184 THE DARWINIAN THEORY. 
in which species differ from other species of the same genus are called 
specific characters, and as these specific characters have varied and 
come to differ within the period of the branching off of the species 
from a common progenitor, it is probable that they should still often 
be in some degree variable, —at least more variable than those parts of 
the organization which have for a very long period remained constant " 
(pp. 183-4). 
In this statement the imagination has been very active, and several 
propositions are advanced as unquestioned facts which require yet to 
be proved, though we may add that the proof which we have a right 
to demand it would be impossible to furnish. We first hear of a com- 
mon progenitor of a genus,—let us suppose of the Felide,—that is, 
there was once a common progenitor of the lion, tiger, panther, puma, 
leopard, ocelot, cat, etc, ; all the species are supposed to have branched 
off from this common progenitor, and to have become distinct species 
by the process of natural selection ; they are like oue another in ge- 
nerie distinctions, but unlike in specific distinctions. The generic 
character has been much more ancient than the specific, and ¢herefore 
will probably not change any more; the specific character, being a 
more modern affair, may be, and probably will be, more variable,— 
‘at least more variable than those parts of the organization which 
have for a very loug period remained constant." 
Thus we are to look at an animal as having a body composed of 
parts of different ages; for instance, a lion is in general character like 
the other Felide, but unlike them in his mane and the tuft at the end 
of his tail; so his claws, common to the genus, may be a hundred 
thousand or perhaps a million years or ages older than his mane; his 
mane and his tail may be more variable, and probably will be, whilst 
the rest of his body, which is of the generic category, will remain sta- 
tionary. 
That Mr. Darwin really means all this is quite certain ; for he gravely 
informs us that the wing of a bat is a very ancient part of its body, 
and, owing to its antiquity, will probably not be changed any more. 
“In the case of the wing of the bat, which has been transmitted in the 
same condition £o many modified descendants, it must have existed ac- 
cording to my theory for an immense period in the same state, and 
thus it comes to be no more variable than any other structure ” 
(p. 181 
