ristic."

Again, the knowledge of ancestry is an essential factor in the wise
selection of a husband or wife. Insistence has been laid on this point
in an earlier chapter of this book, and it is not necessary here to
repeat what was there said. But it seems certain that ancestry will
steadily play a larger part in marriage selection in the future; it is
at least necessary to know that one is not marrying into a family that
carries the taint of serious hereditary defect, even if one knows
nothing more. An intelligent study of genealogy will do much, we
believe, to bring about the intelligent selection of the man or woman
with whom one is to fall in love.

In addition to these general considerations, it is evident that
genealogy, properly carried out, would throw light on most of the
specific problems with which eugenics is concerned, or which fall in the
field of genetics. A few examples of these problems may be mentioned, in
addition to those which are discussed in various other chapters of this
book.

[Illustration: HISTORY OF 100 BABIES

FIG. 42.--The top of the diagram shows the children "starting
from scratch." By following down the vertical lines, one can see that
their longevity depends largely on the size of family from which they
come. Those who had 10 or a dozen brothers and sisters are most likely
to live to extreme age. Alexander Graham Bell's data, 2964 members of
the Hyde family in America.]

[Illustration: ADULT MORTALITY

FIG. 43--If child mortality is eliminated, and only those
individuals studied who live to the age of 20 or longer, the small
families are still found to be handicapped. In general it may be said
that the larger the family, the longer a member of it will live. Large
families (in a normal, healthy section of the population) indicate
vitality on the part of the parents. This does not, of course, hold good
in the slums, where mental and financial inefficiency are abundant.
Within certain classes, however, it may be said with confidence that the
weaklings in the population are most likely to be from small families.
Alexander Graham Bell's data.]

1. The supposed inferiority of first-born children has been debated at
some length during the last decade, but is not yet wholly settled. It
appears possible that the first-born may be, on the average, inferior
both physically and mentally to the children who come directly after
him; on the other hand, the number of first-born who attain e