castle: role of selection in evolution 371 



of variations which is both logical and sound, but which has 

 resulted in some confusion owing to efforts to combine it with 

 earlier classifications. He classifies variations into those which 

 are inherited (genotypic) and those which are not inherited 

 (phenotypic). No objection can be made to this classification 

 except that it raises new difficulties and solves none. For how 

 is one to distinguish a phenotypic from a genotypic variation? 

 Only by trying them out. A variation which is inherited is 

 genotypic; one w r hich is not inherited is phenotypic. Since 

 there is no other way then actual experiment by which to dis- 

 tinguish genotypic from phenotypic variations, we acquire only 

 a new set of synonyms for inherited and non-inherited, a thing 

 for which there was no urgent need. 



Attempts to combine the classifications of variations made re- 

 spectively by Darwin, by DeVries, and by Johannsen have re- 

 sulted in serious confusion which is largely responsible for the 

 apparently contradictory views held at present concerning selec- 

 tion. There really is no diversity of view concerning selection 

 but only concerning the nature of the material that it acts upon 

 (viz. , variations) . 



To complicate the situation still farther we have the discovery 

 of Mendelian unit-characters which introduces a new un- 

 certainty. Are these .unit-characters fluctuations or sports? 

 Do they arise solely by mutation or also by the cumulation of 

 fluctuations? These are vital but perplexing questions. As 

 matters stand concerning terminology, we have the term 

 "sport," introduced by Darwin but now largely discarded, 

 meaning any discontinuous, striking, suddenly appearing varia- 

 tion, known to be strongly inherited. Some of the examples 

 cited by Darwin, such as the Ancon sheep, obviously involve 

 Mendelian unit-characters. 



The term mutant as used by DeVries signifies much the same 

 as Darwin's term sport but involves a particular conception of 

 the circumstances and manner of its origin which is not involved 

 in Darwin's term. Some of DeVries' mutants of the evening 

 primrose involve Mendelian unit-characters, as for example 

 his dwarf mutant (nanella), while others such as gigas do not. 



