pect
that there would be about 65 tubercular first born, 60 tubercular
second born, and so forth, on the basis of its average frequency in
the whole community, provided the chances are equal that any member of
the family should be affected with tuberculosis. What we actually
find, however, is that 112 first born are affected, about 80 second
born, and after that no relation between order of birth and
susceptibility to tuberculosis. That is, susceptibility to
tuberculosis is double the normal among first born children. The same
thing is true for gross mental defect. Fig. 11, _B_, shows that the
ratio of observed to expected insane first born children is about 4 to
3. Such a relation has long been known to criminologists and
frequently commented upon. Fig. 11, _C_, gives a definite expression
to the facts here. Whereas, in the number of families observed about
56 criminal first born were to be expected, the number actually found
is about 120; for the second born the corresponding numbers are about
54 and 78, and after that no marked relation is found between order of
birth and criminality. For albinism (Fig. 11, _D_) the expected and
observed numbers among first born are about 185 and 265, second born
165 and 190, and thereafter no definite relation. It remains to be
seen whether a similar relation holds for the unusually able and
valuable members of a family; something has been said on both sides
here, but there are available at present no data sufficiently exact to
be worthy of consideration.

[Illustration: FIG. 11.--Diagrams showing the relation
between order of birth and incidence of pathological defect.
(From Pearson).]

We have here a result that has very important bearings upon the value
to the race of the large family and of the danger of the small family.
The small family of one, two, or three children contributes on the
average much more than its share of pathological and defective
persons. No matter just now what the causes are, they seem to be more
or less beyond remedy. The result for the future, however, must be
reckoned with. This relation has important bearings upon the custom of
primogeniture as well as upon the eugenic values of the large family.

In conclusion let us give a few sentences only slightly modified from
Pearson's "Grammar of Science." The subject of differential fertility
is not only vitally important for the theory of evolution, but it is
crucial for the stability of civili