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diff --git a/old/2927.txt b/old/2927.txt new file mode 100644 index 0000000..6976117 --- /dev/null +++ b/old/2927.txt @@ -0,0 +1,833 @@ +The Project Gutenberg Etext of The Darwinian Hypothesis +#16 in our series by Thomas H. Huxley + +Copyright laws are changing all over the world, be sure to check +the laws for your country before redistributing these files!!! + +Please take a look at the important information in this header. +We encourage you to keep this file on your own disk, keeping an +electronic path open for the next readers. + +Please do not remove this. + +This should be the first thing seen when anyone opens the book. +Do not change or edit it without written permission. 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Huxley + + + + + [footnote] *'Times', December 26th, 1850. + +DARWIN ON THE ORIGIN OF SPECIES. + +THERE is a growing immensity in the speculations of science to which no +human thing or thought at this day is comparable. Apart from the +results which science brings us home and securely harvests, there is an +expansive force and latitude in its tentative efforts, which lifts us +out of ourselves and transfigures our mortality. We may have a +preference for moral themes, like the Homeric sage, who had seen and +known much:-- + + "Cities of men + And manners, climates, councils, governments"; + +yet we must end by confession that + + "The windy ways of men + Are but dust which rises up + And is lightly laid again," + +in comparison with the work of nature, to which science testifies, but +which has no boundaries in time or space to which science can +approximate. + +There is something altogether out of the reach of science, and yet the +compass of science is practically illimitable. Hence it is that from +time to time we are startled and perplexed by theories which have no +parallel in the contracted moral world; for the generalizations of +science sweep on in ever-widening circles, and more aspiring flights, +through a limitless creation. While astronomy, with its telescope, +ranges beyond the known stars, and physiology, with its microscope, is +subdividing infinite minutiae, we may expect that our historic +centuries may be treated as inadequate counters in the history of the +planet on which we are placed. We must expect new conceptions of the +nature and relations of its denizens, as science acquires the materials +for fresh generalizations; nor have we occasion for alarms if a highly +advanced knowledge, like that of the eminent Naturalist before us, +confronts us with an hypothesis as vast as it is novel. This +hypothesis may or may not be sustainable hereafter; it may give way to +something else, and higher science may reverse what science has here +built up with so much skill and patience, but its sufficiency must be +tried by the tests of science alone, if we are to maintain our position +as the heirs of Bacon and the acquitters of Galileo. We must weigh +this hypothesis strictly in the controversy which is coming, by the only +tests which are appropriate, and by no others whatsoever. + +The hypothesis to which we point, and of which the present work of Mr. +Darwin is but the preliminary outline, may be stated in his own +language as follows:--"Species originated by means of natural +selection, or through the preservation of the favoured races in the +struggle for life." To render this thesis intelligible, it is +necessary to interpret its terms. In the first place, what is a +species? The question is a simple one, but the right answer to it is +hard to find, even if we appeal to those who should know most about +it. It is all those animals or plants which have descended from a +single pair of parents; it is the smallest distinctly definable group +of living organisms; it is an eternal and immutable entity; it is a mere +abstraction of the human intellect having no existence in nature. Such +are a few of the significations attached to this simple word which may +be culled from authoritative sources; and if, leaving terms and +theoretical subtleties aside, we turn to facts and endeavour to gather a +meaning for ourselves, by studying the things to which, in practice, +the name of species is applied, it profits us little. For practice +varies as much as theory. Let the botanist or the zoologist examine and +describe the productions of a country, and one will pretty certainly +disagree with the other as to the number, limits, and definitions of +the species into which he groups the very same things. In these +islands, we are in the habit of regarding mankind as of one species, but +a fortnight's steam will land us in a country where divines and +savants, for once in agreement, vie with one another in loudness of +assertion, if not in cogency of proof, that men are of different +species; and, more particularly, that the species negro is so distinct +from our own that the Ten Commandments have actually no reference to +him. Even in the calm region of entomology, where, if anywhere in this +sinful world, passion and prejudice should fail to stir the mind, one +learned coleopterist will fill ten attractive volumes with descriptions +of species of beetles, nine-tenths of which are immediately declared by +his brother beetle-mongers to be no species at all. + +The truth is that the number of