DARWINISM 
CHAP. 
produce fertile individuals, and which reproduce themselves 
by generation, in such a manner that we may from analogy 
suppose them all to have sprung from one single individual.” 
And the zoologist Swainson gives a somewhat similar defini¬ 
tion : “ A species, in the usual acceptation of the term, is an 
animal which, in a state of nature, is distinguished by certain 
peculiarities of form, size, colour, or other circumstances, from 
another animal. It propagates, ‘ after its kind,’ individuals 
perfectly resembling the parent; its peculiarities, therefore, 
are permanent.” 1 
To illustrate these definitions we will take two common 
English birds, the rook (Corvus frugilegus) and the crow 
(Corvus corone). These are distinct species, because, in the first 
place, they always differ from each other in certain slight 
peculiarities of structure, form, and habits, and, in the second 
place, because rooks always produce rooks, and crows produce 
crows, and they do not interbreed. It was therefore con¬ 
cluded that all the rooks in the world had descended from a 
single pair of rooks, and the crows in like manner from a 
single pair of crows, while it was considered impossible that 
crows could have descended from rooks or vice versa. The 
“ origin ” of the first pair of each kind was a mystery. 
Similar remarks may be applied to our two common plants, 
the sweet violet (Viola odorata) and the dog violet (Viola 
canina). These also produce their like and never produce 
each other or intermingle, and they were therefore each 
supposed to have sprung from a single individual whose 
“ origin ” was unknown. But besides the crow and the rook 
there are about thirty other kinds of birds in various parts of 
the world, all so much like our species that they receive the 
common name of crows ; and some of them differ less from 
each other than does our crow from our rook. These are all 
species of the genus Corvus, and were therefore believed to 
have been always as distinct as they are now, neither more 
nor less, and to have each descended from one pair of ances¬ 
tral crows of the same identical species, which themselves had 
an unknown “origin.” Of violets there are more than a 
hundred different kinds in various parts of the world, all 
differing very slightly from each other and forming distinct 
1 Geography and Classification oj A nimals, p. 350. 
