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 0—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 0 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 0 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 selection we find that 1 in 6 of the offspring have plus grades and their average is lower (that is, less minus) than the offspring in the minus series after a single generation of selection. (Cf. Tables [16] and [36].)
The amount and persistency of the reversed regression in this series show clearly that return selection is not easier or more rapid than the original modification of the race by selection, but that selection in either a plus or minus direction has cumulative and permanent effects.
Further support for this conclusion is furnished by return selections (one each) made from the seventh generation, from the eighth generation, and from the eleventh generation of the minus selection series. (See Tables [37, 38, and 39].) Generation 7 ([Table 22]) was produced by parents of average grade -2.01. Their offspring were of average grade -1.73, a regression (toward 0) amounting to 0.28. Certain pairs of these offspring of grade -0.75 and -0.87 (mean -0.78) constitute the return selection from generation 7 ([Table 37]). They had 33 offspring of average grade -1.15, a regression away from 0 amounting to 0.37.
Generation 8 of the minus-selection series ([Table 23]) was produced by parents of mean grade -2.05. Their offspring were of mean grade -1.80, a regression (toward 0) of 0.25. Certain pairs of these offspring of grades -0.50, -0.62, and -1.00 (mean -0.72), when chosen as parents, produced 41 young of mean grade -1.51, a regression away from 0 amounting to 0.79. (See [Table 38].)
Generation 11 of the minus series ([Table 26]) was produced by parents of mean grade -2.30. The offspring were of mean grade -2.15, a regression of 0.15 toward 0. A pair of the offspring of mean grade -1.62 ([Table 39]) produced 16 young of mean grade -1.95, a regression of 0.32 away from 0. This result shows that the selected race had now passed the point represented by the grade of the parents (-1.62) and the offspring regressed toward a racial mean as advanced as the most extreme individuals obtained previous to selection.
To show that, in the plus selection series, a return selection has a result similar to that just described, two experiments may be cited: