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Causes of Variability -- Effects of Habit and the use and disuse of Parts-- Correlated Variation -- Inheritance -- Character of Domestic Varieties-- Difficulty of distinguishing between Varieties and Species -- Origin ofDomestic Varieties from one or more Species -- Domestic Pigeons, theirDifferences and Origin -- Principles of Selection, anciently followed,their Effects -- Methodical and Unconscious Selection -- Unknown Origin ofour Domestic Productions -- Circumstances favourable to Man's power ofSelection.

CAUSES OF VARIABILITY.

When we compare the individuals of the same variety or sub-variety of ourolder cultivated plants and animals, one of the first points which strikesus is, that they generally differ more from each other than do theindividuals of any one species or variety in a state of nature. And if wereflect on the vast diversity of the plants and animals which have beencultivated, and which have varied during all ages under the most differentclimates and treatment, we are driven to conclude that this greatvariability is due to our domestic productions having been raised underconditions of life not so uniform as, and somewhat different from, those towhich the parent species had been exposed under nature. There is, also,some probability in the view propounded by Andrew Knight, that thisvariability may be partly connected with excess of food. It seems clearthat organic beings must be exposed during several generations to newconditions to cause any great amount of variation; and that, when theorganisation has once begun to vary, it generally continues varying formany generations. No case is on record of a variable organism ceasing tovary under cultivation. Our oldest cultivated plants, such as wheat, stillyield new varieties: our oldest domesticated animals are still capable ofrapid improvement or modification.

As far as I am able to judge, after long attending to the subject, theconditions of life appear to act in two ways--directly on the wholeorganisation or on certain parts alone and in directly by affecting thereproductive system. With respect to the direct action, we must bear inmind that in every case, as Professor Weismann has lately insisted, and asI have incidently shown in my work on "Variation under Domestication,"there are two factors: namely, the nature of the organism and the natureof the conditions. The former seems to be much the more important; fornearly similar variations sometimes arise under, as far as we can judge,dissimilar conditions; and, on the other hand, dissimilar variations ariseunder conditions which appear to be nearly uniform. The effects on theoffspring are either definite or in definite. They may be considered asdefinite when all or nearly all the offspring of individuals exposed tocertain conditions during several generations are modified in the samemanner. It is extremely difficult to come to any conclusion in regard tothe extent of the changes which have been thus definitely induced. Therecan, however, be little doubt about many slight changes, such as size fromthe amount of food, colour from the nature of the food, thickness of theskin and hair from climate, etc. Each of the endless variations which wesee in the plumage of our fowls must have had some efficient cause; and ifthe same cause were to act uniformly during a long series of generations onmany individuals, all probably would be modified in the same manner. Suchfacts as the complex and extraordinary out growths which variably followfrom the insertion of a minute drop of poison by a gall-producing insect,shows us what singular modifications might result in the case of plantsfrom a chemical change in the nature of the sap.

In definite variability is a much more common result of changed conditionsthan definite variability, and has probably played a more important part inthe formation of our domestic races. We see in definite variability in theendless slight peculiarities which distinguish the individuals of the samespecies, and which cannot be accounted for by inheritance from eitherparent or from some more remote ancestor. Even strongly-marked differencesoccasionally appear in the young of the same litter, and in seedlings fromthe same seed-capsule. At long intervals of time, out of millions ofindividuals reared in the same country and fed on nearly the same food,deviations of structure so strongly pronounced as to deserve to be calledmonstrosities arise; but monstrosities cannot be separated by any distinctline from slighter variations. All such changes of structure, whetherextremely slight or strongly marked, which appear among many individualsliving together, may be considered as the in definite effects of theconditions of life on each individual organism, in nearly the same manneras the chill effects different men in an in definite manner, according totheir state of body or constitution, causing coughs or colds, rheumatism,or inflammation of various organs.

With respect to what I have called the in direct action of changedconditions, namely, through the reproductive system of being affected, wemay infer that variability is thus induced, partly from the fact of thissystem being extremely sensitive to any change in the conditions, andpartly from the similarity, as Kolreuter and others have remarked, betweenthe variability which follows from the crossing of distinct species, andthat which may be observed with plants and animals when reared under new orunnatural conditions. Many facts clearly show how eminently susceptiblethe reproductive system is to very slight changes in the surroundingconditions. Nothing is more easy than to tame an animal, and few thingsmore difficult than to get it to breed freely under confinement, even whenthe male and female unite. How many animals there are which will notbreed, though kept in an almost free state in their native country! Thisis generally, but erroneously attributed to vitiated instincts. Manycultivated plants display the utmost vigour, and yet rarely or never seed! In some few cases it has been discovered that a very trifling change, suchas a little more or less water at some particular period of growth, willdetermine whether or not a plant will produce seeds. I cannot here givethe details which I have collected and elsewhere published on this curioussubject; but to show how singular the laws are which determine thereproduction of animals under confinement, I may mention that carnivorousanimals, even from the tropics, breed in this country pretty freely underconfinement, with the exception of the plantigrades or bear family, whichseldom produce young; whereas, carnivorous birds, with the rarestexception, hardly ever lay fertile eggs. Many exotic plants have pollenutterly worthless, in the same condition as in the most sterile hybrids. When, on the one hand, we see domesticated animals and plants, though oftenweak and sickly, breeding freely under confinement; and when, on the otherhand, we see individuals, though taken young from a state of natureperfectly tamed, long-lived, and healthy (of which I could give numerousinstances), yet having their reproductive system so seriously affected byunperceived causes as to fail to act, we need not be surprised at thissystem, when it does act under confinement, acting irregularly, andproducing offspring somewhat unlike their parents. I may add that as someorganisms breed freely under the most unnatural conditions--for instance,rabbits and ferrets kept in hutches--showing that their reproductive organsare not easily affected; so will some animals and plants withstanddomestication or cultivation, and vary very slightly--perhaps hardly morethan in a state of nature.

Some naturalists have maintained that all variations are connected with theact of sexual reproduction; but this is certainly an error; for I havegiven in another work a long list of "sporting plants;" as they are calledby gardeners; that is, of plants which have suddenly produced a single budwith a new and sometimes widely different character from that of the otherbuds on the same plant. These bud variations, as they may be named, can bepropagated by grafts, offsets, etc., and sometimes by seed. They occurrarely under nature, but are far from rare under culture. As a single budout of many thousands produced year after year on the same tree underuniform conditions, has been known suddenly to assume a new character; andas buds on distinct trees, growing under different conditions, havesometimes yielded nearly the same variety--for instance, buds on peach-trees producing nectarines, and buds on common roses producing moss-roses--we clearly see that the nature of the conditions is of subordinateimportance in comparison with the nature of the organism in determiningeach particular form of variation; perhaps of not more importance than thenature of the spark, by which a mass of combustible matter is ignited, hasin determining the nature of the flames.

EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; CORRELATED VARIATION;INHERITANCE.

