Survival of the Fittest. 437 



Seeing what a potent influence the principle of Selection 

 has in the hands of man, in regard to variation, can it be 

 applied in nature ? We can see that it can act most effect- 

 ually. But in our domestic productions the variability is 

 not directly produced by man, for he can neither originate 

 varieties nor prevent their occurrence. All he can do is to 

 preserve and accumulate such as do occur. Unintentionally 

 he exposes organic beings to new and changing conditions of 

 life, for under domestication, plant and animal organizations 

 become in some degree plastic, and variability ensues. Sim- 

 ilar changes, however, do occur in nature. When it is borne 

 in mind how infinitely complex and close-fitting are the mutual 

 relations of all organic beings to each other, and to their 

 environment, and consequently what infinitely-varied diver- 

 sities of structure may be of advantage to each being under 

 altered conditions, can it then be thought improbable, 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 sometimes occur in 

 the course of tens of thousands of generations ? If such do 

 occur, can we doubt, when it is remembered that many more 

 individuals are born than can possibly survive, that individ- 

 uals possessing any advantage, no matter how slight, over 

 their fellows would have the best chance of surviving and of 

 procreating their kind ? Any variation, on the other hand, 

 we may feel sure if in the least degree injurious would be 

 rigidly destroyed. This preservation of useful and favorable 

 variations, and the destruction of those that are injurious, is 

 called Natural Selection, or the Survival of the Fittest. 

 Variations neither advantageous nor deleterious would not 

 be affected by Natural Selection, and would be left either a 

 fluctuating element, as seen in certain polymorphic species, 

 or would alternately become fixed, owing to the nature both 

 of the organism and its conditions. 



We shall best understand the probable cause of Natural 

 Selection by taking a country undergoing some physical 



