lack eyes are "dominant" over blue eyes because the black color is due
to a pigment, while the blue color is due to the absence of this
pigment. In general a quality which is due to the presence of some
positive element is dominant over a quality due to the absence of that
element. A child inheriting from a blue-eyed person simply draws a blank
from that side in the lottery.

In order to understand how these principles of Mendel apply in any given
case we need first to know what traits are "dominant" and what are
"recessive."

Among traits known to be "dominant" are, besides pigmentation of the
eye, certain peculiarities of the skeleton, such as short-fingeredness
(two phalanges only on each digit), Huntington's chorea, presenile
cataract, congenital thickening of the skin, early absence of hair,
diabetes insipidus, stationary night-blindness, liability to periodic
outbreak of temper, etc.

Among traits known to be "recessive" are albinism (or lack of
pigmentation), a certain degenerative disease of the eye, deafmutism,
imbecility, insanity of certain types, certain nervous diseases; also
mental traits, such as musical ability.

Suppose now that a normal or "strong-minded" person, if we may use that
term as distinct from feeble-minded, marries a feeble-minded person.
Assuming that the "strong-minded" person is a "thoroughbred" all of the
children will be apparently normal. None will be feeble-minded.
"Strong-mindedness" is dominant over weak-mindedness. Yet all these
children that seem to be perfectly normal lack something in their
bodies. This deficiency is simply covered up but can crop out in later
generations. If two of these hybrids between the weak-minded and the
strong-minded marry each other, one-quarter of the children will be
feeble-minded, one-quarter thoroughbred strong-minded and the remaining
half, though apparently strong-minded, will carry the taint in them just
as their parents did. They are half-breeds. On the other hand, if two
feeble-minded people marry, all of the children will be feeble-minded.
Certainly we can and ought to forbid and prevent such marriages.

But feeble-mindedness is a recessive quality, so that if the
feeble-minded marry only with normal individuals, the feeble-mindedness
does not blight the next generation, and if these apparently normal
children of such marriages take pains to marry only really normal
individuals, avoiding not only the feeble-minded but even those like
the