VARIATION UNDER NATURE. 



CHAPTEE II. 



Variation under Nature. 



Variability — Individual differences — Doubtful species — Wide ranging, 

 much diffused, and common species, vary most — Species of the larger 

 genera in each country vary more frequently 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 

 properly, a long catalogue of dry facts ought to be given ; but these 

 I shall reserve for a future work. Nor shall I here discuss the 

 various definitions which have been given of the term species. No 

 one definition has 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, generally injurious, or not useful to the species. Some 

 authors use the term " variation " in a technical sense, as implying 

 a modification directly due to the physical conditions of life ; and 

 " variations " in this sense are supposed not to be inherited ; but 

 who can say that the dwarfed condition of shells in the brackish 

 waters of the Baltic, or dwarfed plants on Alpine summits, or the 

 thicker fur of an animal from far northwards, would not in some 

 cases be inherited for at least a few generations ? and in this case I 

 presume that the form would be called a variety. 



It may be doubted whether sudden and considerable deviations 

 of structure such as we occasionally see in our domestic productions, 

 more especially with plants, are ever permanently propagated in a 

 state of nature. Almost every part of every organic being is so 

 beautifully related to its complex conditions of life that it seems as 



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