: in point of fact, he might
get one-tenth or nine-tenths, none or all of a given trait. But, when
dealing with a large population, the errors on one side balance the
errors on the other, and the law is found, in the cases to which it has
been applied, to express the facts.[51]

While, therefore, this Galton-Pearson law gives no advice in regard to
individual marriages, it is yet of great value to applied eugenics. In
the first place, it crystallizes the vague realization that remote
ancestry is of much less importance than immediate ancestry, to an
individual, while showing that every generation has a part in making a
man what he is. In the second place, it is found, by mathematical
reasoning which need not here be repeated, that the type of a population
may be quickly changed by the mating of like with like; and that this
newly established type may be maintained when not capable of further
progress. Regression is not inevitable, for it may be overcome by
selection.

To put the matter in a more concrete form, there is reason to think that
if for a few generations superior people would marry only people on the
average superior in like degree (superior in ancestry as well as
individuality), a point would be reached where all the offspring would
tend to be superior, mediocrities of the former type being eliminated;
and this superiority could be maintained as long as care was taken to
avoid mating with inferior. In other words, the Galton-Pearson Law gives
statistical support for a belief that eugenic marriages will create an
improved breed of men. And this, it seems to us, is the most important
implication of that law for eugenics, although it is an implication that
is generally ignored.

We do not propose to discuss further the laws of heredity; but it is
likely that the reader who has made no other study of the subject may by
this time find himself somewhat bewildered. "Can we talk only in
generalities?" he may well ask; "Does eugenics know no laws of heredity
that will guide me in the choice of a wife? I thought that was the
purpose of eugenics!"

We reply: (1) The laws of heredity are vastly complicated in man by the
complex nature of most of his characters. The definite way in which some
abnormalities are inherited is known; but it has not been thought
necessary to include an account of such facts in this work. They are set
forth in other books, especially Davenport's _Heredity in Relation to
Eugenics_. The know