Читать книгу: «The Old Riddle and the Newest Answer», страница 8

According to their highest authority, Mr. Herbert Spencer, Evolution means "the production of all organic forms by the accumulation of modifications and of divergences by the addition of differences to differences."

Beyond all question [he adds] unlikenesses of structure gradually arise among the members of successive generations. We find that there is going on a modifying process of the kind alleged as the source of specific differences, a process which, though slow, does, in time, produce changes – a process which to all appearance would produce in millions of years any amount of changes.¹⁷⁶

The Transformist doctrine is, therefore, that one species of plants or animals, has in natural course grown out of another, through the aggregation of changes each exceedingly minute. Darwinism adds that the ruling principle of this process is Natural Selection. These are the points on which our enquiry turns, and we may conveniently commence with the second.

XV
DARWINISM

IT must first be observed that special consideration of Mr. Darwin's theory is rendered necessary even more imperatively on account of the claims advanced on his behalf by others, than of those to which he himself made any pretence. Without question the idea prevails almost universally, that he has furnished a scientific explanation of all organic phenomena through the operation of purely natural laws, and has thus rendered obsolete the idea that any power beyond Nature is required in order to account for the totality of things, or that there are any features of the world which indicate the operation of intelligent purpose.

That such ideas should be widely prevalent amongst those who, having no special acquaintance with the subject, must depend for their knowledge on the popularizers of Science, is scarcely wonderful, for such teachers, with scarcely an exception, so declare, and occasionally real men of Science lend the weight of their authority to similar statements.

It will be sufficient to cite Professor Haeckel, who writes thus:¹⁷⁷

It seemed to Kant so impossible to explain the orderly processes in the living organism without postulating super-natural final causes (that is, a purposive creative force) that he said, "It is quite certain that we cannot even satisfactorily understand, much less elucidate, the nature of an organism and its internal faculty on purely mechanical natural principles – it is so certain, indeed, that we may confidently say: It is absurd for a man even to conceive the idea that some day a Newton will arise who can explain the origin of a single blade of grass by natural laws uncontrolled by design. Such a hope is entirely forbidden us." Seventy years afterwards this impossible Newton of the organic world appeared in the person of Charles Darwin, and achieved the great task that Kant had deemed impracticable.

It is quite impossible to understand how such an assertion can be made by any one who knows the facts. Not only did Mr. Darwin never profess to have achieved any thing of the kind, – he repeatedly and distinctly disclaimed and repudiated any such supposition. Thus at the very end of his life (August 28, 1881) he wrote concerning one who had spoken of him like Professor Haeckel:

He implies that my views explain the universe; but it is a most monstrous exaggeration. The more one thinks, the more one feels the hopeless immensity of man's ignorance. If we consider the whole universe, the mind refuses to look at it as the outcome of chance.¹⁷⁸ The whole question seems to me insoluble.

But it should not be necessary to appeal to such disclaimers in order to show how absolutely unwarrantable are the pretensions made on Mr. Darwin's behalf to have solved, or to have attempted to solve, the fundamental problems which scientific research unceasingly suggests but has never been able to elucidate. It should be quite sufficient to examine his theory as it actually is, and although its scope is immensely less ambitious than has been represented, it still occupies, even in its genuine form, a position of sufficient importance to challenge investigation.

Mr. Darwin's famous and epoch-making book, published in November, 1859, was entitled On the Origin of Species by means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. In it he undertook to show how from one species¹⁷⁹ of animals or plants, another, quite distinct from it, may be derived by means of processes which go on in Nature every day, through the accumulation of minute differences occurring in successive generations, and guided to their collective result by the force of "Natural Selection." As man, he argues, has by means of selection been able to produce in a brief space such astonishing varieties among his domestic animals and plants – as dogs, pigeons, roses or apples, – Nature, with the practically unlimited ages of geological time at her disposal, must be able to produce far greater and more enduring transformations, through the accumulation of minute differences, such as those upon which man has worked, – if only a factor can be found which amid the infinity of diverse and discordant variations spontaneously occurring, could, like the breeder or the gardener, pick out those leading to one particular result, and thus secure its accomplishment. Such a force Mr. Darwin conceives is found in "Natural Selection," which he thus explains.

