298 Evolution and Adaptation 



feature of these mutations is the constancy with which the 

 new form is inherited. It is this fact, not previously fully ap- 

 preciated, that De Vries's work has brought prominently into 

 the foreground. There is another point of great interest in 

 this connection. Many of the groups that Darwin recognized 

 as varieties correspond to the elementary species of De Vries. 

 These varieties, Darwin thought, are the first stages in the for- 

 mations of species, and, in fact, cannot be separated from 

 species in most cases. The main difference between the 

 selection theory and the mutation theory is that the one sup- 

 poses these varieties to arise through selection of individual 

 variations, the other supposes that they have arisen spontane- 

 ously and at once from the original form. The development 

 of these varieties into new species is again supposed, on the 

 Darwinian theory, to be the result of further selection, on the 

 mutation theory, the result of the appearance of new mutations. 

 In consequence of this difference in the two theories, it 

 will not be difficult to show that the mutation theory escapes 

 some of the gravest difficulties that the Darwinian theory 

 has encountered. Some of the advantages of the mutation 

 theory may be briefly mentioned here. 



1. Since the mutations appear fully formed from the be- 

 ginning, 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 be- 

 come further developed by later mutations 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 



