Kitabı oku: «Charles Darwin»
CHAPTER I
THE WORLD INTO WHICH DARWIN WAS BORN
Charles Darwin was a great man, and he accomplished a great work. The Newton of biology, he found the science of life a chaotic maze; he left it an orderly system, with a definite plan and a recognisable meaning. Great men are not accidents; great works are not accomplished in a single day. Both are the product of adequate causes. The great man springs from an ancestry competent to produce him; he is the final flower and ultimate outcome of converging hereditary forces, that culminate at last in the full production of his splendid and exceptional personality. The great work which it is his mission to perform in the world is never wholly of his own inception. It also is the last effect of antecedent conditions, the slow result of tendencies and ideas long working unseen or but little noticed beneath the surface of opinion, yet all gradually conspiring together towards the definitive revolution at whose head, in the fulness of time, the as yet unborn genius is destined to place himself. This is especially the case with those extraordinary waves of mental upheaval, one of which gave us the Italian renaissance, and another of which is actually in progress around us at the present day. They have their sources deep down in the past of human thought and human feeling, and they are themselves but the final manifestation of innumerable energies which have long been silently agitating the souls of nations in their profoundest depths.
Thus, every great man may be regarded as possessing two distinct lines of ancestry, physical and spiritual, each of which separately demands elucidation. He owes much in one way to his father and his mother, his grandfathers and his grandmothers, and his remoter progenitors, from some or all of whom he derives, in varying degrees and combinations, the personal qualities whose special interaction constitutes his greatness and his idiosyncrasy; he owes much in another way to his intellectual and moral ancestors, the thinkers and workers who have preceded him in his own department of thought or action, and have made possible in the course of ages the final development of his special revolution or his particular system. Viewed as an individual, he is what he is, with all his powers and faculties and potentialities, in virtue of the brain, the frame, the temperament, the energy he inherits directly from his actual ancestors, paternal and maternal; viewed as a factor or element in a great movement, he is what he is because the movement had succeeded in reaching such and such a point in its progress already without him, and waited only for such and such a grand and commanding personality in order to carry it yet a step further on its course of development.
No man who ever lived would more cordially have recognised these two alternative aspects of the great worker's predetermining causes than Charles Darwin. He knew well that the individual is the direct cumulative product of his physical predecessors, and that he works and is worked upon in innumerable ways by the particular environment into whose midst he is born. Let us see, then, in his own case what were these two main sets of conditioning circumstances which finally led up to the joint production of Charles Darwin, the man and the philosopher, the thinking brain and the moving energy. In other words, what was the state of the science of life at the time when he first began to observe and to speculate; and what was the ancestry which made him be born a person capable of helping it forward at a single bound over its great restricting dogmatic barrier of the fixity of species?
Let us begin, in the first place, by clearing the path beforehand of a popular misconception, so extremely general and almost universal that, unless it be got rid of at the very outset of our sketch, much of the real scope and purport of Darwin's life and work must, of necessity, remain entirely misunderstood by the vast mass of English readers. In the public mind Darwin is, perhaps, most commonly regarded as the discoverer and founder of the evolution hypothesis. Two ideas are usually associated with his name and memory. It is believed that he was the first propounder of the theory which supposes all plant and animal forms to be the result, not of special creation, but of slow modification in pre-existent organisms. It is further and more particularly believed that he was the first propounder of the theory which supposes the descent of man to be traceable from a remote and more or less monkey-like ancestor. Now, as a matter of fact, Darwin was not the prime originator of either of these two great cardinal ideas. Though he held both as part of his organised theory of things, he was not by any means the first or the earliest thinker to hold them or to propound them publicly. Though he gained for them both a far wider and more general acceptance than they had ever before popularly received, he laid no sort of claim himself to originality or proprietorship in either theory. The grand idea which he did really originate was not the idea of 'descent with modification,' but the idea of 'natural selection,' by which agency, as he was the first to prove, definite kinds of plants and animals have been slowly evolved from simpler forms, with definite adaptations to the special circumstances by which they are surrounded. In a word, it was the peculiar glory of Charles Darwin, not to have suggested that all the variety of animal and vegetable life might have been produced by slow modifications in one or more original types, but to have shown the nature of the machinery by which such a result could be actually attained in the practical working out of natural causes. He did not invent the development theory, but he made it believable and comprehensible. He was not, as most people falsely imagine, the Moses of evolutionism, the prime mover in the biological revolution; he was the Joshua who led the world of thinkers and workers into full fruition of that promised land which earlier investigators had but dimly descried from the Pisgah-top of conjectural speculation.
