THE AMERICAN NATURALIST [Vol. XLV 



Natural selection with diverse meanings and manifold 

 implications lias been made to explain development, dif- 

 ferentiation and general evolutionary progress. The tu- 

 mult is greatest at the present time, however, about the 

 idea of mutation. Standing to one side, the biologist 

 hears a medley of assertions "that mutations have long 

 been known," "do not exist," "were discovered by Dar- 

 win," "are always an evidence of hybridization," "re- 

 sult in the formation of nothing but elementary species," 

 "give only weakened derivatives that are quickly 

 swamped by parental forms," "are encountered only 

 among cultivated plants," "the mutation theory is based 

 upon the conception of unit characters," "constitutes the 

 only adequate means of accounting for the enormous 

 number of living forms and myriad characters of living 

 things," "unit characters are unreal, have never been 

 seen, do not exist and are incapable of demonstration." 

 ' ' The difference between mutation and variation is one of 

 amplitude only," and lastly mutation signally "refutes 

 Darwinism," and "swings us back in harmony with the 

 theologian's arguments for special creation." 



The absurdity of the many injudicial assertions by the 

 partisans concerned need not blind us to the stubborn 

 fact that saltatory changes do occur in hereditary pure 

 lines in a large number of forms in both plants and 

 animals. Observations and experiments have estab- 

 lished beyond doubt that mutation is one way by which 

 organisms bearing new combinations of qualities may 

 arise, although it is probable that its importance as a 

 general procedure varies in different groups of organisms 

 and certain that many shades of opinion as to its exact 

 part in the evolution of living things will always be held. 

 Our appraisement of the value of all the protheses 



