LIMITS OF NATURAL SELECTION. 23 



in the individual is a gradual process, and the acqui- 

 sition of experience is likewise a gradual process, — 

 occurring later in the same organ. 



Viewing just the plain facts as they stand before 

 us, so striking is their relation to one another that we 

 cannot escape the conviction that an instinct is an 

 inherited idea — an inherited plan of action. We 

 see in it the inheritance of knowledge which has 

 been acquired by ancestors. From the physical 

 point of view we see in it the inheritance of struct- 

 ural changes which were caused in the nervous sys- 

 tem by the action of the forces of the environment 

 upon each individual ancestor. This seems to be 

 a well-defined case of the inheritance of acquired 

 characters. We cannot deny that the idea or knowl- 

 edge has been acquired, neither can we deny that it 

 has been inherited. To refuse this plain inference 

 and then to appeal to natural selection as explanation 

 of the evolution of instincts, is to argue wide of the 

 mark ; for we must believe that knowledge is the 

 direct result of an intelligent creature's contact with 

 its environment, and not the result of any fortu- 

 itous happenings or undirected variations inside the 

 animal. 



The problem to be solved is : how are changes 

 brought about in the structure of organisms, and how 

 are these changes transmitted to succeeding genera- 



