MUTATION 



BY 

 CHARLES B. DAVENPORT 



FoRTY-THEEE years after the Origin of Spe- 

 cies there appeared the first part of a book by the 

 Dutch naturalist, Hugo de Vries, entitled Die 

 Mutationstheorie. Many other theories of evo- 

 lution have been propounded and defended in the 

 last half-century, but hardly any other has 

 commanded such immediate consideration and 

 received such widespread acceptance. The muta- 

 tion theory must therefore contain certain evi- 

 dent elements of truth. Let us consider its 

 scope and some of the evidence on which it rests. 



MUTATION DEFINED 



First of all it is necessary to define mutation 

 in De Vries' sense and to show its relation to 

 other evolutionary principles. Mutation in any 



,' strain is a change in the unhybridized germ- 

 plasm of that strain which is characterized by the 



1 acquisition or loss of one or more unit charac- 

 ters. There has already been presented to you 

 the evidence for unit characters, a conception 

 first clearly elucidated by Darwin. I think it 

 may fairly be said that the mutation theory rests 

 on the doctrine of imit characters and applies 



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