How far Darwin's special idea of natural selection supplemented and rendered credible the earlier idea of descent with modification we shall see more fully when we come to treat of the inception and growth of his great epoch-making work, 'The Origin of Species;' for the present, it must suffice to point out that in the world into which he was born, the theory of evolution already existed in a more or less shadowy and undeveloped shape. And since it was his task in life to raise this theory from the rank of a mere plausible and happy guess to the rank of a highly elaborate and almost universally accepted biological system, we may pause awhile to consider on the threshold what was the actual state of natural science at the moment when the great directing and organising intelligence of Charles Darwin first appeared.
From time immemorial, in modern Christendom at least, it had been the general opinion of learned and simple alike that every species of plant or animal owed its present form and its original existence to a distinct act of special creation. This naïf belief, unsupported as it was by any sort of internal evidence, was supposed to rest directly upon the express authority of a few obscure statements in the Book of Genesis. The Creator, it was held, had in the beginning formed each kind after a particular pattern, had endowed it with special organs devised with supreme wisdom for subserving special functions, and had bestowed upon it the mystical power of reproducing its like in its own image to all generations. No variation of importance ever occurred within the types thus constituted; all plants and animals always retained their special forms unaltered in any way from era to era. This is the doctrine of the fixity and immutability of species, almost universal in the civilised world up to the end of the last century.
Improbable as such a crude idea now seems to any person even moderately acquainted with the extraordinary variety and variability of living forms, it nevertheless contained nothing at all likely to contradict the ordinary experience of the everyday observer in the last century. The handful of plants and animals with which he was personally acquainted consisted for the most part of a few large, highly advanced, and well-marked forms, not in the least liable to be mistaken for one another even by the most hasty and casual spectator. A horse can immediately be discriminated by the naked eye from a donkey, and a cow from a sheep, without risk of error; nobody is likely to confuse wheat with barley, or to hesitate between classing any given fruit that is laid before him as a pear or an apple, a plum or a nectarine. Variability seldom comes under the notice of the ordinary passing spectator as it does under that of the prying and curious scientific observer; and when it comes at all, as in the case of dogs and pigeons, roses and hyacinths, it is no doubt set down carelessly on a superficial view as a mere result of human selection or of deliberate mongrel interbreeding. To the eye of the average man, all the living objects ordinarily perceived in external nature fall at once under certain fixed and recognisable kinds, as dogs and horses, elms and ashes, whose limits he is never at all inclined to confound in any way one with the other.
Linnæus, the great father of modern scientific biology, had frankly and perhaps unthinkingly accepted this current and almost universal dogma of the fixity and immutability of species. Indeed, by defining a kind as a group of plants or animals so closely resembling one another as to give rise to the belief that they might all be descended from a single ancestor or pair of ancestors, he implicitly gave the new sanction of his weighty authority to the creation hypothesis, and to the prevalent doctrine of the unchangeability of organic forms. To Linnæus, the species into which he mapped out all the plants and animals then known, appeared as the descendants each of a solitary progenitor or of a primitive couple, called into existence at the beginning of all things by the direct fiat of a designing Creator. He saw the world of organic life as composed of so many well-demarcated types, each separate, distinct, and immutable, each capable of producing its like ad infinitum, and each unable to vary from its central standard in any of its individuals, except perhaps within very narrow and unimportant limits.
