按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
oints 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； has become feral in several places。 Again； all recent experience shows that it is most difficult to get any wild animal to breed freely under domestication； yet on the hypothesis of the multiple origin of our pigeons； it must be assumed that at least seven or eight species were so thoroughly domesticated in ancient times by half…civilized man； as to be quite prolific under confinement。
An argument； as it seems to me； of great weight； and applicable in several other cases； is； that the above…specified breeds； though agreeing generally in constitution； habits； voice； colouring； and in most parts of their structure； with the wild rock…pigeon； yet are certainly highly abnormal in other parts of their structure： we may look in vain throughout the whole great family of Columbidae for a beak like that 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 of the pouter； for tail…feathers like those of the fantail。 Hence it must be assumed not only that half…civilized man succeeded in thoroughly domesticating several species； but that he intentionally or by chance picked out extraordinarily abnormal species； and further； that these very species have since all become extinct or unknown。 So many strange contingencies seem to me improbable in the highest degree。
Some facts in regard to the colouring of pigeons well deserve consideration。 The rock…pigeon is of a slaty…blue； and has a white rump （the Indian sub…species； C。 intermedia of Strickland； having it bluish）； the tail has a terminal dark bar； with the bases of the outer feathers externally edged with white； the wings have two black bars： some semi…domestic breeds and some apparently truly wild breeds have； besides the two black bars； the wings chequered with black。 These several marks do not occur together in any other species of the whole family。 Now； in every one of the domestic breeds； taking thoroughly well…bred birds； all the above marks； even to the white edging of the outer tail…feathers； sometimes concur perfectly developed。 Moreover； when two birds belonging to two distinct breeds are crossed； neither of which is blue or has any of the above…specified marks； the mongrel offspring are very apt suddenly to acquire these characters； for instance； I crossed some uniformly white fantails with some uniformly black barbs； and they produced mottled brown and black birds； these I again crossed together； and one grandchild of the pure white fantail and pure black barb was of as beautiful a blue colour； with the white rump； double black wing…bar； and barred and white…edged tail…feathers； as any wild rock…pigeon！ We can understand these facts； on the well…known principle of reversion to ancestral characters； if all the domestic breeds have descended from the rock…pigeon。 But if we deny this； we must make one of the two following highly improbable suppositions。 Either； firstly； that all the several imagined aboriginal stocks were coloured and marked like the rock…pigeon； although no other existing species is thus coloured and marked； so that in each separate breed there might be a tendency to revert to the very same colours and markings。 Or； secondly； that each breed； even the purest； has within a dozen or； at most； within a score of generations； been crossed by the rock…pigeon： I say within a dozen or twenty generations； for we know of no fact countenancing the belief that the child ever reverts to some one ancestor； removed by a greater number of generations。 In a breed which has been crossed only once with some distinct breed； the tendency to reversion to any character derived from such cross will naturally become less and less； as in each succeeding generation there will be less of the foreign blood； but when there has been no cross with a distinct breed； and there is a tendency in both parents to revert to a character； which has been lost during some former generation； this tendency； for all that we can see to the contrary； may be transmitted undiminished for an indefinite number of generations。 These two distinct cases are often c