ledge of how such a trait as color-blindness is
inherited may be of importance to one man out of a thousand in choosing
a wife; but we are taking a broader view of eugenics than this. As far
as the great mass of human characters go, they are, in our opinion, due
to so many separately inheritable factors that it is not safe to
dogmatize about exactly how they will behave in heredity. Such
knowledge, desirable as it may be, is not necessary for race progress.

(2) But it is possible, with present knowledge, to say that human
traits, mental as well as physical, are inherited, in a high degree.
Even before the final details as to the inheritance of all traits are
worked out--a task that is never likely to be accomplished--there is
ample material on which to base action for eugenics. The basal
differences in the mental traits of man (and the physical as well, of
course) are known to be due to heredity, and little modified by
training. It is therefore possible to raise the level of the human
race--the task of eugenics--by getting that half of the race which is,
on the whole, superior in the traits that make for human progress and
happiness, to contribute a larger proportion to the next generation than
does the half which is on the whole inferior in that respect. Eugenics
need know nothing more, and the smoke of controversy over the exact way
in which some trait or other is inherited must not be allowed for an
instant to obscure the known fact that the level can be raised.

CHAPTER VI

NATURAL SELECTION

Man has risen from the ape chiefly through the action of natural
selection. Any scheme of conscious race betterment, then, should
carefully examine nature's method, to learn to what extent it is still
acting, and to what extent it may better be supplanted or assisted by
methods of man's own invention.

Natural selection operates in two ways: (1) through a selective
death-rate and (2) through a selective birth-rate. The first of these
forms has often been considered the whole of natural selection, but
wrongly. The second steadily gains in importance as an organism rises in
the scale of evolution; until in man it is likely soon to dwarf the
lethal factor into insignificance. For it is evident that the appalling
slaughter of all but a few of the individuals born, which one usually
associates with the idea of natural selection, will take place only when
the number of individuals born is very large. As the reproductive