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Show 202 DOMESTIC PIGEONS. CHAP. VI. were all colour d blue, and had tho wing-bars and other cbamctcristic marks of C. livia,-a suppojtion which is highly improbable, as besides this one species no existing mcmb~r of the Columbidm presents these combined character ; and ~t ~ould not be possible t.o find any other instance of several specws Jdentica. l in plumage, yet as different in important points of strueture as are pouters, fantails, carriers, tumblers, &c. Or lastly, .'~e may assume that all the races, whether descended from C. lwza or from several aboriginal species, although they have boon bred with so much care and are so highly valued by fanciers, have all been crossed witl1in a dozen or score of generations with C. livia, and have thus acquired their tendency to produce blue birds with tho several characteristic marks. I have said that it must be a snmod that each race has been crossed with 0. livia within fl. dozen, or, at the utmost, within a score of generations; for there is no rca on to believe that cro sod offspring over revert to one of their ancestors when removed by a greater number of g ncrations. In a brood which has boon eros eel only once, the tendency to reversion will naturally become loss and less in tho succueding gen rations, as in each there will be less and less of the blood of the foreign breed ; but when there has been no eros with a eli tinct breed, and thoro is a tenuency in both parents to revert to some long-lost character, this tendency, for all that we can soc to the contrary, may be transmitted undiminished for an indefinite number of generations. rrhese two distinct cases of reversion are often' confounded together by those who have written on inheritance. Considering, on tho one hand, the improbability of the three assumptions which have just been discussed, and, on the other hand, how simply the facts are explained on the principle of reversion, we may conclude that the occasional appearance in all the races, both when purely bred and more especially when crossed, of blue birds, sometimes chequerou, with double wingbars, with white or blue croups, with a bar at tho end of ·tho tail, and with tho outer tail-feathers edged with white, affords an argument of the greatest weight in favour of the view that all are descenued from Columba livia, including under this name the throe or four wild varieties or sub-species before enumerated. CHAP. VI. TIIEIR REVERSION IN COLOUR. 203 To snm up tho six foregoing arguments, which arc opposed to tho belief that the chief domestic races are the descendants of at least eight or nino or perhaps a dozen species; for the crossing of any 1 ss number would not yi ld the characteyjstic differences between the several races. Firstly, the improbability that so many sp ·cios should sti11 exist somewhere, but be unknown to ornithologists, or that they should have become within tho historical period extinct, although man has had so little· influonco in exterminating tho wild C. livia. Secondly, the improbal>ility of man in former times having thoronghly domesticated antl rendered fertile under confinement so many species. Thirdly, th se supposed species having nowhere become feral. J?ourtltly, tho extraordinary fact that man slJOuld, intentionally or by chan ·e, have cho ·en for domestication several species, extremely abnormal in character; and furthermore, tho points of structure which render those supposed spec:ies so abnormal being now highly variable. I!'iftldy, the fact of all the races, though differing in many important points of structure, producing perfectly fertile mongrels; whilst all the hybrids which have been produced between oven closely allied species in the pigeon-family are sterile. Sixthly, tho remarkable tatomonts just given on tho toncleucy in all the races, both when pnrely bred and when crosscu, to revert in numerous minute details of colouring to the character of the wild rock-pigeon, and to vary in a similar manner. To these arguments may be add cl the extreme improbability that a number of species formerly existed, wh~ch differed greatly from each other in some few points, but whiCh resembled each other as clos ly as do tho domestic races in other pointt:> of structure, in voice, and in all their habits of life.. When those several facts and arguments are fairly taken mto consiueration, it would require an overwhelming amount of evidence to make us admit tha:t the chief domestic race~ are descended from everal aboriginal stocks; and of such evidence there is absolutely none. 'l'bo belief that the chief domestic races are descended from several. ~vild stocks no doubt has arisen from the apparent improbalnlJty of such grefl.t modifications of structure havinO' been effectcc~ siuco man first domesti<:ated the rock-pigeon. Nor am I surpnsed at any degree of hesitation in admitting their common |