Читать книгу The Foundations of the Origin of Species - Чарльз Дарвин, Darwin Charles - Страница 3

Let us see how far above principles of variation apply to wild animals. Wild animals vary exceedingly little – yet they are known as individuals47. British Plants, in many genera number quite uncertain of varieties and species: in shells chiefly external conditions48. Primrose and cowslip. Wild animals from different [countries can be recognized]. Specific character gives some organs as varying. Variations analogous in kind, but less in degree with domesticated animals – chiefly external and less important parts.

Our experience would lead us to expect that any and every one of these organisms would vary if «the organism were» taken away «?» and placed under new conditions. Geology proclaims a constant round of change, bringing into play, by every possible «?» change of climate and the death of pre-existing inhabitants, endless variations of new conditions. These «?» generally very slow, doubtful though «illegible» how far the slowness «?» would produce tendency to vary. But Geolog«ists» show change in configuration which, together with the accidents of air and water and the means of transportal which every being possesses, must occasionally bring, rather suddenly, organism to new conditions and «?» expose it for several generations. Hence «?» we should expect every now and then a wild form to vary49; possibly this may be cause of some species varying more than others.

According to nature of new conditions, so we might expect all or majority of organisms born under them to vary in some definite way. Further we might expect that the mould in which they are cast would likewise vary in some small degree. But is there any means of selecting those offspring which vary in the same manner, crossing them and keeping their offspring separate and thus producing selected races: otherwise as the wild animals freely cross, so must such small heterogeneous varieties be constantly counter-balanced and lost, and a uniformity of character [kept up] preserved. The former variation as the direct and necessary effects of causes, which we can see can act on them, as size of body from amount of food, effect of certain kinds of food on certain parts of bodies &c. &c.; such new varieties may then become adapted to those external [natural] agencies which act on them. But can varieties be produced adapted to end, which cannot possibly influence their structure and which it is absurd to look «at» as effects of chance. Can varieties like some vars of domesticated animals, like almost all wild species be produced adapted by exquisite means to prey on one animal or to escape from another, – or rather, as it puts out of question effects of intelligence and habits, can a plant become adapted to animals, as a plant which cannot be impregnated without agency of insect; or hooked seeds depending on animal“s existence: woolly animals cannot have any direct effect on seeds of plant. This point which all theories about climate adapting woodpecker50 to crawl «?» up trees, «illegible» miseltoe, «sentence incomplete». But if every part of a plant or animal was to vary «illegible», and if a being infinitely more sagacious than man (not an omniscient creator) during thousands and thousands of years were to select all the variations which tended towards certain ends ([or were to produce causes «?» which tended to the same end]), for instance, if he foresaw a canine animal would be better off, owing to the country producing more hares, if he were longer legged and keener sight, – greyhound produced51. If he saw that aquatic «animal would need» skinned toes. If for some unknown cause he found it would advantage a plant, which «?» like most plants is occasionally visited by bees &c.: if that plant’s seed were occasionally eaten by birds and were then carried on to rotten trees, he might select trees with fruit more agreeable to such birds as perched, to ensure their being carried to trees; if he perceived those birds more often dropped the seeds, he might well have selected a bird who would «illegible» rotten trees or [gradually select plants which «he» had proved to live on less and less rotten trees]. Who, seeing how plants vary in garden, what blind foolish man has done52 in a few years, will deny an all-seeing being in thousands of years could effect (if the Creator chose to do so), either by his own direct foresight or by intermediate means, – which will represent «?» the creator of this universe. Seems usual means. Be it remembered I have nothing to say about life and mind and all forms descending from one common type53. I speak of the variation of the existing great divisions of the organised kingdom, how far I would go, hereafter to be seen.

Before considering whether «there» be any natural means of selection, and secondly (which forms the 2nd Part of this sketch) the far more important point whether the characters and relations of animated «things» are such as favour the idea of wild species being races «?» descended from a common stock, as the varieties of potato or dahlia or cattle having so descended, let us consider probable character of [selected races] wild varieties.

Natural Selection. De Candolle’s war of nature, – seeing contented face of nature, – may be well at first doubted; we see it on borders of perpetual cold54. But considering the enormous geometrical power of increase in every organism and as «?» every country, in ordinary cases «countries» must be stocked to full extent, reflection will show that this is the case. Malthus on man, – in animals no moral [check] restraint «?» – they breed in time of year when provision most abundant, or season most favourable, every country has its seasons, – calculate robins, – oscillating from years of destruction55. If proof were wanted let any singular change of climate «occur» here «?», how astoundingly some tribes «?» increase, also introduced animals56, the pressure is always ready, – capacity of alpine plants to endure other climates, – think of endless seeds scattered abroad, – forests regaining their percentage57, – a thousand wedges58 are being forced into the œconomy of nature. This requires much reflection; study Malthus and calculate rates of increase and remember the resistance, – only periodical.

