MUTATION 57 



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 (CO 2 ), are discontinuous, 

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

 that frequently it is difficult 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- 



