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THE AMERICAN NATURALIST [Vol. XLIII 



the largest individuals for breeding steadily increase the 

 mean size of a race! 



Breeding from the extreme specimens— the largest and 

 smallest— of a single race, we get several hundred indi- 

 viduals from each. Both produce progeny of the same 

 mean size. Each produces a whole series of varying in- 

 dividuals, just like the original racial series (Fig. 4) ; 

 the series produced by the largest individual is exactly 

 like that produced by the smallest, or by any other. The 

 differences between the individuals within such a series 

 are due to growth and environment. Such differences 

 are not inherited: the race breeds true, without regard 

 to the peculiarities of the individual parent. A great 

 number of such breeding experiments were carried out, 

 in which selection was continued for many generations, 

 but the results were invariably the same. Selection 

 within the pure race is of no effect on the size. 



Furthermore, marked differences in the parents due to 

 different environments become quickly equalized in the 

 progeny when the environments are made the same. 

 Thus environmental effects are not inherited. Neither 

 selection nor environmental action changes the size of the 

 pure race. 



Thus in our study of the "normal" variations we come 

 to the same result as in our previous study of abnor- 

 malities, new characters, apparent mutations, and the 

 like. What is produced in inheritance depends, not on 

 the evident external features of the parent cell, but on 

 the fundamental constitution of the race. Each race has 

 its own peculiar constitution, and under different condi- 

 tions this same constitution gives rise to various sizes and 

 forms, producing thus the variations within a race, illus- 

 trated in Fig. 4. But all these different individuals of 

 a race are potentially the same ; at the same age and under 

 the same conditions throughout, all would be alike. 



Now consider again the species as a whole: in this 



