So far as the scientific world was concerned the ‘Origin of Species’ fell, like a grain of mustard seed, upon good and well-prepared ground; the plant that sprang from it grew up forthwith into a great and stately tree, that overshadowed with its spreading branches all the corners of the earth.

The soil, indeed, had been carefully broken for it beforehand: Lamarck and St. Hilaire, Spencer and Chambers, had ploughed and harrowed in all diligence; and the minds of men were thoroughly ready for the assimilation of the new doctrine. But the seed itself, too, was the right germ for the exact moment; it contained within itself the vivifying principle that enabled it to grow and wax exceeding great where kindred germs before had withered away, or had borne but scanty and immature fruit.

Two conditions contributed to this result, one external, the other internal.

First for the less important external consideration. Darwin himself was a sound man with an established reputation for solidity and learning. That gained for his theory from the very first outset universal respect and a fair hearing. Herbert Spencer was known to be a philosopher: and the practical English nation mistrusts philosophers: those people probe too deep and soar too high for any sensible person to follow them in all their flights. Robert Chambers, the unknown author of ’Vestiges of Creation,’ was a shallow sciolist; it was whispered abroad that he was even inaccurate and slovenly in his facts: and your scientific plodder detests the very shadow of minute inaccuracy, though it speak with the tongues of men and angels, and be bound up with all the grasp and power of a Newton or a Goethe. But Charles Darwin was a known personage, an F.R.S., a distinguished authority upon coral reefs and barnacles, a great geologist, a great biologist, a great observer and indefatigable collector. His book came into the public hands stamped with the imprimatur of official recognition. Darwin was the father of the infant theory; Lyell and Hooker stood for its sponsors. The world could not afford to despise its contents; they could not brand its author offhand as a clever dreamer or a foolish amateur, or consign him to the dreaded English limbo of the ‘mere theorist.’

Next, for the other and far more important internal consideration. The book itself was one of the greatest, the most learned, the most lucid, the most logical, the most crushing, the most conclusive, that the world had ever yet seen. Step by step, and principle by principle, it proved every point in its progress triumphantly before it went on to demonstrate the next. So vast an array of facts so thoroughly in hand had never before been mustered and marshalled in favour of any biological theory. Those who had insight to learn and understand were convinced at once by the cogency of the argument; those who had not were overpowered and silenced by the weight of the authority and the mass of the learning. A hot battle burst forth at once, no doubt, around the successful volume; but it was one of those battles which are aroused only by great truths, a battle in which the victory is a foregone conclusion, and the rancour of the assailants the highest compliment to the prowess of the assailed.

Darwin himself, in his quiet country home at Down, was simply astonished at the rapid success of his own work. The first edition was published at the end of November 1859; it was exhausted almost immediately, and a second was got ready in hot haste by the beginning of January 1860. In less than six weeks the book had become famous, and Darwin found himself the centre of a European contest, waged with exceeding bitterness, over the truth or falsity of his wonderful volume. To the world at large Darwinism and evolution became at once synonymous terms. The same people who would entirely ascribe the Protestant Reformation to the account of Luther, and the inductive philosophy to the account of Bacon, also believed, in the simplicity of their hearts, that the whole vast evolutionary movement was due at bottom to that very insidious and dangerous book of Mr. Darwin’s.

The fact is, profound as had been the impulses in the evolutionary direction among men of science before Darwin’s work appeared at all, immense as were the throes and pangs of labour throughout all Europe which preceded and accompanied its actual birth, when it came at last it came to the general world of unscientific readers with all the sudden vividness and novelty of a tremendous earthquake. Long predestined, it was yet wholly unexpected. Men at large had known nothing or next to nothing of this colossal but hidden revolutionary force which had been gathering head and energy for so many years unseen within the bowels of the earth; and now that its outer manifestation had actually burst upon them, they felt the solid ground of dogmatic security bodily giving way beneath their feet, and knew not where to turn in their extremity for support. Naturally, it was the theological interest that felt itself at first most forcibly assailed. The first few chapters of Genesis, or rather the belief in their scientific and historical character, already sapped by the revelations of geology, seemed to orthodox defenders to be fatally undermined if the Darwinian hypothesis were once to meet with general recognition. The first resource of menaced orthodoxy is always to deny the alleged facts; the second is to patch up tardily the feeble and hollow modus vivendi of an artificial pact. On this occasion the orthodox acted strictly after their kind: but to their credit it should be added that they yielded gracefully in the long run to the unanimous voice of scientific opinion. Twenty-three years later, when all that was mortal of Charles Darwin was being borne with pomp and pageantry to its last resting-place in Westminster Abbey, enlightened orthodoxy, with generous oblivion, ratified a truce over the dead body of the great leader, and, outgrowing its original dread of naturalistic interpretations, accepted his theory without reserve as ’not necessarily hostile to the main fundamental truths of religion.’ Let us render justice to the vanquished in a memorable struggle. Churchmen followed respectfully to the grave with frank and noble inconsistency the honoured remains of the very teacher whom less than a quarter of a century earlier they had naturally dreaded as loosening the traditional foundations of all accepted religion and morality.

