124 THE ORIGIN OF SPECIES 



a general rule, still expect to find more variability in such parts 

 than in other parts of the organization which have remained for 

 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 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 im- 

 mense 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 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 color would be only a specific 

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

 varying into red, or conversely; but if all the species had blue 

 flowers, the color would become a generic character, and its vari- 

 ation would be a more unusual circumstance. I have chosen this 

 example because the explanation which most naturalists would 

 advance is not here applicable, namely, that specific characters 

 are more variable than generic, because they are taken from parts 

 of less physiological importance than those commonly used for 

 classing genera. I believe this explanation is partly, yet only in- 

 directly, true; I shall, however, have to return to this point in 

 the chapter on Classification. It would be almost superfluous to 

 adduce evidence in support of the statement, that ordinary specific 

 characters are more variable than generic; but with respect to im- 

 portant characters, I have repeatedly noticed in works on natural 

 history, that when an author remarks with surprise that some 



