They
are intended to predict only general trends, only average results; and
for this purpose they are wholly legitimate. Moreover, evolution itself
is a problem of statistics, and therefore the statistical method of
studying heredity may offer results of great value to eugenics, even
though it can not furnish in individual cases the prediction which would
be desirable.
From this standpoint, we return to attack the problem of the relation
between parent and offspring. We noted that there is no uniform sequence
in a single family, and illustrated this by the case of brown eyes. But
if a thousand parents and their offspring be selected and some trait,
such as eye-color, or stature, or general intelligence, be measured, a
uniformity at once appears in the fact of regression. Its discoverer,
Sir Francis Galton, gives this account of it:
[Illustration: FINGER-PRINTS OF TWINS
FIG. 25.--Above are the finger-prints, supplied by J. H. Taylor
of the Navy Department, of the two young sailors shown in Fig. 24. The
reader might examine them once or twice without seeing any differences.
Systematic comparison reveals that the thumbs of the left hands and the
middle fingers of the right hands particularly are distinguishable.
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