But if the attack was fierce and bitter, the defence was assisted by a sudden access of powerful forces from friendly quarters. A few of the elder generation of naturalists held out, indeed, for various shorter or longer periods; some of them never came into the camp at all, but lingered on, left behind, like stragglers from the onward march, by the younger biologists, in isolated non-conformity on the lonely heights of austere officialism. Their business was to ticket and docket and pigeon-hole, not to venture abroad on untried wings into the airy regions of philosophical speculation. The elder men, in fact, had many of them lost that elasticity and modifiability of intellect which is necessary for the reception of new and revolutionary fundamental concepts. A mind that has hardened down into the last stage of extreme maturity may assimilate fresh facts and fresh minor principles, but it cannot assimilate fresh synthetic systems of the entire cosmos. Moreover, some of the elder thinkers were committed beforehand to opposing views, with which they lacked either the courage or the intellectual power to break; while others were entangled by religious restrictions, and unable to free themselves from the cramping fetters of a narrow orthodoxy. But even among his own contemporaries and seniors Darwin found not a few whose minds were thoroughly prepared beforehand for the reception of his lucid and luminous hypothesis; while the younger naturalists, with the plasticity of youth, assimilated almost to a man, with the utmost avidity, the great truths thus showered down upon them by the preacher of evolution.

Sir Joseph Hooker and Professor Huxley were among the first to give in their adhesion and stand up boldly for the new truth by the side of the reckless and disturbing innovator. In June 1859, nearly a year after the reading of the Darwin-Wallace papers at the Linnean Society, but five months previously to the publication of the ‘Origin of Species,’ Huxley lectured at the Royal Institution on ‘Persistent Types of Animal Life,’ and declared against the old barren theory of successive creations, in favour of the new and fruitful hypothesis of gradual modification. In December 1859, a month later than the appearance of Darwin’s book, Hooker published his ‘Introduction to the Flora of Australia,’ in the first part of which he championed the belief in the descent and modification of species, and enforced his views by many original observations drawn from the domain of botanical science. For fifteen years, as Darwin himself gratefully observed in his introduction to the ‘Origin of Species,’ that learned botanist had shared the secret of natural selection, and aided its author in every possible way by his large stores of knowledge and his excellent judgment. Bates, the naturalist on the Amazons, followed fast with his beautiful and striking theory of mimicry, a crucial instance well explained. The facts of the strange disguises which birds and insects often assume had long been present to his acute mind, and he hailed with delight the discovery of the new principle, which at once enabled him to reduce them with ease to symmetry and order. To Herbert Spencer, an evolutionist in fibre from the very beginning, the fresh doctrine of natural selection came like a powerful ally and an unexpected assistant in deciphering the deep fundamental problems on which he was at that moment actually engaged; and in his ‘Principles of Biology,’ even then in contemplation, he at once adopted and utilised the new truth with all the keen and vigorous insight of his profound analytic and synthetic intellect. The first part of that important work was issued to subscribers just three years after the original appearance of the ‘Origin of Species;’ the first volume was fully completed in October 1864. It is to Mr. Spencer that we owe the pellucid expression ‘survival of the fittest,’ which conveys even better than Darwin’s own phrase, ‘natural selection,’ the essential element added by the ‘Origin of Species’ to the pre-existing evolutionary conception.

