140 ON THE ORIGIN OF SPECIES 



rejection of those tending to revert to a former and less 

 modified condition. 



The principle included in these remarks may be 

 extended. It is notorious that specific characters are 

 more variable than generic. To explain by a simple 

 example what is meant. If some species in a large 

 genus of plants 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 blue species varying 

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

 flowers, the colour would become a generic character, 

 and its variation would be a more unusual circumstance. 

 I have chosen this example because an explanation is 

 not in this case applicable, which most naturalists 

 would advance, 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 indirectly, true ; I 

 shall, however, have to return to this subject in our 

 chapter on Classification. It would be almost super- 

 fluous to adduce evidence in support of the above 

 statement, that specific characters are more variable 

 than generic ; but I have repeatedly noticed in works 

 on natural history, that when an author has remarked 

 with surprise that some important organ or part, which 

 is generally very constant throughout large groups 

 of species, has differed considerably in closely-allied 

 species, that it has, also, been variable in the individuals 

 of some of the species. And this fact shows that a 

 character, which is generally of generic value, when it 

 sinks in value and becomes only of specific value, often 

 becomes variable, though its physiological importance 

 may remain the same. Something of the same kind 

 applies to monstrosities : at least Is. Geoffroy St. 

 Hilaire seems to entertain no doubt, that the more 

 an organ normally differs in the different species of 

 the same group, the more subject it is to individual 

 anomalies. 



On the ordinary view of each species having been 



