84 Heredity and Social Progress 



appear in great abundance in places where they 

 have no function. Evolution eliminates the 

 useless teeth and makes those that remain more 

 useful. A mere struggle between growth and 

 reproduction could thus cause the beginnings of 

 teeth and permit selection so to operate that 

 they would be converted into useful organs. 



A nerve, from this viewpoint, is a series of 

 sex products so enclosed within an envelope 

 that it cannot break out. In the plant the 

 flower that reproduces is at the end of a stem, 

 and becomes a sex organ if it gets the mastery 

 over growth. The brain and the spinal cord 

 may be thought of in the same category as a 

 stem and flower, only the brain never succeeds 

 in forcing its way through the envelope that 

 encloses it. It is a sex organ that never 

 attains its elementary functions. It would be 

 even better to think of it as a loosely organized 

 colony subdividing and trying to give off sex 

 products, but prevented by the encasement that 

 checks division. Failing in its original pur- 

 pose, it becomes an organ of sense discrimina- 

 tion and serves as a centre of nervous currents 

 moving to and fro along the spinal cord. If 



