VARIATION UNDER NATURE. V 



CHAPTER II. 



VARIATION UNDER NATURE. 



Variability — Individual Differences — Doubtful Species — Wide ran- 

 ging, 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 vari- 

 ation. 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. 

 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 

 northward, 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 



