Darwin! s Artificial and Natural Selection 117 



probable, seeing that variations useful to man have undoubt- 

 edly occurred, that other variations useful in some way to 

 each being in the great and complex battle for life, should 

 occur in the course of many successive generations ? If such 

 do occur can we doubt (remembering how many more indi- 

 viduals 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 varia- 

 tion in the least degree injurious would be rigidly destroyed." 



The process of natural selection is defined as follows, 

 "The preservation of favorable individual differences and 

 variations and the destruction of those that are injurious I 

 have called Natural Selection or the Survival of the Fittest." 

 And immediately there follows the significant statement, 

 that, "Variations neither useful nor injurious would not be 

 affected by natural selection, and would be left either a 

 fluctuating element, as perhaps we see in certain polymorphic 

 species, or would ultimately become fixed, owing to the 

 nature of the organism and the nature of the conditions." 

 It will be seen from this quotation, as well as from others 

 already given, that Darwin leaves many structures outside 

 of the pale of natural selection, and uses his theory to ex- 

 plain only those cases that are of sufficient use to be decisive 

 in the life and death struggle of the individuals with each 

 other and with the surrounding conditions. 



Darwin states that we can best understand " the probable 

 course of natural selection by taking the case of a country 

 undergoing some slight physical change, for instance, of 

 climate. The proportional numbers of its inhabitants will 

 almost immediately undergo a change, and some species will 

 probably become extinct. We may conclude, from what we 

 have seen of the intimate and complex manner in which the 

 inhabitants of each country are bound together, that any 

 change in the numerical proportions of the inhabitants, in- 



