THE SUMMIT OF THE YEARS 



which they do offhand the first time the occasion 

 arises — how the writer explains all these things, I 

 say, I am at a loss to know. 



These instincts or native impulses, as they are 

 passed along down the line of animal descent, are 

 slightly modified now and then, but remain practi- 

 cally the same from generation to generation. The 

 cliff swallows have built their nests of mud — how 

 long? The chimney swifts have built theirs of twigs 

 — how long? The brooding grouse, when started 

 from her nest, has feigned lameness and paralysis — 

 how long? The beaver has been building its dam of 

 sticks and mud — how long? 



The word "instinct" is of metaphysical rather 

 than of scientific origin, but it means so much more 

 than reaction or tropism that we cannot dispense 

 with it. It marks off the animal world from the 

 human almost as distinctly as the animal is marked 

 off from the vegetable. It covers all the animal be- 

 havior that is independent of experience, and that 

 an animal does perfectly when the first occasion for 

 it arises. In the orders immediately below man nine 

 tenths of the actions of the animals are the result of 

 involuntary inherited impulse. The other tenth 

 may be the result of experience or acquired habit. 



A large fraction of our lives also is the result of 



inborn inherited impulses or tendencies, but these 



are constantly checked and controlled by reason 



and experience. An animal never checks its natural 



158 