distinguishable living creatures almost +surpasses imagination. At least a hundred thousand such kinds of +insects alone have been described and may be identified in collections, +and the number of separable kinds of living things is under estimated +at half a million. Seeing that most of these obvious kinds have their +accidental varieties, and that they often shade into others by +imperceptible degrees, it may well be imagined that the task of +distinguishing between what is permanent and what fleeting, what is a +species and what a mere variety, is sufficiently formidable. + +But is it not possible to apply a test whereby a true species may be +known from a mere variety? Is there no criterion of species? Great +authorities affirm that there is--that the unions of members of the +same species are always fertile, while those of distinct species are +either sterile, or their offspring, called hybrids, are so. It is +affirmed not only that this is an experimental fact, but that it is a +provision for the preservation of the purity of species. Such a +criterion as this would be invaluable; but, unfortunately, not only is +it not obvious how to apply it in the great majority of cases in which +its aid is needed, but its general validity is stoutly denied. The +Hon. and Rev. Mr. Herbert, a most trustworthy authority, not only +asserts as the result of his own observations and experiments that many +hybrids are quite as fertile as the parent species, but he goes so far +as to assert that the particular plant 'Crinum capense' is much more +fertile when crossed by a distinct species than when fertilised by its +proper pollen! On the other hand, the famous Gaertner, though he took +the greatest pains to cross the primrose and the cowslip, succeeded +only once or twice in several years; and yet it is a well-established +fact that the primrose and the cowslip are only varieties of the same +kind of plant. Again, such cases as the following are well +established. The female of species A, if crossed with the male of +species B, is fertile; but, if the female of B is crossed with the male +of A, she remains barren. Facts of this kind destroy the value of the +supposed criterion. + +If, weary of the endless difficulties involved in the determination of +species, the investigator, contenting himself with the rough practical +distinction of separable kinds, endeavours to study them as they occur +in nature--to ascertain their relations to the conditions which +surround them, their mutual harmonies and discordances of structure, +the bond of union of their parts and their past history, he finds +himself, according to the received notions, in a mighty maze, and with, +at most, the dimmest adumbration of a plan. If he starts with any one +clear conviction, it is that every part of a living creature is +cunningly adapted to some special use in its life. Has not his Paley +told him that that seemingly useless organ, the spleen, is beautifully +adjusted as so much packing between the other organs? And yet, at the +outset of his studies, he finds that no adaptive reason whatsoever can +be given for one-half of the peculiarities of vegetable structure; he +also discovers rudimentary teeth, which are never used, in the gums of +the young calf and in those of the foetal whale; insects which never +bite have rudimental jaws, and others which never fly have rudimental +wings; naturally blind creatures have rudimental eyes; and the halt +have rudimentary limbs. So, again, no animal or plant puts on its +perfect form at once, but all have to start from the same point, +however various the course which each has to pursue. Not only men and +horses, and cats and dogs, lobsters and beetles, periwinkles and +mussels, but even the very sponges and animalcules commence their +existence under forms which are essentially undistinguishable; and this +is true of all the infinite variety of plants. Nay, more, all living +beings march side by side along the high road of development, and +separate the later the more like they are; like people leaving church, +who all go down the aisle, but having reached the door some turn into +the parsonage, others go down the village, and others part only in the +next parish. A man in his development runs for a little while parallel +with, though never passing through, the form of the meanest worm, then +travels for a space beside the fish, then journeys along with the bird +and the reptile for his fellow travellers; and only at last, after a +brief companionship with the highest of the four-footed and four-handed +world, rises into the dignity of pure manhood. No competent thinker of +the present day dreams of explaining these indubitable facts by the +notion of the existence of unknown and undiscoverable adaptations to +purpose. And we would remind those who, ignorant of the facts, must be +moved by authority, that no one has asserted the incompetence of the +doctrine of final causes, in its application to physiology and anatomy, +more strongly than our own eminent anatomist, Professor Owen, who, +speaking of such cases, says ('On the Nature of Limbs', pp. 39, 40): "I +think it will be obvious that the principle of final adaptations fails +to satisfy all the conditions of the problem." + +But, if the doctrine of final causes will not help us to comprehend the +anomalies of living