line of "unsoundness" the descent of
which it is interesting to trace. It is instructive to compare here
the progeny of matings of different kinds. In generation IV of Fig.
26, the 9th and 10th persons are brother and sister. The sister was of
considerable ability and married into a family of ability, producing 8
offspring, 5 of whom were able. The brother was a "normal" person and
married a similar individual, producing 10 "normal" children. It would
be interesting to know the details regarding these two large families
of cousins. Another interesting comparison is found in this pedigree.
The four able brothers in generation III, coming from a stock of
demonstrated ability, married women of undemonstrated ability and all
told had 13 children (IV) of whom only 3 showed ability and all of
these were in a single family. In this family of the fourth brother
two of the able members married into able families, and among their 11
children (second and fifth families in generation V) 8 showed ability;
the third able member of this family, however, married as her uncles
had, a person not known as able, and none of their 6 children showed
unusual ability (sixth family in generation V). Fig. 27 affords other
illustrations of this same kind. Thus in generation III the 5th and
7th persons are able cousins of able parentage. The former married a
normal and 1 of their 5 children showed ability; the latter married a
person of ability and 5 of their 8 children showed ability. In both
pedigrees the "careers" of those in the last generation are partly
incomplete.

[Illustration: FIG. 27.--Family history showing ability.
Paternal ancestry of family shown in Fig. 26. (From
Whetham.)]

In discussing pedigrees of ability it should be borne in mind that the
larger proportion of able males as compared with females is hardly
significant for the study of heredity; it may merely reflect the
unfortunate fact that women have not had the same opportunity to
demonstrate inherent ability as have men; or it may evidence the still
more unfortunate fact that the distinguished achievements of able
women have not been socially recognized as such and recorded as they
have been for the other sex.

Fig. 28 gives an interesting, though abbreviated, pedigree of three
very able and well-known families. In this history only persons whose
ability is in science are marked as able. Charles Darwin is the third
individual in the third generation. His co