Mutation and Natural Selection 381 



Advantages of the Mutation Theory 



From the point of view of giving a reasonable explana- 

 tion of how organic evolution comes about, the mutation 

 theory has certain advantages over the theory of natural 

 selection. It is interesting to learn that these advantages 

 were more promptly recognized in this country and on the 

 Continent than they were in England, where the thought of 

 scientists was more completely under the domination of 

 Darwinism, although some of the keenest criticisms of Dar- 

 winism had also come from England. 



The first advantage of the mutation theory is that it 

 accounts for new characters that are too trifling to be of any 

 value. Such an incipient character may persist, despite its 

 lack of value, until it acquires, through later mutations, an 

 important place in the life of the individual or of the 

 species. 



In the next place, the mutation theory contemplates 

 the simultaneous or repeated appearance of many individuals 

 with the same new character. It thus explains how a rela- 

 tively rare, and perhaps useless, set of traits might get a 

 foothold, or avoid being swamped. 



Third, mutations may appear in the form of a new 

 variety or species that is at once adapted to living in an en- 

 vironment somewhat different from that occupied by the 

 parental form. It thus makes possible an isolation that pro- 

 tects the new strain from being swamped or crowded out 

 by the prevailing type. 



Fourth, the mutation theory accounts for the appear- 

 ance of numerous characters that distinguish species from 

 each other but that are not of sufficient adaptive value to be 

 saved by natural selection. 



Fifth, mutations may include not only indifferent but 

 even some injurious characters. The existence of such char- 

 acters in plants and animals is in conflict with the selection 

 theory. If they are not too injurious, however, it is in har- 

 mony with the mutation theory. 



