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THE AMERICAN NATURALIST [Vol. XLIII 



tics in answering it is a most subordinate one. When an 

 author deals in standard deviations and coefficients of 

 variation, the first question the reader should ask is : Has 

 the author determined what part of the diversities thus 

 measured have any bearing on heredity ? They may have 

 absolutely none. 



Thus the mere fact that observable variations exist 

 between individuals can not properly be appealed to as 

 furnishing material for selection and evolution, as has 

 been so generally done. Most such variations have in the 

 organisms studied absolutely no bearing on the evolu- 

 tionary process, and there seems little doubt but that this 

 is true for organisms in general. 



Illustrations of the practical bearing of these points 

 may be found without departing from the particular or- 

 ganism with which we are dealing. It has been shown 

 that the two products of the division of a single individual 

 Paramecium often differ in size at a given time, so that 

 " variation" occurs in non-sexual as well as in sexual 

 reproduction. 9 But these " variations" are mere tempo- 

 rary fluctuations, without effect in heredity, so that their 

 relation to evolution is nil. Again, Pearl 10 showed that 

 conjugants are less variable than non-conjugants. This 

 is true even within the limits of a single race, as I can con- 

 firm from extensive studies. But all the variations in 

 such a case, both in the conjugants and non-conjugants, 

 are purely temporary matters, without effect on poster- 

 ity ; so far as evolution or heredity or selection goes they 

 can be left quite out of account. 11 



Comparative studies have often been made of the varia- 

 bility of higher animals under different methods of re- 

 production, under different conditions, etc.; the varia- 



9 Simpson, J. Y., "The Eelation of Binary Fission to Variation," 

 Biomt trika. 1, 1902, 400-404. Pearson, K., "Note on Dr. Simpson's Memoir 

 on Paramecium caudatum," Biometrila, 1, 1902, 404-407. 



10 Pearl, E., "A Biometrical Study of Conjugation in Paramecium," 

 Biometrila, 5, 1907, 213-297. 



u This of course is no criticism of Pearl's paper, which is one of the 

 foundational ones for this line of work. When different races are present, 

 the less variability of the conjugants is of the greatest significance. 



