To some among us still, as to Lyell before us, this new belief in the animal origin of man seems far less beautiful, n.o.ble, and inspiriting than the older faith in his special and separate divine creation. Such thinkers find it somehow more pleasant and comfortable to suppose that man has fallen than that man has risen; the doctrine of the universal degradation of humanity paradoxically appears to them more full of promise and aspiration for the times to come than the doctrine of its universal elevation. To Darwin himself, however, it seemed otherwise.
"Man," he says, "may be excused for feeling some pride at having risen, though not through his own exertions, to the very summit of the organic scale; and the fact of his having thus risen, instead of having been aboriginally placed there, may give him hope for a still higher destiny in the distant future." Surely this is the truer and manlier way of looking at the reversed and improved att.i.tude of man. Surely it is better to climb to the top than to have been placed there--and fallen--at the very outset. Surely it is a n.o.bler view of life that we may yet by our own strenuous exertions raise our race some places higher in the endless and limitless hierarchy of nature than that we are the miserable and hopelessly degenerate descendants of a ruined and degraded angelic progenitor. Surely it is well, while we boast with Glaucus that we indeed are far braver and better than our ancestors, to pray at the same time, in the words of Hector, that our sons may be yet braver and better than ourselves.
CHAPTER IX.
THE THEORY OF COURTSHIP.
In the same volumes with the "Descent of Man" Darwin included his admirable treatise on s.e.xual selection. This form of selection he had already dealt with briefly in the "Origin of Species;" but as in his opinion it was largely instrumental in producing the minor differences which separate one race of men from another, he found it necessary to enlarge and expand it in connection with his account of the rise and progress of the human species.
Among many animals, and especially in the higher cla.s.ses of animals, the males and females do not mate together casually; there is a certain amount of selection or of courtship. In some cases, as with deer and antelopes, the males fight with one another for the possession of the females. In other cases, as with the peac.o.c.k and the humming-birds, the males display their beauty and their skill before the eyes of the a.s.sembled females. In the first instance, the victor obtains the mates; in the second instance, the mates themselves select from the group the handsomest and most personally pleasing compet.i.tor. s.e.xual selection, of which these are special cases, depends on the advantage possessed by certain individuals over others of the same s.e.x and species solely in respect to the question of mating. In all such instances, the males have acquired their weapons of offence and defence or their ornamental decorations, not from being better fitted to survive in the struggle for existence, but from having gained an advantage over other males of the same kind, and from having transmitted this advantage to offspring of their own s.e.x alone.
Just as man can improve the breed of his game-c.o.c.ks by the selection of those birds which are victorious in the c.o.c.kpit, so the strongest and most vigorous males, or those provided with the best weapons, have prevailed in the state of nature over their feebler and more cowardly compet.i.tors. Just as man can give beauty, according to his own standard of taste, to his male poultry, by selecting special birds for their plumage, their port, their wattles, or their hackles, so female birds in a state of nature have by a long-continued choice of the more attractive males added to their beauty and their ornamental adjuncts. In these two ways, Darwin believed, a limited selection has slowly developed weapons like the horns of buffaloes, the antlers of stags, the tusks of boars, and the spurs of game-birds, together with the courage, strength, and pugnacity always a.s.sociated with such special organs. It has also developed the ornamental plumage of the peac.o.c.k, the argus pheasant, and the birds of paradise; the song of the lark, the thrush, and the nightingale; the brilliant hues on the face of the mandrill; and the attractive perfume of the musk-deer, the snakes, and the scented b.u.t.terflies. Wherever one s.e.x possesses any decorative or alluring adjunct not equally shared by the other, Darwin attributed this special gift either to the law of battle, or to the long and slowly exerted selective action of their fastidious mates.
The germ of the doctrine of s.e.xual selection is to be found, like so many other of Charles Darwin"s theories, in a prophetic pa.s.sage of his grandfather"s "Zoonomia." Stags, the Lichfield physician tells us, are provided with antlers "for the purpose of combating other stags for the exclusive possession of the females, who are observed, like the ladies in the time of chivalry, to attend the car of the victor. The birds which do not carry food to their young, and do not therefore marry, are armed with spurs for the purpose of fighting for the exclusive possession of the females, as c.o.c.ks and quails. It is certain that these weapons are not provided for their defence against other adversaries, because the females of these species are without this armour. The final cause of this contest among the males seems to be that the strongest and most active animal should propagate the species, which should thence become improved."
It must be noticed, however, that Erasmus Darwin here imports into the question the metaphysical and teleological notion of the final cause, implying that the struggle of the males was ordained from without, for this express and preconceived purpose; whereas Charles Darwin, never transcending the world of phenomena, more logically regards the struggle itself as an efficient cause, having for its result the survival of the strongest or the handsomest as the case may be. This distinction is fundamental; it marks the gulf between the essentially teleological spirit of the eighteenth century and the essentially positive spirit of philosophy and science at the present day.