Changed habits produce an inherited effect as in the period of theflowering of plants when transported from one climate to another. Withanimals the increased use or disuse of parts has had a more markedinfluence; thus I find in the domestic duck that the bones of the wingweigh less and the bones of the leg more, in proportion to the wholeskeleton, than do the same bones in the wild duck; and this change may besafely attributed to the domestic duck flying much less, and walking more,than its wild parents. The great and inherited development of the uddersin cows and goats in countries where they are habitually milked, incomparison with these organs in other countries, is probably anotherinstance of the effects of use. Not one of our domestic animals can benamed which has not in some country drooping ears; and the view which hasbeen suggested that the drooping is due to disuse of the muscles of theear, from the animals being seldom much alarmed, seems probable.

Many laws regulate variation, some few of which can be dimly seen, and willhereafter be briefly discussed. I will here only allude to what may becalled correlated variation. Important changes in the embryo or larva willprobably entail changes in the mature animal. In monstrosities, thecorrelations between quite distinct parts are very curious; and manyinstances are given in Isidore Geoffroy St. Hilaire's great work on thissubject. Breeders believe that long limbs are almost always accompanied byan elongated head. Some instances of correlation are quite whimsical; thuscats which are entirely white and have blue eyes are generally deaf; but ithas been lately stated by Mr. Tait that this is confined to the males. Colour and constitutional peculiarities go together, of which manyremarkable cases could be given among animals and plants. From factscollected by Heusinger, it appears that white sheep and pigs are injured bycertain plants, while dark-coloured individuals escape: Professor Wymanhas recently communicated to me a good illustration of this fact; on askingsome farmers in Virginia how it was that all their pigs were black, theyinformed him that the pigs ate the paint-root (Lachnanthes), which colouredtheir bones pink, and which caused the hoofs of all but the black varietiesto drop off; and one of the "crackers" (i.e. Virginia squatters) added, "weselect the black members of a litter for raising, as they alone have a goodchance of living." Hairless dogs have imperfect teeth; long-haired andcoarse-haired animals are apt to have, as is asserted, long or many horns;pigeons with feathered feet have skin between their outer toes; pigeonswith short beaks have small feet, and those with long beaks large feet. Hence if man goes on selecting, and thus augmenting, any peculiarity, hewill almost certainly modify unintentionally other parts of the structure,owing to the mysterious laws of correlation.

The results of the various, unknown, or but dimly understood laws ofvariation are infinitely complex and diversified. It is well worth whilecarefully to study the several treatises on some of our old cultivatedplants, as on the hyacinth, potato, even the dahlia, etc.; and it is reallysurprising to note the endless points of structure and constitution inwhich the varieties and sub-varieties differ slightly from each other. Thewhole organisation seems to have become plastic, and departs in a slightdegree from that of the parental type.

Any variation which is not inherited is unimportant for us. But the numberand diversity of inheritable deviations of structure, both those of slightand those of considerable physiological importance, are endless. Dr.Prosper Lucas' treatise, in two large volumes, is the fullest and the beston this subject. No breeder doubts how strong is the tendency toinheritance; that like produces like is his fundamental belief: doubtshave been thrown on this principle only by theoretical writers. When anydeviation of structure often appears, and we see it in the father andchild, we cannot tell whether it may not be due to the same cause havingacted on both; but when among individuals, apparently exposed to the sameconditions, any very rare deviation, due to some extraordinary combinationof circumstances, appears in the parent--say, once among several millionindividuals--and it reappears in the child, the mere doctrine of chancesalmost compels us to attribute its reappearance to inheritance. Every onemust have heard of cases of albinism, prickly skin, hairy bodies, etc.,appearing in several members of the same family. If strange and raredeviations of structure are truly inherited, less strange and commonerdeviations may be freely admitted to be inheritable. Perhaps the correctway of viewing the whole subject would be, to look at the inheritance ofevery character whatever as the rule, and non-inheritance as the anomaly.

The laws governing inheritance are for the most part unknown; no one cansay why the same peculiarity in different individuals of the same species,or in different species, is sometimes inherited and sometimes not so; whythe child often reverts in certain characteristics to its grandfather orgrandmother or more remote ancestor; why a peculiarity is often transmittedfrom one sex to both sexes, or to one sex alone, more commonly but notexclusively to the like sex. It is a fact of some importance to us, thatpeculiarities appearing in the males of our domestic breeds are oftentransmitted, either exclusively or in a much greater degree, to the malesalone. A much more important rule, which I think may be trusted, is that,at whatever period of life a peculiarity first appears, it tends toreappear in the offspring at a corresponding age, though sometimes earlier. In many cases this could not be otherwise; thus the inherited peculiaritiesin the horns of cattle could appear only in the offspring when nearlymature; peculiarities in the silk-worm are known to appear at thecorresponding caterpillar or cocoon stage. But hereditary diseases andsome other facts make me believe that the rule has a wider extension, andthat, when there is no apparent reason why a peculiarity should appear atany particular age, yet that it does tend to appear in the offspring at thesame period at which it first appeared in the parent. I believe this ruleto be of the highest importance in explaining the laws of embryology. These remarks are of course confined to the first APPEARANCE of thepeculiarity, and not to the primary cause which may have acted on theovules or on the male element; in nearly the same manner as the increasedlength of the horns in the offspring from a short-horned cow by along-horned bull, though appearing late in life, is clearly due to the maleelement.

Having alluded to the subject of reversion, I may here refer to a statementoften made by naturalists--namely, that our domestic varieties, when runwild, gradually but invariably revert in character to their aboriginalstocks. Hence it has been argued that no deductions can be drawn fromdomestic races to species in a state of nature. I have in vain endeavouredto discover on what decisive facts the above statement has so often and soboldly been made. There would be great difficulty in proving its truth: we may safely conclude that very many of the most strongly marked domesticvarieties could not possibly live in a wild state. In many cases we do notknow what the aboriginal stock was, and so could not tell whether or notnearly perfect reversion had ensued. It would be necessary, in order toprevent the effects of intercrossing, that only a single variety should beturned loose in its new home. Nevertheless, as our varieties certainly dooccasionally revert in some of their characters to ancestral forms, itseems to me not improbable that if we could succeed in naturalising, orwere to cultivate, during many generations, the several races, forinstance, of the cabbage, in very poor soil--in which case, however, someeffect would have to be attributed to the DEFINITE action of the poor soil--that they would, to a large extent, or even wholly, revert to the wildaboriginal stock. Whether or not the experiment would succeed is not ofgreat importance for our line of argument; for by the experiment itself theconditions of life are changed. If it could be shown that our domesticvarieties manifested a strong tendency to reversion--that is, to lose theiracquired characters, while kept under the same conditions and while kept ina considerable body, so that free intercrossing might check, by blendingtogether, any slight deviations in their structure, in such case, I grantthat 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 assertthat we could not breed our cart and race-horses, long and short-hornedcattle, and poultry of various breeds, and esculent vegetables, for anunlimited number of generations, would be opposed to all experience.

CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF DISTINGUISHING BETWEENVARIETIES AND SPECIES; ORIGIN OF DOMESTIC VARIETIES FROM ONE OR MORESPECIES.

