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“Having reflected much on the foregoing facts, it seemed to me probable that allied species were descended from a common ancestor. But during several years I could not conceive how each form could have been modified so as to become admirably adapted to its place in nature. I began, therefore, to study domesticated animals and cultivated plants,⁷ and after a time perceived that man’s power of selecting and breeding from certain individuals was the most powerful of all means in the production of new races. Having attended to the habits of animals, and their relations to the surrounding conditions, I was able to realise the severe struggle for existence to which all organisms are subjected; and my geological observations had allowed me to appreciate, to a certain extent, the duration of past geological periods. With my mind thus prepared, I fortunately happened to read Malthus’s ‘Essay on Population;’ and the idea of natural selection through the struggle for existence at once occurred to me. Of all the subordinate points in the theory, the last which I understood was the cause of the tendency in the descendants from a common progenitor to diverge in character.”⁸

Malthus taught the inevitable tendency of all animal life to increase beyond the means of subsistence, and expounded the checks which begin to act when population increases too rapidly. But his book had lain unfruitful to naturalists since 1798, until Darwin read it, and with his special knowledge evolved from it the brilliant idea of the preservation of better-equipped races in the struggle for life, or, as Herbert Spencer put it, the survival of the fittest. At one bound the gloomy revelations of misery which the “Essay on Population” contained, were exchanged for the bright view of perpetual progress and improvement as being necessitated and brought about by the very struggle which ensued upon the natural increase of animal and plant life. Instead of struggle and pain, producing starvation and extinction merely, struggle and pain were seen as the conditions of development and improvement; the death of the lower, the life of the higher.

It is less profitable here to attempt to sketch the history of ideas of evolution in general, because that history as now revealed by research, and as detailed by many writers, was not the path along which Darwin travelled. Indeed, many of these ideas were not disinterred, and certainly were not brought to Darwin’s notice till after the publication of the “Origin of Species.” True he read Robert Chambers’s “Vestiges of Creation,” which, with its “powerful and brilliant style,” although displaying in its earlier editions “little accurate knowledge and a great want of scientific caution,” Darwin acknowledges to have done excellent service in calling attention to the subject, in removing prejudice, and in preparing the ground for the reception of analogous views. Herbert Spencer, in his Essay on the Development Hypothesis, first published in The Leader in March, 1852, and republished in his “Essays” (first series, 1858), argued that species have been modified owing to change of circumstances, basing his argument upon the analogy of domestic animals and plants, the changes which the embryos of many species undergo, and the difficulty of distinguishing species and varieties.

But we need not here dwell on the works of these thinkers, important as they are to the general history of evolutionary thought, because Darwin’s speculations had taken form long before, and he could be but slightly indebted to them. Far in advance of them he was at work collecting and testing the facts which alone could win general support for his views, and experimenting incessantly with the same object in view. Lyell and Hooker were in his confidence, and in Lyell’s letters we meet with references such as the following, dated November 13, 1854: “You probably know about this (the remarkable orchid, Catasetum), which will figure in C. Darwin’s book on ‘Species,’ with many other ‘ugly facts,’ as Hooker, clinging like me to the orthodox faith, calls these and other abnormal vagaries,” showing at the same time how completely Darwin was the leader, while his friends, advanced as they were, hung back. Again (Lyell to Hooker, July 25, 1856): “Whether Darwin persuades you and me to renounce our faith in species (when geological epochs are considered) or not, I foresee that many will go over to the indefinite modifiability doctrine.”

Further light is thrown on the progress of ideas on species by Sir Joseph Hooker’s admirably written Introductory Essay to the “Flora Novæ Zelandiæ,” dated November, 1853, in which he discusses among other questions, “The Limits of Species; their Dispersion and Variation.” While still adhering on the whole to the origin of species from single parents, or from one pair, and the permanence of specific characters, he insists that species vary more, and are more widely distributed, than is generally admitted, and that their distribution has been brought about by natural causes. In this essay he makes the following statements: “Mr. Darwin not only directed my earliest studies in the subjects of the distribution and variation of species, but has discussed with me all the arguments, and drawn my attention to many of the facts which I have endeavoured to illustrate in this essay. I know of no other way in which I can acknowledge the extent of my obligation to him, than by adding that I should never have taken up the subject in its present form but for the advantages I have derived from his friendship and encouragement.”

