NATURAL SELECTION 9 



variety would gradually be eliminated. On the other hand, the 

 whiteness of the hare's fur would tend ever to increase, because, 

 firstly, the mating of two white hares would be more frequent 

 owing to the growing rarity of the dark variety ; and, secondly, 

 because the " struggle " would resolve itself into one between 

 hares of greater or less whiteness. And thus, ultimately, a race 

 of exclusively pure white hares would arise, as is the case with 

 the Arctic hare. 



Variabihty, heredity, excessive fecundity, selection — these are 

 the four factors whose co-operation has resulted in all the count- 

 less varieties which we find in the world of organic nature. 

 Given the variability of all living organisms, given the power of 

 hereditary transmission, and given the fact that a greater number 

 of organisms are born than can, in the ordinary conditions of life, 

 survive, it necessarily ensues that those alone wiU survive who 

 are best adapted to their environment, who are best equipped 

 for the struggle for existence. Natural selection, as Weismaim 

 says, is a process of self-regulation by which the persistence of a 

 species is secured ; its result is the ever greater adaptation of the 

 species to the conditions of life in which it is placed. Natural 

 selection has produced an ever greater variety of organisms 

 adapted to the endless variety of natural conditions, and also 

 a never-ceasing progression and complication of organic types 

 which form a long chain from the Amoeba to Man. 



Darwin remarks at the close of his monumental work that the 

 laws which have produced all the infinite variety of forms are 

 five in number : Growth and reproduction ; inheritance, which 

 is implied in reproduction (we have combined these two laws) ; 

 variability, due to the indirect and direct action of the con- 

 ditions of hfe, and also to use and disuse ; a ratio of increase so 

 high as to lead to a struggle for existence ; and, as a consequence, 

 natural selection, entailing divergence of character and the 

 ehmination of the less fit forms. And he adds : 



" Thus, from the war of nature, from famine and death, the 



