WHAT EVOLUTION IS 139 



the same species and which are com- 

 monly designated as variations. Vari- 

 ations, according to de Vries, are 

 always very slight and insignificant. 

 They never even approximate the 

 magnitude of a mutation. Mutations 

 on the other hand are striking differ- 

 ences such as black or white in the 

 coat of a guinea pig and represent, 

 in this sense, considerable jumps or 

 breaks. Variations are like the slight 

 movements that a cube may be made 

 to execute when it is wabbled about 

 on one of its faces. Mutations are 

 like the changes that arise when 

 the cube is turned from one face to 

 another. 



The mutation theory is to the effect 

 that evolution takes place not through 

 small differences or variations, as Dar- 

 win believed, but through large and 

 sudden changes, mutations. Just as 

 the cube does not progress when it 