Appropriately enough, it was through Lyell and Hooker that the new theory was introduced to the public, and it was owing to them that Darwin did not obliterate his own claims to priority, and give them over to Alfred Russel Wallace, who had independently come to similar conclusions. The letter, dated June 30, 1858, in which the announcement was conveyed to the Linnean Society, deserves quotation, as being the authoritative and accurate record of the circumstances which launched the “Origin of Species” upon the world:

“The accompanying papers, which we have the honour of communicating to the Linnean Society, and which all relate to the same subject, viz., ‘The Laws which affect the Production of Varieties, Races, and Species,’ contain the results of the investigations of two indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred Wallace.

“These gentlemen having, independently and unknown to one another, conceived the same very ingenious theory to account for the appearance and perpetuation of varieties and of specific forms on our planet, may both fairly claim the merit of being original thinkers in this important line of inquiry; but neither of them having published his views, though Mr. Darwin has been repeatedly urged by us to do so, and both authors having now unreservedly placed their papers in our hands, we think it would best promote the interests of science that a selection from them should be laid before the Linnean Society.

“Taken in the order of their dates, they consist of —

“1. Extracts from a MS. work on species, by Mr. Darwin, which was sketched in 1839, and copied in 1844, when the copy was read by Dr. Hooker, and its contents afterwards communicated to Sir Charles Lyell. The first part is devoted to ‘The Variation of Organic Beings under Domestication and in their Natural State’; and the second chapter of that part, from which we propose to read to the Society the extracts referred to, is headed, ‘On the Variation of Organic Beings in a State of Nature; on the Natural Means of Selection; on the Comparison of Domestic Races and true Species.’

“2. An abstract of a private letter addressed to Professor Asa Gray, of Boston, U.S., in October, 1857, by Mr. Darwin, in which he repeats his views, and which shows that these remained unaltered from 1839 to 1857.

“3. An essay by Mr. Wallace, entitled ‘On the Tendency of Varieties to depart indefinitely from the Original Type.’ This was written at Ternate in February, 1858, for the perusal of his friend and correspondent, Mr. Darwin, and sent to him with the expressed wish that it should be forwarded to Sir Charles Lyell, if Mr. Darwin thought it sufficiently novel and interesting. So highly did Mr. Darwin appreciate the value of the views therein set forth, that he proposed, in a letter to Sir Charles Lyell, to obtain Mr. Wallace’s consent to allow the essay to be published as soon as possible. Of this step we highly approved, provided Mr. Darwin did not withhold from the public, as he was strongly inclined to do (in favour of Mr. Wallace) the memoir which he had himself written on the same subject, and which, as before stated, one of us had perused in 1844, and the contents of which we had both of us been privy to for many years. On representing this to Mr. Darwin, he gave us permission to make what use we thought proper of his memoir, &c.; and in adopting our present course, of presenting it to the Linnean Society, we have explained to him that we are not solely considering the relative claims to priority of himself and his friend, but the interests of science generally; for we feel it to be desirable that views founded on a wide deduction from facts, and matured by years of reflection, should constitute at once a goal from which others may start, and that, while the scientific world is waiting for the appearance of Mr. Darwin’s complete work, some of the leading results of his labours, as well as those of his able correspondent, should together be laid before the public.”

In these papers, read on July 1, 1858, Darwin’s share amounts to little more than six pages, yet within this space he describes the geometrical rate of increase of animals, the checks that occur, the effects of changed conditions, the natural selection of the better equipped forms resulting from the struggle for existence, and the influence of sexual selection. Wallace insists on essentially the same view, which he calls that of progression and continued divergence. “This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organised beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit.” Those who read Wallace’s original essay can best appreciate the extraordinary simplicity and nobility of character which inclined the elder naturalist, who had so long held the same views, to step aside in favour of the younger man, who from different researches was led to such similar conclusions. It may here be added that Hooker, in the Introductory Essay to the “Flora Tasmaniæ,” dated November 4, 1859, before the publication of the “Origin of Species,” but after seeing much of it in manuscript, accepted and advocated the view that species are derivative and mutable, and developed it as regards the geographical distribution of plants.