But towards the close of the eighteenth century, side by side with the general awakening of the human intellect and the arrival of a new era of free social investigation, which culminated in a fresh order of things, there was developed a more critical and sceptical attitude in the world of science, which soon produced a notable change of front among thinking naturalists as to the origin and meaning of specific distinctions.
Buffon was the first great biological innovator who ventured, in very doubtful and tentative language, to suggest the possibility of the rise of species from one another by slow modification of ancestral forms. Essentially a popular essayist, writing in the volcanic priest-suppressed France of the ancien régime, during the inconsistent days of Louis XV. and Louis XVI., when it was uncertain whether novel and heterodox opinions would bring down upon their author fame and reputation or the Sorbonne and the Bastille, Buffon was careful to put his conjectural conclusions in a studiously guarded and often even ironical form. But time after time, in his great discursive work, the 'Histoire Naturelle' (published in successive volumes between 1749 and 1788), he recurs anew to the pregnant suggestion that plants and animals may not be bound by fixed and immovable limits of species, but may freely vary in every direction from a common centre, so that one kind may gradually and slowly be evolved by natural causes from the type of another. He points out that, underlying all external diversities of character and shape, fundamental likenesses of type occur in many animals, which irresistibly suggest the novel notion of common descent from a single ancestor. Thus regarded, he says, not only the ass and the horse (to take a particular passage) but even man himself, the monkeys, the quadrupeds, and all vertebrate animals, might be viewed as merely forming divergent branches of one and the same great family tree. Every such family, he believed, whether animal or vegetable, might have sprung originally from a single stock, which after many generations had here developed into a higher form, and there degenerated into a lower and less perfect type of organisation. Granting this – granting that nature could by slow variation produce one species in the course of direct descent from another unlike it (for example, the ass from the horse), then, Buffon observed, there was no further limit to be set to her powers in this respect, and we might reasonably conclude that from a single primordial being she has gradually been able in the course of time to develop the whole continuous gamut of existing animal and vegetable life. To be sure, Buffon always saves himself from censure by an obvious afterthought – 'But no; it is certain from revelation that every species was directly created by a separate fiat.' This half-hearted and somewhat subrisive denial, however, must be taken merely as a concession to the Sorbonne and to the fashionable exegesis of his own day; and, even so, the Sorbonne was too much in the end for the philosophic thinker. He had once in his life at least to make his submission and demand pardon from the offended orthodoxy of the Paris faculty.
The wave of thought and feeling, thus apologetically and tentatively stirred on the unruffled pond of eighteenth century opinion by the startling plop of Buffon's little smooth-cut pebble, soon widened out on every side in concentric circles, and affected with its wash the entire world of biological science in every country. Before the close of the eighteenth century speculation as to the origin of species was rife in all quarters of Europe. In France itself, Geoffroy St. Hilaire, constitutionally cautious and undecided, but wide of view and free from prejudice, came slowly to the conclusion, in 1795, that all species are really derived by modification from one or more primitive types. In Germany, in the very same year, Goethe, with the keen vision of the poet and the calm eye of the philosopher uniquely combined, discerned independently as by a lightning flash the identical idea of the origin of kinds by modification of pre-existent organisms. 'We may assert without hesitation,' says that great nebulous thinker and observer, 'that all the more perfect organic natures, such as fishes, amphibians, birds and mammals, with man at their head, were formed at first on one original type, which still daily changes and modifies its form by propagation.' In England, twelve months earlier, Dr. Erasmus Darwin, Charles Darwin's grandfather (of whom more anon), published his 'Zoonomia,' a treatise on the laws of animal life, in which he not only adopted Buffon's theory of the origin of species by evolution, but also laid down as the chief cause of such development the actions and needs of the animals themselves. According to Dr. Erasmus Darwin, animals came to vary from one another chiefly because they were always altering their habits and voluntarily accommodating themselves to new actions and positions in life. His work produced comparatively little effect upon the world at large in his own time, but it had immense influence upon the next great prophet of evolution, Lamarck, and through Lamarck on Lyell, Charles Darwin, Herbert Spencer, and the modern school of evolutionists generally. We shall consider his views in greater detail when we pass from the spiritual to the physical antecedents of Charles Darwin.
