ly upon the transmission of mental
characteristics. But our knowledge of the dependence of mind upon body
should prepare us to infer mental heredity from physical heredity. Such
studies as throw light on the question bear us out in making such an
inference.

The studies that have been more directly concerned with mental heredity
are those dealing with the resemblances of twins, studies of heredity in
royalty, studies of the inheritance of genius, and studies of the
transmission of mental defects and defects of sense organs. The results
of all these studies indicate the inheritance of mental characteristics
in the same way that physical characteristics are transmitted. Not only
are human mental characteristics transmitted from parent to offspring,
but they seem to be transmitted in Mendelian fashion.

Feeble-mindedness, for example, seems to be a Mendelian character and
recessive. From the studies that have been made, it seems that two
congenitally feeble-minded parents will have only feeble-minded
children. Feeble-mindedness acts in heredity as does the white corn in
the example given above. If one parent only is feeble-minded, the other
being normal, all of the children will be normal, just as all of the
corn, in the first generation after the crossing, was yellow. But these
children whose parents are the one normal and the other feeble-minded,
while themselves normal, transmit feeble-mindedness in equal ratio with
normality. It works out as follows: If a feeble-minded person marry a
person of sound mind and sound stock, the children will all be of sound,
normal mind. If these children take as husbands and wives men and women
who had for parents one normal and one feeble-minded person, their
children will be one fourth feeble-minded and three fourths of them
normal.

To summarize the various conditions: If a feeble-minded person marry a
feeble-minded person, all the children will be feeble-minded. If a
feeble-minded person marry a sound, normal person (pure stock), all the
children will be normal. If the children, in the last case, marry others
like themselves as to origin, one fourth of their offspring will be
feeble-minded. If such hybrid children marry feeble-minded persons, one
half of the offspring will be feeble-minded. It is rash to prophesy, but
future studies of heredity may show that Mendelism, or some
modification of the principle, always holds true of mind as well as of
body.

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