NATURAL SELECTION 



487 



we can suppose such variations to gradually accumulate until 

 their amount is so large as to constitute a new species. 



Darwin's conclusions as to the joint result of variation and 

 heredity were largely based on observations made upon domes- 





Fig. 1337. Blue Rock and some of the domesticated varieties of Pigeon: (i), Blue Rock (CoZiunba livza); (2), Tumbler; 

 (3), Owl; (4), Jacobin; (5), Fantail; (6), Pouter 



ticated animals. We know, for example, that all the numerous 

 breeds of pigeons (fig. 1337), such as Pouters, Fantails, Carriers, 

 Tumblers, &c. &c., are descended from one original species, 

 i.e. the Blue Rock (Columba livia), as the result of artificial 

 selection by human agency. That is to say, individuals varying 

 in some particular direction have been selected by man with a 



