90 NATIONAL TRENDS IN BIOLOGY 



in turn, form in the various organisms? How do such 

 systems then respond diversely to the same environment 

 and experiment ? How does it happen that organisms are 

 diverse systems of structures and functions to begin with ? 

 What are the laws underlying the production of these 

 diversities? Why is the same diversity of characters pro- 

 duced in two ways — one by environment and the other 

 by gene differences? 



And above all this there is the mystery, not of a part 

 or of any one part of the organism, but pervading the 

 whole — the operation of selective elimination with its 

 complement — selective persistence. 



For "in our experimental material, many diverse com- 

 binations are formed, diverse chemicals, diverse motions, 

 diverse genes, diverse systems. Experimental conditions 

 cause the elimination of some of these ; others persist. At 

 the end, the material before us has changed. Our experi- 

 mental agent appears to have worked a transformation ; 

 in fact, it has worked only an elimination." 



Failure to take these facts into account is the cause of 

 much fruitless speculation and discussion. 



"Stock is subjected to given environment. After a few 

 generations, it is found changed ; the change is inherited 

 even upon the restoration to the usual environment. Be- 

 hold! We have discovered the inheritance of acquired 

 characters. And then selective elimination is found lurk- 

 ing beneath the surface, and we know not what we have 

 discovered." 