CHAPTER V

DARWIN’S great work “On the Origin of Species by means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life,” was published in November, 1859. It begins with the simplest narrative of the events leading to its publication, and an apology for the imperfection of “this abstract.” The author is well aware, he says, that on most points he deals with, facts can be adduced which often apparently lead to conclusions directly opposite to his own. He states clearly the important truth that a mere belief in the origin of species by descent from other species is unsatisfactory until it can be shown how species can have been modified so as to acquire their present remarkable perfection of structure and coadaptation. Consequently cases of observed modification of species are of the highest value, and precedence is given to the variation of animals and plants in a state of domestication.

The individuals belonging to the same variety of any of our long-cultivated animals or plants differ much more from each other than the individuals of any one species or variety in a state of nature. Darwin explains this by the changed conditions of their life, excess or changed quality of food, climate, changed habits, &c. Thus man has effected remarkable changes in many species by consciously or unconsciously selecting particular qualities in the animals or plants kept for use or beauty. Domestic productions seem in fact to have become plastic in man’s hands, and the inheritance of acquired qualities by offspring is reckoned on as almost certain. The breeds of cattle, poultry, dogs, and pigeons, are striking examples.

Darwin, as he tells us, kept every breed of domestic pigeons he could purchase or obtain, in order to study their variations. In this he was himself reverting to the associations of childhood, when the beauty, variety, and tameness of The Mount pigeons at Shrewsbury were well known.

We can imagine the astonishment with which the “eminent fanciers” and members of the London Pigeon Clubs, whose acquaintance the great naturalist cultivated, received the simplicity, yet depth, of his inquiries, as he came among them day after day, utilising all their lore, and yet continually asking what they neither knew nor suspected the drift of. He began his study with a prepossession against the idea of the immense diversity of modern pigeons having originated from one common stock. Yet if such modification has taken place in any creature, pigeons may furnish an example, for they have been kept and bred for thousands of years, being recorded in Egypt about 3000 b. c., and Pliny relates that their pedigree and race could be reckoned by the Romans of his time. “We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we now see them; indeed, in several cases we know that this has not been their history. The key is man’s power of accumulative selection; nature gives successive variations; man adds them up in certain directions useful to him.” This is an undoubted fact, to which breeders and fanciers give far more emphatic testimony even than Darwin. As Lord Somerville said, speaking of what breeders have done for sheep, “It would seem as if they had chalked upon a wall a form perfect in itself, and then had given it existence.”

Side by side with conscious selection goes unconscious. Two breeders, breeding from similar stock, aiming at the same end, will get different results. Aiming at a particular result, they find that with it is associated some other of which they had not dreamed. Thus through long ages our cultivated vegetables and flowers have been produced, by always selecting the best variety, and sowing its seeds. The fact which Darwin notes, that our cultivated plants and domestic breeds date from so ancient a time that we know really nothing of their origin, has an important bearing on the great antiquity of man, then scarcely imagined, now generally accepted; seeing that all domestic development depends on a variability in living creatures, which man can not produce, but can only work upon.

That variation of species occurs in a state of nature Darwin proves not only by recorded facts, but by a consideration of the chaotic condition of species-description, owing to the differences between authors as to what are species and what are varieties, one observer describing a dozen species where another reckons only one. If such divergence of opinion is possible between good observers, it is evident that there is no sufficiently clear rule for deciding what a species is, although for centuries naturalists have laboured to establish them. If species vary continually, and become modified, then this difficulty is explained.

