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. 
THE RELATION OF MENDELISM AND THE MUTATION THEORY 
TO NATURAL SELECTION‘ 
Cc. 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 
' 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. 
