32 FECUNDITY IN THE DOMESTIC FOWL 



organisms, on the other hand. But beyond all these lie the difficult cases 

 where in dioecious forms quantitative variations must be dealt with. If 

 these can be cleared up and brought harmoniously into a general scheme or 

 view-point regarding inheritance, we shall have gone a long way in the 

 solution of this world-old biological problem. 



For some four years past the writer has been engaged in a study of the 

 inheritance of fecundity in the domestic fowl. The problem presented 

 here is an important one from the practical as well as the theoretical stand- 

 point. If definite and sure methods of improving the average egg produc- 

 tion of poultry by breeding can be discovered it will mean much to the 

 farmers of the nation. At the same time egg production is a character in 

 some ways well adapted to furnish definite and crucial data regarding 

 inheritance. Variations in egg production are readily measured, and can 

 be directly expressed in figures. 



The general results of this study of the inheritance of fecundity may be 

 said, in a word, to be, so far as they go, in entire accord with the genotype 

 concept, and not to agree at all with the "statistico-ancestral" theory of 

 inheritance. Indeed, so ill is the accord here that the chief exponent of the 

 latter doctrine has recently attempted to throw the whole case out of court 3 

 by asserting that fecundity is not inherited in fowls, and that the present 

 writer's investigations show essentially nothing more than that. It will be 

 the purpose of this paper to present some figures sufficient to indicate with 

 some degree of probability, I think, first that egg production in fowls is 

 inherited, and second that it is probably inherited in accord with the geno- 

 type concept, in spite of the fact that we do not and can not here have 

 "pure lines" in the strict sense of Johannsen's definition. In the present 

 paper, owing to limitations of space, the whole of the data in hand obviously 

 can not be presented. Only a few illustrative cases can be given here. 



Before entering upon the discussion of the evidence it is necessary to call 

 attention to two points. The first is in regard to the unit of measuring egg 

 production used in the work. For reasons which have been discussed in 

 detail elsewhere 4 the unit of study has been taken as the egg production of 

 the bird before March 1 of her pullet year. This "winter production" is a 

 better unit for the study of the inheritance of fecundity than any other 

 which can be used practically. All records of production given in this 

 paper are then to be understood as "winter" records, comprising all eggs 

 laid up to March 1 of the first year of a bird's life. It may be said that the 



3 Pearson, K., "Darwinism, Biometry and some Recent Biology, I," Biometrika, 

 Vol. 7, pp. 368-385, 1910. 



4 Bull. Me. Agr. Exp. Sta., No. 165. U. S. Dept. Agr. Bur. Anim. Ind., Bui. no, 

 Part II. 



