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Date Posted: 03:47:04 11/04/05 Fri
In reply to:
jesus
's message, "origin of species" on 06:03:30 11/02/05 Wed
>
>
>
>The Origin of Species
>Chapter 1: Variation Under Domestication
>by Charles Darwin
>
>
>
>
>Introduction
>Contents
>Chapter 2
>
>
>
>Causes of Variability - Effects of Habit - Correlation
>of Growth - Inheritance - Character of Domestic
>Varieties - Difficulty of distinguishing between
>Varieties and Species - Origin of Domestic Varieties
>from one or more Species - Domestic pigeons, their
>Differences and Origin - Principle of Selection
>anciently followed, its Effects - Methodical and
>Unconscious Selection - Unknown Origin of our Domestic
>Productions - Circumstances favourable to Man's power
>of Selection
>
>
>hen we look to the individuals of the same variety or
>sub-variety of our older cultivated plants and
>animals, one of the first points which strikes us, is,
>that they generally differ much more from each other,
>than do the individuals of any one species or variety
>in a state of nature. When we reflect on the vast
>diversity of the plants and animals which have been
>cultivated, and which have varied during all ages
>under the most different climates and treatment, I
>think we are driven to conclude that this greater
>variability is simply due to our domestic productions
>having been raised under conditions of life not so
>uniform as, and somewhat different from, those to
>which the parent-species have been exposed under
>nature. There is, also, I think, some probability in
>the view propounded by Andrew Knight, that this
>variability may be partly connected with excess of
>food. It seems pretty clear that organic beings must
>be exposed during several generations to the new
>conditions of life to cause any appreciable amount of
>variation; and that when the organisation has once
>begun to vary, it generally continues to vary for many
>generations. No case is on record of a variable being
>ceasing to be variable under cultivation. Our oldest
>cultivated plants, such as wheat, still often yield
>new varieties: our oldest domesticated animals are
>still capable of rapid improvement or modification.
>
>It has been disputed at what period of time the causes
>of variability, whatever they may be, generally act;
>whether during the early or late period of development
>of the embryo, or at the instant of conception.
>Geoffroy St Hilaire's experiments show that unnatural
>treatment of the embryo causes monstrosities; and
>monstrosities cannot be separated by any clear line of
>distinction from mere variations. But I am strongly
>inclined to suspect that the most frequent cause of
>variability may be attributed to the male and female
>reproductive elements having been affected prior to
>the act of conception. Several reasons make me believe
>in this; but the chief one is the remarkable effect
>which confinement or cultivation has on the functions
>of the reproductive system; this system appearing to
>be far more susceptible than any other part of the
>organization, to the action of any change in the
>conditions of life. Nothing is more easy than to tame
>an animal, and few things more difficult than to get
>it to breed freely under confinement, even in the many
>cases when the male and female unite. How many animals
>there are which will not breed, though living long
>under not very close confinement in their native
>country! This is generally attributed to vitiated
>instincts; but how many cultivated plants display the
>utmost vigour, and yet rarely or never seed! In some
>few such cases it has been found out that very
>trifling changes, such as a little more or less water
>at some particular period of growth, will determine
>whether or not the plant sets a seed. I cannot here
>enter on the copious details which I have collected on
>this curious subject; but to show how singular the
>laws are which determine the reproduction of animals
>under confinement, I may just mention that carnivorous
>animals, even from the tropics, breed in this country
>pretty freely under confinement, with the exception of
>the plantigrades or bear family; whereas, carnivorous
>birds, with the rarest exceptions, hardly ever lay
>fertile eggs. Many exotic plants have pollen utterly
>worthless, in the same exact condition as in the most
>sterile hybrids. When, on the one hand, we see
>domesticated animals and plants, though often weak and
>sickly, yet breeding quite freely under confinement;
>and when, on the other hand, we see individuals,
>though taken young from a state of nature, perfectly
>tamed, long-lived, and healthy (of which I could give
>numerous instances), yet having their reproductive
>system so seriously affected by unperceived causes as
>to fail in acting, we need not be surprised at this
>system, when it does act under confinement, acting not
>quite regularly, and producing offspring not perfectly
>like their parents or variable.