The British Association for the Advancement of Science held its big annual doctrinaire picnic the next summer after the publication of Darwin’s book, at Oxford. The Oxford meeting was a stormy and a well-remembered one. The ‘Origin of Species’ was there discussed and attacked before a biological section strangely enough presided over by Darwin’s old Cambridge teacher, Professor Henslow. Though then a beneficed parish priest, Henslow had the boldness frankly to avow his own acceptance of his great pupil’s startling conclusions. Huxley followed in the same path, as did also Lubbock and Hooker. On the whole, the evolutionists were already in the ascendant; the fresh young intellects especially being quick to seize upon the new pabulum so generously dealt out to them by the new evolutionism.

Among scientific minds of the first order, Lyell alone in England, heavily weighted by theological preconceptions, for awhile hung back. All his life long, as his letters show us, the great geologist had felt the powerful spell of the Lamarckian hypothesis continually enticing him with its seductive charm. He had fought against it blindly, in the passionate endeavour to preserve what he thought his higher faith in the separate and divine creation of man; but ever and anon he returned anew to the biological Circe with a fresh fascination, as the moth returns to the beautiful flame that has scorched and singed it. In a well-known passage in the earlier editions of his ‘Principles of Geology,’ the father of uniformitarianism gives at length his own reasons for dissenting from the doctrine of evolution as then set forth; and even after Darwin’s discovery had supplied him with a new clue, a vera causa, a sufficient power for the modification of species into fresh forms, theological difficulties made him cling still as long as possible to the old theory of the origin of man which he loved to describe as that of the ‘archangel ruined.’ He was loth to exchange this cherished belief for the degrading alternative (as it approved itself to him) of the ape elevated. But in the end, with the fearless honesty of a searcher after truth, he gave way slowly and regretfully. Always looking back with something like remorse to the flesh-pots of the ecclesiastical Egypt, with its enticing visions of fallen grandeur, the great thinker whose uniformitarian theory of geology had more than aught else paved the way for the gradual acceptance of Darwin’s evolutionism, came out at last from the house of bondage, and nobly ranged himself on the side of what his intellect judged to be the truth of nature, though his emotions urged him hard to blind his judgment and to neglect its lights for an emotional figment. Science has no more pathetic figure than that of the old philosopher, in his sixty-sixth year, throwing himself with all the eagerness of youth into what he had long considered the wrong scale, and vigorously wrecking in the ‘Antiquity of Man’ what seemed to the dimmed vision of his own emotional nature the very foundations of his beloved creed. But still he did it. He came out and was separate. In his own idiomatic language, he found at last that ’we must go the whole ourang;’ and, deep as was the pang that the recantation cost him, he formally retracted the condemnation of ‘transformism’ in his earlier works, and accepted, however unwillingly, the theory he had so often and so deliberately rejected.

The ‘Antiquity of Man’ came out in February 1863, some three years after the ‘Origin of Species.’ For some time speculation had been active over the strange hatchets which Boucher de Perthes had recently unearthed among the Abbeville drift shapeless masses of chipped flint rudely fashioned into the form of an axe, which we now call palaeolithic implements, and know to be the handicraft of preglacial men. But until Lyell’s authoritative work appeared the unscientific public could not tell exactly what to think of these curious and almost unhuman-looking objects. Lyell at once set all doubts at rest; the magic of his name silenced the derisive whispers of the dissidents. Already, in the previous year, the first fasciculus of Colenso’s famous work on the Pentateuch had dealt a serious blow from the ecclesiastical and critical side at the authenticity and historical truth of the Mosaic cosmogony. Lyell now from the scientific side completely demolished its literal truth, as ordinarily interpreted, by throwing back the primitive origin of our race into a dim past of immeasurable antiquity. In so doing he was clearing the way for Charles Darwin’s second great work, ’The Descent of Man;’ and by incorporating in his book Huxley’s remarks on the Neanderthal skull, and much similar evolutionary matter, he advertised the new creed in the animal origin of our race with all the acquired weight of his immense and justly-deserved European reputation. As a matter of taste, Lyell did not relish the application of evolutionism to his own species. But, with that perfect loyalty to fact which he shared so completely with Charles Darwin, as soon as he found the evidence overwhelming, he gave in. By that grudging concession he immensely strengthened the position of the new creed. ‘I plead guilty,’ he writes to Sir Joseph Hooker, ’to going farther in my reasoning towards transmutation than in my sentiments and imagination, and perhaps for that very reason I shall lead more people on to Darwin and you, than one who, being born later, like Lubbock, has comparatively little to abandon of old and long-cherished ideas, which constituted the charm to me of the theoretical part of the science in my earlier days.’ And to Darwin himself he writes regretfully. ’The descent of man from the brutes takes away much of the charm from my speculations on the past relating to such matters.’ This very reluctance itself told powerfully in favour of Charles Darwin’s novel theories: there is no evidence more valuable to a cause than that which it extorts by moral force, in spite of himself, from the faltering lips of an unwilling witness.