Here again, too, the immense logical superiority of Charles Darwin"s rigorous and exhaustive inductive method over the loose suggestiveness of his grandfather Erasmus may easily be observed. For while Erasmus merely throws out a clever and interesting hint as to the supposed method and intention of nature, Charles Darwin proves his thesis, point by point, with almost mathematical exact.i.tude, leaving no objection unmet behind him, but giving statistical and inductive warrant for every step in his c.u.mulative argument. He goes carefully into the numerical proportion of the two s.e.xes in various species; into the relative dates of arrival in any particular country of the males and females of migratory birds; into the question whether any individuals ever remain in the long run unpaired; into the chances of the earliest-mated or most vigorous couples leaving behind more numerous or stronger offspring to represent them in the next generation. He collects from every quarter and from all sources whatever available evidence can be obtained as to the courtship and rivalry of birds and b.u.t.terflies, of deer and antelopes, of fish and lizards. He shows by numerous examples and quotations how even flies coquet together in their pretty rhythmical aerial dances; how wasps battle eagerly with one another to secure possession of their unconcerned mates; how cicadas strive to win their "voiceless brides" with stridulating music; how sphinx-moths endeavour to allure their partners with the musky odour of their pencilled wings; and how emperors and orange-tips display their gorgeous spots and bands in the broad sunshine before the admiring and attentive eyes of their observant dames. He traces up the same spirit of rivalry and ostentation to the c.o.c.k-pheasant strutting about before the attendant hen, and to the meeting-places of the blackc.o.c.k, where all the males of the district fight with one another and undertake long love-dances in regular tournaments, while the females stand by and watch the chances and changes of the contest with affected indifference. Finally, he points out how similar effects are produced by like causes among the higher animals, especially among our near relations the monkeys; and then he proceeds to apply the principles thus firmly grounded to the particular instance of the human race itself, the primary object of his entire treatise.
Some of the most interesting of the modifications due to this particular form of selective action are to be found amongst the insects and other low types of animal life. The crickets, the locusts, and the gra.s.shoppers, for example, are all famous for their musical powers; but the sounds themselves are produced in the different families by very different and quaintly varied organs. The song of the crickets is evoked by the sc.r.a.ping of minute teeth on the under side of either wing-cover; in the case of the locusts, the left wing, which acts as a bow, overlies the right wing, which serves as a fiddle; while with the gra.s.shoppers, the leg does duty as the musical instrument, and has a row of lancet-shaped elastic k.n.o.bs along its outer surface, which the insect rubs across the nerves of the wing-covers when it wishes to charm the ears and rouse the affection of its silent mate. In a South African species of the same family, the whole body of the male is fairly converted into a musical instrument, being immensely inflated, hollow, and distended like a pellucid air-bladder in order to act as an efficient sounding-board. Among the beetles, taste seems generally to have specialised itself rather on form than on music or colour, and the males are here usually remarkable for their singular and very complicated horns, often compared in various species to those of stags or rhinoceroses, and entirely absent in the females of most kinds. But it is among the b.u.t.terflies and moths that insect aestheticism has produced its greatest artistic triumphs; for here the beautiful eye-spots and delicate markings on the expanded wing-membranes are almost certainly due to s.e.xual selection.
The higher animals display like evidence of the same slow selective action. The courtship of the stickleback, who dances "mad with delight"
around the mate he has allured into the nest he prepares for her, has been observed by dozens of observers both before and since in the domestic aquarium. The gem-like colours of the male dragonet, the b.u.t.terfly wings of certain gurnards, and the decorated tails of some exotic carps all point in the same direction. Our own larger newt is adorned during the breeding season with a serrated crest edged with orange; while in the smaller kind the colours of the body acquire at the same critical period of love-making a vivid brilliancy. The strange horns and luridly coloured throat-pouches of tropical lizards are familiar to all visitors in equatorial climates, and they are confined exclusively to the male s.e.x. Among birds, the superior beauty of the male plumage is known to everybody; and their greatest glory invariably coincides with the special season for the selection of mates. In the spring, as even our poets have told us, the wanton lapwing gets himself another crest. The law of battle produces the spur of the game-birds and the still stranger wing-spurs of certain species of the plover kind.
aesthetic rivalry is answerable rather for vocal music, and for the plumage of the umbrella-bird, the lyre-bird, the humming-birds, and the c.o.c.k of the rocks. Among mammals, strength rather than beauty seems to have carried the day; horns, and tusks, and spikes, and antlers are here the special guerdon of the victorious males. Yet even mammals show occasional signs of distinctly aesthetic and artistic preferences, as in the gracefully twisted horns of the koodoo, the scent-glands of the musk-deer or of certain antelopes, the brilliant hues of the male mandrill, and the tufts and moustaches of so many monkeys.
It must be frankly conceded that the reception accorded to Darwin"s doctrine of s.e.xual selection, even among the biological public, was far less unanimous, enthusiastic, and full than that which had been granted to his more extensive theory of survival of the fittest. Many eminent naturalists declined from the very outset to accept the conclusions thus definitely set before them, and others who at first seemed disposed to bow to the immense weight of Darwin"s supreme authority gradually withdrew their grudging a.s.sent from the new doctrine, as they found their relapse backed up by others, and refused to believe that the theory of courtship had been fairly proven before the final tribunal of science. Several critics began by objecting that the whole theory was a mere afterthought. Darwin, they said, finding that natural selection did not suffice by itself to explain all the details of structure in man, had invented s.e.xual selection as a supplementary principle to help it over the hard places. Those who wrote and spoke in this thoughtless fashion could have had but a very inadequate idea of Darwin"s close experimental methods of enquiry. As a matter of fact, indeed, they were entirely wrong; the doctrine of s.e.xual selection itself, already faintly foreshadowed by Erasmus Darwin in the "Zoonomia," had been distinctly developed in the first edition of the "Origin of Species" with at least as much provisional elaboration as any other equally important factor in the biological drama as set forth in that confessedly introductory work.