The tendency of organic life, whether vegetable or animal, being to propagate itself enormously, – and the life-sustaining capacity of the earth being limited, – it necessarily follows that only a fraction of the creatures which are born can survive to maturity, and that while those best fitted to live will live, those less well fitted will die. Thus, there is set up a constant struggle for existence, in which every advantage, however slight, must tell, so that those possessing such advantages in one generation will be the parents of the next. But in the course of propagation, the offspring never exactly reproduce the parent form, from which they vary, some in one way some in another, and as some of these variations cannot help being advantageous to their possessors in the struggle, we have here the required factor for the production of new forms. Any thus beneficially equipped, (although the variation, and consequently the advantage, must in each instance be exceedingly slight,) will have the chances on their side against their less favoured fellows, whom in the long run they will supplant. And as their offspring, or some of them, will carry the profitable variation somewhat further, the stream of life will thus be set in such a direction as will ultimately bring about what might at first appear impossible metamorphoses.

Thus, to take a simple and favourite illustration,¹⁸⁰ winged insects inhabiting an island far from other land, are liable to be blown out to sea and drowned. It is in consequence, an advantage to them to have their power of flight curtailed, or taken away, and consequently in such situations their wings are generally found to be so reduced as to permit little or even nothing in the way of flying. Or to take an example of another kind,¹⁸¹ the extraordinary length of neck which characterizes the giraffe enables it to browse on the higher branches of trees inaccessible to other vegetable feeders, and thus gives it an advantage over them in times of drought and scarcity of fodder. It can accordingly be easily understood, how its present structure has resulted from gradual elongations of the neck, each conferring on its possessor a slight advantage.

The work attributed to Natural Selection in such instances, though no doubt highly important, is comparatively facile, and it would be difficult to say that it could not be accomplished. But Mr. Darwin ascribes to the same factor, not merely such modification of existing structures, but the creation of entirely new mechanisms for specific purposes. We have, for instance, heard his description of the eye and its manifold "inimitable contrivances: " yet all these, he persuaded himself, might be thus accounted for. The idea, he confessed,¹⁸² seems at first sight preposterous; yet, though not without much difficulty,¹⁸³ he succeeded in convincing himself, that given the rudest and most rudimentary form of eye to start with – no more than a nerve sensitive to light but incapable of forming an image – Natural Selection might develop therefrom, through an infinite series of gradations the inconceivably complex machine that is now found in the higher vertebrates,¹⁸⁴ and the totally different but equally marvellous organs of sight possessed by insects, crustaceans, and other creatures.

In like manner, Mr. Darwin contended, might the most complex and wonderful instincts be generated. As an example may be cited that by which the hive-bee constructs its combs – of which he thus speaks:¹⁸⁵

He must be a dull man who can examine the exquisite structure of a comb, so beautifully adapted to its end, without enthusiastic admiration. We hear from mathematicians that bees have practically solved a recondite problem, and have made their cells of the proper shape to hold the greatest possible amount of honey, with the least possible consumption of precious wax in their construction. It has been remarked that a skilful workman with fitting tools and measures, would find it very difficult to make cells of wax of the true form, though this is perfectly effected by a crowd of bees working in a dark hive.¹⁸⁶ Granting whatever instincts you please, it seems at first sight quite inconceivable how they can make all the necessary angles and planes, or even perceive when they are correctly made. But the difficulty is not nearly so great as it at first appears: all this beautiful work can be shown, I think, to follow from a few simple instincts.

He accordingly proceeds to argue, that beginning with circular cells, like those of Humble Bees, and progressing through an intermediate form, circular where free, but with flat partition walls where two or more cells touch one another, it is quite possible to suppose that Natural Selection has effected the whole improvement, those insects which accomplished any advance towards more scientific workmanship, and thus made materials go further, having been able to secure a livelihood better than their competitors.

Such in brief outline is the Darwinian system, which undertakes to account for all the alleged facts of Organic Evolution by means of the above factor, variously described as "Natural Selection," or the "Survival of the fittest in the Struggle for Existence." It should be remembered, though it is constantly forgotten, that it is this particular theory as to the working-cause of evolutionary transformations which is the essence of Darwinism. Mr. Darwin did not originate the idea of genetic transformism, which is almost necessarily suggested by the systematic development of life-forms to which Geology bears witness. Consequently, long before he came on the scene, the doctrine of transformation had been propounded, especially by Lamarck, and if it had met with no general acceptance, this was chiefly because no force was indicated which seemed to offer a satisfactory account of the mode in which the required changes could have been wrought. Such a force Mr. Darwin's "Natural Selection" was widely taken to furnish, and his theory was eagerly welcomed and adopted by those who only required such a basis on which to ground beliefs to which they were already predisposed, and Darwinism thus obtained that pre-eminent position which it still retains, at least in popular estimation.

Two special arguments may here be mentioned, which, although they really apply to all systems of Organic Evolution, have obtained a prescriptive right to be quoted particularly in favour of Darwinism, their bearing on which is easily seen.