When we look to the hereditary varieties or races of our domestic animalsand plants, and compare them with closely allied species, we generallyperceive in each domestic race, as already remarked, less uniformity ofcharacter than in true species. Domestic races often have a somewhatmonstrous character; by which I mean, that, although differing from eachother and from other species of the same genus, in several triflingrespects, they often differ in an extreme degree in some one part, bothwhen compared one with another, and more especially when compared with thespecies under nature to which they are nearest allied. With theseexceptions (and with that of the perfect fertility of varieties whencrossed--a subject hereafter to be discussed), domestic races of the samespecies differ from each other in the same manner as do the closely alliedspecies of the same genus in a state of nature, but the differences in mostcases are less in degree. This must be admitted as true, for the domesticraces of many animals and plants have been ranked by some competent judgesas the descendants of aboriginally distinct species, and by other competentjudges as mere varieties. If any well marked distinction existed between adomestic race and a species, this source of doubt would not so perpetuallyrecur. It has often been stated that domestic races do not differ fromeach other in characters of generic value. It can be shown that thisstatement is not correct; but naturalists differ much in determining whatcharacters are of generic value; all such valuations being at presentempirical. When it is explained how genera originate under nature, it willbe seen that we have no right to expect often to find a generic amount ofdifference in our domesticated races.

In attempting to estimate the amount of structural difference betweenallied domestic races, we are soon involved in doubt, from not knowingwhether they are descended from one or several parent species. This point,if it could be cleared up, would be interesting; if, for instance, it couldbe shown that the greyhound, bloodhound, terrier, spaniel and bull-dog,which we all know propagate their kind truly, were the offspring of anysingle species, then such facts would have great weight in making us doubtabout the immutability of the many closely allied natural species--forinstance, of the many foxes--inhabiting the different quarters of theworld. I do not believe, as we shall presently see, that the whole amountof difference between the several breeds of the dog has been produced underdomestication; I believe that a small part of the difference is due totheir being descended from distinct species. In the case of stronglymarked races of some other domesticated species, there is presumptive oreven strong evidence that all are descended from a single wild stock.

It has often been assumed that man has chosen for domestication animals andplants having an extraordinary inherent tendency to vary, and likewise towithstand diverse climates. I do not dispute that these capacities haveadded largely to the value of most of our domesticated productions; but howcould a savage possibly know, when he first tamed an animal, whether itwould vary in succeeding generations, and whether it would endure otherclimates? Has the little variability of the ass and goose, or the smallpower of endurance of warmth by the reindeer, or of cold by the commoncamel, prevented their domestication? I cannot doubt that if other animalsand plants, equal in number to our domesticated productions, and belongingto equally diverse classes and countries, were taken from a state ofnature, and could be made to breed for an equal number of generations underdomestication, they would on an average vary as largely as the parentspecies of our existing domesticated productions have varied.

In the case of most of our anciently domesticated animals and plants, it isnot possible to come to any definite conclusion, whether they are descendedfrom one or several wild species. The argument mainly relied on by thosewho believe in the multiple origin of our domestic animals is, that we findin the most ancient times, on the monuments of Egypt, and in the lake-habitations of Switzerland, much diversity in the breeds; and that some ofthese ancient breeds closely resemble, or are even identical with, thosestill existing. But this only throws far backward the history ofcivilisation, and shows that animals were domesticated at a much earlierperiod than has hitherto been supposed. The lake-inhabitants ofSwitzerland cultivated several kinds of wheat and barley, the pea, thepoppy for oil and flax; and they possessed several domesticated animals. They also carried on commerce with other nations. All this clearly shows,as Heer has remarked, that they had at this early age progressedconsiderably in civilisation; and this again implies a long continuedprevious period of less advanced civilisation, during which thedomesticated animals, kept by different tribes in different districts,might have varied and given rise to distinct races. Since the discovery offlint tools in the superficial formations of many parts of the world, allgeologists believe that barbarian men existed at an enormously remoteperiod; and we know that at the present day there is hardly a tribe sobarbarous as not to have domesticated at least the dog.

The origin of most of our domestic animals will probably forever remainvague. But I may here state that, looking to the domestic dogs of thewhole world, I have, after a laborious collection of all known facts, cometo the conclusion that several wild species of Canidae have been tamed, andthat their blood, in some cases mingled together, flows in the veins of ourdomestic breeds. In regard to sheep and goats I can form no decidedopinion. From facts communicated to me by Mr. Blyth, on the habits, voice,constitution and structure of the humped Indian cattle, it is almostcertain that they are descended from a different aboriginal stock from ourEuropean cattle; and some competent judges believe that these latter havehad two or three wild progenitors, whether or not these deserve to becalled species. This conclusion, as well as that of the specificdistinction between the humped and common cattle, may, indeed, be lookedupon as established by the admirable researches of Professor Rutimeyer. With respect to horses, from reasons which I cannot here give, I amdoubtfully inclined to believe, in opposition to several authors, that allthe races belong to the same species. Having kept nearly all the Englishbreeds of the fowl alive, having bred and crossed them, and examined theirskeletons, it appears to me almost certain that all are the descendants ofthe wild Indian fowl, Gallus bankiva; and this is the conclusion of Mr.Blyth, and of others who have studied this bird in India. In regard toducks and rabbits, some breeds of which differ much from each other, theevidence is clear that they are all descended from the common duck and wildrabbit.

The doctrine of the origin of our several domestic races from severalaboriginal stocks, has been carried to an absurd extreme by some authors. They believe that every race which breeds true, let the distinctivecharacters be ever so slight, has had its wild prototype. At this ratethere must have existed at least a score of species of wild cattle, as manysheep, and several goats, in Europe alone, and several even within GreatBritain. One author believes that there formerly existed eleven wildspecies of sheep peculiar to Great Britain! When we bear in mind thatBritain has now not one peculiar mammal, and France but few distinct fromthose of Germany, and so with Hungary, Spain, etc., but that each of thesekingdoms possesses several peculiar breeds of cattle, sheep, etc., we mustadmit that many domestic breeds must have originated in Europe; for whenceotherwise could they have been derived? So it is in India. Even in thecase of the breeds of the domestic dog throughout the world, which I admitare descended from several wild species, it cannot be doubted that therehas been an immense amount of inherited variation; for who will believethat animals closely resembling the Italian greyhound, the bloodhound, thebull-dog, pug-dog, or Blenheim spaniel, etc.--so unlike all wildCanidae--ever existed in a state of nature? It has often been loosely saidthat all our races of dogs have been produced by the crossing of a fewaboriginal species; but by crossing we can only get forms in some degreeintermediate between their parents; and if we account for our severaldomestic races by this process, we must admit the former existence of themost extreme forms, as the Italian greyhound, bloodhound, bull-dog, etc.,in the wild state. Moreover, the possibility of making distinct races bycrossing has been greatly exaggerated. Many cases are on record showingthat a race may be modified by occasional crosses if aided by the carefulselection of the individuals which present the desired character; but toobtain a race intermediate between two quite distinct races would be verydifficult. Sir J. Sebright expressly experimented with this object andfailed. The offspring from the first cross between two pure breeds istolerably and sometimes (as I have found with pigeons) quite uniform incharacter, and every thing seems simple enough; but when these mongrels arecrossed one with another for several generations, hardly two of them arealike, and then the difficulty of the task becomes manifest.

BREEDS OF THE DOMESTIC PIGEON, THEIR DIFFERENCES AND ORIGIN.