Nay, Haeckel had caught gladly at the luminous conception there expressed, even before the appearance of the "Descent of Man," and had worked it out in his "Generelle Morphologie," with great insight, to its legitimate conclusions in many directions. Indeed, the sole reason why so much s.p.a.ce was devoted to the subject in Darwin"s work on human development was simply because there for the first time an opportunity arose of utilising his vast store of collected information on this single aspect of the evolutionary process. It was no afterthought, but a necessary and inevitable component element of the fully-developed evolutionary concept.
Still, it cannot be denied that naturalists generally did not accept with effusion the new clause in the evolutionary creed. Many of them hesitated; a few acquiesced; the majority more or less openly dissented.
But Darwin"s belief remained firm as a rock. "I am glad you defend s.e.xual selection," he wrote a few years later in a private letter; "I have no fear about its ultimate fate, though it is now at a discount;"
and in the preface to the second edition of the "Descent of Man," he remarks acutely, "I have been struck with the likeness of many of the half-favourable criticisms on s.e.xual selection with those which appeared at first on natural selection; such as that it would explain some few details, but certainly was not applicable to the extent to which I have employed it. My conviction of the power of s.e.xual selection remains unshaken.... When naturalists have become familiar with the idea, it will, as I believe, be much more largely accepted; and it has already been fully and favourably received by several capable judges."
In spite of the still continued demurrer of not a few among the leading evolutionists, it is probable, I think, that Darwin"s prophecy on this matter will yet be justified by the verdict of time. For the opposition to the doctrine of s.e.xual selection proceeds almost invariably, as it seems to me, from those persons who still desire to erect an efficient barrier of one sort or another between the human and animal worlds; while on the contrary the theory in question is almost if not quite universally accepted by just those rigorously evolutionary biologists who are freest from preconceptions or special _a priori_ teleological objections of any kind whatever. The half of the doctrine which deals with the law of battle, indeed, can hardly be doubted by any competent naturalist; the other half, which deals with the supposed aesthetic preferences of the females, is, no doubt, distasteful to certain thinkers because it seems to imply the existence in the lower animals of a sense of beauty which many among us are not even now prepared generously to admit. The desire to arrogate to mankind alone all the higher faculties either of sense or intellect has probably much to do with the current disinclination towards the Darwinian idea of s.e.xual selection. Thinkers who allow themselves to be emotionally swayed by such extraneous considerations forget that the beautiful is merely that which pleases; that beauty has no external objective existence; and that the range of taste, both among ourselves and among animals at large, is practically infinite. The greatest blow ever aimed at the Darwinian theory of s.e.xual selection was undoubtedly that dealt out by Mr. Alfred Russel Wallace (et tu, Brute!) in his able and subtle article on the Colours of Animals in "Macmillan"s Magazine," since reprinted in his delightful work on "Tropical Nature." Wallace there urges with his usual acuteness, ingenuity, and skill several fundamental objections to the Darwinian hypothesis of no little importance and weight. But it must always be remembered (with all due respect to the joint discoverer of natural selection) that Mr. Wallace himself, after publishing his own admirable essay on the development of man, drew back aghast in the end from the full consequences of his own admission, and uttered his partial recantation in the singular words, "Natural selection could only have endowed the savage with a brain a little superior to that of an ape." It seems probable that in every case an a.n.a.logous desire to erect a firm barrier between man and brute by positing the faculty for perceiving beauty as a special quasi-divine differentia of the human race has been at the bottom of the still faintly surviving dislike amongst a section of scientific men to s.e.xual selection. Nevertheless, a candid and impartial critic would be compelled frankly to admit that Darwin"s admirable theory of courtship has not on the whole proved so generally acceptable to the biological world up to the present time as his greater and far more comprehensive theory of survival of the fittest. It still waits for its final recognition, towards which it is progressing more rapidly and surely every day it lives.
CHAPTER X.
VICTORY AND REST.
The last eleven years of Darwin"s life were spent in enforcing and developing the principles already reached, and in enjoying the almost unchequered progress of the revolution he had so unconsciously to himself succeeded in inaugurating.
