208 The Origin of Species by Mutation. 



Two theses, which help to remove many difficulties 

 standing in the way of the mutation theory, have been 

 put forward : 



1. The assumption that the new form or species does 

 not arise merely once from the parent species but, 

 while the period lasts, a great many times and with 

 some degree of regularity. 



2. The possibility of the appearance of useless or 

 even harmful specific characters — whose existence 

 is not compatible with the ordinary theory of selec- 

 tion. 



The object of these considerations was to show that 

 newly arisen forms could increase sufficiently to enter 

 the struggle for existence with at any rate a fair prospect 

 of success, without the help of natural selection. But 

 the fact that the actual behavior of new forms when they 

 arose was insufficiently known and that arguments there- 

 fore could not start from a posteriori premises had the 

 result that this subject received little attention. Gulick 

 and Delboeuf are the two chief writers who have de- 

 voted themselves to this aspect of the question. 



Gulick's generalization was: A^i initial tendency 

 due to accidental variation can increase and develop in 

 succeeding generations, zvithout reference to the advan- 

 tage of the species. He is referring not to an extreme 

 variant of individual variation but to a mutation; and 

 moreover to one on which natural selection, at first at 

 any rate, has no effect.^ 



J. Delboeuf is concerned to show how the final usur- 

 pation, by the transmuted forms, of the space and means 

 of subsistence which supported the original type is a 



* See Journ. Linn. Soc. Zool., Vol. XI, p. 496 and Vol. XX (iSSS") 

 p. 215. 