>
>Sterility has been said to be the bane of
>horticulture; but on this view we owe variability to
>the same cause which produces sterility; and
>variability is the source of all the choicest
>productions of the garden. I may add, that as some
>organisms will breed most freely under the most
>unnatural conditions (for instance, the rabbit and
>ferret kept in hutches), showing that their
>reproductive system has not been thus affected; so
>will some animals and plants withstand domestication
>or cultivation, and vary very slightly perhaps hardly
>more than in a state of nature.
>
>A long list could easily be given of 'sporting
>plants;' by this term gardeners mean a single bud or
>offset, which suddenly assumes a new and sometimes
>very different character from that of the rest of the
>plant. Such buds can be propagated by grafting, &c.,
>and sometimes by seed. These 'sports' are extremely
>rare under nature, but far from rare under
>cultivation; and in this case we see that the
>treatment of the parent has affected a bud or offset,
>and not the ovules or pollen. But it is the opinion of
>most physiologists that there is no essential
>difference between a bud and an ovule in their
>earliest stages of formation; so that, in
>fact,'sports' support my view, that variability may be
>largely attributed to the ovules or pollen, or to
>both, having been affected by the treatment of the
>parent prior to the act of conception. These cases
>anyhow show that variation is not necessarily
>connected, as some authors have supposed, with the act
>of generation.
>
>Seedlings from the same fruit, and the young of the
>same litter, sometimes differ considerably from each
>other, though both the young and the parents, as
>Muller has remarked, have apparently been exposed to
>exactly the same conditions of life; and this shows
>how unimportant the direct effects of the conditions
>of life are in comparison with the laws of
>reproduction, and of growth, and of inheritance; for
>had the action of the conditions been direct, if any
>of the young had varied, all would probably have
>varied in the same manner. To judge how much, in the
>case of any variation, we should attribute to the
>direct action of heat, moisture, light, food, &c., is
>most difficult: my impression is, that with animals
>such agencies have produced very little direct effect,
>though apparently more in the case of plants. Under
>this point of view, Mr Buckman's recent experiments on
>plants seem extremely valuable. When all or nearly all
>the individuals exposed to certain conditions are
>affected in the same way, the change at first appears
>to be directly due to such conditions; but in some
>cases it can be shown that quite opposite conditions
>produce similar changes of structure. Nevertheless
>some slight amount of change may, I think, be
>attributed to the direct action of the conditions of
>life as, in some cases, increased size from amount of
>food, colour from particular kinds of food and from
>light, and perhaps the thickness of fur from climate.
>
>Habit also has a deciding influence, as in the period
>of flowering with plants when transported from one
>climate to another. In animals it has a more marked
>effect; for instance, I find in the domestic duck that
>the bones of the wing weigh less and the bones of the
>leg more, in proportion to the whole skeleton, than do
>the same bones in the wild-duck; and I presume that
>this change may be safely attributed to the domestic
>duck flying much less, and walking more, than its wild
>parent. The great and inherited development of the
>udders in cows and goats in countries where they are
>habitually milked, in comparison with the state of
>these organs in other countries, is another instance
>of the effect of use. Not a single domestic animal can
>be named which has not in some country drooping ears;
>and the view suggested by some authors, that the
>drooping is due to the disuse of the muscles of the
>ear, from the animals not being much alarmed by
>danger, seems probable.
>
>There are many laws regulating variation, some few of
>which can be dimly seen, and will be hereafter briefly
>mentioned. I will here only allude to what may be
>called correlation of growth. Any change in the embryo
>or larva will almost certainly entail changes in the
>mature animal. In monstrosities, the correlations
>between quite distinct parts are very curious; and
>many instances are given in Isidore Geoffroy St
>Hilaire's great work on this subject. Breeders believe
>that long limbs are almost always accompanied by an
>elongated head. Some instances of correlation are
>quite whimsical; thus cats with blue eyes are
>invariably deaf; colour and constitutional
>peculiarities go together, of which many remarkable
>cases could be given amongst animals and plants. From
>the facts collected by Heusinger, it appears that
>white sheep and pigs are differently affected from
>coloured individuals by certain vegetable poisons.
