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: (r\ VAuc Rock [Coluniha livia); (2), Tumbler: 

 (3), Owl; (4), Jacobin; {5), Fantail; \t>). 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 {Cohtmba 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 



