THEORIES OF EVOLUTION 149 



tion: "What particular variations will be perpet- 

 uated?' was, "only those that prove of benefit to 

 the race in the struggle for existence and in adapting 

 themselves to environment." The chance inheritance 

 of the multitudinous variations would produce 

 chaotic results unless directed by some agency and 

 this directing agency was designated by Darwin, 

 Natural Selection. This is the central idea of Dar- 

 win's theory and the essentially new factor that he 

 added to the discussion. He observed the changes 

 produced by artificial selection under domestication 

 of animals and cultivation of plants. Certain varia- 

 tions are selected by breeders and agriculturalists to 

 be bred intensively, and, by this means, marked 

 changes are produced in pigeons, poultry, dogs, cat- 

 tle, flowers, etc. Now since these changes are 

 obviously the result of a process of selection on the 

 part of man, Darwin concluded that conditions exist 

 in nature which lead to the selection of certain 

 variations to survive and to the suppression of others. 

 Some such assumption is necessary, because there 

 is a tendency to overproduction in animals and 

 plants, leading to a struggle for existence, and, the 

 determination of survival, would scarcely be a matter 

 of chance. One illustration will suffice to carry the 



