when both parents lack stoutness (are slender), all children tend
to lack it.

We may now consider briefly the inheritance of certain pathological or
abnormal states, to see in how far the foregoing principles hold for
them also. Sometimes the abnormal condition is positive, due to a new
trait; but sometimes, on the contrary, the normal condition is the
positive one and the trait is due to a defect.

Deaf-mutism is due to a defect; but the nature of the defect is
different in different cases. Deaf-mutism is so varied that frequently
two unrelated deaf mutes may have hearing children. But if the deaf-mute
parents are cousins, the chances that the deafness is due to the _same_
unit defect are increased and all of the children will probably be deaf.

From the studies of Dr. Goddard and others, it appears that when both
parents are feeble-minded all of the children will be so likewise; this
conclusion has been tested again and again. But if _one_ of the parents
be normal and of normal ancestry, all of the children may be normal;
whereas, if the normal person have defective germ cells, half of his
progeny by a feeble-minded woman will be defective.

Many criminals, especially those who offend against the person, are
feeble-minded, as is shown by the way they occur in fraternities with
feeble-mindedness, or have feeble-minded parents. The test of the mental
condition of relatives is one that may well be applied by judges in
deciding upon the responsibility of an aggressor.

Not only the condition of imperfect mental development, but also that of
inability to withstand stress upon the nervous system, may be inherited.
From the studies of Dr. Rosanoff and his collaborators, it appears that
if both parents be subject to manic depressive insanity or to dementia
precox, all children will be neuropathic also; that if one parent be
affected and come from a weak strain, half of the children are liable to
go insane; and that nervous breakdowns of these types never occur if
both parents be of sound stock.

Finally, a study of families with special abilities reveals a method of
inheritance quite like that of nervous defect. If both parents be color
artists or have a high grade of vocal ability or are litterateurs of
high grade, then all of their children tend to be of high grade also. If
one parent has high ability, while the other has low ability but has
ancestry with high ability, part of the children will have high ability
and