NATURAL SELECTION 1483 



nature? I think we shall see that it can act most 

 efficiently. Let the endless number of slight varia- 

 tions and individual differences occurring in our do- 

 mestic productions, and, in a lesser degree, in those 

 under nature, be borne in mind; as well as the 

 strength of the hereditary tendency. Under domesti- 

 cation, it may be truly said that the whole organiza- 

 tion becomes in some degree plastic. But the varia- 

 bility, which we almost universally meet with in our 

 domestic productions, is not directly produced, as 

 Hooker and Asa Gray have well remarked, by man; 

 he can neither originate varieties, nor prevent their 

 occurrence; he can only preserve and accumulate 

 such as do occur. Unintentionally he exposes organic 

 beings to new and changing conditions of life, and 

 variability ensues; but similar changes of conditions 

 might and do occur under nature. Let it also be 

 borne in mind how infinitely complex and close-fit- 

 ting are the mutual relations of all organic beings 

 to each other and to their physical conditions of life; 

 and consequently what infinitely varied diversities of 

 structure might be of use to each being under chang- 

 ing conditions of life. Can it, then, be thought im- 

 probable, seeing that variations useful to man have 

 undoubtedly occurred, that other variations useful in 

 some way to each being in the great and complex 

 battle of life, should occur in the course of many suc- 

 cessive generation*? If such do occur, can we doubt 

 (remembering that many more individuals are born 

 than can possibly survive) that individuals having 

 any advantage, however slight, over others, would 

 have the best chance of surviving and of procreating 