Believing that it is always best to study some special group, I have, afterdeliberation, taken up domestic pigeons. I have kept every breed which Icould purchase or obtain, and have been most kindly favoured with skinsfrom several quarters of the world, more especially by the Hon. W. Elliotfrom India, and by the Hon. C. Murray from Persia. Many treatises indifferent languages have been published on pigeons, and some of them arevery important, as being of considerable antiquity. I have associated withseveral eminent fanciers, and have been permitted to join two of the LondonPigeon Clubs. The diversity of the breeds is something astonishing. Compare the English carrier and the short-faced tumbler, and see thewonderful difference in their beaks, entailing corresponding differences intheir skulls. The carrier, more especially the male bird, is alsoremarkable from the wonderful development of the carunculated skin aboutthe head, and this is accompanied by greatly elongated eyelids, very largeexternal orifices to the nostrils, and a wide gape of mouth. Theshort-faced tumbler has a beak in outline almost like that of a finch; andthe common tumbler has the singular inherited habit of flying at a greatheight in a compact flock, and tumbling in the air head over heels. Therunt is a bird of great size, with long, massive beak and large feet; someof the sub-breeds of runts have very long necks, others very long wings andtails, others singularly short tails. The barb is allied to the carrier,but, instead of a long beak, has a very short and broad one. The pouterhas a much elongated body, wings, and legs; and its enormously developedcrop, which it glories in inflating, may well excite astonishment and evenlaughter. The turbit has a short and conical beak, with a line of reversedfeathers down the breast; and it has the habit of continually expanding,slightly, the upper part of the oesophagus. The Jacobin has the feathersso much reversed along the back of the neck that they form a hood, and ithas, proportionally to its size, elongated wing and tail feathers. Thetrumpeter and laugher, as their names express, utter a very different coofrom the other breeds. The fantail has thirty or even forty tail-feathers,instead of twelve or fourteen, the normal number in all the members of thegreat pigeon family: these feathers are kept expanded and are carried soerect that in good birds the head and tail touch: the oil-gland is quiteaborted. Several other less distinct breeds might be specified.

In the skeletons of the several breeds, the development of the bones of theface, 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 ina highly remarkable manner. The caudal and sacral vertebrae vary innumber; as does the number of the ribs, together with their relativebreadth and the presence of processes. The size and shape of the aperturesin the sternum are highly variable; so is the degree of divergence andrelative size of the two arms of the furcula. The proportional width ofthe gape of mouth, the proportional length of the eyelids, of the orificeof the nostrils, of the tongue (not always in strict correlation with thelength of beak), the size of the crop and of the upper part of theoesophagus; the development and abortion of the oil-gland; the number ofthe primary wing and caudal feathers; the relative length of the wing andtail to each other and to the body; the relative length of the leg andfoot; the number of scutellae on the toes, the development of skin betweenthe toes, are all points of structure which are variable. The period atwhich the perfect plumage is acquired varies, as does the state of the downwith which the nestling birds are clothed when hatched. The shape and sizeof the eggs vary. The manner of flight, and in some breeds the voice anddisposition, differ remarkably. Lastly, in certain breeds, the males andfemales have come to differ in a slight degree from each other.

Altogether at least a score of pigeons might be chosen, which, if shown toan ornithologist, and he were told that they were wild birds, wouldcertainly be ranked by him as well-defined species. Moreover, I do notbelieve that any ornithologist would in this case place the Englishcarrier, the short-faced tumbler, the runt, the barb, pouter, and fantailin the same genus; more especially as in each of these breeds severaltruly-inherited sub-breeds, or species, as he would call them, could beshown him.

Great as are the differences between the breeds of the pigeon, I am fullyconvinced that the common opinion of naturalists is correct, namely, thatall are descended from the rock-pigeon (Columba livia), including underthis term several geographical races or sub-species, which differ from eachother in the most trifling respects. As several of the reasons which haveled me to this belief are in some degree applicable in other cases, I willhere briefly give them. If the several breeds are not varieties, and havenot proceeded from the rock-pigeon, they must have descended from at leastseven or eight aboriginal stocks; for it is impossible to make the presentdomestic breeds by the crossing of any lesser number: how, for instance,could a pouter be produced by crossing two breeds unless one of theparent-stocks possessed the characteristic enormous crop? The supposedaboriginal stocks must all have been rock-pigeons, that is, they did notbreed or willingly perch on trees. But besides C. livia, with itsgeographical sub-species, only two or three other species of rock-pigeonsare known; and these have not any of the characters of the domestic breeds. Hence the supposed aboriginal stocks must either still exist in thecountries where they were originally domesticated, and yet be unknown toornithologists; and this, considering their size, habits and remarkablecharacters, seems improbable; or they must have become extinct in the wildstate. But birds breeding on precipices, and good flyers, are unlikely tobe exterminated; and the common rock-pigeon, which has the same habits withthe domestic breeds, has not been exterminated even on several of thesmaller British islets, or on the shores of the Mediterranean. Hence thesupposed extermination of so many species having similar habits with therock-pigeon seems a very rash assumption. Moreover, the severalabove-named domesticated breeds have been transported to all parts of theworld, and, therefore, some of them must have been carried back again intotheir native country; but not one has become wild or feral, though thedovecot-pigeon, which is the rock-pigeon in a very slightly altered state,has become feral in several places. Again, all recent experience showsthat it is difficult to get wild animals to breed freely underdomestication; yet on the hypothesis of the multiple origin of our pigeons,it must be assumed that at least seven or eight species were so thoroughlydomesticated in ancient times by half-civilized man, as to be quiteprolific under confinement.

An argument of great weight, and applicable in several other cases, is,that the above-specified breeds, though agreeing generally with the wildrock-pigeon in constitution, habits, voice, colouring, and in most parts oftheir structure, yet are certainly highly abnormal in other parts; we maylook in vain through the whole great family of Columbidae for a beak likethat of the English carrier, or that of the short-faced tumbler, or barb;for reversed feathers like those of the Jacobin; for a crop like that ofthe pouter; for tail-feathers like those of the fantail. Hence it must beassumed, not only that half-civilized man succeeded in thoroughlydomesticating several species, but that he intentionally or by chancepicked out extraordinarily abnormal species; and further, that these veryspecies have since all become extinct or unknown. So many strangecontingencies are improbable in the highest degree.

