+-----------+-----------------------+------------------------+
|Generation.| Mean of offspring of | Mean of offspring of |
| | 3.75 parents. | 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.