Kitabı oku: «Charles Darwin», sayfa 4

CHAPTER V
THE PERIOD OF INCUBATION

When Charles Darwin landed in England on his return from the voyage of the 'Beagle' he was nearly twenty-eight. When he published the first edition of the 'Origin of Species' he was over fifty. The intermediate years, though much occupied by many minor works of deep specialist scientific importance, were still mainly devoted to collecting material for the one crowning effort of his life, the chief monument of his great co-ordinating and commanding intellect – the settlement of the question of organic evolution.

'There is one thing,' says Professor Fiske, 'which a man of original scientific or philosophical genius in a rightly ordered world should never be called upon to do. He should never be called upon to earn a living; for that is a wretched waste of energy, in which the highest intellectual power is sure to suffer serious detriment, and runs the risk of being frittered away into hopeless ruin.' From this unhappy necessity Charles Darwin, like his predecessor Lyell, was luckily free. He settled down early in a home of his own, and worked away at his own occupations, with no sordid need for earning the day's bread, but with perfect leisure to carry out the great destiny for which the chances of the universe had singled him out. His subsequent history is the history of his wonderful and unique contributions to natural science.

The first thing to be done, of course, was the arrangement and classification of the natural history spoils gathered during the cruise, and the preparation of his own journal of the voyage for publication. The strict scientific results of the trip were described in the 'Zoology of the Voyage of the "Beagle,"' the different parts of which were undertaken by rising men of science of the highest distinction, under Charles Darwin's own editorship. Sir Richard Owen took in hand the fossil mammals; Waterhouse arranged their living allies; Gould discussed the birds, Jenyns the fish, and Bell the amphibians and reptiles. In this vast co-operative publication Darwin thus obtained the assistance of many among the most competent specialists in the England of his day, and learned to understand his own collections by the light thrown upon them from the focussed lamps of the most minute technical learning. As for the journal, it was originally published with the general account of the cruise by Captain Fitzroy in 1839, but was afterwards set forth in a separate form under the title of 'A Naturalist's Voyage Round the World.'

But while Darwin was thus engaged in arranging and classifying the animals and plants he had brought home with him, the germs of those inquiring ideas about the origin of species which we have already observed in his account of the voyage were quickening into fresh life within him. As he ruminated at his leisure over the results of his accumulations, he was beginning to work upon the great problem with the definite and conscious resolution of solving it. 'On my return home, it occurred to me,' he says, 'in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work, I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions that then seemed to me probable; from that period to the present day [1859] I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision.'

So Darwin wrote at fifty. The words are weighty and well worthy of consideration. They give us in a nutshell the true secret of Darwin's success in compelling the attention and assent of his contemporaries to his completed theory. For speculations and hypotheses like those of Lamarck and Erasmus Darwin, however brilliant and luminous they may be, the hard, dry, scientific mind cares as a rule less than nothing. Men of genius and insight like Goethe and Oken may, indeed, seize greedily upon the pregnant suggestion; their intellects are already attuned by nature to its due reception and assimilation; but the mere butterfly-catchers and plant-hunters of the world, with whom after all rests ultimately the practical acceptance or rejection of such a theory, can only be convinced by long and patient accumulations of facts, by infinite instances and endless examples, by exhaustive surveys of the whole field of nature in a thousand petty details piecemeal. They have to be driven by repeated beating into the right path. Everywhere they fancy they see the loophole of an objection, which must be carefully closed beforehand against them with anticipatory argument, as we close hedges by the wayside against the obtrusive donkey with a cautious bunch of thorny brambles. Even if Charles Darwin had hit upon the fundamental idea of natural selection, and had published it, as Wallace did, in the form of a mere splendid aperçu, he would never have revolutionised the world of biology. When the great discovery was actually promulgated, it was easy enough to win the assent of philosophical thinkers like Herbert Spencer; easy enough, even, to gain the ready adhesion of non-biological but kindred minds, like Leslie Stephen's and John Morley's; those might all, perhaps, have been readily convinced by far less heavy and crushing artillery than that so triumphantly marshalled together in the 'Origin of Species.' But in order to command the slow and grudging adhesion of the rank and file of scientific workers, the 'hodmen of science,' as Professor Huxley calls them, it was needful to bring together an imposing array of closely serried facts, to secure every post in the rear before taking a single step onward, and to bring to bear upon every antagonist the exact form of argument with which he was already thoroughly familiar. It was by carefully pursuing these safe and cautious philosophical tactics that Charles Darwin gained his great victory. Where others were pregnant, he was cogent. He met the Dryasdusts of science on their own ground, and he put them fairly to flight with their own weapons. More than that, he brought them all over in the long run as deserters into his own camp, and converted them from doubtful and suspicious foes into warm adherents of the evolutionary banner.

Moreover, fortunately for the world, Darwin's own mind was essentially one of the inductive type. If a great deductive thinker and speculator like Herbert Spencer had hit upon the self-same idea of survival of the fittest, he might have communicated it to a small following of receptive disciples, who would have understood it and accepted it, on a priori grounds alone, and gradually passed it on to the grades beneath them; but he would never have touched the slow and cautious elephantine intellect of the masses. The common run of mankind are not deductive; they require to have everything made quite clear to them by example and instance. The English intelligence in particular shows itself as a rule congenitally incapable of appreciating the superior logical certitude of the deductive method. Englishmen will not even believe that the square on the hypotenuse is equal to the squares on the containing sides until they have measured and weighed as well as they are able by rude experimental devices a few selected pieces of rudely shaped rectangular paper. It was a great gain, therefore, that the task of reconstructing the course of organic evolution should fall to the lot of a highly trained and masterly intelligence of the inductive order. Darwin had first to convince himself, and then he could proceed to convince the world. He set about the task with characteristic patience and thoroughness. No man that ever lived possessed in a more remarkable degree than he did the innate capacity for taking trouble. For five years, as a mere preliminary, he accumulated facts in immense variety, and then for the first time and in the vaguest possible way he – 'allowed himself to speculate.' That brings us down to the year 1842, when the first notes of the 'Origin of Species' must have been tentatively committed to paper. It was in 1859 that the first edition of the complete work was given to the world. Compare this with the case of Newton, who similarly kept his grand idea of gravitation for many years in embryo, until more exact measurements of the moon's mass and distance should enable him to verify it to his own satisfaction.

One other item of immense importance in the genesis of the full Darwinian doctrine deserves mention here – I mean, the exact moment of time occupied by Charles Darwin in the continuous history of scientific thought. A generation or two earlier, in Erasmus Darwin's days, biology had not yet arrived at the true classification of animals and plants upon an essentially hereditary basis. The Linnæan arrangement, then universally accepted, was wholly artificial in its main features; it distributed species without regard to their fundamental likenesses of structure and organisation. But the natural system of Jussieu and De Candolle, by arranging plants into truly related groups, made possible the proofs of an order of affiliation in the vegetable kingdom; while Cuvier's similar reconstruction of the animal world gave a like foothold to the evolutionary philosopher in the other great department of organic nature. The recognition of kinship between the various members of the same family necessarily preceded the establishment of a regular genealogical theory of life in its entirety.

Though we are here concerned mainly with Charles Darwin the thinker and writer – not with Charles Darwin the husband and father – a few words of explanation as to his private life must necessarily be added at the present point, before we pass on to consider the long, slow, and cautious brewing of that wonderful work, the 'Origin of Species,' Darwin returned home from the voyage of the 'Beagle' at the end of the year 1836. Soon after, he was elected a Fellow of the Royal Society, no doubt through the influence of his friend Lyell, who was quite enthusiastic over his splendid geological investigations on the rate of elevation in the Pampas and the Cordillera. Acting on Lyell's advice, too, he determined to seek no official appointment, but to devote himself entirely for the rest of his life to the pursuit of science. In 1838, at the age of twenty-nine, he read before the Geological Society his paper on the 'Connection of Volcanic Phenomena with the Elevation of Mountain Chains,' when, says Lyell admiringly in a private letter, 'he opened upon De la Beche, Phillips, and others' – the veterans of the science – 'his whole battery of the earthquakes and volcanoes of the Andes.' Shortly after, the audacious young man was appointed secretary to the Geological Society, a post which he filled when the voyage of the 'Beagle' was first published in 1839.

In the early part of that same year, the rising naturalist took to himself a wife from one of the houses to which he himself owed no small part of his conspicuous greatness. His choice fell upon his cousin, Miss Emma Wedgwood, daughter of Josiah Wedgwood, of Maer Hall; and, after three years of married life in London, he settled at last at Down House, near Orpington, in Kent, where for the rest of his days he passed his time among his conservatories and his pigeons, his garden and his fowls, with his children growing up quietly beside him, and the great thinking world of London within easy reach of a few minutes' journey. His private means enabled him to live the pleasant life of an English country gentleman, and devote himself unremittingly to the pursuit of science. Ill health, indeed, interfered sadly with his powers of work; but system and patience did wonders during his working days, which were regularly parcelled out between study and recreation, and utilised and economised in the very highest possible degree. Early to bed and early to rise, wandering unseen among the lanes and paths, or riding slowly on his favourite black cob, the great naturalist passed forty years happily and usefully at Down, where all the village knew and loved him. A man of singular simplicity and largeness of heart, Charles Darwin never really learnt to know his own greatness. And that charming innocence and ignorance of his real value made the value itself all the greater. His moral qualities, indeed, were no less admirable and unique in their way than his intellectual faculties. To that charming candour and delightful unostentatiousness which everybody must have noticed in his published writings, he united in private life a kindliness of disposition, a width of sympathy, and a ready generosity which made him as much beloved by his friends as he was admired and respected by all Europe. The very servants who came beneath his roof stopped there for the most part during their whole lifetime. In his earlier years at Down, the quiet Kentish home was constantly enlivened by the visits of men like Lyell, Huxley, Hooker, Lubbock, and Wollaston. During his later days, it was the Mecca of a world-wide scientific and philosophic pilgrimage, where all the greatest men our age has produced sought at times the rare honour of sitting before the face of the immortal master. But to the very last Darwin himself never seemed to discover that he was anything more than just an average man of science among his natural peers.

Shortly after Darwin went to Down he began one long and memorable experiment, which in itself casts a flood of light upon his patient and painstaking method of inquiry. Two years before, he had read at the Geological Society a paper on the 'Formation of Mould,' which more than thirty years later he expanded into his famous treatise on the 'Action of Earthworms.' His uncle and father-in-law, Josiah Wedgwood, suggested to him that the apparent sinking of stones on the surface might really be due to earthworm castings. So, as soon as he had some land of his own to experiment upon, he began, in 1842, to spread broken chalk over a field at Down, in which, twenty-nine years later, in 1871, a trench was dug to test the results. What other naturalist ever waited so long and so patiently to discover the upshot of a single experiment? Is it wonderful that a man who worked like that should succeed, not by faith but by logical power, in removing mountains?

Unfortunately, we do not know the exact date when Darwin first read Malthus. But that the perusal of that remarkable book formed a crisis and turning-point in his mental development we know from his own distinct statement in a letter to Haeckel, prefixed to the brilliant German evolutionist's 'History of Creation.' 'It seemed to me probable,' says Darwin, speaking of his own early development, 'that allied species were descended from a common ancestor. But during several years I could not conceive how each form could have been modified so as to become admirably adapted to its place in nature. I began therefore to study domesticated animals and cultivated plants, and after a time perceived that man's power of selecting and breeding from certain individuals was the most powerful of all means in the production of new races. Having attended to the habits of animals and their relations to the surrounding conditions, I was able to realise the severe struggle for existence to which all organisms are subjected; and my geological observations had allowed me to appreciate to a certain extent the duration of past geological periods. With my mind thus prepared I fortunately happened to read Malthus's "Essay on Population" and the idea of natural selection through the struggle for existence at once occurred to me. Of all the subordinate points in the theory, the last which I understood was the cause of the tendency in the descendants from a common progenitor to diverge in character.'

It is impossible, indeed, to overrate the importance of Malthus, viewed as a schoolmaster to bring men to Darwin, and to bring Darwin himself to the truth. Without the 'Essay on the Principle of Population' it is quite conceivable that we should never have had the 'Origin of Species' or the 'Descent of Man.'

At the same time, Darwin had not been idle in other departments of scientific work. Side by side with his collections for his final effort he had been busy on his valuable treatise upon Coral Reefs, in which he proved, mainly from his own observations on the Keeling archipelago, that atolls owe their origin to a subsidence of the supporting ocean-floor, the rate of upward growth of the reefs keeping pace on the whole with the gradual depression of the sea-bottom. 'No more admirable example of scientific method,' says Professor Geikie forty years later, 'was ever given to the world; and even if he had written nothing else, this treatise alone would have placed Darwin in the very front of investigators of nature.' But, from our present psychological and historical point of view, as a moment in the development of Darwin's influence, and therefore of the evolutionary impulse in general, it possesses a still greater and more profound importance, because the work in which the theory is unfolded forms a perfect masterpiece of thorough and comprehensive inductive method, and gained for its author a well-deserved reputation as a sound and sober scientific inquirer. The acquisition of such a reputation, afterwards increased by the publication of the monograph on the Family Cirripedia (in 1851), proved of immense use to Charles Darwin in the fierce battle which was to rage around the unconscious body of the 'Origin of Species.' To be 'sound' is everywhere of incalculable value; to have approved oneself to the slow and cautious intelligence of the Philistine classes is a mighty spear and shield for a strong man; but in England, and above all in scientific England, it is absolutely indispensable to the thinker who would accomplish any great revolution. Soundness is to the world of science what respectability is to the world of business – the sine qua non for successfully gaining even a hearing from established personages.

To read the book on Coral Reefs is indeed to take a lesson of the deepest value in applied inductive canons. Every fact is duly marshalled: every conclusion is drawn by the truest and most legitimate process from careful observation or crucial experiment. Bit by bit, Darwin shows most admirably that, through gradual submergence, fringing reefs are developed into barrier-reefs, and these again into atolls or lagoon islands; and incidentally he throws a vivid light on the slow secular movements upward or downward for ever taking place in the world's crust. But the value of the work as a geological record, great as it is, is as nothing compared with its value as a training exercise in inductive logic. Darwin was now learning by experience how to use his own immense powers.

Meanwhile, the environment too had been gradually moving. In 1832, the year after young Darwin set out upon his cruise, Lyell published the first edition of his 'Principles of Geology,' establishing once for all the uniformitarian concept of that branch of science. In 1836, the year when he returned, Rafinesque, in his 'New Flora of North America,' had accepted within certain cramping limits the idea that 'all species might once have been varieties, and that many varieties are gradually becoming species by assuming constant and peculiar characters.' Haldeman in Boston, and Grant at University College, London, were teaching from their professorial chairs the self-same novel and revolutionary doctrine. At last, in 1844, Robert Chambers published anonymously his famous and much-debated 'Vestiges of Creation,' which brought down the question of evolution versus creation from the senate of savants to the arena of the mere general public, and set up at once a universal fever of inquiry into the mysterious question of the origin of species. Chambers himself was a man rather of general knowledge and some native philosophical insight than of any marked scientific accuracy or depth. His work in its original form displayed comparatively little acquaintance with the vast groundwork of the question at issue – zoological, botanical, geological, and so forth – and in Charles Darwin's own opinion showed 'a great want of scientific caution.' But its graphic style, its vivid picturesqueness, and to the world at large the startling novelty of its brilliant and piquant suggestions, made it burst at once into an unwonted popularity for a work of so distinctly philosophical a character. In nine years it leaped rapidly through no less than ten successive editions, and remained until the publication of the 'Origin of Species' the chief authoritative exponent in England of the still struggling evolutionary principle.