structure, the principle of adaptation must surely +lead us to understand why certain living beings are found in certain +regions of the world and not in others. The palm, as we know, will not +grow in our climate, nor the oak in Greenland. The white bear cannot +live where the tiger thrives, nor 'vice versa', and the more the +natural habits of animal and vegetable species are examined, the more +do they seem, on the whole, limited to particular provinces. But when +we look into the facts established by the study of the geographical +distribution of animals and plants it seems utterly hopeless to attempt +to understand the strange and apparently capricious relations which +they exhibit. One would be inclined to suppose 'a priori' that every +country must be naturally peopled by those animals that are fittest to +live and thrive in it. And yet how, on this hypothesis, are we to +account for the absence of cattle in the Pampas of South America, when +those parts of the New World were discovered? It is not that they were +unfit for cattle, for millions of cattle now run wild there; and the +like holds good of Australia and New Zealand. It is a curious +circumstance, in fact, that the animals and plants of the Northern +Hemisphere are not only as well adapted to live in the Southern +Hemisphere as its own autochthones, but are in many cases absolutely +better adapted, and so overrun and extirpate the aborigines. Clearly, +therefore, the species which naturally inhabit a country are not +necessarily the best adapted to its climate and other conditions. The +inhabitants of islands are often distinct from any other known species +of animal or plants (witness our recent examples from the work of Sir +Emerson Tennent, on Ceylon), and yet they have almost always a sort of +general family resemblance to the animals and plants of the nearest +mainland. On the other hand, there is hardly a species of fish, shell, +or crab common to the opposite sides of the narrow isthmus of Panama. +Wherever we look, then, living nature offers us riddles of difficult +solution, if we suppose that what we see is all that can be known of it. + +But our knowledge of life is not confined to the existing world. +Whatever their minor differences, geologists are agreed as to the vast +thickness of the accumulated strata which compose the visible part of +our earth, and the inconceivable immensity of the time of whose lapse +they are the imperfect, but the only accessible witnesses. Now, +throughout the greater part of this long series of stratified rocks are +scattered, sometimes very abundantly, multitudes of organic remains, +the fossilized exuviae of animals and plants which lived and died while +the mud of which the rocks are formed was yet soft ooze, and could +receive and bury them. It would be a great error to suppose that these +organic remains were fragmentary relics. Our museums exhibit fossil +shells of immeasurable antiquity, as perfect as the day they were +formed, whole skeletons without a limb disturbed--nay, the changed +flesh, the developing embryos, and even the very footsteps of primieval +organisms. Thus the naturalist finds in the bowels of the earth +species as well defined as, and in some groups of animals more numerous +than, those that breathe the upper air. But, singularly enough, the +majority of these entombed species are wholly distinct from those that +now live. Nor is this unlikeness without its rule and order. As a +broad fact, the further we go back in time the less the buried species +are like existing forms; and the further apart the sets of extinct +creatures are the less they are like one another. In other words, +there has been a regular succession of living beings, each younger set +being in a very broad and general sense somewhat more like those which +now live. + +It was once supposed that this succession had been the result of vast +successive catastrophes, destructions, and re-creations 'en masse'; but +catastrophes are now almost eliminated from geological, or at least +palaeontological speculation; and it is admitted on all hands that the +seeming breaks in the chain of being are not absolute, but only relative +to our imperfect knowledge; that species have replaced species, not in +assemblages, but one by one; and that, if it were possible to have all +the phenomena of the past presented to us, the convenient epochs and +formations of the geologist, though having a certain distinctness, would +fade into one another with limits as undefinable as those of the +distinct and yet separable colours of the solar spectrum. + +Such is a brief summary of the main truths which have been established +concerning species. Are these truths ultimate and irresolvable facts, +or are their complexities and perplexities the mere expressions of a +higher law? + +A large number of persons practically assume the former position to be +correct. They believe that the writer of the Pentateuch was empowered +and commissioned to teach us scientific as well as other truth, that +the account we find there of the creation of living things is simply +and literally correct, and that anything which seems to contradict it +is, by the nature of the case, false. All the phenomena which have +been detailed are, on this view, the immediate product of a creative +fiat and consequently are out of the domain of