198 DOMESTIC PIGEONS : Chap, VI. 



arisen since man first doriesticated tlie pigeon. On the 

 ordinary view, variability is due to changed conditions of life ; 

 on the Pallasian doctrine, variability, or the appearance of 

 new characters, is due to some mysterious efli'ect from the cross- 

 ing of two species, neither of which possesses the characters 

 in question. In some few instances it is possible that well- 

 marked races may have been formed by crossing ; for instance, 

 a Barb might perhaps be formed by a cross between a long- 

 beaked Carrier, having large eye-wattles, and some short- 

 beaked pigeon. That many races have been in some degree 

 modified by crossing, and that certain varieties which are 

 distinguished only by peculiar tints have arisen from crosses 

 between differently-coloured varieties, is almost certain. On 

 the doctrine, therefore, that the chief races owe their differ- 

 ences tc their descent from distinct species, we must admit 

 that at least eight or nine, or more probably a dozen species, 

 all having the same habit of breeding and roosting on rocks 

 and living in society, either now exist somewhere, or formerly 

 existed, but have become extinct as wild birds. Considering 

 how carefully wild pigeons have been collected throughout 

 the world, and what conspicuous birds they are, especially 

 when frequenting rocks, it is extremely improbable that 

 eight or nine species, which were long ago domesticated and 

 therefore must have inhabited Pome anciently knowoi country, 

 should still exist in the wild state and be unknown to orni- 

 thologists. 



The hypothesis that such species formerly existed, but have 

 become extinct, is in some slight degree more probable. But 

 the extinction of so many species within the historical period is 

 a bold hypothesis, seeing how little influence man has had in 

 exterminating the common rock-pigeon, which agrees in all its 

 habits of life with the domestic races. The G. livia now exists 

 and flourishes on the small northern islands of Faroe, on many 

 islands oft' the coast of Scotland, on Sardinia, and the shores of 

 the Mediterranean, and in the centre of India. Fanciers have 

 sometimes imagined that the several supposed parent species 

 were originally confined to small islands, and thus might 

 readily have been exterminated ; but the facts just given do not 

 favour the probability of their extinction, even on small islands. 



