Modification of Germinal Constitution of Organisms 165 



THE DIRECT MODIFICATION OF THE GERM PLASM 



Since there are the best of reasons for the conclusion that 

 there is conditioned in the germ plasm the basis which 

 determines the presence and manifestations of organic 

 characteristics which are permanent in the race and in evolu- 

 tion ; and in that there are equally good reasons for a tena- 

 cious adherence to the idea that all variations which are 

 productive of evolutionary changes arise primarily in the 

 germ and appear secondarily in the soma, it follows that 

 any and all methods whereby changes are produced in the 

 germinal material are of paramount interest. Modifications 

 in this germinal material are the basis of permanent depar- 

 tures from the racial mean, and at present the methods of 

 production and cause of germinal variations are of great 

 practical interest and value as well as of theoretical impor- 

 tance. Germinal variations have been suggested to arise 

 by five main methods. 



The direct action of external forces was the first to be 

 suggested and is generally admitted to be an effective cause 

 in the production of germinal variations. This was a mode 

 of modification suggested by Buffon and Erasmus Darwin, 

 later elaborated by Lamarck, and made the basis of his 

 theory of evolution without any consideration whatsoever 

 as to whether the variations were somatic or germinal. A 

 half-century later variations which were supposed to have 

 originated through the action of external conditions pro- 

 vided in the main the array of individual differences upon 

 which Darwin founded his theory of the "origin of species,'' 

 by means of natural selection. 



Arising from the work of Darwin, and accentuated by the 

 neo-Darwinians, is the idea of the production of variations 



