l6o THE HISTORY OF CEEATION. 



conditions of life. The external influences of the latter are 

 communicated to the individual parts of the body by the 

 molecular processes of nutrition. In every act of Adaptation 

 the individual molecular motion of the protoplasm, peculiar 

 to each part, disturbs and modifies the whole individual, or 

 part of it, by mechanical, physical, or chemical influences. 

 The innate, inherited vital actions of the protoplasm — that is, 

 the molecular phenomena of motion of the smallest albu- 

 minous particles — are therefore more or less modified by it. 

 The phenomenon of Adaptation, or transmutation, depends 

 therefore upon the material influence which the organism 

 experiences from its surroundings, or its conditions of 

 existence; while the transmission by Inheritance is due 

 to the partial identity of the producing and produced 

 organism. These are the real, simple, mechanical founda- 

 tions of the artificial process of breeding. 



Now Darwin asked himself. Does there exist a similar 

 process of selection in nature, and are there forces in nature 

 which take the place of man's activity in artificial selection ? 

 Is there a natural tendency among wild animals and plants 

 which acts selectingly, in a similar manner to the artificial 

 selection practised by the designing will of man? All 

 here depended upon the discovery of such a relation, and 

 Darwin succeeded in this so satisfactorily, that we con- 

 sider his theory of selection completely sufficient to 

 explain, mechanically, the origin of the wild species of 

 animals and plants. That relation which in free 

 nature influences the forms of animals and plants, by 

 selecting and transforming them, is called by Darwin 

 the " Struggle for Existence." 



The " Struggle for Existence " has rapidly become a 