The unavoidable effect of this «is» that many of every species are destroyed either in egg or [young or mature (the former state the more common)]. In the course of a thousand generations infinitesimally small differences must inevitably tell59; when unusually cold winter, or hot or dry summer comes, then out of the whole body of individuals of any species, if there be the smallest differences in their structure, habits, instincts [senses], health &c., «it» will on an average tell; as conditions change a rather larger proportion will be preserved: so if the chief check to increase falls on seeds or eggs, so will, in the course of 1000 generations or ten thousand, those seeds (like one with down to fly60) which fly furthest and get scattered most ultimately rear most plants, and such small differences tend to be hereditary like shades of expression in human countenance. So if one parent «?» fish deposits its egg in infinitesimally different circumstances, as in rather shallower or deeper water &c., it will then «?» tell.

Let hares61 increase very slowly from change of climate affecting peculiar plants, and some other «illegible» rabbit decrease in same proportion [let this unsettle organisation of], a canine animal, who formerly derived its chief sustenance by springing on rabbits or running them by scent, must decrease too and might thus readily become exterminated. But if its form varied very slightly, the long legged fleet ones, during a thousand years being selected, and the less fleet rigidly destroyed must, if no law of nature be opposed to it, alter forms.

Remember how soon Bakewell on the same principle altered cattle and Western, sheep, – carefully avoiding a cross (pigeons) with any breed. We cannot suppose that one plant tends to vary in fruit and another in flower, and another in flower and foliage, – some have been selected for both fruit and flower: that one animal varies in its covering and another not, – another in its milk. Take any organism and ask what is it useful for and on that point it will be found to vary, – cabbages in their leaf, – corn in size «and» quality of grain, both in times of year, – kidney beans for young pod and cotton for envelope of seeds &c. &c.: dogs in intellect, courage, fleetness and smell «?»: pigeons in peculiarities approaching to monsters. This requires consideration, – should be introduced in first chapter if it holds, I believe it does. It is hypothetical at best62.

Nature’s variation far less, but such selection far more rigid and scrutinising. Man’s races not [even so well] only not better adapted to conditions than other races, but often not «?» one race adapted to its conditions, as man keeps and propagates some alpine plants in garden. Nature lets «an» animal live, till on actual proof it is found less able to do the required work to serve the desired end, man judges solely by his eye, and knows not whether nerves, muscles, arteries, are developed in proportion to the change of external form.

Besides selection by death, in bisexual animals «illegible» the selection in time of fullest vigour, namely struggle of males; even in animals which pair there seems a surplus «?» and a battle, possibly as in man more males produced than females, struggle of war or charms63. Hence that male which at that time is in fullest vigour, or best armed with arms or ornaments of its species, will gain in hundreds of generations some small advantage and transmit such characters to its offspring. So in female rearing its young, the most vigorous and skilful and industrious, «whose» instincts «are» best developed, will rear more young, probably possessing her good qualities, and a greater number will thus «be» prepared for the struggle of nature. Compared to man using a male alone of good breed. This latter section only of limited application, applies to variation of [specific] sexual characters. Introduce here contrast with Lamarck, – absurdity of habit, or chance?? or external conditions, making a woodpecker adapted to tree64.

Before considering difficulties of theory of selection let us consider character of the races produced, as now explained, by nature. Conditions have varied slowly and the organisms best adapted in their whole course of life to the changed conditions have always been selected, – man selects small dog and afterwards gives it profusion of food, – selects a long-backed and short-legged breed and gives it no particular exercise to suit this function &c. &c. In ordinary cases nature has not allowed her race to be contaminated with a cross of another race, and agriculturists know how difficult they find always to prevent this, – effect would be trueness. This character and sterility when crossed, and generally a greater amount of difference, are two main features, which distinguish domestic races from species.

[Sterility not universal admitted by all65. Gladiolus, Crinum, Calceolaria66 must be species if there be such a thing. Races of dogs and oxen: but certainly very general; indeed a gradation of sterility most perfect67 very general. Some nearest species will not cross (crocus, some heath «?»), some genera cross readily (fowls68 and grouse, peacock &c.). Hybrids no ways monstrous quite perfect except secretions69 hence even the mule has bred, – character of sterility, especially a few years ago «?» thought very much more universal than it now is, has been thought the distinguishing character; indeed it is obvious if all forms freely crossed, nature would be a chaos. But the very gradation of the character, even if it always existed in some degree which it does not, renders it impossible as marks «?» those «?» suppose distinct as species70]. Will analogy throw any light on the fact of the supposed races of nature being sterile, though none of the domestic ones are? Mr Herbert «and» Koelreuter have shown external differences will not guide one in knowing whether hybrids will be fertile or not, but the chief circumstance is constitutional differences71, such as being adapted to different climate or soil, differences which [must] probably affect the whole body of the organism and not any one part. Now wild animals, taken out of their natural conditions, seldom breed. I do not refer to shows or to Zoological Societies where many animals unite, but «do not?» breed, and others will never unite, but to wild animals caught and kept quite tame left loose and well fed about houses and living many years. Hybrids produced almost as readily as pure breds. St Hilaire great distinction of tame and domestic, – elephants, – ferrets72. Reproductive organs not subject to disease in Zoological Garden. Dissection and microscope show that hybrid is in exactly same condition as another animal in the intervals of breeding season, or those animals which taken wild and not bred in domesticity, remain without breeding their whole lives. It should be observed that so far from domesticity being unfavourable in itself «it» makes more fertile: [when animal is domesticated and breeds, productive power increased from more food and selection of fertile races]. As far as animals go might be thought «an» effect on their mind and a special case.