The first is based on the frequent occurrence of "rudimentary," "fragmentary," or "vestigial" structures in animals and plants, which, although now seemingly useless, or even harmful, to their possessors, may be assumed to have been of service to their ancestors, but under changed conditions to have been thrown out of work by Natural Selection, and atrophied by disuse. Such are – the splint-bones of the horse, representing lost digits, – the rudimentary legs of some whales and serpents, – the mammae and mammary glands of male mammals; and in the vegetable kingdom, – the aborted pistil in male florets of some compositae, – the useless corolla of certain wind-fertilized flowers, as plantago, and indeed the whole floral apparatus of plants which, like Wordsworth's pet the Lesser Celandine,¹⁸⁷ seldom ripen their seeds, but depend on other methods of propagation. The other fact cited on behalf of Darwinism is unquestionably very striking. In the course of their embryonic development, and even in the initial stages of their life after birth, higher animals pass through various phases in which they exhibit the characteristics of lower forms. Thus all life starts from a cell, in which there is nothing to shew whether it is ever to be anything more than a cell, or is to evolve a plant or animal, – nor, in this latter case, what sort of animal it is to be – a mollusc, for instance, a frog, or a mammal. At a later stage¹⁸⁸ it is impossible to distinguish the embryos of lizards, birds, and mammals except by size. Even the human fetus at an early period bears vestiges of gill-clefts or arches, pointing to an aquatic existence. When the extremities come to be developed,¹⁸⁹ "The feet of lizards and mammals, the wings and feet of birds, no less than the hands and feet of man, all arise from the same fundamental form." The young of flat-fish such as soles and turbots, when they leave the egg are not flat, but shaped like ordinary fish, and they wear their eyes in the normal fashion, one on each side of their head, not both on the same side like their parents – whose form however they presently by degrees assume. Young lions and black birds are spotted, showing their affinity respectively to panthers and thrushes – and so on in numberless instances. All such features, it is assumed, indicate the phylogeny of each animal, or the history of the race to which it belongs. As Professor Milnes Marshall succinctly put the matter:¹⁹⁰

The phases through which an animal passes in its progress from the egg to the adult are no accidental freaks, no mere matters of developmental convenience, but represent more or less closely … the successive ancestral stages through which the present condition has been acquired. Evolution tells us that each animal has had a pedigree in the past. Embryology reveals to us this ancestry, because every animal in its own development repeats this history, climbs up its own genealogical tree.

Such are not by any means the only instances in which the Darwinist can appeal to Nature for facts with which his theory well agrees, and which therefore so far furnish a persuasive argument in its favour; but these are perhaps the chief ones, and the best known, and may serve as representative of their class which it is impossible for us to examine in detail.

It now remains to enquire how far, from the point of view of Science, with which alone we are concerned, the Darwinian hypothesis can make good its claim to our acceptance. When we proceed accordingly to examine the grounds upon which it rests, it must be confessed that as we do so it becomes increasingly difficult to understand how such a theory has been able to obtain such wide acceptance, especially on the ground that scientific evidence is in its favour.

On the very threshold of any such enquiry lies a difficulty the gravity of which seems to be strangely overlooked. Darwinism by its own confession knows nothing of Origins, not even of the Origin of Species itself. There must be life already existing before Natural Selection has anything to select; there must be eyes and honey-cells of some kind, before they can be improved; there must be Species, before one can be transformed into another. Is it not evident, however, that the cause – of whatever kind it may be – which brought any of these into being, must have something, – not to say everything, – to do with the capacities and potentialities by which its future history is conditioned? But this supreme and vital factor Mr. Darwin entirely eliminates from his calculation. In his system, the initiating force has no more to do with the subsequent career of its productions, than has the gas which lifts a balloon with the direction in which it travels. It is not, on his theory, as the impulse which, besides raising from earth an arrow or rifle bullet, directs it to a goal, but, on the contrary, an organism once launched on its course is left to be driven hither and thither and twisted into this form and that, as clouds are by the wind. For the variations through which transformations are wrought, Darwin could find no better epithet than "fortuitous," and it is laid down by his staunchest disciples that if such variations be predetermined towards certain results, there is an end of Darwinism.

It is not easy to understand how any theory can be deemed satisfactory which thus ignores the initial force, of whose existence and potency we have far clearer evidence than of any other.