>Hairless dogs have imperfect teeth; long-haired and
>coarse-haired animals are apt to have, as is asserted,
>long or many horns; pigeons with feathered feet have
>skin between their outer toes; pigeons with short
>beaks have small feet, and those with long beaks large
>feet. Hence, if man goes on selecting, and thus
>augmenting, any peculiarity, he will almost certainly
>unconsciously modify other parts of the structure,
>owing to the mysterious laws of the correlation of
>growth.
>
>The result of the various, quite unknown, or dimly
>seen laws of variation is infinitely complex and
>diversified. It is well worth while carefully to study
>the several treatises published on some of our old
>cultivated plants, as on the hyacinth, potato, even
>the dahlia, &c.; and it is really surprising to note
>the endless points in structure and constitution in
>which the varieties and sub varieties differ slightly
>from each other. The whole organization seems to have
>become plastic, and tends to depart in some small
>degree from that of the parental type.
>
>Any variation which is not inherited is unimportant
>for us. But the number and diversity of inheritable
>deviations of structure, both those of slight and
>those of considerable physiological importance, is
>endless. Dr Prosper Lucas's treatise, in two large
>volumes, is the fullest and the best on this subject.
>No breeder doubts how strong is the tendency to
>inheritance: like produces like is his fundamental
>belief: doubts have been thrown on this principle by
>theoretical writers alone. When a deviation appears
>not unfrequently, and we see it in the father and
>child, we cannot tell whether it may not be due to the
>same original cause acting on both; but when amongst
>individuals, apparently exposed to the same
>conditions, any very rare deviation, due to some
>extraordinary combination of circumstances, appears in
>the parent say, once amongst several million
>individuals and it reappears in the child, the mere
>doctrine of chances almost compels us to attribute its
>reappearance to inheritance. Every one must have heard
>of cases of albinism, prickly skin, hairy bodies, &c.
>appearing in several members of the same family. If
>strange and rare deviations of structure are truly
>inherited, less strange and commoner deviations may be
>freely admitted to be inheritable. Perhaps the correct
>way of viewing the whole subject, would be, to look at
>the inheritance of every character whatever as the
>rule, and non-inheritance as the anomaly.
>
>The laws governing inheritance are quite unknown; no
>one can say why the same peculiarity in different
>individuals of the same species, and in individuals of
>different species, is sometimes inherited and
>sometimes not so; why the child often reverts in
>certain characters to its grandfather or grandmother
>or other much more remote ancestor; why a peculiarity
>is often transmitted from one sex to both sexes or to
>one sex alone, more commonly but not exclusively to
>the like sex. It is a fact of some little importance
>to us, that peculiarities appearing in the males of
>our domestic breeds are often transmitted either
>exclusively, or in a much greater degree, to males
>alone. A much more important rule, which I think may
>be trusted, is that, at whatever period of life a
>peculiarity first appears, it tends to appear in the
>offspring at a corresponding age, though sometimes
>earlier. In many cases this could not be otherwise:
>thus the inherited peculiarities in the horns of
>cattle could appear only in the offspring when nearly
>mature; peculiarities in the silkworm are known to
>appear at the corresponding caterpillar or cocoon
>stage. But hereditary diseases and some other facts
>make me believe that the rule has a wider extension,
>and that when there is no apparent reason why a
>peculiarity should appear at any particular age, yet
>that it does tend to appear in the offspring at the
>same period at which it first appeared in the parent.