The 'Vestiges of Creation' may be succinctly described as Lamarck and water, the watery element being due in part to the unnecessary obtrusion (more Scotico) of a metaphysical and theological principle into the physical universe. Chambers himself, in his latest edition (before the book was finally killed by the advent of Darwinism), thus briefly describes his main concepts: 'The several series of animated beings, from the simplest and oldest up to the highest and most recent, are, under the providence of God, the results, first, of an impulse which has been imparted to the forms of life, advancing them, in definite times, by generation, through grades of organisation, terminating in the highest dicotyledons and vertebrata, these grades being few in number, and generally marked by intervals of organic character, which we find to be a practical difficulty in ascertaining affinities; second, of another impulse connected with the vital forces, tending, in the course of generations, to modify organic structures in accordance with external circumstances, as food, the nature of the habitat, and the meteoric agencies.' Now it is clear at once that these two supposed 'impulses' are really quite miraculous in their essence. They do not help us at all to a distinct physical and realisable conception of any natural agency whereby species became differentiated one from the other. They lay the whole burden of species-making upon a single primordial supernatural impetus, imparted to the first living germ by the will of the Creator, and acting ever since continuously it is true, but none the less miraculously for all that. For many creations Chambers substitutes one single long creative nisus: where Darwin saw natural selection, his Scotch predecessor saw a deus ex machina, helping on the course of organic development by a constant but unseen interference from above. He supposed evolution to be predetermined by some intrinsic and externally implanted proclivity. In short, Chambers's theory is Lamarck's theologised, and spoilt in the process.

The book had nevertheless a most prodigious and perfectly unprecedented success. The secret of its authorship was keenly debated and jealously kept. The most ridiculous surmises as to its anonymous origin were everywhere afloat. Some attributed it to Thackeray, and some to Prince Albert, some to Lyell, some to Sir John Herschel, and some to Charles Darwin himself. Obscurantists thought it a wicked book; 'intellectual' people thought it an advanced book. As a matter of fact it was neither the one nor the other. It was just a pale and colourless transcript of the old familiar teleological Lamarckism. Yet it did good in its generation. The public at large were induced by its ephemeral vogue to interest themselves in a question to which they had never previously given even a passing thought, though more practised biologists of evolutionary tendencies were grieved at heart that evolution should first have been popularly presented to the English world under so unscientific, garbled, and mutilated a form. From the philosophic side, Herbert Spencer found 'this ascription of organic evolution to some aptitude naturally possessed by organisms or miraculously imposed upon them' to be 'one of those explanations which explain nothing – a shaping of ignorance into the semblance of knowledge. The cause assigned,' he says, 'is not a true cause – not a cause assimilable to known causes – not a cause that can be anywhere shown to produce analogous effects. It is a cause unrepresentable in thought: one of those illegitimate symbolic conceptions which cannot by any mental process be elaborated into a real conception.' From the scientific side, on the other hand, Darwin felt sadly the inaccuracy and want of profound technical knowledge everywhere displayed by the anonymous author. These things might naturally cause the enemy to blaspheme. No worse calamity, indeed, can happen to a great truth than for its defence to be intrusted to inefficient hands. Nevertheless, long after, in the 'Origin of Species,' the great naturalist wrote with generous appreciation of the 'Vestiges of Creation,' 'In my own opinion it has done excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views.'

