124 



EDWIN CARLETON MACDOWELL 



crease in the means of the parents produced an increase in the 

 means of their offspring; in all the other generations an in- 

 crease or decrease in the means of the parents had no influence 

 on the means of the offspring. Higher parents produced higher 

 offspring in the early generations; higher parents did not pro- 

 duce higher offspring in the following generations. 



LOW SELECTED RACE 



Already substantial evidence has been presented that shows 

 that in the earlier generations the lower grade parents produce 

 children with lower mean grade. ^ 



MEANS 



FEMALES 



Fig. 6 Low race, low selected from the beginning, before the high selected 

 race was differentiated. The means of the parents and offspring in this race 

 are compared with the means of the parents and offspring in the high selected 

 race. Means of the parents in the high race are weighted according to the num- 

 bers of their sons and their daughters. 



But perhaps clearer than any other evidence in support of 

 this conclusion is found in the establishment of a low race as the 

 result of selecting low grade flies at the beginning of the ex- 

 periment. One pair of flies, grade 2, from the second genera- 

 tion of the high race, gave rise to a line that was carried on for 

 eight generations by mating only the flies of grade 2 or under. 

 As in the high race, all matings were made between brothers 

 and sisters in pairs. Figure 6 shows the means of this low 



" MacDowell: loc. cit., p. 70. 