>I believe this rule to be of the highest importance in
>explaining the laws of embryology. These remarks are
>of course confined to the first appearance of the
>peculiarity, and not to its primary cause, which may
>have acted on the ovules or male element; in nearly
>the same manner as in the crossed offspring from a
>short-horned cow by a long-horned bull, the greater
>length of horn, though appearing late in life, is
>clearly due to the male element.
>
>Having alluded to the subject of reversion, I may here
>refer to a statement often made by naturalists namely,
>that our domestic varieties, when run wild, gradually
>but certainly revert in character to their aboriginal
>stocks. Hence it has been argued that no deductions
>can be drawn from domestic races to species in a state
>of nature. I have in vain endeavoured to discover on
>what decisive facts the above statement has so often
>and so boldly been made. There would be great
>difficulty in proving its truth: we may safely
>conclude that very many of the most strongly-marked
>domestic varieties could not possibly live in a wild
>state. In many cases we do not know what the
>aboriginal stock was, and so could not tell whether or
>not nearly perfect reversion had ensued. It would be
>quite necessary, in order to prevent the effects of
>intercrossing, that only a single variety should be
>turned loose in its new home. Nevertheless, as our
>varieties certainly do occasionally revert in some of
>their characters to ancestral forms, it seems to me
>not improbable, that if we could succeed in
>naturalising, or were to cultivate, during many
>generations, the several races, for instance, of the
>cabbage, in very poor soil (in which case, however,
>some effect would have to be attributed to the direct
>action of the poor soil), that they would to a large
>extent, or even wholly, revert to the wild aboriginal
>stock. Whether or not the experiment would succeed, is
>not of great importance for our line of argument; for
>by the experiment itself the conditions of life are
>changed. If it could be shown that our domestic
>varieties manifested a strong tendency to reversion,
>that is, to lose their acquired characters, whilst
>kept under unchanged conditions, and whilst kept in a
>considerable body, so that free intercrossing might
>check, by blending together, any slight deviations of
>structure, in such case, I grant that we could deduce
>nothing from domestic varieties in regard to species.
>But there is not a shadow of evidence in favour of
>this view: to assert that we could not breed our cart
>and race-horses, long and short-horned cattle and
>poultry of various breeds, and esculent vegetables,
>for an almost infinite number of generations, would be
>opposed to all experience. I may add, that when under
>nature the conditions of life do change, variations
>and reversions of character probably do occur; but
>natural selection, as will hereafter be explained,
>will determine how far the new characters thus arising
>shall be preserved.
>
>When we look to the hereditary varieties or races of
>our domestic animals and plants, and compare them with
>species closely allied together, we generally perceive
>in each domestic race, as already remarked, less
>uniformity of character than in true species. Domestic
>races of the same species, also, often have a somewhat
>monstrous character; by which I mean, that, although
>differing from each other, and from the other species
>of the same genus, in several trifling respects, they
>often differ in an extreme degree in some one part,
>both when compared one with another, and more
>especially when compared with all the species in
>nature to which they are nearest allied. With these
>exceptions (and with that of the perfect fertility of
>varieties when crossed, a subject hereafter to be
>discussed), domestic races of the same species differ
>from each other in the same manner as, only in most
>cases in a lesser degree than, do closely-allied
>species of the same genus in a state of nature. I
>think this must be admitted, when we find that there
>are hardly any domestic races, either amongst animals
>or plants, which have not been ranked by some
>competent judges as mere varieties, and by other
>competent judges as the descendants of aboriginally
>distinct species. If any marked distinction existed
>between domestic races and species, this source of
>doubt could not so perpetually recur. It has often
>been stated that domestic races do not differ from
>each other in characters of generic value. I think it
>could be shown that this statement is hardly correct;
>but naturalists differ most widely in determining what
>characters are of generic value; all such valuations
>being at present empirical. Moreover, on the view of
>the origin of genera which I shall presently give, we
>have no right to expect often to meet with generic
>differences in our domesticated productions.