Still Darwin gave no sign. A flaccid, cartilaginous, unphilosophic evolutionism had full possession of the field for the moment, and claimed, as it were, to be the genuine representative of the young and vigorous biological creed, while he himself was in truth the real heir to all the honours of the situation. He was in possession of the master-key which alone could unlock the bars that opposed the progress of evolution, and still he waited. He could afford to wait. He was diligently collecting, amassing, investigating; eagerly reading every new systematic work, every book of travels, every scientific journal, every record of sport, or exploration, or discovery, to extract from the dead mass of undigested fact whatever item of implicit value might swell the definite co-ordinated series of notes in his own commonplace books for the now distinctly contemplated 'Origin of Species.' His way was to make all sure behind him, to summon up all his facts in irresistible array, and never to set out upon a public progress until he was secure against all possible attacks of the ever-watchful and alert enemy in the rear. Few men would have had strength of mind enough to resist the temptation offered by the publication of the 'Vestiges of Creation,' and the extraordinary success attained by so flabby a presentation of the evolutionary case: Darwin resisted it, and he did wisely.

We may, however, take it for granted, I doubt not, that it was the appearance and success of Chambers's invertebrate book which induced Darwin, in 1844 (the year of its publication), to enlarge his short notes 'into a sketch of the conclusions which then seemed to him probable.' This sketch he showed to Dr. (now Sir Joseph) Hooker, no doubt as a precaution to ensure his own claim of priority against any future possible competitor. And having thus eased his mind for the moment, he continued to observe, to read, to devour 'Transactions,' to collate instances, with indefatigable persistence for fifteen years longer. If any man mentally measures out fifteen years of his own life, and bethinks him of how long a space it seems when thus deliberately pictured, he will be able to realise a little more definitely – but only a little – how profound was the patience, the self-denial, the single-mindedness of Darwin's intense search after the ultimate truths of natural science.

What was the sketch that he thus committed to paper in 1844, and submitted to the judgment of his friend Hooker? It was the germ of the theory of natural selection. According to that theory, organic development is due to the survival of the fittest among innumerable variations, good, bad, and indifferent, from one or more parent stocks. Darwin's reading of Malthus had suggested to him (apparently as early as the date of publication of the 'Naturalist's Journal') the idea that every species of plant and animal must always be producing a far greater number of seeds, eggs, germs, or young offspring than could possibly be needed for the maintenance of the average number of the species. Of these young, by far the greater number must always perish from generation to generation, for want of space, of food, of air, of raw material. The survivors in each brood must be those naturally best adapted for survival. The many would be eaten, starved, overrun, or crowded out; the few that survive would be those that possessed any special means of defence against aggressors, any special advantage for escaping starvation, any special protection against overrunning or overcrowding foes. Animals and plants, Darwin found on inquiry and investigation, tended to vary under diverse circumstances from the parent or parents that originally produced them. These variations were usually infinitesimal in amount, but sometimes more considerable or even striking. If any particular variation tended in any way to preserve the life of the creatures that exhibited it, beyond the average of their like competitors, that variation would in the long run survive, and the individuals that possessed it, being thus favoured in the struggle for existence, would replace the less adapted form from which they sprang. Darwinism is Malthusianism on the large scale: it is the application of the calculus of population to the wide facts of universal life.

In one sense, indeed, it may be said that, given Malthus on the one hand and the Lamarckian evolutionism on the other, some great man somewhere must sooner or later, almost of necessity, have combined the two, and hit out the doctrine of natural selection as we actually know it. Quite so; but then the point is just this: Darwin was the great man in question; he did the work which in the very essence of things some such great man was naturally and inevitably predestined to do. You can always easily manage to get on without any particular great man, provided, of course, you have ready to hand another equally able great man by whom to replace him in the scheme of existence. But how many ordinary naturalists possess the width of mind and universality of interest which would prompt them to read, mark, learn, and inwardly digest a politico-economical treatise of the calibre of Malthus? How many, having done so, have the keenness of vision to perceive the ensuing biological implications? How many, having seen them, have the skill and the patience to work up the infinite chaos of botanical and zoological detail into the far-reaching generalisations of the 'Origin of Species'? Merely to have caught at the grand idea is in itself no small achievement; others did so and deserve all honour for their insight; but to flesh it out with all the minute care and conclusive force of Darwin's masterpiece is a thousand times a greater and nobler monument of human endeavour.