The same year that saw the publication of Lyell’s ‘Antiquity of Man’ saw also the first appearance of Huxley’s work on ‘Man’s Place in Nature.’ Darwin himself had been anxious rather than otherwise to avoid too close reference to the implications of his theory as regards the origin and destiny of the human race. He had desired that his strictly scientific views on the rise of specific distinctions should be judged entirely on their own merits, unhampered by the interference of real or supposed theological and ethical considerations. His own language on all such subjects, wherever he was compelled to trench on them in the ’Origin of Species,’ was guarded and conciliatory; he scarcely referred at all to man or his history; and his occasional notices of the moving principle and first cause of the entire cosmos were reverential and religious in the truest sense and in the highest degree. But you cannot let loose a moral whirlwind, and then attempt to direct its course; you cannot open the floodgates of opinion or of speculation, and then pretend to set limits to the scope of their restless motion. Darwin soon found out that people would insist in drawing inferences beyond what was written, and in seeing implicit conclusions when they were not definitely formulated in the words of their author. ‘Man is perennially interesting to man,’ says the great chaotic American thinker; and whatever all-embracing truth you set before him, you may be sure that man will see in it chiefly the implications that most closely affect his own happiness and his own destiny. The biological question of the origin of species is a sufficiently wide one, but it includes also, among other cases, the origin of the very familiar species Homo sapiens of Linnaeus. Some theologians jumped at once at the conclusion, right or wrong, that if Darwinism were true man was nothing more than a developed monkey, the immortal soul was an exploded myth, the foundations of religion itself were shattered, and the wave of infidelity was doomed to swamp the whole of Christendom with its blank nihilism. Scientific men, on the other hand, drew the conclusion that man must be descended, like other mammals, from some common early vertebrate ancestor, and that the current views of his origin and destiny must be largely modified by the evolutionary creed. Of this profound scientific belief Professor Huxley’s maiden work was the earliest outcome.

Meantime, on the continent of Europe and over-sea in America, the Darwinian theory was being hotly debated and warmly defended. France, coldly sceptical and critical, positive rather than imaginative in matters of science, and little prone by native cast of mind to the evolutionary attitude, stood aloof to a great extent from the onward course of the general movement. Here and there, to be sure, a Gaudry or a Ribot, a Delboeuf or a De Candolle (the two latter a Liege Belgian and a Genevan Swiss) might heartily throw himself into the new ideas, and contribute whole squadrons of geological or botanical fact to the final victory. Yet, as a whole, the dry and cautious French intelligence, ever inclined to a scientific opportunism, preferred for the moment to stand by expectant and await the result of the European consensus. But philosophical Germany, on the other hand, beaming enthusiasm from its myriad spectacles, eagerly welcomed the novel ideas, and proclaimed from the housetops the evolutionary faith as a main plank in the rising platform of the newly-roused Kulturkampf. Fritz Mueller began with all the ardour of a fresh convert to collect his admirable ’Facts for Darwin;’ his brother Hermann sat down with indomitable patience, like the master’s own, to watch the ceaseless action of the bees and butterflies in the fertilisation of flowers. Ruetimeyer applied the Darwinian principles to the explanation of mammalian relationships, and Haeckel set to work upon his vast reconstructive ‘History of Creation,’ a largely speculative work which, with all its faults, distinctly carried forward the evolutionary impulse, and set fresh researchers working upon new lines, to confirm or to disprove its audacious imaginings. In America, Asa Gray gave to the young creed the high authority of his well-known name, and Chauncey Wright helped it onward on the road with all the restrained force of his singular and oblique but powerful and original personality. If Agassiz and Dawson still hesitated, Fiske and Youmans were ardent in the faith. If critical Boston put up its eye-glass doubtfully, Chicago and St. Louis were ready for conversion. Everywhere Darwin and Darwinism became as household words; it was the singular fate of the great prophet of evolution, alone almost among the sons of men, to hear his own name familiarly twisted during his own lifetime into a colloquial adjective, and to see the Darwinian theory and the errors of Darwinism staring him in the face a hundred times a day from every newspaper and every periodical.

