350 DARWINISM TO-DAY. 



scientific evidence for the theory as a theory capable of ex- 

 plaining species-forming as a ivhole. There is probably no 

 gainsaying the actuality of the occurrence of certain muta- 

 tions (in de Vries's sense) nor of their establishment of 

 certain apparently fixed new organic types (de Vries's 

 elementary species of CEnothera). But this is very far 

 from accepting the mutations theory as a sufficient causal 

 explanation of the origin of the hundreds of thousands of 

 species of animals and plants that are now or were formerly 

 existent. 



As for the help that the establishment of the mutations 



theory would give those biologists who reject the natural 



Morgan's sum- section theory of species-forming, Morgan 26 



mationofthe writes as follows, summing up the advantages 



advantages of . . . 



the mutations of the theory: 



tneoj 7- "i. Since the mutations appear fully formed 



from the beginning, there is no difficulty in accounting for 

 the incipient stages in the development of an organ, and 

 since the organ may persist, even when it has no value to 

 the race, it may become further developed by later muta- 

 tions and may come to have finally an important relation to 

 the life of the individual. 



"2. The new mutations may appear in large numbers, and 

 of the different kinds those will persist that can get a foot- 

 hold. On account of the large number of times that the 

 same mutations appear, the danger of becoming swamped 

 through crossing with the original form will be lessened 

 in proportion to the number of new individuals that arise. 



"3. If the time of reaching maturity in the new form is 

 different from that in the parent forms, then the new species 

 will be kept from crossing with the parent form, and since 

 this new character will be present from the beginning, the 

 new form will have much better chances of surviving than 

 if a difference in time of reaching maturity had to be gradu- 

 ally acquired. 



