly appeared in nearly the same state as we now see them.[88] Lastly, Mr. Darwin tells us, that there has been an occasional development (in five distinct cases) in England of the "j.a.panned" or "black-shouldered peac.o.c.k" (_Pavo nigripennis_), a distinct species, according to Dr. Sclater,[89] yet arising in Sir J. Trevelyan's flock composed entirely of the common kind, and increasing, "_to the extinction of the previously existing breed_."[90] Mr. Darwin's only explanation of the phenomena (on the supposition of the species being distinct) is by{101} reversion, owing to a supposed ancestral cross. But he candidly admits, "I have heard of no other such case in the animal or vegetable kingdom." On the supposition of its being only a variety, he observes, "The case is the most remarkable ever recorded of the abrupt appearance of a new form, which so closely resembles a true species, that it has deceived one of the most experienced of living ornithologists."

As to plants, M. C. Naudin[91] has given the following instances of the sudden origination of apparently permanent forms. "The first case mentioned is that of a poppy, which took on a remarkable variation in its fruit--a crown of secondary capsules being added to the normal central capsule. A field of such poppies was grown, and M. Goppert, with seed from this field, obtained still this monstrous form in great quant.i.ty. Deformities of ferns are sometimes sought after by fern-growers. They are now always obtained by taking spores from the abnormal parts of the monstrous fern; from which spores ferns presenting the same peculiarities invariably grow.... The most remarkable case is that observed by Dr. G.o.dron, of Nancy. In 1861 that botanist observed, amongst a sowing of _Datura tatula_, the fruits of which are very spinous, a single individual of which the capsule was perfectly smooth. The seeds taken from this plant all furnished plants having the character of this individual. The fifth and sixth generations are now growing without exhibiting the least tendency to revert to the spinous form. More remarkable still, when crossed with the normal _Datura tatula_, hybrids were produced, which, in the second generation, reverted to the original types, as true hybrids do."

There are, then, abundant instances to prove that considerable {102} modifications may suddenly develop themselves, either due to external conditions or to obscure internal causes in the organisms which exhibit them. Moreover, these modifications, from whatever cause arising, are capable of reproduction--the modified individuals "breeding true."

The question is whether new species have been developed by non-fortuitous variations which are insignificant and minute, or whether such variations have been comparatively sudden, and of appreciable size and importance?

Either hypothesis will suit the views here maintained equally well (those views being opposed only to fortuitous, indefinite variations), but the latter is the more remote from the Darwinian conception, and yet has much to be said in its favour.

Professor Owen considers, with regard to specific origination, that natural history "teaches that the change would be sudden and considerable: it opposes the idea that species are transmitted by minute and slow degrees."[92] "An innate tendency to deviate from parental type, operating through periods of adequate duration," being "the most probable nature, or way of operation of the secondary law, whereby species have been derived one from the other."[93]

Now, considering the number of instances adduced of sudden modifications in domestic animals, it is somewhat startling to meet with Mr. Darwin's dogmatic a.s.sertion that it is "a _false belief_" that natural species have often originated in the same abrupt manner. The belief _may_ be false, but it is difficult to see how its falsehood can be positively a.s.serted.

It is demonstrated by Mr. Darwin's careful weighings and measurements, that, though little used parts in domestic animals get reduced in weight and somewhat in size, yet that they show no inclination to become truly "rudimentary structures." Accordingly he a.s.serts[94] that such {103} rudimentary parts are formed "suddenly, by arrest of development" in domesticated animals, but in wild animals slowly. The latter a.s.sertion, however, is a _mere a.s.sertion_; necessary, perhaps, for the theory of "Natural Selection," but as yet unproved by facts.

But why should not these changes take place suddenly in a state of nature?

As Mr. Murphy says,[95] "It may be true that we have no evidence of the origin of wild species in this way. But this is not a case in which negative evidence proves anything. We have never witnessed the origin of a wild species by any process whatever; and if a species were to come suddenly into being in the wild state, as the Ancon Sheep did under domestication, how could you ascertain the fact? If the first of a newly-begotten species were found, the fact of its discovery would tell nothing about its origin. Naturalists would register it as a very rare species, having been only once met with, but they would have no means of knowing whether it were the first or the last of its race."

To this Mr. Wallace has replied (in his review of Mr. Murphy's work in _Nature_[96]), by objecting that sudden changes could very rarely be useful, because each kind of animal is a nicely balanced and adjusted whole, any one sudden modification of which would in most cases be hurtful unless accompanied by other simultaneous and harmonious modifications. If, however, it is not unlikely that there is an innate tendency to deviate at certain times, and under certain conditions, it is no more unlikely that that innate tendency should be an harmonious one, calculated to simultaneously adjust the various parts of the organism to their new relations. The objection as to the sudden abortion of rudimentary organs may be similarly met.

Professor Huxley seems now disposed to accept the, at least {104} occasional, intervention of sudden and considerable variations. In his review of Professor Kolliker's[97] criticisms, he himself says,[98] "We greatly suspect that she" (_i.e._ Nature) "does make considerable jumps in the way of variation now and then, and that these saltations give rise to some of the gaps which appear to exist in the series of known forms."

[Ill.u.s.tration: MUCH ENLARGED HORIZONTAL SECTION OF THE TOOTH OF A LABYRINTHODON.]

In addition to the instances brought forward in the second chapter against the minute action of Natural Selection, may be mentioned such {105} structures as the wonderfully folded teeth of the labyrinthodonts. The marvellously complex structure of these organs is not merely unaccountable as due to Natural "Selection," but its production by insignificant increments of complexity is hardly less difficult to comprehend.

Similarly the aborted index of the Potto (_Perodicticus_) is a structure not likely to have been induced by minute changes; while, as to "Natural Selection," the reduction of the fore-finger to a mere rudiment is inexplicable indeed! "How this mutilation can have aided in the struggle for life, we must confess, baffles our conjectures on the subject; for that any very appreciable gain to the individual can have resulted from the slightly lessened degree of required nourishment thence resulting (_i.e._ from the suppression), seems to us to be an almost absurd proposition."[99]