258 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



experimental evidence in favor of the type of natural selection that 

 Darwin stood for. 



THE PRESENT STATUS OF NATURAL SELECTION 



It has come to be rather generally believed that the natural 

 selection that Darwin himself believed in stands almost unscathed as 

 one very important causal factor. In fact it is the only explanation 

 ever offered for adaptation that even approaches adequacy. As an 

 explanation of the origin of new types or new species it falls far short 

 of adequacy, and I think Darwin evidently realized this, although he 

 was unfortunate enough to entitle his book Origin of Species. As 

 an explanation of the origin and perfection of adaptation natural 

 selection has only one rival, the far less satisfactory Lamarckian theory 

 of the inheritance of acquired characters. There is a strong tendency 

 among geneticists to conclude that the modern germ-plasm hypothe- 

 sis, with the aid of mutations and the mechanism of Mendelian inherit- 

 ance, furnishes all the necessary explanation of the causes of evolution. 

 There is, however, marked dissent to this extreme position. In his 

 critique of De Vries's rather extreme position that the mutation 

 theory needs no aid from natural selection, Weismann shows in most 

 able fashion the inadequacy of mutations to account for adaptation, 

 and, in contrast, how well natural selection accounts for them. 



In a very recent paper Professor C. C. Nutting attempts to show 

 that natural selection is still an important factor in evolution and quite 

 in harmony with both the mutation theory and Mendelism. We 

 perhaps can close the present chapter no more fittingly than by 

 quoting Professor Nutting's paper.' ED.] 



THE RELATION OF MENDELISM AND THE MUTATION THEORY 

 TO NATURAL SELECTION 1 



C. C. NUTTING 



Two marked tendencies are evident in the history of any important 

 theory after its publication. 



First. The followers of the discoverer carry the theory too far 

 and attempt too universal an application. This is manifestly true 

 of Wallace and Weismann who out-Darwined Darwin in their claims 

 for natural selection; of the followers of Mendel, such as Morgan and 



1 From an address given before the Genetics branch of the American Associa- 

 tion for the Advancement of Science, December, 1920; Science, N.S., Vol. LIII. 



