No. 534] 



THE PURE LINE THEORY 



359 



ignorant of the physiology of reproduction in the do- 

 mestic fowl might innocently suppose that even a hen 

 needs a rest. If this be true, may it not be that 200 eggs 

 is about the attainable maximum (the physical or physi- 

 ological limit of the organism) of this variety under the 

 environmental conditions available ami that the Maine 

 strain of poultry will not do better than it has? If this 

 is not the attainable limit, why not assume over an egg 



C. Selection can not in general carry a Character be- 

 yond a Degree Consistent icitli the Optimum 

 for Maintenance and Be production 



This proposition is perhaps in a sense explanatory of 

 the one immediately preceding. A characteristic is not 

 independent of, but correlated with the other character- 

 istics of the organism, and if it increases or decreases 

 unduly they must also change or the organism be made 

 more or less unfit for survival. 



Have those who claim to have found selection ineffect- 

 ive been selecting against the morphological or physio- 

 logical balance of the organism, that is in a manner to 

 render the organism less capable of maintenance, 

 growth and reproduction? 



If this be true their failure to obtain results will be in 

 some measure explained. 



A possible illustration of this case may be furnished 

 by the work of Pearl and Surface on egg production in 

 the domestic fowl. Their work is again chosen not be- 

 cause of any malicious desire to differ from them 28 in 

 interpretation, but because in a brief discussion of the 

 evidence for the genotype theory one must confine his 

 attention to the most important of Johannsen's sup- 

 porters. 



The data are: (a) The results of an eight years' selec- 



