362 LUTHER BURBANK 



drastic measures as this are rather exceptional 

 and that in general the processes through which 

 species are eliminated are more subtle in their 

 operation, although their ultimate results are no 

 less striking. 



All this has to do, however, with the de- 

 struction rather than with the evolution of 

 species. 



I have already said that the principles of nat- 

 ural selection apply with equal force, and seem- 

 ingly with entire impartiality, to the destruction 

 and to the preservation of species. 



But it is obvious that mere preservation of 

 species does not necessarily imply also the evolu- 

 tion of species. Natural selection might give a 

 dominant position to a particular species, and 

 preserve it for indefinite periods without essen- 

 tial change. 



But this could only occur in case the con- 

 ditions of environment themselves remained 

 essentially unchanged. 



It is fundamental to a clear understanding 

 of evolution to realize that in a changing envi- 

 ronment, under natural conditions, no species 

 could be preserved unless it proved adaptable. 



Indeed, the more perfectly adjusted the 

 species might be to its environment at a given 

 period, the more certainly must that species be 



