Acquired Characters 29 



prove advantageous in struggle if the organ- 

 ism possessing it is put in the proper environ- 

 ment. 



In harmony with this thought, I would say 

 animals do not develop teeth because they eat 

 hard food. They eat hard food because they 

 have teeth. They do not attain wings because 

 they fly; they fly because they have wings. 

 They do not develop nails because they 

 scratch ; they scratch because they have nails. 

 Nor do they develop hair because they go into 

 cold regions ; they go north because they have 

 hair. By this I mean that the tooth, the nail, 

 the wing, the hair, and other specific characters 

 appear as secondary qualities, and are at first 

 merely expressions of surplus energy. A use 

 is found for an organ already in existence 

 through other causes, and then by develop- 

 ment and selection it becomes an efficient 

 instrument. Use does not cause anything; it 

 only modifies and improves what other causes 

 have already formed. 



The limited extent to which use is avail- 

 able in creating organic changes is illustrated 

 by what Professor Cope called the doctrine of 