>
>When we attempt to estimate the amount of structural
>difference between the domestic races of the same
>species, we are soon involved in doubt, from not
>knowing whether they have descended from one or
>several parent-species. This point, if could be
>cleared up, would be interesting; if, for instance, it
>could be shown that the greyhound, bloodhound,
>terrier, spaniel, and bull-dog, which we all know
>propagate their kind so truly, were the offspring of
>any single species, then such facts would have great
>weight in making us doubt about the immutability of
>the many very closely allied and natural species for
>instance, of the many foxes inhabiting different
>quarters of the world. I do not believe, as we shall
>presently see, that all our dogs have descended from
>any one wild species; but, in the case of some other
>domestic races, there is presumptive, or even strong,
>evidence in favour of this view.
>
>It has often been assumed that man has chosen for
>domestication animals and plants having an
>extraordinary inherent tendency to vary, and likewise
>to withstand diverse climates. I do not dispute that
>these capacities have added largely to the value of
>most of our domesticated productions; but how could a
>savage possibly know, when he first tamed an animal,
>whether it would vary in succeeding generations, and
>whether it would endure other climates? Has the little
>variability of the ass or guinea-fowl, or the small
>power of endurance of warmth by the reindeer, or of
>cold by the common camel, prevented their
>domestication? I cannot doubt that if other animals
>and plants, equal in number to our domesticated
>productions, and belonging to equally diverse classes
>and countries, were taken from a state of nature, and
>could be made to breed for an equal number of
>generations under domestication, they would vary on an
>average as largely as the parent species of our
>existing domesticated productions have varied.
>
>In the case of most of our anciently domesticated
>animals and plants, I do not think it is possible to
>come to any definite conclusion, whether they have
>descended from one or several species. The argument
>mainly relied on by those who believe in the multiple
>origin of our domestic animals is, that we find in the
>most ancient records, more especially on the monuments
>of Egypt, much diversity in the breeds; and that some
>of the breeds closely resemble, perhaps are identical
>with, those still existing. Even if this latter fact
>were found more strictly and generally true than seems
>to me to be the case, what does it show, but that some
>of our breeds originated there, four or five thousand
>years ago? But Mr Horner's researches have rendered it
>in some degree probable that man sufficiently
>civilized to have manufactured pottery existed in the
>valley of the Nile thirteen or fourteen thousand years
>ago; and who will pretend to say how long before these
>ancient periods, savages, like those of Tierra del
>Fuego or Australia, who possess a semi-domestic dog,
>may not have existed in Egypt?
>
>The whole subject must, I think, remain vague;
>nevertheless, I may, without here entering on any
>details, state that, from geographical and other
>considerations, I think it highly probable that our
>domestic dogs have descended from several wild
>species. In regard to sheep and goats I can form no
>opinion. I should think, from facts communicated to me
>by Mr Blyth, on the habits, voice, and constitution,
>&c., of the humped Indian cattle, that these had
>descended from a different aboriginal stock from our
>European cattle; and several competent judges believe
>that these latter have had more than one wild parent.
>With respect to horses, from reasons which I cannot
>give here, I am doubtfully inclined to believe, in
>opposition to several authors, that all the races have
>descended from one wild stock. Mr Blyth, whose
>opinion, from his large and varied stores of
>knowledge, I should value more than that of almost any
>one, thinks that all the breeds of poultry have
>proceeded from the common wild Indian fowl (Gallus
>bankiva). In regard to ducks and rabbits, the breeds
>of which differ considerably from each other in
>structure, I do not doubt that they all have descended
>from the common wild duck and rabbit.
