SPECIFIC CHARACTERS HIGHLY VARIABLE 1G5 



have repeatedly noticed in works on natural history, that 

 when an author remarks with surprise that some important 

 organ or part, wliich is generally very constant throughout 

 a large group of species, differs considerably in closely 

 allied species, it is often variable in the individuals of the 

 same 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 apparently entertains no doubt, 

 that the more an organ normally differs in the different spe- 

 cies of the same group, the more subject it is to anomalies 

 in the individuals. 



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 which are closely alike in the several species? 

 I do not see that any explanation can be given. But on the 

 view that species are only strongly marked and fixed varie- 

 ties, we might expect often to find them still continuing to 

 vary in those parts of their structure which have varied 

 within a moderately recent period, and which have thus 

 come to differ. Or to state the case in another manner : — 

 the points in which all the species of a genus resemble each 

 other, and in which they differ from allied genera, are called 

 generic characters; and these characters may be attributed 

 to inheritance from a common progenitor, for it can rarely 

 have happened that natural selection will have modified sev- 

 eral distinct species, fitted to more or less widely different 

 habits, in exactly the same manner : and as these so-called 

 generic characters have been inherited from before the 

 period when the several species first branched off from their 

 common progenitor, and subsequently have not varied or 

 come to differ in any degree, or only in a slight degree, it is 

 not probable that they should vary at the present day. On 

 the other hand, the points in which species differ from other 

 species of the same genus are called specific characters; and 

 as these specific characters have varied and come to differ 



