98 NATURAL SELECTION. [Chap. IV. 



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 occur- 

 rence; he can 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 iniinitely complex and close-fitting are the mutual 

 relations of all organic beings to each other and to their 

 physical conditions of life; and consequently what in- 

 finitely varied diversities of structure might be of use to 

 each being under changing conditions of life. Can it, 

 then, be thought improbable, seeing that variations use- 

 ful to man have undoubtedly occurred, that other varia- 

 tions useful in some way to each being in the great and 

 complex battle of life, should occur in the course of 

 many successive generations? 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 their 

 kind? On the other hand, we may feel sure that any 

 variation in the least degree injurious would be rigidly 

 destroyed. This preservation of favourable individual 

 differences and variations, and the destruction of those 

 which are injurious, I have called Natural Selection, or 

 the Survival of the Fittest. Variations neither useful 

 nor injurious would not be affected by natural selection, 

 and would be left either a fluctuating element, as per- 

 haps we see in certain polymorphic species, or would ul- 

 timately become fixed, owing to the nature of the organ- 

 ism and the nature of the conditions. 



