No. 510] HEREDITY AND VARIATION 



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bility of parthenogenetic generations has been compared 

 with that of sexual generations, and the like. These have 

 no meaning for evolutionary questions unless we know 

 whether any of the diversities are heritable. In general, 

 it would appear that most observed variations are not 

 heritable. 



Perhaps more important even than the distinction be- 

 tween temporary modifications and really heritable dif- 

 ferences is another point regarding "variations." Even 

 leaving aside the temporary modifications, much discus- 

 sion of variation assumes that the word implies an 

 actual change from one condition to another. This is 

 obviously a very different matter from mere observance 

 of two different conditions in different individuals. If 

 our object is to discover how far we have actually ob- 

 served evolution taking place, the distinction between 

 variation as an active change and variation as an exist- 

 ing condition (of permanent differentiation between two 

 races) is absolutely fundamental. Evidently, observa- 

 tion of the mere fact that permanent differentiations exist 

 between races is a totally different matter from observa- 

 tion of the changes by which evolution occurs ; it is com- 

 patible with almost any theory of the origin of diversities ; 

 for example, with that of special creation. As a matter 

 of fact, do we find the existing races changing or perma- 

 nent? What light does our study of variations throw on 

 this? 



In Paramecium, in the extensive study of many races 

 for hundreds of generations by exact statistical and ex- 

 perimental methods, not one single instance was observed 

 of variation in the sense of an actual change in a race. In 

 the detailed paper, coefficients of variation are given al- 

 most by the hundred, and permanent diversities of race 

 are registered minutely and in numbers. But these mean 

 nothing so far as real change in any race is concerned. 

 So far as the evidence goes, every race was essentially 

 the same throughout the work, and may have been the 

 same for unnumbered ages before. 



