by Grant Allen
This last consideration leads us up to the argument from Geographical Distribution. In considering the various local faunas and floras on the face of the globe, no point strikes one more forcibly than the fact that neither their similarities nor their dissimilarities can be accounted for by climate or physical conditions. The animals of South Africa do not in the least resemble the animals of the corresponding belt of South America; the Australian beasts and birds and trees are utterly unlike those of France and Germany; the fishes and crustaceans of the Pacific at Panama are widely different from those of the Caribbean at the same point, separated from them only by the narrow belt of intervening isthmus. On the other hand, within the same continuous areas of sea or land, however great the differences of physical conditions, we find everywhere closely related types in possession of the most distinct and varied situations. On the burning plains of La Plata we get the agouti and the bizcacha as the chief rodents; we ascend the Cordillera, and close to the eternal snows we discover, not hares and rabbits like those of Europe, but a specialised chilly mountain form of the same distinctly South American type. We turn to the rivers, and we see no musk-rat or beaver, but the coypu and capybara, slightly altered varieties of the original bizcacha ancestor. Australia has no wolf, but it has instead fierce and active carnivorous marsupials; it has no mice, but some of its tiny kangaroo-like creatures fulfil analogous functions in its animal economy. Everywhere the evidence points to the conclusion that local species have been locally evolved from pre-existing similar species. The oceanic isles, of which Darwin had had so large an experience, and especially his old friends the Galapagos, come in usefully for this stage of the question. They are invariably inhabited, as Darwin pointed out, and as Wallace has since abundantly shown in the minutest detail, by waifs and strays from neighbouring continents, altered and specialised by natural selection in accordance with the conditions of their new habitat. As a rule, they point back to the districts whence blow the strongest and most prevalent winds; and the modifications they have undergone are largely dependent upon the nature of the other species with which they have to compete, or to whose habits they must needs accommodate themselves. In such cases it is easy to see how far Darwin’s special conception of natural selection helps to explain and account for facts not easily explicable by the older evolutionism of mere descent with modification.
Embryology, the study of early development in the individual animal or plant, also throws much side light upon the nature and ancestry of each species or family. For example, gorse, which is a member of the pea-flower tribe, has in its adult stage solid, spiny, thorn-like leaves, none of which in the least resemble the foliage of the clover, to which it is closely related; but the young seedling in its earliest stages has trefoil leaves, which only slowly pass by infinitesimal gradations into flat blades and finally into the familiar defensive prickles. Here, natural selection under stress of herbivorous animals on open heaths and commons has spared only those particular gorse-bushes which varied in the direction of the stiffest and most inedible foliage; but the young plant in its first days still preserves for us the trefoil leaf which it shared originally with a vast group of clover-like congeners. The adult barnacle, once more, presents a certain fallacious external resemblance to a mollusk, and was actually so classed even by the penetrating and systematic intellect of Cuvier; but a glance at the larva shows an instructed eye at once that it is really a shell-making and abnormal crustacean. On a wider scale, the embryos of mammals are at first indistinguishable from those of birds or reptiles; the feet of lizards, the hoofs of horses, the hands of man, the wings of the bat, the pinions of birds, all arise from the same fundamental shapeless bud, in the same spot of an almost identical embryo. Even the human foetus, at a certain stage of its development, is provided with gill-slits, which point dimly back to the remote ages when its ancestor was something very like a fish. The embryo is a picture, more or less obscured and blurred in its outline, of the common progenitor of a whole great class of plants or animals.
Finally, classification points in the same way to the affiliation of all existing genera and species upon certain early divergent ancestors. The whole scheme of the biological system, as initiated by Linnæus and improved by Cuvier, Jussieu, De Candolle, and their successors, is essentially that of a genealogical tree. The prime central vertebrate ancestor — to take the case of the creatures most familiar to the general reader — appears to have been an animal not unlike the existing lancelet, a mud-haunting, cartilaginous, undeveloped fish, whose main lineaments are also embryologically preserved for us in the ascidian larva and the common tadpole. From this early common centre have been developed, apparently, in one direction the fishes, and in another the amphibian tribes of frogs, newts, salamanders, and axolotls. From an early amphibian, again, the common ancestor of birds, reptiles, and mammals seems to have diverged: the intermediate links between bird and reptile being faintly traced among the extinct deinosaurians and the archæopteryx, some years subsequently to the first appearance of the ‘Origin of Species;’ while the ornithorhyncus, which to some extent connects the mammals, and especially the marsupials, with the lower egg-laying types of vertebrate, was already well-known and thoroughly studied before the publication of Darwin’s great work. Throughout, the indications given by all the chief tribes of animals and plants point back to slow descent and divergence from common ancestors; and all the subsequent course of palæontological research has supplied us rapidly, one after another, with the remains of just such undifferentiated family starting-points.
Stress has mainly been laid, in this brief and necessarily imperfect abstract, on the essentially Darwinian principle of natural selection. But Darwin did not himself attribute everything to this potent factor in the moulding of species. ‘I am convinced,’ he wrote pointedly in the introduction to his first edition, ‘that natural selection has been the main but not the exclusive means of modification.’ He attributed considerable importance as well to the Lamarckian principle of use and disuse, already so fully insisted upon before him by Mr. Herbert Spencer. The chief factors in his compound theory, as given in his own words at the end of his work, areas follows: ‘Growth with Reproduction; Inheritance, which is almost implied by reproduction; Variability, from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase, so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character, and the Extinction of the less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows.’
Such was the simple and inoffensive-looking bombshell which Darwin launched from his quiet home at Down into the very midst of the teleological camp in the peaceful year 1859. Subsequent generations will remember the date as a crisis and turning-point in the history of mankind.
The remainder of the present chapter, which consists almost entirely of an exposition of the doctrine of natural selection, may safely be skipped by the reader already well acquainted with the Origin of Species. The abstract is taken for the most part from the latest and fullest enlarged edition, but attention is usually called in passing to the points which did not appear in the first issue of 1859.
The researches of Seebohm and others have since proved that this is really the case to a far greater extent than Darwin was aware of in 1859, or, indeed, till many years afterward.
CHAPTER VII.
THE DARWINIAN REVOLUTION BEGINS.
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.