When we turn from its omissions to study Darwinism as it is, obviously, in the first place, still, more than forty years since it was given to the world, it remains only an hypothesis, based not upon observation or experiment but speculation. In no single instance, past or contemporary, is one species known to have originated from another. The fact upon which Mr. Darwin primarily relies is that of variation. Undoubtedly amongst both plants and animals the offspring are not mere slavish reproductions of their parents, as if cast in the same mould, but exhibit individual differences, working upon which in domesticated instances, man can by selection produce wonderful varieties, as has already been admitted. But, as M. de Quatrefages says,¹⁹¹ this tells us no more than that species admit of variation; it does not prove that they are capable of transformation, which is the whole point. Certainly, such transformation has never within our knowledge been effected. No breeder or fancier has succeeded, or can hope to succeed, in producing a new species. Moreover, as was pointed out by a critic whose ability Mr. Darwin himself candidly acknowledged,¹⁹² the range of variability as we find it in any species is strictly limited, and although at first it is easy, – in the case of some few animals or plants, – to make great changes in particular directions, by selective breeding, it becomes more and more difficult as we proceed to continue in the same line. If, for instance, in the case of pigeons, a bird can be produced in six years with head and beak only one-half the size of those whence the process started, are we to say that in twelve years their bulk will be reduced to a quarter, and in twenty-four to an eighth? No one could suppose anything so absurd. Mr. Darwin would answer, that he relies upon the vast periods of geologic time to produce alterations such as we cannot possibly attempt within the few years at our disposal. But, it is replied, no length of time will avail anything for such a purpose, unless there be some force to produce variations in the required direction, to the required extent. Such a force is not proved to exist – all the evidence is against it. Where art is most practised in improvement of breeds, or the obtaining of any peculiarities – as with the speed of racehorses, the size of toy-terriers, or the "points" of prize cattle, it becomes most strikingly apparent that we have reached a limit beyond which species will not vary. And until such a cause as we require is fully proved to exist, its supposed effects cannot be made the basis of scientific argument.

A given animal or plant, [says the Reviewer] appears to be contained, as it were, within a sphere of variation; one individual lies near one portion of the surface, another individual near another part of the surface; the average animal at the centre. Any individual may produce descendants varying in any direction, but is more likely to produce descendants varying towards the centre of the sphere, and the variations in that direction will be greater in amount than the variations towards the surface. Thus a set of racers of equal merit indiscriminately breeding will produce more colts and foals of inferior than of superior breed, and the falling off of the degenerate will be greater than the improvement of the select (p. 282).

Similarly M. Blanchard declares:¹⁹³

All investigation and observation make it clear that, while the variability of creatures in a state of nature displays itself in very different degrees, yet in its most astonishing manifestations it remains confined within a circle beyond which it cannot pass.

And the facts of nature, as we know them, far from favouring the instability of species, exhibit a tenacity of form compelling us to treat them as practically immutable. Thus, as Mr. Carruthers points out,¹⁹⁴ in the notoriously variable genus Salix, or willow-tribe, which seems to be actively advancing towards a multiplication of its subdivisions, sub-genera, species, varieties, and hybrid forms, – one species is found, S. polaris, dating from before the Glacial Epoch, which has been driven from England and other lands, by climatic changes, to within the Arctic circle of both Hemispheres, – yet amid this stress of circumstances has preserved its specific identity, down even to the casual variations, which might be supposed to furnish the starting-points for new developments. Yet in this tribe, if anywhere, evidence of specific evolution might be looked for.¹⁹⁵

Other instances seem to show that even under new and trying conditions those creatures survive best which keep closest to the central family type, not those which diverge in any direction. Thus, of European sparrows introduced in America, Mr. Bumpus writes:¹⁹⁶

Natural Selection is most destructive of those birds which have departed most from the ideal type, and its activity raises the general standard by favouring those birds which approach the structural ideal.

Variation supplies the raw material upon which Natural Selection is supposed to work. When we turn to examine the process by which its results should be produced, we find, quite apart from the above difficulties, a crop of others still more formidable.

It must be remembered, that the variations on which Natural Selection must work are in each instance extremely minute, well-nigh infinitesimal. Mr. Darwin was as strongly opposed to the idea of Nature making sudden bounds, as to that of a predetermined course of development. But, he argued, an extra chance of living, however slight, must necessarily tell in the long run, the theory of probabilities giving results as certain as any others in mathematics, and, according to these, we may confidently say that, given sufficient time, the favoured individuals would infallibly distance their competitors.

