28 Heredity and Social Progress 



giving nutrition and energy in excess of the 

 needs of mere existence and propagation. 

 Secondary characters are not necessary to the 

 acquisition of energy, but are the natural ex- 

 pressions of it when acquired. They often 

 prove useful because they permit a change in 

 the habits or the environment of organisms; 

 and in the new situation, or under the new con- 

 ditions, they become as essential to the new form 

 of existence as the primary characters were. 

 The difference between the two groups of 

 characters having now disappeared, they both 

 may be classed as primary. In this way 

 the number of essential characters may grad- 

 ually increase. The non-essentials of a simple 

 life become the essentials of the more complex. 

 Each new environment tends to develop ac- 

 quired characters through which it is better 

 utilized, and these become primary by a move- 

 ment into a new environment. Use is not the 

 cause of characters but a result of their appear- 

 ance. It is of course true that most characters 

 have a use, but this fact is a consequence of the 

 multitude of environments into which organisms 

 can go. Any combination of characters may 



