ARTIFICIAL AND NATURAL SELECTION 29 



feathered. The coo is very peculiar, and unlike that 

 of any other pigeon, being rapidly repeated and con- 

 tinued for several minutes. 



Among these forms there is thus great diversity 

 in both form and colour. This diversity also affects 

 the internal structure, for example the skull : the 

 caudal and sacral vertebrae and also the ribs vary in 

 number. The number of primary wing and tail 

 feathers, the shape and size of the eggs, the manner 

 of flight, and almost all other characters, also differ. If 

 these birds were now found in a wild state, they would 

 be considered to constitute distinct genera, yet they 

 are known to be all descended from Columba livia, 

 the blue rock-pigeon of Europe, Africa, India, &c. 



The arguments brought forward by Darwin to 

 prove this are as follows : — 



(i.) All domestic races are highly soSial, and none 

 of them habitually build or roost in trees ; hence it is 

 in the highest degree probable that their ancestor was 

 a social bird nesting on rocks. 



(ii.) Only five or six wild species have these habits, 

 and nearly all these but Columba livia can be ruled 

 out at once. 



(iii.) Columba livia has a vast range of dis- 

 tribution—from Norway to the Mediterranean, from 

 Madeira to Abyssinia, and from India to Japan. It 

 is very variable in plumage and very easily tamed. 

 It is identical with the ordinary dove-cot pigeon, and 

 except in colour practically identical with toy pigeons 

 generally. 



(iv.) There is no trace of domestic pigeons in the 

 feral condition- 