Some facts in regard to the colouring of pigeons well deserveconsideration. The rock-pigeon is of a slaty-blue, with white loins; butthe Indian sub-species, C. intermedia of Strickland, has this part bluish. The tail has a terminal dark bar, with the outer feathers externally edgedat the base with white. The wings have two black bars. Some semi-domesticbreeds, and some truly wild breeds, have, besides the two black bars, thewings chequered with black. These several marks do not occur together inany other species of the whole family. Now, in every one of the domesticbreeds, taking thoroughly well-bred birds, all the above marks, even to thewhite edging of the outer tail-feathers, sometimes concur perfectlydeveloped. Moreover, when birds belonging to two or more distinct breedsare crossed, none of which are blue or have any of the above-specifiedmarks, the mongrel offspring are very apt suddenly to acquire thesecharacters. To give one instance out of several which I have observed: Icrossed some white fantails, which breed very true, with some black barbs--and it so happens that blue varieties of barbs are so rare that I neverheard of an instance in England; and the mongrels were black, brown andmottled. I also crossed a barb with a spot, which is a white bird with ared tail and red spot on the forehead, and which notoriously breeds verytrue; the mongrels were dusky and mottled. I then crossed one of themongrel barb-fantails with a mongrel barb-spot, and they produced a bird ofas beautiful a blue colour, with the white loins, double black wing-bar,and barred and white-edged tail-feathers, as any wild rock-pigeon! We canunderstand these facts, on the well-known principle of reversion toancestral characters, if all the domestic breeds are descended from therock-pigeon. But if we deny this, we must make one of the two followinghighly improbable suppositions. Either, first, that all the severalimagined aboriginal stocks were coloured and marked like the rock-pigeon,although no other existing species is thus coloured and marked, so that ineach separate breed there might be a tendency to revert to the very samecolours and markings. Or, secondly, that each breed, even the purest, haswithin a dozen, or at most within a score, of generations, been crossed bythe rock-pigeon: I say within a dozen or twenty generations, for noinstance is known of crossed descendants reverting to an ancestor offoreign blood, removed by a greater number of generations. In a breedwhich has been crossed only once the tendency to revert to any characterderived from such a cross will naturally become less and less, as in eachsucceeding generation there will be less of the foreign blood; but whenthere has been no cross, and there is a tendency in the breed to revert toa character which was lost during some former generation, this tendency,for all that we can see to the contrary, may be transmitted undiminishedfor an indefinite number of generations. These two distinct cases ofreversion are often confounded together by those who have written oninheritance.

Lastly, the hybrids or mongrels from between all the breeds of the pigeonare perfectly fertile, as I can state from my own observations, purposelymade, on the most distinct breeds. Now, hardly any cases have beenascertained with certainty of hybrids from two quite distinct species ofanimals being perfectly fertile. Some authors believe that long-continueddomestication eliminates this strong tendency to sterility in species. >From the history of the dog, and of some other domestic animals, thisconclusion is probably quite correct, if applied to species closely relatedto each other. But to extend it so far as to suppose that species,aboriginally as distinct as carriers, tumblers, pouters, and fantails noware, should yield offspring perfectly fertile, inter se, seems to me rashin the extreme.

>From these several reasons, namely, the improbability of man havingformerly made seven or eight supposed species of pigeons to breed freelyunder domestication--these supposed species being quite unknown in a wildstate, and their not having become anywhere feral--these species presentingcertain very abnormal characters, as compared with all other Columbidae,though so like the rock-pigeon in most other respects--the occasionalreappearance of the blue colour and various black marks in all the breeds,both when kept pure and when crossed--and lastly, the mongrel offspringbeing perfectly fertile--from these several reasons, taken together, we maysafely conclude that all our domestic breeds are descended from the rock-pigeon or Columba livia with its geographical sub-species.

In favour of this view, I may add, firstly, that the wild C. livia has beenfound capable of domestication in Europe and in India; and that it agreesin habits and in a great number of points of structure with all thedomestic breeds. Secondly, that although an English carrier or ashort-faced tumbler differs immensely in certain characters from therock-pigeon, yet that by comparing the several sub-breeds of these tworaces, more especially those brought from distant countries, we can make,between them and the rock-pigeon, an almost perfect series; so we can insome other cases, but not with all the breeds. Thirdly, those characterswhich are mainly distinctive of each breed are in each eminently variable, for instance, the wattle and length of beak of the carrier, the shortnessof that of the tumbler, and the number of tail-feathers in the fantail; andthe explanation of this fact will be obvious when we treat of selection. Fourthly, pigeons have been watched and tended with the utmost care, andloved by many people. They have been domesticated for thousands of yearsin several quarters of the world; the earliest known record of pigeons isin the fifth Aegyptian dynasty, about 3000 B.C., as was pointed out to meby Professor Lepsius; but Mr. Birch informs me that pigeons are given in abill of fare in the previous dynasty. In the time of the Romans, as wehear from Pliny, immense prices were given for pigeons; "nay, they are cometo this pass, that they can reckon up their pedigree and race." Pigeonswere much valued by Akber Khan in India, about the year 1600; never lessthan 20,000 pigeons were taken with the court. "The monarchs of Iran andTuran sent him some very rare birds;" and, continues the courtly historian,"His Majesty, by crossing the breeds, which method was never practisedbefore, has improved them astonishingly." About this same period the Dutchwere as eager about pigeons as were the old Romans. The paramountimportance of these considerations in explaining the immense amount ofvariation which pigeons have undergone, will likewise be obvious when wetreat of selection. We shall then, also, see how it is that the severalbreeds so often have a somewhat monstrous character. It is also a mostfavourable circumstance for the production of distinct breeds, that maleand female pigeons can be easily mated for life; and thus different breedscan be kept together in the same aviary.

I have discussed the probable origin of domestic pigeons at some, yet quiteinsufficient, length; because when I first kept pigeons and watched theseveral kinds, well knowing how truly they breed, I felt fully as muchdifficulty in believing that since they had been domesticated they had allproceeded from a common parent, as any naturalist could in coming to asimilar conclusion in regard to the many species of finches, or othergroups of birds, in nature. One circumstance has struck me much; namely,that nearly all the breeders of the various domestic animals and thecultivators of plants, with whom I have conversed, or whose treatises Ihave read, are firmly convinced that the several breeds to which each hasattended, are descended from so many aboriginally distinct species. Ask,as I have asked, a celebrated raiser of Hereford cattle, whether his cattlemight not have descended from Long-horns, or both from a common parent-stock, and he will laugh you to scorn. I have never met a pigeon, orpoultry, or duck, or rabbit fancier, who was not fully convinced that eachmain breed was descended from a distinct species. Van Mons, in histreatise on pears and apples, shows how utterly he disbelieves that theseveral sorts, for instance a Ribston-pippin or Codlin-apple, could everhave proceeded from the seeds of the same tree. Innumerable other examplescould be given. The explanation, I think, is simple: from long-continuedstudy they are strongly impressed with the differences between the severalraces; and though they well know that each race varies slightly, for theywin their prizes by selecting such slight differences, yet they ignore allgeneral arguments, and refuse to sum up in their minds slight differencesaccumulated during many successive generations. May not those naturalistswho, knowing far less of the laws of inheritance than does the breeder, andknowing no more than he does of the intermediate links in the long lines ofdescent, yet admit that many of our domestic races are descended from thesame parents--may they not learn a lesson of caution, when they deride theidea of species in a state of nature being lineal descendants of otherspecies?

PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED, AND THEIR EFFECTS.

