14 PIEBALD RATS AND SELECTION. 



minus selection series. The large amount of the regression might seem 

 to imply that it was even more difficult to return toward the former 

 state of the race (in the neighborhood of 0) than it had been to depart 

 from it, but this can not be insisted on, because the number of indi- 

 viduals under observation is not sufficiently large. To test the reality 

 and permanency of the reversed regression, the selection was repeated 

 five additional times, altogether six successive return selections being 

 made with the idea of undoing what had been effected by six original 

 selections in an opposite direction. The result of the second successive 

 return selection is shown in Table 32. The parents here were of grade 

 -0.50 and they produced 19 offspring of the average grade 0.95, a 

 regression of 0.45 away from as before. 



Table 33 shows the result of the third return selection. Individuals 

 entered in Table 32 as offspring appear here as parents. Only those 

 pairs which were of mean grade, -0.25 or 0.37, should really be 

 regarded as a third return selection. They gave offspring with mean 

 grades of -0.63 and 0.86 respectively, which show regression of 0.38 

 and 0.49 away from 0. 



But Table 33 shows also the character of young produced by --1.12 

 and --1.25 parents in this same third return-selection generation, i. e., 

 by unselected parents of the generation in question. Their young also 

 regress away from that is, in the direction of the original selection. 

 The 1.12 parents produced - - 1.61 offspring, a regression of 0.49, while 

 the -- 1.25 parents produced -- 1.35 offspring, a regression of 0.10. For 

 Table 33 as a whole the regression away from averages 0.31. 



A fourth generation in the return-selection series is summarized in 

 Table 34. The parents are of mean grade 0.63; their 50 offspring are 

 of mean grade --1.17,a regression amounting to 0.54 away from and 

 in the direction of the six generations of original selection. 



Table 35 contains the results of the fifth generation of the series. 

 The parents are here of mean grade 0.65. The number of offspring 

 is very small (13), but they nevertheless show the reversed regression 

 which characterized the four preceding generations. Their mean was 

 0.75, a regression of 0.10 away from 0. 



A sixth and final generation in this return-selection experiment is 

 summarized in Table 36. It includes 36 offspring of mean grade 0.39, 

 the mean of the parents being 0.26, a regression of 0.13 away from 0. 

 It will be seen, therefore, that the effect of the six original selections had 

 not been entirely overcome by an equal number of return selections. 

 The reason for this is obvious. Much smaller numbers are concerned in 

 the return selections than in the original minus selections. The return 

 selections are accordingly less efficient. Nevertheless, after the sixth 

 return select ion we find flint 1 in 6 of the offspring have plus grades and 

 their average is lower (that is, lex* nrin us) than the offspring in the minus 

 series after a single generation of selection. (Cf. Tables 16 and 36.) 



