Chap, v.] HIGHLY VARIABLE. 189 



a much longer period nearly constant. And this, I am 

 convinced, is the case. That the struggle hetween 

 natural selection on the one hand, and the tendency to 

 reversion and variability on the other hand, will in the 

 course of time cease; and that the most abnormally 

 developed organs may be made constant, I see no reason 

 to doubt. Hence, when an organ, however abnormal 

 it may be, has been transmitted in approximately the 

 same condition to many modified descendants, as in 

 the case of the wing of the bat, it must have existed, 

 according to our theory, for an immense period in 

 nearly the same state; and thus it has come not to 

 be more variable than any other structure. It is only 

 in those cases in which the modification has been 

 comparatively recent and extraordinarily great that 

 we ought to find the generative variability, as it may 

 be called, still present in a high degree. For in this 

 case the variability will seldom as yet have been fixed 

 by the continued selection of the individuals varying 

 in the required manner and degree, and by the con- 

 tinued rejection of those tending to revert to a former 

 and less-modified condition. 



Specific Characters more Variable than Generic 

 Characters. 



The principle discussed under the last heading may 

 be applied to our present subject. It is notorious that 

 specific characters are more variable than generic. To 

 explain by a simple example what is meant: if in a 

 large genus of plants some species had blue flowers and 

 some had red, the colour would be only a specific char- 

 acter, and no one would be surprised at one of the 