science altogether. + +Whether this view prove ultimately to be true or false, it is, at any +rate, not at present supported by what is commonly regarded as logical +proof, even if it be capable of discussion by reason; and hence we +consider ourselves at liberty to pass it by, and to turn to those views +which profess to rest on a scientific basis only, and therefore admit of +being argued to their consequences. And we do this with the less +hesitation as it so happens that those persons who are practically +conversant with the facts of the case (plainly a considerable advantage) +have always thought fit to range themselves under the latter category. + +The majority of these competent persons have up to the present time +maintained two positions,--the first, that every species is, within +certain defined or definable limits, fixed and incapable of +modification; the second, that every species was originally produced by +a distinct creative act. The second position is obviously incapable of +proof or disproof, the direct operations of the Creator not being +subjects of science; and it must therefore be regarded as a corollary +from the first, the truth or falsehood of which is a matter of evidence. +Most persons imagine that the arguments in favour of it are +overwhelming; but to some few minds, and these, it must be confessed, +intellects of no small power and grasp of knowledge, they have not +brought conviction. Among these minds, that of the famous naturalist +Lamarck, who possessed a greater acquaintance with the lower forms of +life than any man of his day, Cuvier not excepted, and was a good +botanist to boot, occupies a prominent place. + +Two facts appear to have strongly affected the course of thought of this +remarkable man--the one, that finer or stronger links of affinity +connect all living beings with one another, and that thus the highest +creature grades by multitudinous steps into the lowest; the other, that +an organ may be developed in particular directions by exerting itself +in particular ways, and that modifications once induced may be +transmitted and become hereditary. Putting these facts together, +Lamarck endeavoured to account for the first by the operation of the +second. Place an animal in new circumstances, says he, and its needs +will be altered; the new needs will create new desires, and the attempt +to gratify such desires will result in an appropriate modification of +the organs exerted. Make a man a blacksmith, and his brachial muscles +will develop in accordance with the demands made upon them, and in like +manner, says Lamarck, "the efforts of some short-necked bird to catch +fish without wetting himself have, with time and perseverance, given +rise to all our herons and long-necked waders." + +The Lamarckian hypothesis has long since been justly condemned, and it +is the established practice for every tyro to raise his heel against +the carcass of the dead lion. But it is rarely either wise or +instructive to treat even the errors of a really great man with mere +ridicule, and in the present case the logical form of the doctrine +stands on a very different footing from its substance. + +If species have really arisen by the operation of natural conditions, we +ought to be able to find those conditions now at work; we ought to be +able to discover in nature some power adequate to modify any given kind +of animal or plant in such a manner as to give rise to another kind, +which would be admitted by naturalists as a distinct species. Lamarck +imagined that he had discovered this 'vera causa' in the admitted facts +that some organs may be modified by exercise; and that modifications, +once produced, are capable of hereditary transmission. It does not +seem to have occurred to him to inquire whether there is any reason to +believe that there are any limits to the amount of modification +producible, or to ask how long an animal is likely to endeavour to +gratify an impossible desire. The bird, in our example, would surely +have renounced fish dinners long before it had produced the least effect +on leg or neck. + +Since Lamarck's time, almost all competent naturalists have left +speculations on the origin of species to such dreamers as the author of +the 'Vestiges', by whose well-intentioned efforts the Lamarckian theory +received its final condemnation in the minds of all sound thinkers. +Notwithstanding this silence, however, the transmutation theory, as it +has been called, has been a "skeleton in the closet" to many an honest +zoologist and botanist who had a soul above the mere naming of dried +plants and skins. Surely, has such an one thought, nature is a mighty +and consistent whole, and the providential order established in the +world of life must, if we could only see it rightly, be consistent with +that dominant over the multiform shapes of brute matter. But what is +the history of astronomy, of all the branches of physics, of chemistry, +of medicine, but a narration of the steps by which the human mind has +been compelled, often sorely against its will, to recognize the +operation of secondary causes in events where ignorance beheld an +immediate intervention of a higher power? And when we know that living +things are formed of the same elements as the inorganic world, that they +act and react upon it, bound by a thousand ties of