But what is there in nature to answer to the breeder’s selection? Here comes in Darwin’s remarkable application and amplification of Malthus’s principle of population. “Nothing is easier,” he says, “than to admit in words the truth of the universal struggle for life, or more difficult – at least I have found it so – than constantly to bear this conclusion in mind. Yet unless it be thoroughly engrained in the mind, I am convinced that the whole economy of nature, with every fact on distribution, rarity, abundance, extinction, and variation will be dimly seen or quite misunderstood. We behold the face of nature bright with gladness; we often see superabundance of food; we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings are destroyed by birds and beasts of prey; we do not always bear in mind, that though food may be now superabundant, it is not so at all seasons of each recurring year.” The proofs given of the enormous rate at which animals and plants tend to increase in numbers are very striking; even the elephant, the slowest breeder of all animals, would increase from one pair to fifteen millions in the fifth century, if no check existed.

Thus every animal and plant may be said to struggle for existence with those with which it competes for space, food, light, air. The numbers are kept down by heavy destruction at various periods of life. Take the case of seedling plants. Darwin had a piece of ground three feet long and two feet wide dug and cleared, so that no grown plants existed to check the growth of seedlings of native plants as they came up. He counted and marked all that came up, and out of 357 no fewer than 295 were destroyed, chiefly by slugs and insects. So in a little plot of long-mown turf, allowed to grow freely, out of twenty species nine perished in the struggle. Many further personal observations of the author are given: such as that the winter of 1854-5 destroyed four-fifths of the birds in his own grounds; that he has sometimes failed to get a single seed from wheat or other plants in his garden.

On the estate of a relative in Staffordshire the changes consequent on planting several hundred acres with Scotch fir were remarkable. In twenty-five years twelve species of conspicuous plants, and six different insectivorous birds had become settled and flourishing inhabitants in the plantations. The characteristic of the philosopher, who sees in the unconsidered trifles of others the material for his choicest discoveries, is well exemplified in his mode of observing the results of enclosure near Farnham, in Surrey. Here a multitude of self-sown firs sprang up in the enclosures, and Darwin went to examine into the cause of the strange phenomenon. Not a fir was in sight except some distant clumps. “But on looking closely between the stems of the heath, I found a multitude of seedlings and little trees, which had been perpetually browsed down by the cattle. In one square yard, at a point some hundred yards distant from one of the old clumps, I counted thirty-two little trees; and one of them, judging from the rings of growth, had during twenty-six years tried to raise its head above the stems of the heath, and had failed.”

The interdependence of animal upon animal, of animal upon plant, of plant upon animal, is enforced in many ways by Darwin. For instance, the visits of humble-bees are of special importance to the welfare of red clover; humble-bees are largely destroyed by field-mice; cats largely destroy field-mice near villages, and so favour humble-bees, and secondarily red clover. Every paragraph of the chapter on the struggle for existence is full of suggestion, and subversive of old imaginings. But Darwin’s knowledge is to him slight, his ignorance profound. Yet, he says, notwithstanding our ignorance, “we may console ourselves with the full belief that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply.”

The great chapter on Natural Selection, or the preservation of favourable and the rejection of injurious variations, is crowded with striking passages. One of these vividly contrasts man’s selection with nature’s. “Man can act only on external and visible characters: nature cares nothing for appearances, except in so far as they may be useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good; nature only for that of the being she tends. Every selected character is fully exercised by her; and the being is placed under well-suited conditions of life… Under nature, the slightest difference of structure or constitution may well turn the nicely-balanced scale in the struggle for life, and so be preserved. How fleeting are the wishes and efforts of man! how short his time! and consequently how poor will his products be, compared with those accumulated by nature during whole geological periods. Can we wonder, then, that nature’s productions should be far ‘truer’ in character than man’s productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly bear the stamp of far higher workmanship?” The words in italics certainly are a good answer to those who think Darwin had any tendency to depreciate the marvels of nature by bringing them under the law of natural selection. But we shall gain further light on this subject later on.

The main argument may be summed up thus: if variations beneficial to any creature occur, which cannot be doubted, the individuals in whom they occur will have the best chance of surviving and transmitting their qualities to their offspring. This natural selection will tend to produce divergence of character among offspring, and to intensify differences until they equal those between species or even genera. The same tendency to improvement brings about the decay and ultimate extinction of many lower and unimproved forms of life.

One of the best examples of Darwin’s style is in the passage comparing all members of the same class of beings to a great tree. “I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications.”

What may be the laws controlling or producing variation Darwin candidly tells us he does not know. Some authors, he says, believe it to be as much the function of the reproductive system to produce individual differences, or very slight deviations of structure, as to make the child like its parents. But we certainly do not know the precise effect of any change of conditions, or what changes may be entailed in other parts of an organism by given changes in one part.⁹

Why, if species are continually being modified, do we not see multitudes of transitional forms around us? How can the elaborate structure and special habits of a bat have been formed by the modification of some animal of entirely different habits? How can the marvellous perfections of the human eye or that of one of the higher animals be supposed to have arisen through natural selection? These questions Darwin answers with powerful effect; but for the details we must refer the reader to the book itself. Incidentally he refers to objections urged against the view that every detail of structure has been produced for the good of its possessor. He says plainly that if structures have been created for beauty in the eyes of man, or for mere variety, that is fatal to his theory. Yet he admits that many structures are of no direct use to their possessors; but they have been inherited from ancestors to whom they were of use, or they have arisen as correlated changes or in dependence on some other cause, where use and benefit have been primary.

In dealing with Instinct, we see Darwin personally studying ants and bees in their social habits. The idea of ants making slaves is to him “odious,” which we can well understand after his references to slavery in South America. For three years, during June and July, he watched for many hours several ants’ nests in Surrey and Sussex to see whether the slaves ever left the nest. One day he witnessed a migration of ants from one nest to another, the masters carefully carrying their slaves in their jaws. Again, he saw a party attempting to carry off slaves, succeeding, however, only in carrying their corpses off for food to the nest. Darwin then dug up a small group of pupæ of the slave species from another nest, and put them down near the place of combat. They were eagerly seized and carried off by the tyrants, “who perhaps fancied that, after all, they had been victorious in their late combat.” At the same time the slave-owners were able to distinguish instantly the pupæ of another species, showing much terror at sight of them; yet they ultimately took heart, and carried them off.

The cell-making instinct of the hive-bee, “the most wonderful of all known instincts,” as Darwin terms it, was closely studied. The comb, “so beautifully adapted to its end,” he enthusiastically admired. Yet he finds gradation among bees, and can imagine a method by which this beautiful construction, has been gradually developed. His ideas were tested by setting bees to work on a solid piece of wax between two combs. The detailed account of these experiments is most instructive. It is quite charming to mentally follow the patient experimenter covering the edges of a single cell or the extreme margin of a growing comb with a thin layer of vermilion wax, and soon proving that many bees work in succession at a single cell by the rapid diffusion of the vermilion colouring as delicately as a painter could have done it, atoms of the coloured wax being removed and worked into the growing cells all round.¹⁰ “It was really curious,” Darwin says, “to note in cases of difficulty, as when two pieces of comb met at an angle, how often the bees would entirely pull down and rebuild in different ways the same cell, sometimes recurring to a shape which they had at first rejected.” Here surely he was watching evolution in that slow, gradual process which appears to be the rule.

The castes of neuter ants, constituting as they did “by far the most serious special difficulty” Darwin had encountered, were similarly studied; but, as expected, gradations were found connecting them, although the extremes differ markedly in shape and size. The case is most interesting, because these castes could only be developed if the variations which produced them were profitable to the community; “for no amount of exercise, or habit, or volition, in the utterly sterile members of a community could possibly have affected the structure or instincts of the fertile members, which alone leave descendants.” This fact Darwin considers to be demonstrative against Lamarck’s doctrine. At the same time, he admits that instincts are not always perfect, and are liable to make mistakes; and that no instinct has been produced for the exclusive good of other animals, but that each animal takes advantage of the instincts of others. It is to him “far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers, ants making slaves, the larvæ of ichneumonidæ feeding within the live bodies of caterpillars, not as specially endowed or created instincts, but as small consequences of one general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die.” And here Darwin strikes one of his truest and most helpful notes. It is far more satisfactory to contemplate the rapine and war of nature as incidents which aid in working out a grand progress than as multitudinous cruelties, working no good, and in past ages of unknown length merely preluding the struggle and rapine through which man works out his rise or fall. If we agonise that we and our descendants may rise, life is worth living.