It was in 1801 that Lamarck first gave to the world his epoch-making speculations and suggestions on the origin of species; and from that date to the day of his death, in 1831, the unwearied old philosopher continued to devote his whole time and energy, in blindness and poverty, to the elucidation of this interesting and important subject. A bold, acute, and vigorous thinker, trained in the great school of Diderot and D'Alembert, with something of the vivid Celtic poetic imagination, and a fearless habit of forming his own conclusions irrespective of common or preconceived ideas, Lamarck went to the very root of the matter in the most determined fashion, and openly proclaimed in the face of frowning officialism under the Napoleonic reaction his profound conviction that all species, including man, were descended by modification from one or more primordial forms. In Charles Darwin's own words, 'He first did the eminent service of arousing attention to the probability of all change, in the organic as well as in the inorganic world, being the result of law and not of miraculous interposition. Lamarck seems to have been chiefly led to his conclusion on the gradual change of species by the difficulty of distinguishing species and varieties, by the almost perfect gradation of forms in certain groups, and by the analogy of domestic productions. With respect to the means of modification, he attributed something to the direct action of the physical conditions of life, something to the crossing of already existing forms, and much to use and disuse, that is, to the effects of habit. To this latter agency he seems to attribute all the beautiful adaptations in nature – such as the long neck of the giraffe for browsing on the branches of trees,' He believed, in short, that animals had largely developed themselves, by functional effort followed by increased powers and abilities.
Lamarck's great work, the 'Philosophie Zoologique,' though opposed by the austere and formal genius of the immortal Cuvier – a reactionary biological conservative and obscurantist, equal to the enormous task of mapping out piecemeal with infinite skill and power the separate provinces of his chosen science, but incapable of taking in all the bearings of the whole field at a single vivid and comprehensive sweep – Lamarck's great work produced a deep and lasting impression upon the entire subsequent course of evolutionary thought in scientific Europe. True, owing to the retrograde tendencies of the First Empire, it caused but little immediate stir at the precise moment of its first publication; but the seed it sowed sank deep, and, lying fallow long in men's minds, bore fruit at last in the next generation with the marvellous fecundity of the germs of genius. Indeed, from the very beginning of the present century, a ferment of inquiry on the subject of creation and evolution was everywhere obvious among speculative thinkers. The profound interest which Goethe took in the dispute on this very subject in the French Académie des Sciences between Cuvier and Geoffroy St. Hilaire, amid the thundering guns of a threatened European convulsion, was but a solitary symptom of the general stir which preceded the gestation and birth of the Darwinian hypothesis. It is impossible to take up any scientific memoirs or treatises of the first half of our own century without seeing at a glance how every mind of high original scientific importance was permeated and disturbed by the fundamental questions aroused, but not fully answered, by Buffon, Lamarck, and Erasmus Darwin. In Lyell's letters and in Agassiz's lectures, in the 'Botanic Journal' and the 'Philosophical Transactions,' in treatises on Madeira beetles and the Australian flora, we find everywhere the thoughts of men profoundly influenced in a thousand directions by this universal evolutionary solvent and leaven.
And while the world of thought was thus seething and moving restlessly before the wave of ideas set in motion by these various independent philosophers, another group of causes in another field was rendering smooth the path beforehand for the future champion of the amended evolutionism. Geology on the one hand and astronomy on the other were making men's minds gradually familiar with the conception of slow natural development, as opposed to immediate and miraculous creation.