natural piety, is it +probable, nay is it possible, that they, and they alone, should have no +order in their seeming disorder, no unity in their seeming +multiplicity, should suffer no explanation by the discovery of some +central and sublime law of mutual connexion? + +Questions of this kind have assuredly often arisen, but it might have +been long before they received such expression as would have commanded +the respect and attention of the scientific world, had it not been for +the publication of the work which prompted this article. Its author, +Mr. Darwin, inheritor of a once celebrated name, won his spurs in +science when most of those now distinguished were young men, and has +for the last 20 years held a place in the front ranks of British +philosophers. After a circumnavigatory voyage, undertaken solely for +the love of his science, Mr. Darwin published a series of researches +which at once arrested the attention of naturalists and geologists; his +generalizations have since received ample confirmation, and now command +universal assent, nor is it questionable that they have had the most +important influence on the progress of science. More recently Mr. +Darwin, with a versatility which is among the rarest of gifts, turned +his attention to a most difficult question of zoology and minute +anatomy; and no living naturalist and anatomist has published a better +monograph than that which resulted from his labours. Such a man, at +all events, has not entered the sanctuary with unwashed hands, and when +he lays before us the results of 20 years' investigation and reflection +we must listen even though we be disposed to strike. But, in reading +his work it must be confessed that the attention which might at first +be dutifully, soon becomes willingly, given, so clear is the author's +thought, so outspoken his conviction, so honest and fair the candid +expression of his doubts. Those who would judge the book must read it; +we shall endeavour only to make its line of argument and its +philosophical position intelligible to the general reader in our own +way. + +The Baker-street Bazaar has just been exhibiting its familiar annual +spectacle. Straight-backed, small-headed, big-barrelled oxen, as +dissimilar from any wild species as can well be imagined, contended for +attention and praise with sheep of half-a-dozen different breeds and +styes of bloated preposterous pigs, no more like a wild boar or sow than +a city alderman is like an ourang-outang. The cattle show has been, +and perhaps may again be, succeeded by a poultry show, of whose crowing +and clucking prodigies it can only be certainly predicated that they +will be very unlike the aboriginal 'Phasianus gallus'. If the seeker +after animal anomalies is not satisfied, a turn or two in Seven Dials +will convince him that the breeds of pigeons are quite as extraordinary +and unlike one another and their parent stock, while the Horticultural +Society will provide him with any number of corresponding vegetable +aberrations from nature's types. He will learn with no little surprise, +too, in the course of his travels, that the proprietors and producers +of these animal and vegetable anomalies regard them as distinct +species, with a firm belief, the strength of which is exactly +proportioned to their ignorance of scientific biology, and which is the +more remarkable as they are all proud of their skill in 'originating' +such "species." + +On careful inquiry it is found that all these, and the many other +artificial breeds or races of animals and plants, have been produced by +one method. The breeder--and a skilful one must be a person of much +sagacity and natural or acquired perceptive faculty--notes some slight +difference, arising he knows not how, in some individuals of his stock. +If he wish to perpetuate the difference, to form a breed with the +peculiarity in question strongly marked, he selects such male and +female individuals as exhibit the desired character, and breeds from +them. Their offspring are then carefully examined, and those which +exhibit the peculiarity the most distinctly are selected for breeding, +and this operation is repeated until the desired amount of divergence +from the primitive stock is reached. It is then found that by +continuing the process of selection--always breeding, that is, from +well-marked forms, and allowing no impure crosses to interfere,--a race +may be formed, the tendency of which to reproduce itself is exceedingly +strong; nor is the limit to the amount of divergence which may be thus +produced known, but one thing is certain, that, if certain breeds of +dogs, or of pigeons, or of horses, were known only in a fossil state, +no naturalist would hesitate in regarding them as distinct species. + +But, in all these cases we have 'human interference'. Without the +breeder there would be no selection, and without the selection no +race. Before admitting the possibility of natural species having +originated in any similar way, it must be proved that there is in nature +some power which takes the place of man, and performs a selection 'sua +sponte'. It is the claim of Mr. Darwin that he professes to have +discovered the existence and the 'modus operandi' of this natural +selection, as he terms it; and, if he be right, the process is perfectly +simple and comprehensible, and irresistibly