>
>The doctrine of the origin of our several domestic
>races from several aboriginal stocks, has been carried
>to an absurd extreme by some authors. They believe
>that every race which breeds true, let the distinctive
>characters be ever so slight, has had its wild
>prototype. At this rate there must have existed at
>least a score of species of wild cattle, as many
>sheep, and several goats in Europe alone, and several
>even within Great Britain. One author believes that
>there formerly existed in Great Britain eleven wild
>species of sheep peculiar to it! When we bear in mind
>that Britain has now hardly one peculiar mammal, and
>France but few distinct from those of Germany and
>conversely, and so with Hungary, Spain, &c., but that
>each of these kingdoms possesses several peculiar
>breeds of cattle, sheep, &c., we must admit that many
>domestic breeds have originated in Europe; for whence
>could they have been derived, as these several
>countries do not possess a number of peculiar species
>as distinct parent-stocks? So it is in India. Even in
>the case of the domestic dogs of the whole world,
>which I fully admit have probably descended from
>several wild species, I cannot doubt that there has
>been an immense amount of inherited variation. Who can
>believe that animals closely resembling the Italian
>greyhound, the bloodhound, the bull-dog, or Blenheim
>spaniel, &c. so unlike all wild Canidae ever existed
>freely in a state of nature? It has often been loosely
>said that all our races of dogs have been produced by
>the crossing of a few aboriginal species; but by
>crossing we can get only forms in some degree
>intermediate between their parents; and if we account
>for our several domestic races by this process, we
>must admit the former existence of the most extreme
>forms, as the Italian greyhound, bloodhound, bull-dog,
>&c., in the wild state. Moreover, the possibility of
>making distinct races by crossing has been greatly
>exaggerated. There can be no doubt that a race may be
>modified by occasional crosses, if aided by the
>careful selection of those individual mongrels, which
>present any desired character; but that a race could
>be obtained nearly intermediate between two extremely
>different races or species, I can hardly believe. Sir
>J. Sebright expressly experimentised for this object,
>and failed. The offspring from the first cross between
>two pure breeds is tolerably and sometimes (as I have
>found with pigeons) extremely uniform, and everything
>seems simple enough; but when these mongrels are
>crossed one with another for several generations,
>hardly two of them will be alike, and then the extreme
>difficulty, or rather utter hopelessness, of the task
>becomes apparent. Certainly, a breed intermediate
>between two very distinct breeds could not be got
>without extreme care and long-continued selection; nor
>can I find a single case on record of a permanent race
>having been thus formed.
>
>On the Breeds of the Domestic pigeon.
>
>Believing that it is always best to study some special
>group, I have, after deliberation, taken up domestic
>pigeons. I have kept every breed which I could
>purchase or obtain, and have been most kindly favoured
>with skins from several quarters of the world, more
>especially by the Hon. W. Elliot from India, and by
>the Hon. C. Murray from Persia. Many treatises in
>different languages have been published on pigeons,
>and some of them are very important, as being of
>considerably antiquity. I have associated with several
>eminent fanciers, and have been permitted to join two
>of the London Pigeon Clubs. The diversity of the
>breeds is something astonishing. Compare the English
>carrier and the short-faced tumbler, and see the
>wonderful difference in their beaks, entailing
>corresponding differences in their skulls. The
>carrier, more especially the male bird, is also
>remarkable from the wonderful development of the
>carunculated skin about the head, and this is
>accompanied by greatly elongated eyelids, very large
>external orifices to the nostrils, and a wide gape of
>mouth. The short-faced tumbler has a beak in outline
>almost like that of a finch; and the common tumbler
>has the singular and strictly inherited habit of
>flying at a great height in a compact flock, and
>tumbling in the air head over heels. The runt is a
>bird of great size, with long, massive beak and large
>feet; some of the sub-breeds of runts have very long
>necks, others very long wings and tails, others
>singularly short tails. The barb is allied to the
>carrier, but, instead of a very long beak, has a very
>short and very broad one. The pouter has a much
>elongated body, wings, and legs; and its enormously
>developed crop, which it glories in inflating, may
>well excite astonishment and even laughter. The turbit
>has a very short and conical beak, with a line of
>reversed feathers down the breast; and it has the
>habit of continually expanding slightly the upper part
>of the oesophagus. The Jacobin has the feathers so
>much reversed along the back of the neck that they
>form a hood, and it has, proportionally to its size,
>much elongated wing and tail feathers. The trumpeter
>and laugher, as their names express, utter a very
>different coo from the other breeds. The fantail has
>thirty or even forty tail-feathers, instead of twelve
>or fourteen, the normal number in all members of the
>great pigeon family; and these feathers are kept
>expanded, and are carried so erect that in good birds
>the head and tail touch; the oil-gland is quite
>aborted. Several other less distinct breeds might have
>been specified.