Only one year elapsed between the publication of the "Descent of Man"
and that of its next important successor, the "Expression of the Emotions." The occasion of this learned and bulky treatise in itself stands as an immortal proof of the conscientious way in which Darwin went to work to antic.i.p.ate the slightest and most comparatively impertinent possible objections to his main theories. Sir Charles Bell, in one of the quaintly antiquated Bridgwater treatises--those marvellous monuments of sadly misplaced teleological ingenuity--had maintained that man was endowed with sundry small facial muscles solely for the sake of expressing his emotions. This view was so obviously opposed to the belief in the descent of man from some lower form, "that," says Darwin, "it was necessary for me to consider it;" and so he did, in a lengthy work, where the whole subject is exhaustively treated, and Bell"s idea is completely pulverised by the apt allegation of a.n.a.logous expressions in the animal world. In his old age Darwin grew, in fact, only the more ceaselessly and wonderfully industrious. In 1875, after three years of comparative silence, came the "Insectivorous Plants," a work full of minute observation on the habits and manners of the sundew, the b.u.t.terwort, the Venus"s fly-catcher, and the various heterogeneous bog-haunting species known by the common name of pitcher plants. The bare ma.s.s and weight of the facts which Darwin had collected for the "Origin of Species" might well-nigh have stifled the very existence of that marvellous book: it was lucky that the premature publication of Wallace"s paper compelled him to hurry on his "brief abstract," for if he had waited to select and arrange the whole series of observations that he finally published in his various later justificatory volumes, we might have looked in vain for the great systematic and organising work, which would no doubt have been "surcharged with its own weight, and strangled with its waste fertility." But the task that he himself best loved was to watch in minute detail the principles whose secret he had penetrated, and whose reserve he had broken, working themselves out before his very eyes, naked and not ashamed--to catch Actaeon-like the undraped form of nature herself in the actual process of her inmost being. He could patiently observe the red and slimy hair-glands of the drosera closing slowly and remorselessly round the insect prey, and sucking from their bodies with sensitive tentacles the protoplasmic juices denied to its leaves by the poor and boggy soil, on which alone its scanty rootlets can properly thrive. He could watch the b.u.t.terwort curving round the edges of its wan green foliage upon the captured limbs of fly or aphis. He could note how the serried ma.s.s of finger-like processes in the utricles of the bladderwort slowly absorb organic matter from the larva of a gnat, or the minute water-insects entangled within its living and almost animated lobster-pot. He could track the long line of treacherous honey-glands by which the sarracenia entices flies into the festering manure-wells of its sticky pitchers. The minuteness and skill of all his observations on these lesser problems of natural selection inevitably inspired faith among outsiders in the cautious judgment of the observer and experimenter; and day by day throughout his later years the evidence of the popular acceptance of his doctrine, and of the dying away of the general ridicule with which it was first received by the unlearned public, was very gratifying to the great naturalist.
A year later, in 1876, came the "Effects of Cross and Self Fertilisation in the Vegetable Kingdom." So far as regarded the world of plants, especially with respect to its higher divisions, this work was of immense theoretical importance; and it also cast a wonderful side-light upon the nature of that strange distinction of s.e.x which occurs both in the vegetable and animal kingdom, and in each is the concomitant--one might almost say the necessary concomitant--of high development and complex organisation. The great result attained by Darwin in his long and toilsome series of experiments on this interesting subject was the splendid proof of the law that cross-fertilisation produces finer and healthier offspring, while continuous self-fertilisation tends in the long run to degradation, degeneration, and final extinction.
Here as elsewhere, however, Darwin"s principle does not spring spontaneous, like Athene from the head of Zeus, a G.o.ddess full-formed, uncaused, inexplicable: it arises gradually by a slow process of development and modification from the previous investigations of earlier biologists. At the close of the last century, in the terrible year of upheaval 1793, a quiet German botanist, Christian Konrad Sprengel by name, published at Berlin his long unheeded but intensely interesting work on the "Fertilisation of Flowers." In the summer of 1789, while all Europe was ablaze with the news that the Bastille had been stormed, and a new era of humanity begun, the calm and peaceful Pomeranian observer was noting in his own garden the curious fact that many flowers are incapable of being fertilised without the a.s.sistance of flying insects, which carry pollen from the stamens of one blossom to the sensitive surface or ovary of the next. Hence he concluded that the secretion of honey or nectar in flowers, the contrivances by which it is protected from rain, the bright hues or lines of the corolla, and the sweet perfume distilled by the blossoms, are all so many cunning devices of nature to ensure fertilisation by the insect-visitors. Moreover, Sprengel observed that many flowers are of one s.e.x only, and that in several others the s.e.xes do not mature simultaneously; "so that," said he, "nature seems to intend that no flower shall be fertilised by means of its own pollen." Indeed, in some instances, as he showed by experiments upon the yellow day lily, plants impregnated from their own stamens cannot be made to set seed at all. "So near," says his able successor, Hermann Muller, "was Sprengel to the distinct recognition of the fact that self-fertilisation leads to worse results than cross-fertilisation, and that all the arrangements which favour insect-visits are of value to the plant itself, simply because the insect-visitors effect cross-fertilisation!" As in most other antic.i.p.atory cases, however, it must be here remarked that Sprengel"s idea was wholly teleological: he conceived of nature as animated by a direct informing principle, which deliberately aimed at a particular result; whereas Darwin rather came to the conclusion that cross-fertilisation as a matter of fact does actually produce beneficial results, and that therefore those plants which varied most in the direction of arrangements for favouring insect-visits were likely to be exceptionally fortunate in the struggle for existence against compet.i.tors otherwise arranged. It is just the usual Darwinian subst.i.tution of an efficient for a final cause.
Even before Sprengel, Kolreuter had recognised, in 1761, that self-fertilisation was avoided in nature; and his observations and experiments on intercrossing and on hybridism were largely relied upon by Darwin himself, to whom they suggested at an early period many fruitful lines of original investigation. In 1799, again, Andrew Knight, following up the same line of thought in England as Sprengel in Germany, declared as the result of his close experiments upon the garden pea, that no plant ever fertilises itself for a perpetuity of generations.
But Knight"s law, not being brought into causal connection with any great fundamental principle of nature, was almost entirely overlooked by the scientific world until the publication of Darwin"s "Origin of Species," half a century later. The same neglect also overtook Sprengel"s immensely interesting and curious work on fertilisation of flowers. The world, in fact, was not yet ready for the separate treatment of functional problems connected with the interrelations of organic beings; so Knight and Sprengel were laid aside unnoticed on the dusty top bookshelves of public libraries, while the dry cla.s.sificatory and systematic biology of the moment had it ail its own way for the time being on the centre reading-tables. So many separate and independent strands of thought does it ultimately require to make up the grand final generalisation which the outer world attributes in its totality to the one supreme organising intelligence.
