ARTIFICIAL SELECTION. 133 
descendants from a common progenitor to diverge in 
character.” * 
That organisms are variable and not fixed in rigid 
forms, is a phenomenon so general that variability passes 
current as a self-evident property of organic existence. 
In the next chapter we shall inquire how far everything 
organic is necessarily subject to mutability. On the 
existence of this property rests the artificial breeding, 
or selection by man, consciously and unconsciously 
exercised from the earliest commencement of hunting 
and agriculture, of which, as Darwin says, “the impor- 
tance mainly lies in the power of selecting scarcely 
appreciable differences, which are nevertheless found to 
be transmissible, and which can be accumulated until the 
result is made manifest to the eye of every beholder.” 
In the “ Origin of Species,” as an example of methodic 
selection in the production of breeds, Darwin has chosen 
the pigeon, to the breeding of which he zealously devoted 
himself for many years. 
The pigeon is specially adapted to the purpose of 
scientific observation of the phenomena of breeding, 
because, owing to its monogamic habits, it is easy to 
control, because it may be brought in a short time to 
striking variations, because the records of its breeding 
are tolerably complete, and, finally, because it is one of 
the few domestic animals of which the ancestral stock 
is scarcely open to a doubt. 
The chief races produced by the fanciers may be 
grouped as follows. The Pouter Pigeons have a 
moderate beak, elongated legs and body, their ceso- 
* Mr. Darwin has himself been good enough to re-write his letter from the 
German text. He kept no copy of the original M 
