| Subject: Re: origin of species |
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jesus
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Date Posted: 03:45:56 11/09/05 Wed
In reply to:
kiss my ass!!!!!!!!!!!
's message, "Re: origin of species" on 03:47:04 11/04/05 Fri
>>
>>
>>
>>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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