ON THE ABORIGINAL PARENT-STOCK OF THE SEVERAL DOMESTIC RACES--HABITS OF LIFE--WILD RACES OF THE ROCK-PIGEON--DOVECOT-PIGEONS--PROOFS OF THE DESCENT OF THE SEVERAL RACES FROM COLUMBA LIVIA--FERTILITY OF THE RACES WHEN CROSSED--REVERSION TO THE PLUMAGE OF THE WILD ROCK-PIGEON--CIRCUMSTANCES FAVOURABLE TO THE FORMATION OF THE RACES--ANTIQUITY AND HISTORY OF THE PRINCIPAL RACES--MANNER OF THEIR FORMATION--SELECTION--UNCONSCIOUS SELECTION--CARE TAKEN BY FANCIERS IN SELECTING THEIR BIRDS--SLIGHTLY DIFFERENT STRAINS GRADUALLY CHANGE INTO WELL-MARKED BREEDS--EXTINCTION OF INTERMEDIATE FORMS--CERTAIN BREEDS REMAIN PERMANENT, WHILST OTHERS CHANGE--SUMMARY. The differences described in the last chapter between the eleven chief domestic races and between individual birds of the same race, would be of little significance, if they had not all descended from a single wild stock. The question of their origin is therefore of fundamental importance, and must be discussed at considerable length. No one will think this superfluous who considers the great amount of difference between the races, who knows how ancient many of them are, and how truly they breed at the present day. Fanciers almost unanimously believe that the different races are descended from several wild stocks, whereas most naturalists believe that all are descended from the _Columba livia_ or rock-pigeon. Temminck[316] has well observed, and Mr. Gould has made the same remark to me, that the aboriginal parent must have been a species which roosted and built its nest on rocks; and I may add that it must have been a social bird. For all the domestic races are highly social, and none are known to build or habitually to roost on trees. The awkward manner in which some pigeons, kept by me in a summer-house near an old walnut-tree, occasionally alighted on the barer branches, was {181} evident.[317] Nevertheless, Mr. R. Scot Skirving informs me that he often saw crowds of pigeons in Upper Egypt settling on the low trees, but not on the palms, in preference to the mud hovels of the natives. In India Mr. Blyth[318] has been assured that the wild _C. livia_, var. _intermedia_, sometimes roosts in trees. I may here give a curious instance of compulsion leading to changed habits: the banks of the Nile above lat. 28° 30' are perpendicular for a long distance, so that when the river is full the pigeons cannot alight on the shore to drink, and Mr. Skirving repeatedly saw whole flocks settle on the water, and drink whilst they floated down the stream. These flocks seen from a distance resembled flocks of gulls on the surface of the sea.