But in the "Origin of Species" itself Darwin reiterated and emphasised Knight"s law as a general and all-pervading principle of nature, placing it at the same time on broader and surer biological foundations by affiliating it intimately upon his own great illuminating and unifying doctrine of natural selection. He also soon after rescued from oblivion Sprengel"s curious and fairy-like book, showing in full detail in his work on orchids the wonderful contrivances by which flowers seek to attract and to secure the a.s.sistance of insects for the impregnation of their embryo seeds. In the "Variation of Animals and Plants under Domestication," he further showed that breeding in-and-in diminishes the strength and productiveness of the offspring; while crossing with another stock produces, on the contrary, the best possible physical results in both directions. And now at last, in the "Effects of Cross and Self fertilisation," he proved by careful and frequently repeated experiments that a constant infusion of fresh blood (so to speak) is essential to the production of the healthiest offspring. In the words of his own emphatic summing up, "Nature abhors perpetual self-fertilisation."
The immediate result of these new statements and this fresh rationale of Knight"s law was to bring down Sprengel forthwith from the top shelf, where he had languished ingloriously for seventy years, and to set a whole school of ardent botanical observers working hard in the lines he had laid down upon the mutual correlations of insects and flowers. A vast literature sprang up at once upon this enchanting and long-neglected subject, the most eminent workers in the rediscovered field being Delpino in Italy, Hildebrand and Hermann Muller in Germany, Axel in Sweden, Lubbock in England, and Fritz Muller in tropical South America. Darwin found the question, in fact, almost taken out of his hands before he had time himself to treat of it; for Hildebrand"s chief work was published as early as 1867, while Axel"s appeared in 1869, both of them several years earlier than Darwin"s own final essay on the subject in the "Effects of Cross and Self Fertilisation." No statement, perhaps, could more clearly mark the enormous impetus given to researches in this direction than the fact that D"Arcy Thompson, in his appendix to Muller"s splendid work on the "Fertilisation of Flowers,"
has collected a list of no less than eight hundred and fourteen separate works or important papers bearing on that special department of botany, almost all of them subsequent in date to the first publication of the "Origin of Species." So widely did the Darwinian wave extend, and so profoundly did it affect every minute point of biological and psychological investigation.
Each of these later works of Darwin"s consists, as a rule, of an expansion of some single chapter or paragraph in the "Origin of Species;" or, to speak more correctly, of an arrangement of the materials collected and the experiments designed for that particular portion of the great projected encyclopaedia of evolutionism, of which the "Origin of Species" itself was but a brief antic.i.p.atory summary or rough outline. Thus, the book on Orchids, published in 1862, is already foreshadowed in a part of the chapter on the Difficulties of the Theory of Natural Selection; the "Movements and Habits of Climbing Plants"
(1865) is briefly summarised by antic.i.p.ation in the long section on Modes of Transition; the "Variation of Animals and Plants under Domestication" (1868) consists of the vast array of _pieces justificatives_ for the first chapter of the "Origin of Species;" and the germ of the "Cross and Self Fertilisation" (1876) is to be seen in the pa.s.sage "On the Intercrossing of Individuals" in Chapter IV. of the same work. It was well indeed that Darwin began by publishing the shorter and more manageable abstract; the half, as the wise Greek proverb shrewdly remarks, is often more than the whole; and a world that eagerly devoured the first great deliverance of the Darwinian principle, might have stood aghast had it been asked to swallow it piecemeal in such gigantic treatises as those with which its author afterwards sought thrice to vanquish all his foes and thrice to slay the slain.
Yet, with each fresh manifestation of Darwin"s inexhaustible resources, on the other hand, the opposition to his principles grew feebler and feebler, and the universality of their acceptance more and more p.r.o.nounced, till at last, among biologists at least, not to be a Darwinian was equivalent to being hopelessly left behind by the general onward movement of the time. In 1874 Tyndall delivered his famous address at the Belfast meeting of the British a.s.sociation; and in 1877, from the same presidential chair at Plymouth, Allen Thomson, long reputed a doubtful waverer, enforced his cordial adhesion to the Darwinian principles by his inaugural discourse on "The Development of the Forms of Animal Life." A new generation of active workers, trained up from the first in the evolutionary school, like Romanes, Ray Lankester, Thistleton Dyer, Balfour, Sully, and Moggridge, had now risen gradually around the great master; and in every direction he could see the seed he had himself planted being watered and nourished in fresh soil by a hundred ardent and enthusiastic young disciples. Even in France, ever irresponsive to the touch of new ideas of alien origin, Colonel Moulinie"s admirable and sympathetic translations were beginning to win over to the evolutionary creed many rising workers; while in Germany, Victor Carus"s excellent versions had from the very first brought in the enthusiastic Teutonic biologists with a congenial "swarmery" to the camp of the Darwinians. Correspondents from every part of the world kept pressing fresh facts and fresh applications upon the founder of the faith; and Darwin saw his own work so fast being taken out of his hands by specialist disciples that he abandoned entirely his original intention of publishing in detail the basis of his first book, and contented himself instead with tracing out minutely some minor portions of his contemplated task as specimens of evolutionary method.
