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THE AMERICAN NATURALIST [Vol. XLY 



2. Observation. — Selection lias never been known to 

 produce a change in a genotype. Whenever, as is often 

 the ease, selection does result in modification of type this 

 proves that the material considered was impure — that 

 more than one genotype was originally present — or that 

 others arose by mutation, and entirely irrespective of 

 selection. 



3. Conclusion. — It is therefore proved that selection 

 can not modify the characters of a genotype. 



Johannsen has written a very thick and a very con- 

 vincing-looking book, but if one pins himself down to the 

 task of going from cover to cover he finds that an unfor- 

 tunate amount of the evidence reduces to this kind of 

 reasoning — in short, to no critical evidence at all. 16 But 

 behind this citing of examples which are not inconsistent 

 with his theory although they prove nothing concerning 

 it ; besides this reiteration of testimony which merely ex- 

 cites in the minds of the court-room spectators suspicions 

 concerning the integrity of the defendant without en- 

 titling the plaintiff to a verdict before an impartial 

 jury, 17 there are certain direct experimental studies 



herited."— Jennings, Proc. Am. Phil. Soc, 47: 521, 1908. 



"The standard deviation and coefficient of variation express in a pure 



make all conditions of growth and environment the same throughout our 

 pure race, all the evidence indicates that the standard deviation and coeffi- 

 cient of variation would be iero, and this is the positive value of their 



Lebenslage zu schaffen, miisste die Standardabweichung gleich sein."— 

 RSmer, T., Arch. Hansen- u. Gesells.-Biologie, 7: 437-438, 1910. 



was unable to improve Le Contour's wheat, although he had succeeded in 

 improving seventy other samples from all parts of the world, and explains 



"In working over the literature of the pure line theory the lover of 

 fair play is sometimes on the verge of losing his patience, for although the 



which Johannsen grounds his own theory are very slender, he is unsparing 



