Chap. V. HIGHLY VARIABLE. I55 



by the continued selection of the individuals varj-ing in the 

 •required manner and degree, and by the continued rejection 

 of those tending to revert to a former and less-modified con- 

 dition. 



Si'iecific Characters more variable than Generic Characters^ 



The principle included in the above remarks may be ex- 

 tended. It is notorious that specific characters are more va- 

 riable than generic. To exjilain by a simple example -what is 

 meant : If in a large genus of jilants some species had blue 

 flowers and some had red, the color Avould 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 ilowers, the color would become a generic character, 

 and its variation Avould be a more unusual circumstance. I 

 liave 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 ex- 

 planation is partly, yet only indirectly, true ; I shall, however, 

 have to return to this subject in the cliapter on Classification. 

 It would be almost superfluous to adduce evidence in support 

 of the a])ove statement, that specific characters are more va- 

 riable than generic ; but I have repeatedly noticed in Avorks on 

 natural history, that, when an author has remarked with sur- 

 prise that some imjiortant organ or part, which is generally 

 very constant throughout large groups of species, has differed 

 considerably in closelj'-allied species, it has also been vari- 

 able in the individuals of some of the species. And this fact 

 shows that a character, Avhicli is generally of generic value, 

 when it sinks in value and becomes only of specific value, often 

 becomes variable, though its physiological importance may re- 

 main the same. Something of the same kind applies to mon- 

 strosities : at least Is. GeoflVoy St.-Hilaire seems to entertain 

 no doubt that the more an organ normally differs in the differ- 

 ent species of the same group, the more subject it is to indi- 

 vidual anomalies. 



On the ordinary view of each species having been inde- 

 pendently created, why should that part of the structure, 

 which differs from the same part in other independently-created 

 species of the same genus, be more variable than those parts 