Let us now briefly consider the steps by which domestic races have beenproduced, either from one or from several allied species. Some effect maybe attributed to the direct and definite action of the external conditionsof life, and some to habit; but he would be a bold man who would account bysuch agencies for the differences between a dray and race-horse, agreyhound and bloodhound, a carrier and tumbler pigeon. One of the mostremarkable features in our domesticated races is that we see in themadaptation, not indeed to the animal's or plant's own good, but to man'suse or fancy. Some variations useful to him have probably arisen suddenly,or by one step; many botanists, for instance, believe that the fuller'steasel, with its hooks, which can not be rivalled by any mechanicalcontrivance, is only a variety of the wild Dipsacus; and this amount ofchange may have suddenly arisen in a seedling. So it has probably beenwith the turnspit dog; and this is known to have been the case with theancon sheep. But when we compare the dray-horse and race-horse, thedromedary and camel, the various breeds of sheep fitted either forcultivated land or mountain pasture, with the wool of one breed good forone purpose, and that of another breed for another purpose; when we comparethe many breeds of dogs, each good for man in different ways; when wecompare the game-cock, so pertinacious in battle, with other breeds solittle quarrelsome, with "everlasting layers" which never desire to sit,and with the bantam so small and elegant; when we compare the host ofagricultural, culinary, orchard, and flower-garden races of plants, mostuseful to man at different seasons and for different purposes, or sobeautiful in his eyes, we must, I think, look further than to merevariability. We can not suppose that all the breeds were suddenly producedas perfect and as useful as we now see them; indeed, in many cases, we knowthat this has not been their history. The key is man's power ofaccumulative selection: nature gives successive variations; man adds themup in certain directions useful to him. In this sense he may be said tohave made for himself useful breeds.

The great power of this principle of selection is not hypothetical. It iscertain that several of our eminent breeders have, even within a singlelifetime, modified to a large extent their breeds of cattle and sheep. Inorder fully to realise what they have done it is almost necessary to readseveral of the many treatises devoted to this subject, and to inspect theanimals. Breeders habitually speak of an animal's organisation assomething plastic, which they can model almost as they please. If I hadspace I could quote numerous passages to this effect from highly competentauthorities. Youatt, who was probably better acquainted with the works ofagriculturalists than almost any other individual, and who was himself avery good judge of animals, speaks of the principle of selection as "thatwhich enables the agriculturist, not only to modify the character of hisflock, but to change it altogether. It is the magician's wand, by means ofwhich he may summon into life whatever form and mould he pleases." LordSomerville, speaking of what breeders have done for sheep, says: "It wouldseem as if they had chalked out upon a wall a form perfect in itself, andthen had given it existence." In Saxony the importance of the principle ofselection in regard to merino sheep is so fully recognised, that men followit as a trade: the sheep are placed on a table and are studied, like apicture by a connoisseur; this is done three times at intervals of months,and the sheep are each time marked and classed, so that the very best mayultimately be selected for breeding.

What English breeders have actually effected is proved by the enormousprices given for animals with a good pedigree; and these have been exportedto almost every quarter of the world. The improvement is by no meansgenerally due to crossing different breeds; all the best breeders arestrongly opposed to this practice, except sometimes among closely alliedsub-breeds. And when a cross has been made, the closest selection is farmore indispensable even than in ordinary cases. If selection consistedmerely in separating some very distinct variety and breeding from it, theprinciple would be so obvious as hardly to be worth notice; but itsimportance consists in the great effect produced by the accumulation in onedirection, during successive generations, of differences absolutelyinappreciable by an uneducated eye--differences which I for one have vainlyattempted to appreciate. Not one man in a thousand has accuracy of eye andjudgment sufficient to become an eminent breeder. If gifted with thesequalities, and he studies his subject for years, and devotes his lifetimeto it with indomitable perseverance, he will succeed, and may make greatimprovements; if he wants any of these qualities, he will assuredly fail. Few would readily believe in the natural capacity and years of practicerequisite to become even a skilful pigeon-fancier.

The same principles are followed by horticulturists; but the variations arehere often more abrupt. No one supposes that our choicest productions havebeen produced by a single variation from the aboriginal stock. We haveproofs that this is not so in several cases in which exact records havebeen kept; thus, to give a very trifling instance, the steadily increasingsize of the common gooseberry may be quoted. We see an astonishingimprovement in many florists' flowers, when the flowers of the present dayare compared with drawings made only twenty or thirty years ago. When arace of plants is once pretty well established, the seed-raisers do notpick out the best plants, but merely go over their seed-beds, and pull upthe "rogues," as they call the plants that deviate from the properstandard. With animals this kind of selection is, in fact, likewisefollowed; for hardly any one is so careless as to breed from his worstanimals.

In regard to plants, there is another means of observing the accumulatedeffects of selection--namely, by comparing the diversity of flowers in thedifferent varieties of the same species in the flower-garden; the diversityof leaves, pods, or tubers, or whatever part is valued, in thekitchen-garden, in comparison with the flowers of the same varieties; andthe diversity of fruit of the same species in the orchard, in comparisonwith the leaves and flowers of the same set of varieties. See howdifferent the leaves of the cabbage are, and how extremely alike theflowers; how unlike the flowers of the heartsease are, and how alike theleaves; how much the fruit of the different kinds of gooseberries differ insize, colour, shape, and hairiness, and yet the flowers present very slightdifferences. It is not that the varieties which differ largely in some onepoint do not differ at all in other points; this is hardly ever--I speakafter careful observation--perhaps never, the case. The law of correlatedvariation, the importance of which should never be overlooked, will ensuresome differences; but, as a general rule, it cannot be doubted that thecontinued selection of slight variations, either in the leaves, theflowers, or the fruit, will produce races differing from each other chieflyin these characters.

It may be objected that the principle of selection has been reduced tomethodical practice for scarcely more than three-quarters of a century; ithas certainly been more attended to of late years, and many treatises havebeen published on the subject; and the result has been, in a correspondingdegree, rapid and important. But it is very far from true that theprinciple is a modern discovery. I could give several references to worksof high antiquity, in which the full importance of the principle isacknowledged. In rude and barbarous periods of English history choiceanimals were often imported, and laws were passed to prevent theirexportation: the destruction of horses under a certain size was ordered,and this may be compared to the "roguing" of plants by nurserymen. Theprinciple of selection I find distinctly given in an ancient Chineseencyclopaedia. Explicit rules are laid down by some of the Roman classicalwriters. From passages in Genesis, it is clear that the colour of domesticanimals was at that early period attended to. Savages now sometimes crosstheir dogs with wild canine animals, to improve the breed, and theyformerly did so, as is attested by passages in Pliny. The savages in SouthAfrica match their draught cattle by colour, as do some of the Esquimauxtheir teams of dogs. Livingstone states that good domestic breeds arehighly valued by the negroes in the interior of Africa who have notassociated with Europeans. Some of these facts do not show actualselection, but they show that the breeding of domestic animals wascarefully attended to in ancient times, and is now attended to by thelowest savages. It would, indeed, have been a strange fact, had attentionnot been paid to breeding, for the inheritance of good and bad qualities isso obvious.

UNCONSCIOUS SELECTION.

