134 THE THEORY OF MUTATION 



negative variation* from its own proper type. In this 

 way the novelty may not appear to be very far removed 

 from a high normal variation of the original type. The 

 behaviour of the progeny of the two types, however 

 types which might thus in themselves be readily con- 

 fused is entirely different, and a ready means of dis- 

 tinguishing them is thereby provided. Each set of off- 

 spring shows regression to its own proper modal value ; 

 so that the offspring of the novelty show a further 

 marked development of the new features, whilst the 

 offspring of an extreme normal variation resemble the 

 type of the original form more closely than they do 

 their own immediate progenitor. 



If new types are not produced among domesticated 

 productions by the action of artificial selection, and all 

 that selection can effect is to pick out definite novelties 

 when they occur, the analogy between natural selec- 

 tion and artificial selection breaks down, and a large 

 and important section of the evidence in favour of the 

 production of natural species by the action of natural 

 selection is destroyed. In the place of this explana- 

 tion de Vries would put the theory of mutation, ac- 

 cording to which new species arise by single steps as 

 definite novelties, just in the same way as we find that 

 domestic varieties are produced. More than this, de 

 Vries believes that he has discovered a set of new 

 species in the very act of originating from an old 

 one in this way, a discovery which affords the basis 



* I.e., a variant belonging to a class situated some dis- 

 tance from the mode of normal variability of the novelty, 

 and on the side of it nearest to the mode of the original type. 