The impressiveness of such an argument depends upon its seemingly mathematical character, which is however wholly fallacious, for the probabilities are all the other way. It is perfectly true that a beneficial variation however slight will confer on its happy possessor a corresponding advantage in the struggle for life, as compared with each individual of the non-favoured herd, but, as to that herd collectively, the chances would, on the contrary, ensure that some of its members should outlive the favoured one. Let us even imagine the advantage of the latter to be very great, great enough to double his chances, so that the odds on his surviving each of his fellows will be two to one. Yet if there be a dozen of them to contend with, the odds will be six to one against his surviving the lot. And what of the actual case of minutest benefits conferred by variation? In order to give them even an equal chance of survival, the numbers of those possessing such advantages must be large in proportion as the advantages themselves are small. Thus, if a variation increases the chance of life by one-thousandth part, so that the odds on its possessor are 1001, against 1000 on each non-possessor, yet unless the number of possessors be to that of non-possessors as 1,000 to 1,001, their collective chances will not even be equal. As it is quite absurd to suppose that casual variations could ever occur in such wholesale fashion, how can it be supposed that, were Natural Selection the only factor operating, minute advantages could be accumulated by variation even in the simplest cases?

But it is also hard to suppose that in any actual case is the matter so simple as it appears to our limited comprehension. To take for instance the above example of the giraffe. It is very well to have a neck that will reach high-branches of a tree, – but this is not everything. For the mere prolongation of life, much else is required, fleet limbs to distance lions, and keen senses, sight, hearing, and smell, to give warning of the approach of human or other hunters, to say nothing of the extra strengthening of muscles and bones which increased size and weight demands. Unless, however, improvements in all these respects happened casually to concur in the same individual, which could scarcely happen, it is clear that each would militate against the others, for the survival of an individual beneficially developed in one respect, would tend to the extinction of other beneficial developments, possessed by individuals whom he overcame in the struggle for life.

Even the case of the insular insects is by no means so plain as might at first sight appear. There can be no doubt that wings are of some advantage, or on no system could they be supposed to exist. Nor do their advantages cease because disadvantages outweigh them. If some insects are blown out to sea when flying, others will doubtless perish in one way or another because they cannot fly. It may even be that those which can fly best will survive, as being able to make head against a breeze which overpowers others. Natural Selection will thus have many arrows in its quiver, some of which must reach the wrong objects.

Still more clearly does this appear in the case of complex structures in which, if they were produced as Mr. Darwin supposes, variation must have hit simultaneously upon independent contrivances, without each of which all the others would be useless and confer no benefit at all. In the eye, for example, to mention but one or two of innumerable similar points, it would be of no avail to have a retina, even such as has been described, without a lens to throw an image upon it, set just at the proper distance, and provided with muscles to alter its shape according to the distance of the object. How can Natural Selection be even conceived to have set to work on such a task as this?

It is still more fundamental to observe that, according to Mr. Darwin's own showing, Natural Selection is purely negative in its action. "If it does select, it selects for death and not for life."¹⁹⁷ It can originate nothing, but only destroy. All that it does for favoured races is to spare them while it sweeps away others, and the sole benefit they derive from it is to have more ample resources upon which to draw. But as for anything they possess in the way of structure or character, they must derive it entirely from themselves – Natural Selection can no more confer it, than the labourer who weeds a garden bed makes the flowers that grow there. Let it be imagined that the first human beings on earth, any number of thousand years ago, planted a garden, and determined to produce a rose, by eliminating every plant that did not show some promise of progress rose-wards. Let the gardeners have been endowed with acumen sufficient to detect every symptom of such a tendency, and let their operations have been carried on without interruption to this day, – it is obvious that if roses had resulted, it could only be because among the plants they allowed to remain there existed a rose-making quality of some kind, to which, and not to anything done by human art or skill, the result was due. It would likewise have to be supposed that there were infinite other potentialities latent in the original plants, as of evolving thistles, shamrocks, or leeks – all equally awaiting their opportunity. Selective action could effectually put such competitors out of the way; but in the way of developing a race it could but leave it entirely to itself. Precisely similar is the part played by Natural Selection, except that it must needs play it immensely more slowly, – and if no one can fancy that human agency could by any possibility grow roses unless from some stock predetermined to grow into a rose and nothing else, what grounds have we that can be called scientific for attributing to a blind struggle for life an incomparably greater potency? Nor does it avail to quote the immense extent of time which may be supposed to have been available. No more than Natural Selection has time by itself any creative power. We know on the contrary by experience, that when things are not controlled by some principle of order, the lapse of time serves only to make confusion worse confounded.

Another consideration of prime importance is too frequently ignored. On Darwinian principles, each step in any development can be made, not because it leads to an advantageous result in the future, but only because it is itself advantageous. At each stage favoured individuals survive others because they are favoured here and now, not because, when the development they promote shall be completed, their remote descendants will be favoured. Hence it must, for instance, be possible to suppose, that all the intermediate forms between two extremes, whereof one is supposed to have originated the other, were, each in its day, so beneficial as to preserve their possessors at the expense of non-possessors. But can this possibly be even imagined?