At the present time, eminent breeders try by methodical selection, with adistinct object in view, to make a new strain or sub-breed, superior toanything of the kind in the country. But, for our purpose, a form ofselection, which may be called unconscious, and which results from everyone trying to possess and breed from the best individual animals, is moreimportant. Thus, a man who intends keeping pointers naturally tries to getas good dogs as he can, and afterwards breeds from his own best dogs, buthe has no wish or expectation of permanently altering the breed. Nevertheless we may infer that this process, continued during centuries,would improve and modify any breed, in the same way as Bakewell, Collins,etc., by this very same process, only carried on more methodically, didgreatly modify, even during their lifetimes, the forms and qualities oftheir cattle. Slow and insensible changes of this kind could never berecognised unless actual measurements or careful drawings of the breeds inquestion have been made long ago, which may serve for comparison. In somecases, however, unchanged, or but little changed, individuals of the samebreed exist in less civilised districts, where the breed has been lessimproved. There is reason to believe that King Charles' spaniel has beenunconsciously modified to a large extent since the time of that monarch. Some highly competent authorities are convinced that the setter is directlyderived from the spaniel, and has probably been slowly altered from it. Itis known that the English pointer has been greatly changed within the lastcentury, and in this case the change has, it is believed, been chieflyeffected by crosses with the foxhound; but what concerns us is, that thechange has been effected unconsciously and gradually, and yet soeffectually that, though the old Spanish pointer certainly came from Spain,Mr. Borrow has not seen, as I am informed by him, any native dog in Spainlike our pointer.

By a similar process of selection, and by careful training, English race-horses have come to surpass in fleetness and size the parent Arabs, so thatthe latter, by the regulations for the Goodwood Races, are favoured in theweights which they carry. Lord Spencer and others have shown how thecattle of England have increased in weight and in early maturity, comparedwith the stock formerly kept in this country. By comparing the accountsgiven in various old treatises of the former and present state of carrierand tumbler pigeons in Britain, India, and Persia, we can trace the stagesthrough which they have insensibly passed, and come to differ so greatlyfrom the rock-pigeon.

Youatt gives an excellent illustration of the effects of a course ofselection which may be considered as unconscious, in so far that thebreeders could never have expected, or even wished, to produce the resultwhich ensued--namely, the production of the distinct strains. The twoflocks of Leicester sheep kept by Mr. Buckley and Mr. Burgess, as Mr.Youatt remarks, "Have been purely bred from the original stock of Mr.Bakewell for upwards of fifty years. There is not a suspicion existing inthe mind of any one at all acquainted with the subject that the owner ofeither of them has deviated in any one instance from the pure blood of Mr.Bakewell's flock, and yet the difference between the sheep possessed bythese two gentlemen is so great that they have the appearance of beingquite different varieties."

If there exist savages so barbarous as never to think of the inheritedcharacter of the offspring of their domestic animals, yet any one animalparticularly useful to them, for any special purpose, would be carefullypreserved during famines and other accidents, to which savages are soliable, and such choice animals would thus generally leave more offspringthan the inferior ones; so that in this case there would be a kind ofunconscious selection going on. We see the value set on animals even bythe barbarians of Tierra del Fuego, by their killing and devouring theirold women, in times of dearth, as of less value than their dogs.

In plants the same gradual process of improvement through the occasionalpreservation of the best individuals, whether or not sufficiently distinctto be ranked at their first appearance as distinct varieties, and whetheror not two or more species or races have become blended together bycrossing, may plainly be recognised in the increased size and beauty whichwe now see in the varieties of the heartsease, rose, pelargonium, dahlia,and other plants, when compared with the older varieties or with theirparent-stocks. No one would ever expect to get a first-rate heartsease ordahlia from the seed of a wild plant. No one would expect to raise afirst-rate melting pear from the seed of a wild pear, though he mightsucceed from a poor seedling growing wild, if it had come from agarden-stock. The pear, though cultivated in classical times, appears,from Pliny's description, to have been a fruit of very inferior quality. Ihave seen great surprise expressed in horticultural works at the wonderfulskill of gardeners in having produced such splendid results from such poormaterials; but the art has been simple, and, as far as the final result isconcerned, has been followed almost unconsciously. It has consisted inalways cultivating the best known variety, sowing its seeds, and, when aslightly better variety chanced to appear, selecting it, and so onwards. But the gardeners of the classical period, who cultivated the best pearswhich they could procure, never thought what splendid fruit we should eat;though we owe our excellent fruit in some small degree to their havingnaturally chosen and preserved the best varieties they could anywhere find.

A large amount of change, thus slowly and unconsciously accumulated,explains, as I believe, the well-known fact, that in a number of cases wecannot recognise, and therefore do not know, the wild parent-stocks of theplants which have been longest cultivated in our flower and kitchengardens. If it has taken centuries or thousands of years to improve ormodify most of our plants up to their present standard of usefulness toman, we can understand how it is that neither Australia, the Cape of GoodHope, nor any other region inhabited by quite uncivilised man, has affordedus a single plant worth culture. It is not that these countries, so richin species, do not by a strange chance possess the aboriginal stocks of anyuseful plants, but that the native plants have not been improved bycontinued selection up to a standard of perfection comparable with thatacquired by the plants in countries anciently civilised.

In regard to the domestic animals kept by uncivilised man, it should not beoverlooked that they almost always have to struggle for their own food, atleast during certain seasons. And in two countries very differentlycircumstanced, individuals of the same species, having slightly differentconstitutions or structure, would often succeed better in the one countrythan in the other, and thus by a process of "natural selection," as willhereafter be more fully explained, two sub-breeds might be formed. This,perhaps, partly explains why the varieties kept by savages, as has beenremarked by some authors, have more of the character of true species thanthe varieties kept in civilised countries.

On the view here given of the important part which selection by man hasplayed, it becomes at once obvious, how it is that our domestic races showadaptation in their structure or in their habits to man's wants or fancies. We can, I think, further understand the frequently abnormal character ofour domestic races, and likewise their differences being so great inexternal characters, and relatively so slight in internal parts or organs. Man can hardly select, or only with much difficulty, any deviation ofstructure excepting such as is externally visible; and indeed he rarelycares for what is internal. He can never act by selection, excepting onvariations which are first given to him in some slight degree by nature. No man would ever try to make a fantail till he saw a pigeon with a taildeveloped in some slight degree in an unusual manner, or a pouter till hesaw a pigeon with a crop of somewhat unusual size; and the more abnormal orunusual any character was when it first appeared, the more likely it wouldbe to catch his attention. But to use such an expression as trying to makea fantail is, I have no doubt, in most cases, utterly incorrect. The manwho first selected a pigeon with a slightly larger tail, never dreamed whatthe descendants of that pigeon would become through long-continued, partlyunconscious and partly methodical, selection. Perhaps the parent bird ofall fantails had only fourteen tail-feathers somewhat expanded, like thepresent Java fantail, or like individuals of other and distinct breeds, inwhich as many as seventeen tail-feathers have been counted. Perhaps thefirst pouter-pigeon did not inflate its crop much more than the turbit nowdoes the upper part of its oesophagus--a habit which is disregarded by allfanciers, as it is not one of the points of the breed.

Nor let it be thought that some great deviation of structure would benecessary to catch the fancier's eye: he perceives extremely smalldifferences, and it is in human nature to value any novelty, howeverslight, in one's own possession. Nor must the value which would formerlyhave been set on any slight differences in the individuals of the samespecies, be judged of by the value which is now set on them, after severalbreeds have fairly been established. It is known that with pigeons manyslight variations now occasionally appear, but these are rejected as faultsor deviations from the standard of perfection in each breed. The commongoose has not given rise to any marked varieties; hence the Toulouse andthe common breed, which differ only in colour, that most fleeting ofcharacters, have lately been exhibited as distinct at our poultry-shows.

