arieties, two essential biological facts are made use of. The raw
materials are furnished by variation--by the fact that there are
individual and racial differences. The means of accomplishing results
are furnished by heredity--the fact that offspring resemble the
parents, not only in generalities, but even in particulars, and
according to certain definite formulas.

And, further, in the formation and establishment of a new race of
plant or animal a conscious and ideal process is involved. The will of
some organism guides the process, carefully doing away with hit and
miss methods, and proceeding as directly as may be possible to an end
_desired_. The facts of variation and heredity are sufficiently
demonstrated for all organisms other than man; are they true of man
also? Have we available the possibilities for the improvement of the
human breed? If not, Eugenics is merely an interesting speculation. We
have mentioned already the facts of variation in man; we undoubtedly
do have the raw materials. What about heredity, and what about the
directive agency? Let us look now at some of the facts of human
heredity and consider some of the possibilities in the way of
directive agencies. Is it going to be possible to breed a stable human
race permanently with or without definite characteristics which now
appear only in certain groups, or sporadically as variations?

At the outset we should say that the knowledge of human heredity is as
yet largely of the statistical sort. We know how a great many
characters are inherited, on the average. The subject of Mendelian
heredity is so new that there has been hardly time to investigate more
than a few human characteristics from this point of view. Certain
conditions add to the difficulties here. First, many, probably most,
of the more important human traits are complexes, not units, and it is
a long and difficult process to analyze them into their units, with
which alone Mendelism deals. Second, in human society we cannot carry
on definite experiments under controlled conditions, directed toward
the solution of some concrete problem in heredity. It is true that
Nature herself is making such experiments constantly, but at random,
and rarely under ideal conditions of what the experimenter calls
control or check. We have first to seek and find them out, and when
they are found we often discover that there are lacking many of the
facts essential to a complete or satisfactory analysis of th