In 1877, in pursuance of this changed purpose, Darwin published his book on "Forms of Flowers," in which he dealt closely with the old problem of differently shaped blossoms on plants of the same species. It had long been known, to take a single example, that primroses existed in two forms, the pin-eyed and the thrum-eyed, of which the former has the pin-like summit of the pistil at the top of the tube, and the stamens concealed half way down its throat; while in the latter these relative positions are exactly reversed, the stamens answering in place to the pistil of the alternative form with geometrical accuracy. As early as 1862 Darwin had shown, in the "Journal of the Linnean Society," that this curious arrangement owed its development to the greater security which it afforded for cross-fertilisation, because in this way each flower had to be impregnated with the pollen, from a totally distinct blossom, growing on a different individual plant. In a series of successive papers read before the same Society in the years between 1863 and 1868, he had extended a similar course of explanation to the multiform flowers of the flaxes, the loosestrifes, the featherfoil, the auricula, the buckbean, and several other well-known plants. At last, in 1877, he gathered together into one of the now familiar green-covered volumes the whole of his observations on this strange peculiarity, and proved by abundant ill.u.s.tration and experiment that the diversity of form is always due through natural selection to the advantage gained by perfect security of cross-fertilisation, resulting as it invariably does in the production of the finest, strongest, and most successful seedlings. Any variation, however peculiar, which helps to ensure this constant infusion of fresh blood is certain to be favoured in the struggle for life, owing to the superior vitality of the stock it begets. But it is worthy of notice, as showing the extreme minuteness and exhaustiveness of Darwin"s method on the small scale, side by side with his extraordinary and unusual power of rising to the very highest and grandest generalisations, that the volume which he devoted to the elucidation of this minor factor in the question of hereditary advantages runs to nearly as many pages as the last edition of the "Origin of Species" itself. So great was the wealth of observation and experiment which he could lavish upon the solution of a single, small, incidental problem.
Even fuller in minute original research was the work which Darwin published in 1880, on "The Power of Movement in Plants," detailing the result of innumerable observations on the seemingly irresponsible yet almost purposive rotations of the growing rootlets and young stems of peas and climbers. Anyone who wishes to see on what a wide foundation of irrefragable fact the great biologist built up the stately fabric of his vast theories cannot do better than turn for instruction to this remarkable volume, which the old naturalist gave to the world some time after pa.s.sing the allotted span of threescore years and ten.
It was in the same year (1880) that Huxley delivered at the Royal Inst.i.tution his famous address on the Coming of Age of the "Origin of Species." The time was a favourable one for reviewing the silent and almost un.o.bserved progress of a great revolution. Twenty-one years had come and gone since the father of modern scientific evolutionism had launched upon the world his tentative work. In those twenty-one years the thought of humanity had been twisted around as upon some invisible pivot, and a new heaven and a new earth had been presented to the eyes of seers and thinkers. One-and-twenty years before, despite the influence of Hutton and of Lyell, the dominant view of the earth"s past history revealed but one vast and lawless succession of hideous catastrophes. Wholesale creations and wholesale extinctions, world-wide cataclysms followed by fresh world-wide births of interwoven faunas and floras--these, said Huxley, were the ordinary machinery of the geological epic brought into fashion by the misapplied genius of the mighty Cuvier. One-and-twenty years after, the opponents themselves had given up the game in its fullest form as lost beyond the hope of possible rest.i.tution. Some hesitating thinkers, it is true, while accepting the evolutionary doctrine more or less in its earlier form, like Mivart and Meehan, yet refused their a.s.sent on one ground or another to the specific Darwinian doctrine of natural selection. Others, like Wallace, made a special exception with regard to the development of the human species, which they supposed to be due to other causes from those implied in the remainder of the organic scale. Yet on the whole, biological science had fairly carried the day in favour of evolution, in one form or another, and not even the cavillers dared now to suggest that whole systems of creation had been swept away _en bloc_, and remade again in different forms for a succeeding epoch, in accordance with the belief which was almost universal among geologists up to the exact moment of the publication of Darwin"s masterpiece.
During the twenty-one years, too, as Huxley likewise pointed out, an immense number of new facts had come to strengthen the hands of the evolutionists at the very point where they had before felt themselves most openly vulnerable. Palaeontology had supplied many of those missing links in the organic chain whose absence from the interrupted and imperfect geological record had been loudly alleged against the Darwinian hypothesis in the earlier days of struggle and hesitation. Two years after the publication of the "Origin of Species," the discovery of a winged and feathered creature, happily preserved for us in the Solenhofen slates, with lizard-like head and teeth and tail, and bird-like pinions, feet, and breast, had bridged over in part the great gap that yawns between the existing birds and reptiles. A few years later, new fossil reptilian forms, erect on their hind legs like kangaroos, and with very singular peculiarities of bony structure, had helped still further to show the nature of the modifications by which the scale-bearing quadruped type pa.s.sed slowly into that of the feather-bearing biped. In 1875, again, Professor Marsh"s discovery of the toothed birds in the American cretaceous strata completed the ill.u.s.trative series of transitional forms over what had once been the most remarkable existing break in the continuity of organic development.