These views appear to explain what has sometimes been noticed, namely, thatwe know hardly anything about the origin or history of any of our domesticbreeds. But, in fact, a breed, like a dialect of a language, can hardly besaid to have a distinct origin. A man preserves and breeds from anindividual with some slight deviation of structure, or takes more care thanusual in matching his best animals, and thus improves them, and theimproved animals slowly spread in the immediate neighbourhood. But theywill as yet hardly have a distinct name, and from being only slightlyvalued, their history will have been disregarded. When further improved bythe same slow and gradual process, they will spread more widely, and willbe recognised as something distinct and valuable, and will then probablyfirst receive a provincial name. In semi-civilised countries, with littlefree communication, the spreading of a new sub-breed will be a slowprocess. As soon as the points of value are once acknowledged, theprinciple, as I have called it, of unconscious selection will alwaystend--perhaps more at one period than at another, as the breed rises orfalls in fashion--perhaps more in one district than in another, accordingto the state of civilisation of the inhabitants--slowly to add to thecharacteristic features of the breed, whatever they may be. But the chancewill be infinitely small of any record having been preserved of such slow,varying, and insensible changes.

CIRCUMSTANCES FAVOURABLE TO MAN'S POWER OF SELECTION.

I will now say a few words on the circumstances, favourable or the reverse,to man's power of selection. A high degree of variability is obviouslyfavourable, as freely giving the materials for selection to work on; notthat mere individual differences are not amply sufficient, with extremecare, to allow of the accumulation of a large amount of modification inalmost any desired direction. But as variations manifestly useful orpleasing to man appear only occasionally, the chance of their appearancewill be much increased by a large number of individuals being kept. Hencenumber is of the highest importance for success. On this principleMarshall formerly remarked, with respect to the sheep of part of Yorkshire,"As they generally belong to poor people, and are mostly IN SMALL LOTS,they never can be improved." On the other hand, nurserymen, from keepinglarge stocks of the same plant, are generally far more successful thanamateurs in raising new and valuable varieties. A large number ofindividuals of an animal or plant can be reared only where the conditionsfor its propagation are favourable. When the individuals are scanty allwill be allowed to breed, whatever their quality may be, and this willeffectually prevent selection. But probably the most important element isthat the animal or plant should be so highly valued by man, that theclosest attention is paid to even the slightest deviations in its qualitiesor structure. Unless such attention be paid nothing can be effected. Ihave seen it gravely remarked, that it was most fortunate that thestrawberry began to vary just when gardeners began to attend to this plant. No doubt the strawberry had always varied since it was cultivated, but theslight varieties had been neglected. As soon, however, as gardeners pickedout individual plants with slightly larger, earlier, or better fruit, andraised seedlings from them, and again picked out the best seedlings andbred from them, then (with some aid by crossing distinct species) thosemany admirable varieties of the strawberry were raised which have appearedduring the last half-century.

With animals, facility in preventing crosses is an important element in theformation of new races--at least, in a country which is already stockedwith other races. In this respect enclosure of the land plays a part. Wandering savages or the inhabitants of open plains rarely possess morethan one breed of the same species. Pigeons can be mated for life, andthis is a great convenience to the fancier, for thus many races may beimproved and kept true, though mingled in the same aviary; and thiscircumstance must have largely favoured the formation of new breeds. Pigeons, I may add, can be propagated in great numbers and at a very quickrate, and inferior birds may be freely rejected, as when killed they servefor food. On the other hand, cats, from their nocturnal rambling habits,can not be easily matched, and, although so much valued by women andchildren, we rarely see a distinct breed long kept up; such breeds as we dosometimes see are almost always imported from some other country. AlthoughI do not doubt that some domestic animals vary less than others, yet therarity or absence of distinct breeds of the cat, the donkey, peacock,goose, etc., may be attributed in main part to selection not having beenbrought into play: in cats, from the difficulty in pairing them; indonkeys, from only a few being kept by poor people, and little attentionpaid to their breeding; for recently in certain parts of Spain and of theUnited States this animal has been surprisingly modified and improved bycareful selection; in peacocks, from not being very easily reared and alarge stock not kept; in geese, from being valuable only for two purposes,food and feathers, and more especially from no pleasure having been felt inthe display of distinct breeds; but the goose, under the conditions towhich it is exposed when domesticated, seems to have a singularlyinflexible organisation, though it has varied to a slight extent, as I haveelsewhere described.

Some authors have maintained that the amount of variation in our domesticproductions is soon reached, and can never afterward be exceeded. It wouldbe somewhat rash to assert that the limit has been attained in any onecase; for almost all our animals and plants have been greatly improved inmany ways within a recent period; and this implies variation. It would beequally rash to assert that characters now increased to their utmost limit,could not, after remaining fixed for many centuries, again vary under newconditions of life. No doubt, as Mr. Wallace has remarked with much truth,a limit will be at last reached. For instance, there must be a limit tothe fleetness of any terrestrial animal, as this will be determined by thefriction to be overcome, the weight of the body to be carried, and thepower of contraction in the muscular fibres. But what concerns us is thatthe domestic varieties of the same species differ from each other in almostevery character, which man has attended to and selected, more than do thedistinct species of the same genera. Isidore Geoffroy St. Hilaire hasproved this in regard to size, and so it is with colour, and probably withthe length of hair. With respect to fleetness, which depends on manybodily characters, Eclipse was far fleeter, and a dray-horse is comparablystronger, than any two natural species belonging to the same genus. Sowith plants, the seeds of the different varieties of the bean or maizeprobably differ more in size than do the seeds of the distinct species inany one genus in the same two families. The same remark holds good inregard to the fruit of the several varieties of the plum, and still morestrongly with the melon, as well as in many other analogous cases.

To sum up on the origin of our domestic races of animals and plants. Changed conditions of life are of the highest importance in causingvariability, both by acting directly on the organisation, and indirectly byaffecting the reproductive system. It is not probable that variability isan inherent and necessary contingent, under all circumstances. The greateror less force of inheritance and reversion determine whether variationsshall endure. Variability is governed by many unknown laws, of whichcorrelated growth is probably the most important. Something, but how muchwe do not know, may be attributed to the definite action of the conditionsof life. Some, perhaps a great, effect may be attributed to the increaseduse or disuse of parts. The final result is thus rendered infinitelycomplex. In some cases the intercrossing of aboriginally distinct speciesappears to have played an important part in the origin of our breeds. Whenseveral breeds have once been formed in any country, their occasionalintercrossing, with the aid of selection, has, no doubt, largely aided inthe formation of new sub-breeds; but the importance of crossing has beenmuch exaggerated, both in regard to animals and to those plants which arepropagated by seed. With plants which are temporarily propagated bycuttings, buds, etc., the importance of crossing is immense; for thecultivator may here disregard the extreme variability both of hybrids andof mongrels, and the sterility of hybrids; but plants not propagated byseed are of little importance to us, for their endurance is only temporary. Over all these causes of change, the accumulative action of selection,whether applied methodically and quickly, or unconsciously and slowly, butmore efficiently, seems to have been the predominant power.