44 VARIATION UNDER NATURE. Chap. II. 



CHAPTEE H. 



Variation under Nature. 



Variability — Individual differences — Doubtful species — Wide 

 ranging, much diffused, and common species vary most — Spe- 

 cies of the larger genera in any country vary more than the species 

 of the smaller genera — Many of the species of the larger genera 

 resemble varieties in being very closely, but unequally, related 

 to each other, and in having restricted ranges. 



Before applying the principles arrived at in the last 

 chapter to organic beings in a state of nature, we must 

 briefly discuss whether these latter are subject to any 

 variation. To treat this subject at all properly, a long 

 catalogue of dry facts should be given ; but these I shall 

 reserve for my future work. Nor shall I here discuss 

 the various definitions which have been given of the 

 term species. No one definition has as yet satisfied all 

 naturalists ; yet every naturalist knows vaguely what 

 he means when he speaks of a species. Generally the 

 term includes the unknown element of a distinct act of 

 creation. The term " variety " is almost equally difficult 

 to define; but here community of descent is almost 

 universally implied, though it can rarely be proved. 

 We have also what are called monstrosities ; but they 

 graduate into varieties. By a monstrosity I presume is 

 meant some considerable deviation of structure in one 

 part, either injurious to or not useful to the species, and 

 not generally propagated. Some authors use the term 

 "variation" in a technical sense, as implying a modifica- 

 tion directly due to the physical conditions of life ; and 

 " variations " in this sense are supposed not to be in- 

 herited : but who can say that the dwarfed condition of 

 shells in the brackish waters of the Baltic, or dwarfed 



