CONTROL OF HEREDITY: EUGENICS 379 



lines there was considerable fluctuation in size, 

 but he was unable by selecting extremes to 

 increase these fluctuations, the progeny of any 

 pure line always fluctuating about the mean 

 of that line (Fig. 44). 



Similarly Tower found in his studies on the 

 potato beetle that he was unable to shift the 

 mean or the extremes of any character by se- 

 lection of extreme forms of an inbred line. 



Pearl also made an extensive study of the 

 records of breeding experiments extending 

 over many years in which the attempt was 

 made to increase the egg-laying capacity of 

 hens by selecting in each generation for breed- 

 ing only those which had a high record for 

 egg production. It was found that certain 

 "blood lines" produced a larger number of 

 eggs than other lines, but by no amount of 

 selection was it possible to increase the egg 

 production within any line. 



These and other experiments seem to de- 

 monstrate the absolute inability of selection to 

 produce anything new or to improve any char- 

 acter of a pure race. Nevertheless selection is 

 of great service in separating good lines or 