deducible from very +familiar but well nigh forgotten facts. + +Who, for instance, has duly reflected upon all the consequences of the +marvellous struggle for existence which is daily and hourly going on +among living beings? Not only does every animal live at the expense of +some other animal or plant, but the very plants are at war. The ground +is full of seeds that cannot rise into seedlings; the seedlings rob one +another of air, light and water, the strongest robber winning the day, +and extinguishing his competitors. Year after year, the wild animals +with which man never interferes are, on the average, neither more nor +less numerous than they were; and yet we know that the annual produce of +every pair is from one to perhaps a million young,--so that it is +mathematically certain that, on the average, as many are killed by +natural causes as are born every year, and those only escape which +happen to be a little better fitted to resist destruction than those +which die. The individuals of a species are like the crew of a +foundered ship, and none but good swimmers have a chance of reaching +the land. + +Such being unquestionably the necessary conditions under which living +creatures exist, Mr. Darwin discovers in them the instrument of +natural selection. Suppose that in the midst of this incessant +competition some individuals of a species (A) present accidental +variations which happen to fit them a little better than their fellows +for the struggle in which they are engaged, then the chances are in +favour, not only of these individuals being better nourished than the +others, but of their predominating over their fellows in other ways, and +of having a better chance of leaving offspring, which will of course +tend to reproduce the peculiarities of their parents. Their offspring +will, by a parity of reasoning, tend to predominate over their +contemporaries, and there being (suppose) no room for more than one +species such as A, the weaker variety will eventually be destroyed by +the new destructive influence which is thrown into the scale, and the +stronger will take its place. Surrounding conditions remaining +unchanged, the new variety (which we may call B)--supposed, for +argument's sake, to be the best adapted for these conditions which can +be got out of the original stock--will remain unchanged, all accidental +deviations from the type becoming at once extinguished, as less fit for +their post than B itself. The tendency of B to persist will grow with +its persistence through successive generations, and it will acquire all +the characters of a new species. + +But, on the other hand, if the conditions of life change in any degree, +however slight, B may no longer be that form which is best adapted to +withstand their destructive, and profit by their sustaining, influence; +in which case if it should give rise to a more competent variety (C), +this will take its place and become a new species; and thus, by +'natural selection', the species B and C will be successively derived +from A. + +That this most ingenious hypothesis enables us to give a reason for many +apparent anomalies in the distribution of living beings in time and +space, and that it is not contradicted by the main phenomena of life +and organization appear to us to be unquestionable; and so far it must +be admitted to have an immense advantage over any of its predecessors. +But it is quite another matter to affirm absolutely either the truth or +falsehood of Mr. Darwin's views at the present stage of the inquiry. +Goethe has an excellent aphorism defining that state of mind which he +calls 'Thatige Skepsis'a--active doubt. It is doubt which so loves +truth that it neither dares rest in doubting, nor extinguish itself by +unjustified belief; and we commend this state of mind to students of +species, with respect to Mr. Darwin's or any other hypothesis, as to +their origin. The combined investigations of another 20 years may, +perhaps, enable naturalists to say whether the modifying causes and the +selective power, which Mr. Darwin has satisfactorily shown to exist in +nature, are competent to produce all the effects he ascribes to them, +or whether, on the other hand, he has been led to over-estimate the +value of his principle of natural selection, as greatly as Lamarck +overestimated his vera causa of modification by exercise. + +But there is, at all events, one advantage possessed by the more recent +writer over his predecessor. Mr. Darwin abhors mere speculation as +nature abhors a vacuum. He is as greedy of cases and precedents as any +constitutional lawyer, and all the principles he lays down are capable +of being brought to the test of observation and experiment. The path +he bids us follow professes to be, not a mere airy track, fabricated of +ideal cobwebs, but a solid and broad bridge of facts. If it be so, it +will carry us safely over many a chasm in our knowledge, and lead us to +a region free from the snares of those fascinating but barren Virgins, +the Final Causes, against whom a high authority has so justly warned us. +"My sons, dig in the vineyard," were the last words of the old man in +the fable; and, though the sons found no treasure, they made their +fortunes by the grapes. + + + + + +End of The Project Gutenberg Etext of The Darwinian Hypothesis +by Thomas H. Huxley + |