ON THE QUICK GROWING WALNUT 



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

 tion, 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 pre- 

 serve it for indefinite periods without essential 

 change. 



But this could only occur in case the condi- 

 tions of environment themselves remained essen- 

 tially unchanged. 



It is fundamental to a clear understanding of 

 evolution to realize that in a changing environ- 

 ment, 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 destroyed 

 should the essential conditions of the environment 

 change. 



The great penalty of specialization is the 

 danger that attends it from this source. It is held 

 that the species that were eliminated when the 

 great climatic change occurred to which we have 



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