Similarly, Hofmeister"s investigations in the vegetable world brought close together the flowering and flowerless plants, by indicating that the ferns and the horsetails were connected in curious unforeseen ways, through the pill-worts and club-mosses, with the earliest and simplest of forest trees, the firs and the puzzle-monkeys. In minor matters like progress was continually reported on every side. Gaudry found among the fossils of Attica the successive stages by which the ancient and undeveloped civets pa.s.sed into the more modern and specialised tribe of the hyaenas; Marsh traced out in Western America the ancestry of the horse from a five-toed creature no bigger than a fox, through intermediate four-toed and three-toed forms, to the existing single solid-hoofed type with its digits reduced to the minimum of unity; and Filhol unearthed among the phosphorites of Quercy the common progenitor of the most distinct among the recent carnivores, the cats and the dogs, the plantigrade bears and the digitigrade pumas. "So far as the animal world is concerned," Professor Huxley said in conclusion, reviewing these additions to the evidence upon that memorable occasion, "evolution is no longer a speculation but a statement of historical fact." Of Darwin himself he remarked truly, "He has lived long enough to outlast detraction and opposition, and to see the stone that the builders rejected become the head-stone of the corner."
It was in 1881 that Darwin published his last volume, "The Formation of Vegetable Mould through the Action of Worms." In this singularly fascinating and interesting monograph he took in hand one of the lowliest and humblest of living forms, the common earthworm, and by an exhaustive study of its habits and manners strove to show how the entire existence of vegetable mould--the ordinary covering of fertile soil upon the face of the earth--is due to the long but un.o.btrusive action of these little-noticed and ever-active architects. By the acids which they evolve, they appear to aid largely in the disintegration of the stone beneath the surface; by their constant practice of eating fallen leaves, which they drag down with them into their subterranean burrows, they produce the fine castings of soft earth, so familiar to everybody, and thus reinstate the coating of humus above the bare rock as often as it is washed away again in the course of ordinary denudation by the rain and the torrents. It is true that subsequent investigation has shown the possibility of vegetable mould existing under certain conditions without the intervention of worms to any marked extent; but, as a whole, there can be little doubt that over most parts of the world the presence of soil, and therefore of the vegetable growth rooted in it, is entirely due to the unsuspected yet ceaseless activity of these humble creatures.
The germ of the earthworm theory appears to me to have been first suggested to Darwin"s mind by a pa.s.sage in a work where one would little have suspected it--White"s "Natural History of Selborne." "Earthworms,"
says the idyllic Hampshire naturalist, "though in appearance a small and despicable link in the chain of nature, yet, if lost, would make a lamentable chasm. For to say nothing of half the birds, and some quadrupeds, which are almost entirely supported by them, worms seem to be the great promoters of vegetation, which would proceed but lamely without them, by boring, perforating, and loosening the soil, and rendering it pervious to rains and the fibres of plants, by drawing straws and stalks of leaves into it; and, most of all, by throwing up such infinite numbers of lumps of earth, called worm-casts, which, being their excrement, is a fine manure for grain and gra.s.s. Worms probably provide new soils for hills and slopes where the rain washes the earth away; and they affect slopes, probably, to avoid being flooded.
Gardeners and farmers express their detestation of worms; the former, because they render their walks unsightly, and make them much work; and the latter, because, as they think, worms eat their green corn. But these men would find, that the earth without worms would soon become cold, hard-bound, and void of fermentation; and, consequently, sterile."
If Darwin ever read this interesting pa.s.sage, which he almost certainly must at some time have done, it would appear that he had overlooked it in later life; for he, who was habitually so candid and careful in the acknowledgment of all his obligations, however great or however small, does not make any mention of it at all in his "Vegetable Mould," though he alludes incidentally to some other observations of Gilbert White"s on the minor habits and manners of earthworms. But whether Darwin was originally indebted to White or not for the foundation of his theory on the subject of mould, the important point to notice is really this, that what with the observant parson of Selborne was but a casual glimpse, the mere pa.s.sing suggestion of a fruitful idea, became with Darwin, in his wider fashion, a carefully elaborated and powerfully b.u.t.tressed theory, supported by long and patient investigation, ample experiment, and vast collections of minute facts. The difference is strikingly characteristic of the strong point of Darwin"s genius. While he had all the breadth and universality of the profoundest thinkers, he had also all the marvellous and inexhaustible patience of the most precise and special microscopical student.
For years, indeed, Darwin studied the ways and instincts of the common earthworm with the same close and accurate observation which he gave to every other abstruse subject that engaged in any way his acute intellect. The lawyer"s maxim, "De minimis lex non curat," he used to say, never truly applies to science. As early as the year 1837 he read a paper, before the Geological Society of London, "On the Formation of Mould," in which he developed with some fulness the mother idea of his complete theory on the earthworm question. He there showed that layers of cinders, marl, or ashes, which had been strewn thickly over the surface of meadows, were found a few years after at a depth of some inches beneath the turf, yet still forming in spite of their burial a regular and fairly horizontal stratum. This apparent sinking of the stones, he believed, was due to the quant.i.ty of fine earth brought up to the surface by worms in the form of castings. It was objected to his theory at the time that the work supposed to be accomplished by the worms was out of all reasonable proportion to the size and numbers of the alleged actors. Here Darwin"s foot was on his native heath; he felt himself immediately on solid ground again. The c.u.mulative importance of separately infinitesimal elements is indeed the very keynote and special peculiarity of the great biologist"s method of thinking. He had found out in very truth that many a little makes a mickle, that the infinitely small, infinitely repeated, may become in process of infinite years infinitely important. So he set himself to work, with characteristic contempt of time, to weigh and measure worms and worm-castings.
