GENETICS 107 



vironment is by no means simple, and that the 

 reduction of the theoretical approach to the prob- 

 lems of evolution to a basis of scientific fact is in 

 most points difiicult and in some impossible at pres- 

 ent. It is safe to say that we shall not know exactly 

 how evolution works in terms of absolute observa- 

 tion of details until the nature of the gene and of its 

 action are definitely determined. While at first 

 this suggests the futility of existing methods of 

 approaching evolutionary problems, we may still 

 expect valuable progress from intelligent use of 

 these methods. The organism has not yet been 

 reduced wholly to terms of physics and chemistry. 

 Its reactions in such terms are of the utmost in- 

 terest and importance, but the great range of 

 organic responses which are known only in terms 

 of biology may still give us the key to evolutionary 

 processes long before their ultimate basis becomes 

 known. 



