VARIATION UNDER NATURE, 39 



CHAPTER II. 



VARIATIOif UNDER NATURE. 



Variability — Individual differences — Doubtful species — Wide rang- 

 ing, 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 th© 

 larger genera resemble varieties in being very closely, but un- 

 equally, 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 defini- 

 tions 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. 

 Generallv the term includes the unknown element of r 

 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, gener- 

 ally 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 northward, would not in some cases bo inherited 

 for at least a few generations? And in this case I presume 

 that the form would be called a variety. 



