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CONCERNING THE HEREDITARY ADAPTATION OF 

 ORGANISMS TO HIGHER TEMPERATURE. 



By JOHN H. NORTHROP. 



{From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, January 26, 1920.) 



Since the time of Lamarck the theory of the adaptation of organisms 

 to their environment and the inheritance of these adaptations has been 

 a hotly debated question. The original theory considered that the 

 organism responded to changes in environment in such a way as to 

 become better fitted to it, and that these changes then became heredi- 

 tary. In this form the theory is probably no longer accepted by the 

 majority of students. There is also little doubt that structural 

 adaptations of the individual organisms are not inheritable. A general 

 discussion of this question is out of place here, and the reader is 

 referred to Loeb^ and Conklin.^ It may be pointed out, however, 

 that according to the accepted theory of Weismann in regard to the 

 continuity of the germ plasm, it seems a priori improbable that any 

 change in the individual could affect succeeding generations. 



Morgan and his coworkers^ have shown that structural changes 

 are continually arising in many forms, and that these changes or 

 mutations are inherited according to Mendel's law. There seems no 

 reason to suppose that physiological changes might not arise in the 

 same way. If these physiological changes were such that the organism 

 became better fitted to a new environment, we might expect to find 

 adaptation under some conditions, although it would not be the 

 direct result of the . changed environment. Tower* has reported 



^ Loeb, J., The organism as a whole from a physicochemical viewpoint. New 

 York, 1916. 



^ Conklin, E. G., Heredity and environment in the development of men, Prince- 

 ton, 1915. 



3 Morgan, T. H., Sturtevant, A. H., MuUer, H. J., and Bridges, C. B. The 

 mechanism of Mendelian heredity, New York, 1915. 



4 Tower, W. L., Biol. Bull, 1917, xxxiii, 229. 



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