The Laws of Mutation. 257 



Many authors already hold that species-forming vari- 

 ability must be indiscriminate. We are strongly opposed 

 to the conception of a definite ''tendency to vary" which 

 would bring about useful changes, or at least favor their 

 appearance. The great service which Darwin did was 

 that he demonstrated the possibility of accounting for the 

 evolution of the whole animal and vegetable kingdom 

 without invoking the aid of supernatural agencies. Ac- 

 cording to him species-forming variability exists without 

 any reference to the fitness of the forms to which it gives 

 rise. It simply provides material for natural selection 

 to operate on. And whether this selection takes place 

 between individuals, as Darwin and Wallace thought, 

 or whether it decides between the existence of whole spe- 

 cies, as I think ; it is the possibility of existence under 

 given external conditions which determines whether a 

 new form shall survive or not. 



We can go a step further and say that many more 

 useless and unfavorable variations must arise than favor- 

 able ones. This becomes sufficiently evident when we 

 consider the complexity of the conditions which an organ- 

 ism has to satisfy before it can supplant its fellows. 



The mutability of Oenothera Laniarckiana satisfies 

 all these theoretical conditions perfectly. Nearly all or- 

 gans and all characters mutate, and in almost every con- 

 ceivable direction and combination. Many combinations 

 must obviously be fatal to the life of the germ within the 

 ripening seed and cannot on that account be observed. 

 Others hinder the development of the seedlings and wdiole 

 series of experiments with apparently mutated plants 

 came to nothing in spite of every care on account of the 

 premature death of the young plants. Many combina- 

 tions reduce the fertilitv so much that we cannot jro fur- 



