part low. It seems like an extraordinary conclusion that high
ability is inherited as though due to the absence of a determiner in the
same way as feeble-mindedness and insanity are inherited. We are
reminded of the poet: "Great wits to madness sure are near allied."
Evidence for the relationship is given by pedigrees of men of genius
that often show the combination of ability and insanity. May it not be
that just that lack of control that permits "flights of the imagination"
is related to the flightiness characteristic of those with mental
weakness or defect?

These studies of inheritance of mental defect inevitably raise the
question how to eliminate the mentally defective. This is a matter of
great importance because, on the one hand, it is now coming to be
recognized that mental defect is at the bottom of most of our social
problems. Extreme alcoholism is usually a consequence of a mental
make-up in which self-control of the appetite for liquor is lacking.
Pauperism is a consequence of mental defects that make the pauper
incapable of holding his own in the world's competition. Sex immorality
in either sex is commonly due to a certain inability to appreciate
consequences, to visualize the inevitableness of cause and effect,
combined sometimes with a sex-hyperesthesia and lack of self-control.
Criminality in its worst forms is similarly due to a lack of
appreciation of or receptivity to moral ideas.

If we seek to know what is the origin of these defects, we must admit
that it is very ancient. They are probably derived from our ape-like
ancestors, in which they were _normal_ traits. There occurs in man a
strain that has not yet acquired those traits of inhibition that
characterized the more highly developed civilized persons. The evidence
for this is that, as far back as we go, we still trace back the black
thread of defective heredity.

We have now to answer the question as to the eugenical application of
the laws of inheritance of defects. First, it may be pointed out that
traits due to the absence of a determiner are characterized by their
usual sparseness in the pedigree, especially when the parents are
normal; by the fact that they frequently appear where cousin marriages
abound, because cousins tend to carry the same defects in their germ
plasm, though normal themselves; by the fact that two affected parents
have exclusively normal children, while two normal parents who belong to
the same strain, or who both