e direction of the fraternal or parental
characteristic. Grandchildren tend to deviate from the group average
only about one fourth as far as their grandparents. It should be
remembered that these are statistical and not individual statements,
and that as many "exceptions" will be found in the direction of
greater resemblance as in that of lesser resemblance.

One of the present objects of the student of heredity, perhaps his
chief object, is to be able to state the facts of human heredity in
Mendelian terms, reducing many of the complex human traits to their
simpler elements. Some of the chief objections to the use of the
statistical formula of heredity are that apparently it is applicable
only to the fluctuating variabilities of organisms; that it rarely
takes into account the presence of (and therefore the heredity of)
true variations or mutations--and we have seen that it is just these
characters that are of the greatest value in evolution; and that
heredity is after all fundamentally an individual relation which loses
much of its definiteness and significance when we merge the individual
in with a crowd. To some these seem fatal objections to any use of the
statistical formula and it is certainly true that they greatly limit
its value. But for the present at least the statistical statement of
certain facts of heredity is still useful in this bio-social field. We
may therefore use the statistical formulas of heredity as a kind of
temporary expedient, enabling us to make statements regarding
inheritance of certain characters in the group or class, pending the
time when we shall be able to give the facts a more precise and more
"final" expression in Mendelian formulas. Many human traits are indeed
already known to Mendelize. Most of these are, however, "abnormal"
traits or pathological conditions; we are still in the dark regarding
the actually Mendelian or non-Mendelian inheritance of most of man's
normal characteristics. We might enumerate the following Mendelizing
human characters--eye color, color blindness, hair color and
curliness, albinism (absence of pigment), brachydactylism (two joints
instead of three in fingers and toes), syndactylism (union of certain
fingers and toes), polydactylism (one or more additional fingers or
toes in each hand or foot), keratosis (unusually thick and horny
skin), haemophilia (lack of clotting property in the blood),
nightblindness (ability to see only in strong light--a retinal d