178 HEREDITY AND SELECTION IN SOCIOLOGY 



first chapter of this book we saw that the four great factors 

 which govern organic evolution are variability, heredity, ex- 

 cessive fertility, and the survival of the fittest by means of 

 selection. Now, it is obvious that the survival of the fittest 

 implies an excess of fertiUty ; for if there were sufficient space 

 and food to enable all the organisms which are born to survive, 

 there would be no struggle, consequently no question of fit 

 or less fit individuals. As it is, however, if one himdred 

 individuals are born where the available amount of space and 

 food admits of the existence of not more than fifty, fifty indi- 

 viduals must be destroyed ; and the fifty who remain wiU remain 

 because they are, physically or otherwise, superior to the fifty 

 who have been eliminated. Even as it is with individuals of 

 the same race, so it is with the different races of the same species 

 or with distinct species. More are produced than can survive ; 

 and only those who are superior in one way or other can survive. 

 But this superiority, precisely, is engendered by the struggle 

 for existence, and is maintained by it. Every variation which 

 is useful to the species, which constitutes an advantage for the 

 species, is selected, and becomes permanent ; and it will be pre- 

 served as long as its utility for the species lasts. That is to say, 

 as long as the species remains in the same environment, subject 

 to the same conditions, this variation will remain the same. 

 For every such variation implies an adaptation of a species to its 

 environment ; and every individual in the species in whom 

 this variation is lacking will be destroyed because he is not 

 adapted to his environment. Let us, however, withdraw the 

 species from its natural surroundings and place it under artificial 

 conditions of existence ; it may continue to exist, but it will 

 do so only if it be artificially protected ; withdrawn from its 

 natural surroundings, it will inevitably decay ; and its place will 

 be taken by other species, more vigorous because bred in the 

 only possible school — the school of Nature. 

 Thus we see that the tendency of organic life, when removed 