>
>In the skeletons of the several breeds, the
>development of the bones of the face in length and
>breadth and curvature differs enormously. The shape,
>as well as the breadth and length of the ramus of the
>lower jaw, varies in a highly remarkable manner. The
>number of the caudal and sacral vertebrae vary; as
>does the number of the ribs, together with their
>relative breadth and the presence of processes. The
>size and shape of the apertures in the sternum are
>highly variable; so is the degree of divergence and
>relative size of the two arms of the furcula. The
>proportional width of the gape of mouth, the
>proportional length of the eyelids, of the orifice of
>the nostrils, of the tongue (not always in strict
>correlation with the length of beak), the size of the
>crop and of the upper part of the oesophagus; the
>development and abortion of the oil-gland; the number
>of the primary wing and caudal feathers; the relative
>length of wing and tail to each other and to the body;
>the relative length of leg and of the feet; the number
>of scutellae on the toes, the development of skin
>between the toes, are all points of structure which
>are variable. The period at which the perfect plumage
>is acquired varies, as does the state of the down with
>which the nestling birds are clothed when hatched. The
>shape and size of the eggs vary. The manner of flight
>differs remarkably; as does in some breeds the voice
>and disposition. Lastly, in certain breeds, the males
>and females have come to differ to a slight degree
>from each other.
>
>Altogether at least a score of pigeons might be
>chosen, which if shown to an ornithologist, and he
>were told that they were wild birds, would certainly,
>I think, be ranked by him as well-defined species.
>Moreover, I do not believe that any ornithologist
>would place the English carrier, the short-faced
>tumbler, the runt, the barb, pouter, and fantail in
>the same genus; more especially as in each of these
>breeds several truly-inherited sub-breeds, or species
>as he might have called them, could be shown him.
>
>Great as the differences are between the breeds of
>pigeons, I am fully convinced that the common opinion
>of naturalists is correct, namely, that all have
>descended from the rock-pigeon (Columba livia),
>including under this term several geographical races
>or sub-species, which differ from each other in the
>most trifling respects. As several of the reasons
>which have led me to this belief are in some degree
>applicable in other cases, I will here briefly give
>them. If the several breeds are not varieties, and
>have not proceeded from the rock-pigeon, they must
>have descended from at least seven or eight aboriginal
>stocks; for it is impossible to make the present
>domestic breeds by the crossing of any lesser number:
>how, for instance, could a pouter be produced by
>crossing two breeds unless one of the parent-stocks
>possessed the characteristic enormous crop? The
>supposed aboriginal stocks must all have been
>rock-pigeons, that is, not breeding or willingly
>perching on trees. But besides C. livia, with its
>geographical sub-species, only two or three other
>species of rock-pigeons are known; and these have not
>any of the characters of the domestic breeds. Hence
>the supposed aboriginal stocks must either still exist
>in the countries where they were originally
>domesticated, and yet be unknown to ornithologists;
>and this, considering their size, habits, and
>remarkable characters, seems very improbable; or they
>must have become extinct in the wild state. But birds
>breeding on precipices, and good fliers, are unlikely
>to be exterminated; and the common rock-pigeon, which
>has the same habits with the domestic breeds, has not
>been exterminated even on several of the smaller
>British islets, or on the shores of the Mediterranean.
>Hence the supposed extermination of so many species
>having similar habits with the rock-pigeon seems to me
>a very rash assumption. Moreover, the several
>above-named domesticated breeds have been transported
>to all parts of the world, and, therefore, some of
>them must have been carried back again into their
>native country; but not one has ever become wild or
>feral, though the dovecot-pigeon, which is the
>rock-pigeon in a very slightly altered state
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