114 An Examination of Weismannism. 



resulting from some " spontaneous " change in the 

 hereditary material itself (as in bud-variation), or from 

 some change in the external conditions of life (as in 

 Hoffmann's experiments) — this fact is more than is 

 required in order finally to overthrow the intrinsically 

 untenable doctrine which is in question. 



Now, with the collapse of this doctrine there 

 collapses also the important chain of deductions 

 therefrom, which together constitute Weismann's new 

 theory of evolution. In particular, that natural selec- 

 tion is the exclusive means of modification among all 

 the Metazoa and Metaphyta, while it is as exclusively 

 ruled out with respect to all the Protozoa and Pro- 

 tophyta ; that individual variations among the former 

 can only be determined by sexual unions, while among 

 the latter they can only be determined by the direct 

 action of the environment ; that the origin of con- 

 genital variability in all the Metazoa and Metaphyta 

 is to be sought, and can only be found, in variations 

 which occurred millions of years ago in the Protozoa 

 and Protophyta ; that the " significance of sexual 

 propagation '■ is to be found in the view, that by this 

 means alone can congenital variations have been ever 

 since produced ; 8zc, &c. 



Upon the whole then, it appears to me that both 

 the fundamental postulates of the theory of germ- 

 plasm are unsound. That the substance of heredity 

 is largely continuous and highly stable I see many 

 and cogent reasons for believing. But that this sub- 

 stance has been uninterruptedly continuous since the 

 origin of life, and absolutely stable since the origin 

 of sexual propagation, I see even more and better 



