MUTATION 73 



with fluctuating variations, but they fluctuate around 

 a new average of their own, thus forming a discon- 

 tinuous series with the parent form. 



g. Mutations may occur in all directions, that is, 

 they are not necessarily definite or orthogenetic. 



h. Mutations probably appear periodically. 



i. Every mutation means a possible doubling of the 

 species. 



j. Useless or insignificant fluctuating variations are 

 not necessarily the material from which natural selec- 

 tion must sift out new species. 



The bearing of the whole matter of mutation upon 

 heredity lies in the fact that, contrary to Darwin's 

 belief, it is apparently mutations, and not fluctuations, 

 that make up heritable variations. If this supposition 

 proves to be true, mutations furnish the essential 

 material in the study of heredity. Consequently, 

 whatever knowledge we may gain of them has a direct 

 relation to the entire problem of genetics. 



