THE 



AMERICAN NATURALIST 



Vol. XLIX. December, 1915 No. 588 



SOME EXPERIMENTS IN MASS SELECTION 



PROFESSOR W. E. CASTLE 

 Bussey Institution, Harvard University 



At the close of an interesting review of * 1 seventeen 

 years selection" of the character winter egg production 

 in Barred Plymouth Eock fowls, made at the Maine Agri- 

 cultural Experiment Station, 1 Dr. Pearl compares his re- 

 sults with those of Phillips and myself 2 in selecting for a 

 like number of generations the hooded pattern of rats and 

 concludes that the same interpretation should be given to 

 both series of experiments, viz., that selection can change 

 a population but not a character. 



Without discussing for the moment the validity of the 

 now world-famous generalization of Johannsen, which 

 Pearl here accepts for his fowls and seeks to extend to 

 our rats, I wish to point out some differences between the 

 two cases which make a direct comparison between them 

 difficult and conclusions based upon them of unequal 

 validity. 



The character winter egg production in fowls is on 

 Pearl's showing extremely difficult to determine. It is 

 necessarily an unknown quantity in all male birds, which 

 themselves produce no eggs, and any influence which 



i" Seventeen Years Selection of a Character Showing Sex-linked Mendel- 

 ian Inheritance," American Naturalist, Vol. 49, pp. 595-608, 1915. 



2 "Piebald Rats and Selection," Publ. No. 195, Carnegie Institution of 

 Washington, 1914. 



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