No. 586] SELECTION OF A CHARACTER 



601 



tion obtained in this experiment with independently de- 

 termined norms the general trustworthiness and normal- 

 ity of the present data have been demonstrated. 



2. From the beginning of the experiment through the 

 laying year 1907 08 the general trend of mean produc- 

 tion was downward, with minor fluctuations from year to 

 year. In other words during the period in which the sys- 

 tem of breeding was mass selection for high production 

 without progeny test there was no change of the mean in 

 the direction of the selection. The fluctuations in mean 

 production during this period were, in the main, due prob- 

 ably to two sets of causes: (a) environmental differences 

 in different years acting at one point or another in the 

 life history of the birds ; ( b ) random fluctuations in the 

 genetic constitution of the male birds used as breeders in 

 successive years, brought about because of the ignorance 

 of the breeder, in the absence of any individual progeny 

 testing plan, of the ability of any particular male to trans- 

 mit high fecundity to his daughters. The first of these 

 factors needs no special discussion and is relatively of 

 minor importance. The second will be dealt with in detail 

 farther on in the paper. 



3. Since the laying year 1907-08 there has been a steady 

 increase in mean winter production for the whole flock, ex- 

 cept for the years 1910-11 and 1914-15. In the former year 

 the decline in the mean is slight, and is probably due to 

 unfavorable environmental influences. In 1914-15 the 

 decline is certainly due to such causes. In the hatching 

 season of 1914 an inexperienced man was in charge of 

 the incubation and rearing. He had very poor success, 

 and the Barred Plymouth Eock pullets available for the 

 laying houses in the fall were relatively few in number, 

 of a relatively late average date of batching, and poorly 

 grown. It is remarkable, not that the mean winter pro- 

 duction was lower in 1914-15 than in 1913-14, but rather 

 that it was so high as it was, taking all the circumstances 

 into account. It appears that the system of breeding 

 which made the selections on a progeny test basis was 

 immediately and, to date, continuously effective. 



