SELECTION 155 



also how infinitely close and complex are the 

 mutual relations of 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 changing conditions of life, 

 can it 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 occur in the 

 course of many generations? And if such do 

 occur, can we doubt (remembering that many 

 more individuals are born than can possibly 

 survive) that individuals having any ad- 

 vantage, however slight, over their fellows 

 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 inevi- 

 tably destroyed. 



This preservation of favourable and this 

 destruction of injurious variations are called 

 natural selection, or, less metaphorically, the 

 survival of the fittest, the one term referring 

 mainly to the process, the other to the result. 

 The probable course of natural selection may 

 be understood from the case of a country 

 undergoing change of climate. The pro- 

 portional numerical strengths of its species 