But turning to plants we find same class of facts. I do not refer to seeds not ripening, perhaps the commonest cause, but to plants not setting, which either is owing to some imperfection of ovule or pollen. Lindley says sterility is the [curse] bane of all propagators, – Linnæus about alpine plants. American bog plants, – pollen in exactly same state as in hybrids, – same in geraniums. Persian and Chinese73 lilac will not seed in Italy and England. Probably double plants and all fruits owe their developed parts primarily «?» to sterility and extra food thus «?» applied74. There is here gradation «in» sterility and then parts, like diseases, are transmitted hereditarily. We cannot assign any cause why the Pontic Azalea produces plenty of pollen and not American75, why common lilac seeds and not Persian, we see no difference in healthiness. We know not on what circumstances these facts depend, why ferret breeds, and cheetah76, elephant and pig in India will not.

Now in crossing it is certain every peculiarity in form and constitution is transmitted: an alpine plant transmits its alpine tendency to its offspring, an American plant its American-bog constitution, and «with» animals, those peculiarities, on which77 when placed out of their natural conditions they are incapable of breeding; and moreover they transmit every part of their constitution, their respiration, their pulse, their instinct, which are all suddenly modified, can it be wondered at that they are incapable of breeding? I think it may be truly said it would be more wonderful if they did. But it may be asked why have not the recognised varieties, supposed to have been produced through the means of man, [not refused to breed] have all bred78. Variation depends on change of condition and selection79, as far as man’s systematic or unsystematic selection «has» gone; he takes external form, has little power from ignorance over internal invisible constitutional differences. Races which have long been domesticated, and have much varied, are precisely those which were capable of bearing great changes, whose constitutions were adapted to a diversity of climates. Nature changes slowly and by degrees. According to many authors probably breeds of dogs are another case of modified species freely crossing. There is no variety which «illegible» has been «illegible» adapted to peculiar soil or situation for a thousand years and another rigorously adapted to another, till such can be produced, the question is not tried80. Man in past ages, could transport into different climates, animals and plants which would freely propagate in such new climates. Nature could effect, with selection, such changes slowly, so that precisely those animals which are adapted to submit to great changes have given rise to diverse races, – and indeed great doubt on this head81.

Before leaving this subject well to observe that it was shown that a certain amount of variation is consequent on mere act of reproduction, both by buds and sexually, – is vastly increased when parents exposed for some generations to new conditions82, and we now find that many animals when exposed for first time to very new conditions, are «as» incapable of breeding as hybrids. It [probably] bears also on supposed fact of crossed animals when not infertile, as in mongrels, tending to vary much, as likewise seems to be the case, when true hybrids possess just sufficient fertility to propagate with the parent breeds and inter se for some generations. This is Koelreuter’s belief. These facts throw light on each other and support the truth of each other, we see throughout a connection between the reproductive faculties and exposure to changed conditions of life whether by crossing or exposure of the individuals83.

Difficulties on theory of selection 84. It may be objected such perfect organs as eye and ear, could never be formed, in latter less difficulty as gradations more perfect; at first appears monstrous and to «the» end appears difficulty. But think of gradation, even now manifest, (Tibia and Fibula). Everyone will allow if every fossil preserved, gradation infinitely more perfect; for possibility of selection a perfect «?» gradation is required. Different groups of structure, slight gradation in each group, – every analogy renders it probable that intermediate forms have existed. Be it remembered what strange metamorphoses; part of eye, not directly connected with vision, might come to be [thus used] gradually worked in for this end, – swimming bladder by gradation of structure is admitted to belong to the ear system, – rattlesnake. [Woodpecker best adapted to climb.] In some cases gradation not possible, – as vertebræ, – actually vary in domestic animals, – less difficult if growth followed. Looking to whole animals, a bat formed not for flight85. Suppose we had flying fish86 and not one of our now called flying fish preserved, who would have guessed intermediate habits. Woodpeckers and tree-frogs both live in countries where no trees87.

The gradations by which each individual organ has arrived at its present state, and each individual animal with its aggregate of organs has arrived, probably never could be known, and all present great difficulties. I merely wish to show that the proposition is not so monstrous as it at first appears, and that if good reason can be advanced for believing the species have descended from common parents, the difficulty of imagining intermediate forms of structure not sufficient to make one at once reject the theory.