THE AMERICAN NATURALIST [Vol. XL V 



tion. In this experiment only such females were used as 

 breeders as had laid over 150 eggs in their pullet year 

 (corresponding roughly to an average winter production 

 of 45 or more eggs) and the only males used were such 

 as were out of birds laying 200 or more eggs in the year. 

 This experiment was continued until the end of 1908. 

 The selection, be it understood, was based on the egg 

 record alone, and no account was kept of pedigrees or of 

 genotypes. Every female with a record higher than 150 

 eggs in the year was used as a breeder regardless of 

 whether her high fecundity was genotypic or phsBno- 

 typic. 



The results of this selection experiment covering a 

 period of nine years have been fully reported elsewhere. 7 

 Here it needs only to be said that the net outcome of the 

 experiment was to show that there was no steady or 

 fixed improvement in average flock production after the 

 long period of selection. There was no permanently 

 cumulative effect of the eight (in the last year) genera- 

 tions of selected ancestry. So far from there having 

 been an increase there was actually a decline in mean 

 egg production concurrent with the selection, taking the 

 period as a whole. During parts of the selection period, 

 however, as for example the years 1899-1900 to 1901-02, 

 inclusive, and the years 1902-03 to 1905-06, inclusive, an 

 improvement from year to year was to be noted, but in 

 each case the flock dropped back in intervening years. 

 This is an important point, the meaning of which is now 

 clear. The flock average from year to year depended 

 largely upon whether the breeders of the year before had 

 had their high fecundity genetically represented or only 

 somatically. In some years the selection was fortunate 

 in getting nearly all the breeders from good (i. e., * 'high 

 production") genotypes or from good combinations of 

 genes. In other years just the opposite thing happened: 

 the high layers chosen as breeders came from low geno- 



7 U. S. Dept. Agr. Bur. Anim. Ind., Bui. 110, Parts I and II, 1909 and 

 1911. Zeitschr. f. indukt. Abst. a. I erab.-Lchre, Bd. 2, 1909, pp. 257-275. 



