Life of Charles Darwin

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.

We cannot follow in detail the profoundly suggestive chapters on Hybridism, on the Imperfection of the Geological Record, on the Geological Succession of Organic Beings, on the Geographical Distribution, and on the Mutual Affinity of Plants and Animals. The first of these is one of the most difficult portions of the subject, and yet remains as a stumbling-block of science by its apparently inexplicable phenomena. The author throws on the past history of life on the earth the glamour of a fairy record, as he contemplates the infinite number of generations, which the mind cannot grasp, which must have succeeded one another in the long roll of years, the limited extent to which at any time fossil remains have been preserved, the immense amount of destruction of such records which has taken place; and hence argues most powerfully how improbable it is that the transitional stages from species to species should have been handed down and also (another rare chance) have been laid open to us. The great array of facts about extinct animals and plants is shown to be consistent with, and to be largely explained by, descent with modification, and to be incomprehensible on any other view. The eccentric contrasts and parallelisms displayed in the geographical distribution of plants and animals, the striking effects of barriers such as mountains, deserts, and seas, the phenomena of dispersion of living creatures, the indications of old glacial periods in the present distribution of Alpine plants, the strange distribution of fresh-water animals and plants, the specialities of oceanic islands, and many other subjects of a like kind, are dealt with, all being turned to advantage, and shown to give strong support to Darwin’s view.

Classification and classifiers are all made to bear testimony in the same direction. Morphology, which, in the hands of Huxley, Haeckel, Gegenbaur, Ray Lankester, and Balfour has, since the first issue of the “Origin of Species,” grown into a coherent science, based on embryology, was even then seen by Darwin to yield evidence for his views. Examining very young animals, he found that in very distinct races of dogs and horses the young had by no means acquired their adult differences. He compared pigeons of extremely various breeds twelve hours after being hatched, and found their differences incomparably less than in the full-grown birds. How immensely morphological science has progressed since Darwin directed investigation into this profitable line would need a separate treatise to show; but it is not too much to say that embryology alone, without other evidence, would now suffice to prove the doctrine of descent with adaptive modification.

Rudimentary organs, again, strange appearances, like the presence of teeth in unborn whales and in the front of the upper jaws of unborn calves, the rudimentary wings of many insects, the rudimentary stamens or pistils of many flowers, are all swept into the Darwinian net. “Nothing can be plainer than that wings are formed for flight; yet in how many insects do we see wings so reduced in size as to be utterly incapable of flight, and not rarely lying under wing-cases, firmly soldered together?” These phenomena are all explicable if descent with modification is true.

Approaching the close of his work, the author expressed his doubts of being able to convert naturalists of long standing to his views; but based his main hopes on young and rising men approaching these questions without prejudices. He put some puzzling questions, however, to those who might oppose him. Did they really believe that at innumerable periods in the earth’s history certain atoms had been commanded suddenly to flash into living tissues? Were animals and plants created as eggs or seed or as full grown? At each act of creation was one individual or were many produced? For himself, he came to the conclusion that all organic beings had descended from some one primordial form into which life was first breathed.

On this view Darwin predicted that a great increase of interest in many departments of natural history would arise. “When we no longer look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate every complex structure and instinct as the summing up of many contrivances, each useful to the possessor, nearly in the same way as when we look at any great mechanical invention as the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting – I speak from experience – will the study of natural history become… The whole history of the world, as at present known, although of a length quite incomprehensible to us, will hereafter be recognized as a mere fragment of time compared with the ages which have elapsed since the first creature, the progenitor of innumerable extinct and living descendants, was created… We may look forward with some confidence to a secure future of equally inappreciable length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.” The concluding sentence of the “Origin of Species” has become one of our classical quotations. “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”