Double Adaptations 445 



cases, we may resume our theoretical discus- 

 sion of the subject, and try to get a clearer in- 

 sight into the analogy of ever-sporting varie- 

 ties and the wild species quoted. All of them 

 may be characterized by the general term of 

 dimorphism. Two types are always present, 

 though not in the same individual or in the same 

 member. They exclude one another, and dur- 

 ing their juvenile stage a decision is taken in 

 one direction or in the other. Now, according 

 to the theory of natural selection, wild species 

 can only retain useful or at least innocuous 

 qualities, since all mutations in a wrong direc- 

 tion must perish sooner or later. Cultivated 

 species on the other hand are known to be 

 largely endowed with qualities, which would 

 be detrimental in the wild condition. Mon- 

 strosities are equally injurious and could not 

 hold their own if left to themselves. 



These same principles may be applied to 

 ever-sporting or antagonistic pairs of charac- 

 ters. According to the theory of mutations 

 such pairs may be either useful or useless. But 

 only the useful will stand further test, and if 

 they find suitable conditions will become spe- 

 cific or varietal characters. On this conclusion 

 it becomes at once clear, why natural di- 

 morphism is, as a rule, a very useful quality, 

 while the cultivated dimorphous varieties 



