HEREDITY 497 



mediocrity, all of which requires several years, and accounts 

 for the comparatively small effects of the first one or two years' 

 selections. 



The same principle is evidently present and at work in stature 

 (see table, page 480), for we note that the children cover a wider 

 range than do the parents. It might seem that under the prin- 

 ciple of assortative mating these exceptional children would break 

 away and establish a race of giants and one of dwarfs. We are 

 acquainted with some of the causes that prevent this ; namely, 

 relatively small fertility in giants (see table) and lack of marriage 

 among dwarfs. As it is, however, the mean of stature is some- 

 what above the highest fertility (see table). 



It used to be said that the offspring is a kind of mean of the 

 parentage, and that the most that could be accomplished by 

 selection was the production of fewer mediocre and inferior and 

 a larger proportion of superior individuals. 1 We know now, how- 

 ever, that the great bulk of the population will always be medio- 

 cre, but that by extreme selection we may secure new upper 

 values quite beyond former limits, not only of the parents but 

 of the race, and that at the same time the entire population ^vill 

 respond to an upivard trend, thereby raising the level of mediocrity. 



All experience in breeding agrees with the principle here set 

 forth. At the University of Illinois, when experiments in corn 

 breeding were first undertaken, the question arose whether the 

 results of the first year or two were anything more than assorta- 

 tive. The effects of selection were not at first pronounced, 

 owing, of course, to the "drag" of previous ancestry. But 

 selection was extremely rigid, a fact which rapidly freed the 

 back ancestry from this drag, and with this came a decided rise 

 in the mean of the crop ; that is to say, the standard of medioc- 

 rity was raised, and along with this there appeared from time to 

 time occasional ears with values far above anything ever found 

 in tJie foundation stock. These were new values due to the prin- 

 ciple of progression, and the fact that the coefficient of variability 



1 This position was always untenable, because, given the two best parents in a 

 race, if the offspring is a mean between the two then no offspring can ever equal 

 its better parent. How then was the superior parent produced ? Such a doctrine 

 has but one outcome, the bringing of the total population to a dead level of 

 mediocrity. 



