MUTATION 51 



2. Mutation and Fluctuation 



A mutation is something qualitatively new that 

 appears abruptly without transitions and which breeds 

 true from the very first. To use the musician's 

 phraseology, it is not a variation elaborated upon an 

 old theme, which would correspond to a fluctuating 

 variation, but it is an entirely new theme. The 

 difference between mutations and fluctuating varia- 

 tions is generally not one of quantity or magnitude, 

 although it sometimes may be so, — since muta- 

 tions are often much smaller than fluctuations. 

 Mutations are discontinuous in the same sense that 

 chemical combinations, such as carbon monoxide 

 (CO) and carbon dioxide (CO2), are discontinuous, 

 but the leap from one to the other may be so small 

 that frequently it is diflicult to ascertain by inspec- 

 tion alone whether the difference is due to a mutation 

 or a fluctuation. The test comes in breeding, for the 

 progeny of a fluctuation will vary around the old 

 average of the parental generation, while the progeny 

 of a mutation will vary around a new average, set 

 by the mutation itself. 



When a series of mutations is treated statistically, 

 it does not arrange in frequency polygons as readily 

 as a series of fluctuations do. The latter mass 

 around the average standard according to the laws 

 of chance much in the same way that a hundred shots 

 by a good marksman may center around a bull's- 

 eye. Mutations never act in this way. They find 

 no correspondence even with wild shots at the bull's- 