The rise of geology had been rapid and brilliant. In the last century it had been almost universally believed that fossil organisms were the relics of submerged and destroyed worlds, strange remnants of successive terrible mundane catastrophes. Cuvier himself, who had rendered immense services to geological science by his almost unerring reconstructions of extinct animals, remained a partisan of the old theory of constant cataclysms and fresh creations throughout his whole life; but Lamarck, here as elsewhere the prophet of the modern uniformitarian concept of nature, had already announced his grand idea that the ordinary process of natural laws sufficed to account for all the phenomena of the earth's crust. In England, William Smith, the ingenious land surveyor, riding up and down on his daily task over the face of the country, became convinced by his observations in the first years of the present century that a fixed order of sequence could everywhere be traced among the various superincumbent geological strata. Modern scientific geology takes its rise from the moment of this luminous and luminiferous discovery. With astonishing rapidity the sequence of strata was everywhere noted, and the succession of characteristic fossils mapped out, with the result of showing, however imperfectly at first, that the history of organic life upon the globe had followed a slow and regular course of constant development. Immediately whole schools of eager workers employed themselves in investigating in separate detail the phenomena of these successive stages of unfolding life. Murchison, fresh from the Peninsular campaign, began to study the dawn of organic history in the gloom of the Silurian and Cambrian epochs. A group of less articulate but not less active workers like Buckland and Mantell performed similar services for the carboniferous, the wealden, and the tertiary deposits. Sedgwick endeavoured to co-ordinate the whole range of then known facts into a single wide and comprehensive survey. De La Beche, Phillips, and Agassiz added their share to the great work of reconstruction. Last of all, among those who were contemporary and all but coeval with Charles Darwin himself, Lyell boldly fought out the battle of 'uniformitarianism,' proving, with all the accumulated weight of his encyclopædic and world-wide knowledge, that every known feature of geological development could be traced to the agency of causes now in action, and illustrated by means of slow secular changes still actually taking place on earth before our very eyes.
The influence of these novel conceptions upon the growth and spread of evolutionary ideas was far-reaching and twofold. In the first place, the discovery of a definite succession of nearly related organic forms, following one another with evident closeness through the various ages, inevitably suggested to every inquiring observer the possibility of their direct descent one from the other. In the second place, the discovery that geological formations were not really separated each from its predecessor by violent revolutions, but were the result of gradual and ordinary changes, discredited the old idea of frequent fresh creations after each catastrophe, and familiarised the minds of men of science with the alternative notion of slow and natural evolutionary processes. The past was seen to be in effect the parent of the present; the present was recognised as the child of the past.
Current astronomical theories also pointed inevitably in the same direction. Kant, whose supereminent fame as a philosopher has almost overshadowed his just claims as a profound thinker in physical science, had already in the third quarter of the eighteenth century arrived at his sublime nebular hypothesis, in which he suggested the possible development of stars, suns, planets, and satellites by the slow contraction of very diffuse and incandescent haze-clouds. This magnificent cosmical conception was seized and adapted by the genius of Laplace in his celestial system, and made familiar through his great work to thinking minds throughout the whole of Europe. In England it was further modified and remodelled by Sir William Herschel, whose period of active investigation coincided in part with Charles Darwin's early boyhood. The bearings of the nebular hypothesis upon the rise of Darwinian evolutionism are by no means remote: the entire modern scientific movement forms, in fact, a single great organic whole, of which the special doctrine of biological development is but a small separate integral part. All the theories and doctrines which go to make it up display the one common trait that they reject the idea of direct creative interposition from without, and attribute the entire existing order of nature to the regular unfolding of one undeviating continuous law.
