Chap. V.] HIGHLY VAEIABLE. 189 



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

 convinced, is the case. That the struggle between 

 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 ap- 

 proximately 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 ex- 

 traordinarily 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 continued 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 

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



