II 
ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY 
FROM THE ORIGINAL TYPE 
Instability of Varieties supposed to prove the permanent 
distinctness of Species 
One of the strongest arguments which have been adduced 
to prove the original and permanent distinctness of species is, 
that varieties produced in a state of domesticity are more or 
less unstable, and often have a tendency, if left to them- 
selves, to return to the normal form of the parent species ; 
and this instability is considered to be a distinctive peculi- 
arity of all varieties, even of those occurring among wild 
animals in a state of nature, and to constitute a provision 
for preserving unchanged the originally created distinct 
species. 
In the absence or scarcity of facts and observations as to 
varieties occurring among wild animals, this argument has had 
great weight with naturalists, and has led to a very general 
and somewhat prejudiced belief in the stability of species. 
Equally general, however, is the belief in what are called 
“permanent or true varieties,” — races of animals which con- 
tinually propagate their like, but which differ so slightly 
(although constantly) from some other race, that the one is 
considered to be a variety of the other. Which is the variety 
and which the original species, there is generally no means 
of determining, except in those rare cases in which the 
one race has been known to produce an offspring unlike itself 
and resembling the other. This, however, would seem quite 
incompatible with the “permanent invariability of species,” 