He began by keeping tame earthworms in flower-pots in his own house, counting the number of worms and burrows in certain measured s.p.a.ces of pasture or garden, and starting his long and slow experiment in his field at Down already alluded to. He tried issues on their senses, on their instincts, on their emotions, on their intelligence; he watched them darting wildly like rabbits into their holes when alarmed from without, overcoming engineering difficulties in dragging down oddly-shaped or unfamiliar leaves, and protecting the open mouths of their tunnels from intruders with a little defensive military glacis of rounded pebbles. He found that more than 53,000 worms on an average inhabit every acre of garden land, and that a single casting sometimes weighs as much as three ounces avoirdupois. Ten tons of soil per acre pa.s.s annually through their bodies, and mould is thrown up by them at an average rate of 22 inches in a century. Careful observations on the stones of Stonehenge; on the tiled floors of buried buildings; on Roman ruins at Silchester and Wroxeter, and on his own meadows and pastures at Down, finally enabled the cautious experimenter to prove conclusively the truth of his thesis, and to present to the world the despised earthworm in a new character, as the friend of man and of agriculture, the producer and maintainer of the vegetable mould on our hills or valleys, and the prime cause of the very existence of that cloak of greensward that clothes our lawns, our fields, and our pleasure-grounds.
It was his last work. Persistent ill-health and equally persistent study for seventy-three years had broken down a const.i.tution never really strong, and consumed from within by the ceaseless fires of its own overpowering and undying energy. On Tuesday, April the 18th, 1882, he was seized at midnight by violent pains, and at four o"clock on Wednesday afternoon he died suddenly in his son"s arms, after a very short but painful illness. So retired was the family life at Down that the news of the great biologist"s death was not actually known in London itself till two days after he had breathed his last.
The universal regret and grief expressed at the loss in all civilised countries was the best measure of the immense change of front which had slowly come over the whole educated community, in the twenty-three years since the first publication of the "Origin of Species." No sooner was Darwin"s death announced than all lands and all cla.s.ses vied with one another in their eagerness to honour the name and memory of the great biologist. Indeed, the spontaneous and immediate nature of the outburst of regret and affectionate regard which followed hard upon the news of Darwin"s death, astonished even those who had watched closely the extraordinary revolution the man himself had brought so well to its final consummation. In England, it was felt instinctively on every side that the great naturalist"s proper place was in the aisles of Westminster, hard by the tomb of Newton, his immortal predecessor. To this universal and deep-seated feeling Darwin"s family regretfully sacrificed their own natural preference for a quiet interment in the graveyard at Down. On the Wednesday morning next after his death, Charles Darwin"s remains were borne with unwonted marks, of respect and ceremony, in the a.s.sembled presence of all that was n.o.ble and good in Britain, to an honoured grave in the precincts of the great Abbey.
Wallace and Huxley, Lubbock and Hooker, his nearest peers in the domain of pure science, stood among the bearers who held the pall. Lowell represented the republics of America and of letters. Statesmen, and poets, and philosophers, and theologians mingled with the throng of scientific thinkers who crowded close around the venerated bier. No incident of fitting pomp or dignity was wanting as the organ pealed out in solemn strains the special anthem composed for the occasion, to the appropriate words of the Hebrew poet, "Happy is the man that findeth wisdom." Even the narrow Philistine intelligence itself, which still knew Darwin only as the man who thought we were all descended from monkeys, was impressed with the sole standard of greatness open to its feeble and shallow comprehension by the mere solemnity and ceremony of the occasion, and began to enquire with blind wonderment what this thinker had done whom a whole people thus delighted to honour.
Of Darwin"s pure and exalted moral nature no Englishman of the present generation can trust himself to speak with becoming moderation. His love of truth, his singleness of heart, his sincerity, his earnestness, his modesty, his candour, his absolute sinking of self and selfishness--these, indeed, are all conspicuous to every reader, on the very face of every word he ever printed. Like his works themselves, they must long outlive him. But his sympathetic kindliness, his ready generosity, the staunchness of his friendship, the width and depth and breadth of his affections, the manner in which "he bore with those who blamed him unjustly without blaming them in return," these things can never so well be known to any other generation of men as to the three generations who walked the world with him. Many even of those who did not know him loved him like a father; to many who never saw his face, the hope of winning Charles Darwin"s approbation and regard was the highest incentive to thought and action. Towards younger men, especially, his unremitting kindness was always most noteworthy: he spoke and wrote to them, not like one of the masters in Israel, but like a fellow-worker and seeker after truth, interested in their interests, pleased at their successes, sympathetic with their failures, gentle to their mistakes. Not that he ever spared rightful criticism; on the contrary, the love of truth was with him so overpowering and enthralling a motive that he pointed out what seemed to him errors or misconceptions in the work of others with perfect frankness, fully expecting them to be as pleased and delighted at a suggested amendment of their faulty writing as he himself was in his own case. But his praise was as generous as his criticism was frank; and, amid all the toil of his laborious life in his study at Down, he could always find time to read and comment at full length upon whatever fresh contributions to his own subjects the merest tyro might venture to submit for his consideration.
He had the sympathetic receptivity of all truly great minds, and when he died, thousands upon thousands who had never beheld his serene features and his fatherly eyes felt they had lost indeed a personal friend.
Greatness is not always joined with gentleness: in Charles Darwin"s case, by universal consent of all who knew him, "an intellect which had no superior" was wedded to "a character even n.o.bler than the intellect."