LUTHER BURBANK 



unless it began suddenly as a "sport" or mutation. 

 This is one instance among many. 



And so Professor de Vries' observation, which 

 proved that mutations do sometimes seemingly 

 occur "spontaneously" in nature was seized on as 

 affording a solution of one of the puzzles of 

 •evolution, and the mutation theory was pretty 

 generally regarded as a valuable supplement to 

 the Darwinian theory of evolution. 



It should be clearly understood, however, that 

 neither Professor de Vries himself nor anyone 

 else speaking with authority, has thought of the 

 mutation theory as in any sense contradicting the 

 Darwinian theory of natural selection. On the 

 contrary, it is to be regarded as supplementing 

 and supporting that theory. If creatures are 

 subject to large variations in a single generation, 

 Such variations afford peculiarly good material 

 for the operation of natural selection. Moreover, 

 Evolution by mutation would presumably be 

 much more rapid than evolution that depended 

 for its leverage upon minute variations. 

 What Causes Mutation? 

 Incidentally the idea of relatively rapid 

 evolution, thus given plausibility, answered the 

 objection of certain geologists who had questioned 

 whether the earth had been habitable long 

 enough fo permit the evolution of the existing 



[94] 