Yet another factor in the intellectual stir and bustle of the time must needs be mentioned even in so short and cursory a sketch as this of the causes which led to the Darwinian crisis. In 1798, Thomas Malthus, a clergyman of the Church of England, published the first edition of his famous and much-debated 'Essay on the Principle of Population.' Malthus was the first person who ever called public attention to the tendency of population to increase up to the utmost limit of subsistence, as well as to the necessary influence of starvation in checking its further development beyond that point. Though his essay dealt only with the question of reproduction in human societies, it was clear that it possessed innumerable analogies in every domain of animal and vegetable life. The book ran through many successive editions with extraordinary rapidity for a work of its class, it was fiercely attacked and bravely defended, it caused an immense amount of discussion and debate, and besides its marvellous direct influence as a germinal power upon the whole subsequent course of politico-economical and sociological thought, it produced also a remarkable indirect influence on the side current of biological and speculative opinion. In particular, as we shall more fully see hereafter, it had an immediate effect in suggesting to the mind of the great naturalist who forms our present subject the embryo idea of 'natural selection.'
Such then was the intellectual and social world into which, early in the present century, Charles Darwin found himself born. Everywhere around him in his childhood and youth these great but formless evolutionary ideas were brewing and fermenting. The scientific society of his elders and of the contemporaries among whom he grew up was permeated with the leaven of Laplace and of Lamarck, of Hutton and of Herschel. Inquiry was especially everywhere rife as to the origin and nature of specific distinctions among plants and animals. Those who believed in the doctrine of Buffon and of the 'Zoonomia' and those who disbelieved in it, alike, were profoundly interested and agitated in soul by the far-reaching implications of that fundamental problem. On every side evolutionism, in its crude form, was already in the air. Long before Charles Darwin himself published his conclusive 'Origin of Species,' every thinking mind in the world of science, elder and younger, was deeply engaged upon the self-same problem. Lyell and Horner in alternate fits were doubting and debating. Herbert Spencer had already frankly accepted the new idea with the profound conviction of a priori reasoning. Agassiz was hesitating and raising difficulties. Treviranus was ardently proclaiming his unflinching adhesion. Oken was spinning in metaphysical Germany his fanciful parodies of the Lamarckian hypothesis. Among the depths of Brazilian forests Bates was reading the story of evolution on the gauze-like wings of tropical butterflies. Under the scanty shade of Malayan palm-trees Wallace was independently spelling out in rude outline the very theory of survival of the fittest, which Charles Darwin himself was simultaneously perfecting and polishing among the memoirs and pamphlets of his English study. Wollaston in Madeira was pointing out the strange adaptations of the curious local snails and beetles. Von Buch in the Canaries was coming to the conclusion that varieties may be slowly changed into permanent species. Lecoq and Von Baer were gradually arriving, one by the botanical route, the other by the embryological, at the same opinion. Before Charles Darwin was twenty, Dean Herbert had declared from the profound depth of his horticultural knowledge that kinds were only mere fixed sports; and Patrick Matthew, in the appendix to a work on 'Naval Timber,' had casually developed, without perceiving its importance, the actual distinctive Darwinian doctrine of natural selection. Robert Chambers published in 1844 his 'Vestiges of Creation,' in which Lamarck's theory was impressed and popularised under a somewhat spoilt and mistaken form: it was not till 1859 that the first edition of the 'Origin of Species' burst like a thunderbolt upon the astonished world of unprepared and unscientific thinkers.
This general attitude of interest and inquiry is of deep importance to the proper comprehension of Charles Darwin's life and work, and that for two distinct reasons. In the first place, the universal stir and deep prying into evolutionary questions which everywhere existed among scientific men in his early days was naturally communicated to a lad born of a scientific family, and inheriting directly in blood and bone the biological tastes and tendencies of Erasmus Darwin. In the second place, the existence of such a deep and wide-spread curiosity as to ultimate origins, and the common prevalence of profound uniformitarian and evolutionary views among philosophers and thinkers, made the acceptance of Charles Darwin's particular theory, when it at last arrived, a comparatively easy and certain matter, because by it the course of organic development was assimilated, on credible grounds, to the course of all other development in general, as then already widely recognised. The first consideration helps us to account in part for the man himself; the second consideration helps us even more to account for the great work which he was enabled in the end so successfully to accomplish.
