Table A.
| Generation. | Mean of offspring of 3.75 parents. | Mean of offspring of all parents. |
|---|---|---|
| 4 | 2.75 | 2.73 |
| 5 | 3.07 | 2.90 |
| 6 | 3.22 | 3.11 |
| 7 | 3.35 | 3.20 |
| 8 | 3.49 | 3.48 |
| 9 | 3.50 | 3.54 |
| 10 | 3.69 | 3.73 |
| 11 | 3.75 | 3.77 |
| 12 | 3.83 (35 individuals) | 3.94 (590 individuals) |
In generation 4 the 3.75 parents represented the most advanced individuals of the series, a whole grade in advance of the general average of the race. Their offspring showed a correspondingly large regression. The general average of the race steadily advanced in later generations until in generation 11 it equaled that of the 3.75 parents; then the regression vanished. In the following generation, 12 (which is still incomplete, but in which the average of the offspring thus far is 3.94), the 3.75 group of parents, which are now below the average of the race, actually produce offspring of higher grade than themselves, viz, 3.83. It will thus be seen that the regression is uniformly toward the mean of the race and changes its direction when that mean changes its position with reference to a particular grade of parents. This conclusion is supported by other columns of Table 15, but is best illustrated by this particular case because here the selection has extended over a greater number of generations than elsewhere in the series.
If one examines the horizontal rows of Table 15, he finds in general that numbers increase toward the right. Exceptions are commonest toward the ends of the rows where fewest individuals are represented. This increase means that, within any generation, as the grade of the parents rises, that of their offspring rises also. Since in general the selected parents are above the general average of the race for the time being, regression is naturally downward in nearly all cases.
From what precedes we may conclude (1) that in this series of rats the somatic character (appearance) of an individual is in general a true indication of its germinal character, since the higher the grade of the parents the higher the grade of the offspring, and vice versa; but that (2) the somatic character of an individual is not a perfect index of its germinal character, since the offspring of aberrant individuals are less aberrant than themselves, i. e., the offspring regress toward the mean of the race; yet that (3) by selection of plus variations we can displace, in a plus direction, not only the mean of the race, but also the upper and lower limits of its variation, the total amount of variability (standard deviation) being thereby only slightly decreased.