Of course the ‘Origin of Species’ was largely translated at once into all the civilised languages of Europe, Russian as well as French, Dutch as well as German, Swedish as well as Italian, Spanish as well as Hungarian, nay even, at last, transcending narrow continental limits, Japanese as well as Hindustani. The revolution which it was rapidly effecting was indeed a revolution in every mode of thought and feeling as well as a revolution in mere restricted biological opinion. But all this time, the modest, single-minded, and unassuming author was working unmoved among his plants and pigeons in his home at Down, regardless of the European fame he was so quickly acquiring, and anxious only to bring to a termination the vast work which he still contemplated. A little more than eleven years intervened between the publication of the ’Origin of Species,’ in 1859, and the first appearance of the ‘Descent of Man,’ in 1871. The interval was occupied in carrying out in part the gigantic scheme of his original collections for the full treatment of the development theory. The work published in 1859 Darwin regarded merely as an abstract and preliminary outline of his full opinions: ’No one can feel more sensible than I do,’ he wrote, ’of the necessity of hereafter publishing in detail all the facts, with references, on which my conclusions have been grounded.’ The marvellously learned work on the ‘Variation of Animals and Plants under Domestication,’ which came out in two volumes in 1867, formed the first instalment of this long-projected treatise. The second part, as he told Mr. Fiske, was to have treated of the variation of animals and plants through natural selection; while the third part would have dealt at length with the phenomena of morphology, of classification, and of distribution in space and time. But these latter portions of the work were never written. To say the truth, they were never needed. So universal was the recognition among the younger men of Darwin’s discovery, that before ten years were over innumerable workers were pushing out the consequences of natural selection into every field of biology and palaeontology. It seemed no longer so necessary as it had once seemed to write the larger and more elaborate treatise he had originally contemplated.

The volume on the variation of animals and plants contained also Darwin’s one solitary contribution to the pure speculative philosophy of life his ‘Provisional Hypothesis of Pangenesis,’ by which he strove to account on philosophical principles for the general facts of physical and mental heredity. Not to mince matters, it was his one conspicuous failure, and is now pretty universally admitted as such. Let not the love of the biographer deceive us; Darwin was here attempting a task ultra vires. As already observed, his mind, vast as it was, leaned rather to the concrete than to the abstract side: he lacked the distinctively metaphysical and speculative twist. Strange to say, too, his abortive theory appeared some years later than Herbert Spencer’s magnificent all-sided conception of ‘Physiological Units,’ put forth expressly to meet the self-same difficulty. But while Darwin’s hypothesis is rudely materialistic, Herbert Spencer’s is built up by an acute and subtle analytical perception of all the analogous facts in universal nature. It is a singular instance of a crude and essentially unphilosophic conception endeavouring to replace a finished and delicate philosophical idea.

Earlier still, in 1862, Darwin had published his wonderful and fascinating book on the ‘Fertilisation of Orchids.’ It is delightful to contemplate the picture of the unruffled naturalist, in the midst of that universal storm of ecclesiastical obloquy and scientific enthusiasm which he had roused throughout Europe, sitting down calmly in his Kentish conservatory to watch the behaviour of catasetums and masdevallias, and to work out the details of his chosen subject, with that marvellous patience of which he was so great a master, in the pettiest minutiae of fertilisation as displayed by a single highly developed family of plants. Whoever wishes to learn the full profundity of Darwin’s researches, into every point that he set himself to investigate, cannot do better than turn for a while to the consideration of that exquisite treatise on one of the quaintest fairylands of science. He will there learn by what an extraordinary wealth of cunning devices natural selection has ensured the due conveyance of the fecundating pollen from stamens to stigmas within the limits of a single group of vegetable organisms. Here the fertilising mass is gummed automatically between the eyes of the exploring bee, and then bent round by the drying of its stalk so as to come in contact with the stigmatic surface. There the pollen club is jerked out elastically by a sensitive fibre, and actually flung by its irritable antennæ at the unconscious head of the fertilising insect. In one case, the lip of the flower secretes moisture and forms a sort of cold bath, which wets the wings of the bees, so compelling them to creep out of the bucket by a passage close to the anthers and stigma; in another case, the honey is concealed at the bottom of so long a tube that only the proper fertilising moth with a proboscis of ten or eleven inches in length can probe the deep recess in which it is hidden. These, and a hundred other similar instances, were all carefully considered and described by the great naturalist as the by-work with which he filled up one of the intervals between his greater and more comprehensive treatises.

In the decade between 1860 and 1870 the progress of Darwinism was rapid and continuous. One by one, the few scientific men who still held out were overborne by the weight of evidence. Geology kept supplying fresh instances of transitional forms; the progress of research in unexplored countries kept adding to our knowledge of existing intermediate species and varieties. During those ten years, Herbert Spencer published his ‘First Principles,’ his ‘Biology,’ and the remodelled form of his ‘Psychology;’ Huxley brought out ‘Man’s Place in Nature,’ the ’Lectures on Comparative Anatomy,’ and the ’Introduction to the Classification of Animals;’ Wallace produced his ‘Malay Archipelago’ and his ‘Contributions to the Theory of Natural Selection;’ and Galton wrote his admirable work on ‘Hereditary Genius,’ of which his own family is so remarkable an instance. Tyndall and Lewes had long since signified their warm adhesion. At Oxford, Rolleston was bringing up a fresh generation of young biologists in the new faith; at Cambridge, Darwin’s old university, a whole school of brilliant and accurate physiologists was beginning to make itself both felt and heard in the world of science. In the domain of anthropology, Tylor was welcoming the assistance of the new ideas, while Lubbock was engaged on his kindred investigations into the Origin of Civilisation and the Primitive Condition of Man. All these diverse lines of thought both showed the wide-spread influence of Darwin’s first great work, and led up to the preparation of his second, in which he dealt with the history and development of the human race. And what was thus true of England was equally true of the civilised world, regarded as a whole: everywhere the great evolutionary movement was well in progress; everywhere the impulse sent forth from that quiet Kentish home was permeating and quickening the entire pulse of intelligent humanity.

Why was it that the ‘Origin of Species’ possessed this extraordinary vitalising and kinetic power, this germinal energy, this contagious force, beyond all other forms of evolutionism previously promulgated? Why did the world, that listened so coldly to Lamarck and Chambers, turn so ready an ear to Charles Darwin and natural selection? Partly, no doubt, because in the fulness of time the moment had come and the prophet had arisen. All great movements are long brewing, and burst out at last (like the Reformation and the French Revolution) with explosive energy. But the cause is largely to be found, also, I believe, in the peculiar nature of the Darwinian solution. True, a thoroughly logical mind, a mind of the very highest order, would have said even before Darwin, ’Creation can have no possible place in the physical series of things at all. How organisms came to be I do not yet exactly see; but I am sure they must have come to be by some merely physical process, if we could only find it out.’ And such minds were all actually evolutionary even before Darwin had made the modus operandi of evolution intelligible. But most people are not so clear-sighted. They require to have everything proved to them by the strictest collocation of actual instances. They will not believe unless one rise from the dead. There are men who rejected the raw doctrine of special creation on evidence adduced; and there are men who never even for a moment entertained it as conceivable. The former compose the mass of the scientific world, and it was for their conversion that the Darwinian hypothesis was so highly salutary. As Professor Fiske rightly remarks, ’The truth is that before the publication of the “Origin of Species” there was no opinion whatever current respecting the subject that deserved to be called a scientific hypothesis. That the more complex forms of life must have come into existence through some process of development from simpler forms was no doubt the only sensible and rational view to take of the subject; but in a vague and general opinion of this sort there is nothing that is properly scientific. A scientific hypothesis must connect the phenomena with which it deals by alleging a “true cause;” and before 1859 no one had suggested a “true cause” for the origination of new species, although the problem was one over which every philosophical naturalist had puzzled since the beginning of the century. This explains why Mr. Darwin’s success was so rapid and complete, and it also explains why he came so near being anticipated.’ To put it briefly, a priori, creation is from the very first unbelievable; but, as a matter of evidence, Lamarck failed to make evolution comprehensible, or to give a rationale of its mode of action, while Darwin’s theory of natural selection succeeded in doing so for those who awaited a posteriori proof. Hence Darwin was able to convert the world, where Lamarck had only been able to stir up enquiry among the picked spirits of the scientific and philosophical coterie. Therein lies the true secret of his rapid, his brilliant, and his triumphant progress. He had found out not only that it was so, but how it was so, too. In Aristotelian phrase, he had discovered the pos as well as the hoti.