rious kinds may be indicated, and
samples given, even though this involves the necessity of repeating some
things we have said in earlier chapters. The reader will then be able to
form his own opinion as to whether the geneticists' proofs or the mere
assurances of those who have not studied the subject are the more
weighty.

1. _The analogy from breeding experiments._ Tame rats, for instance, are
very docile; their offspring can be handled without a bit of trouble.
The wild rat, on the other hand, is not at all docile.

W. E. Castle, of Harvard University, writes:[32] "We have repeatedly
mated tame female rats with wild males, the mothers being removed to
isolated cages before the birth of the young. These young which had
never seen or been near their father were very wild in disposition in
every case. The observations of Yerkes on such rats raised by us
indicates that their wildness was not quite as extreme as that of the
pure wild rat but closely approached it."

Who can suggest any plausible explanation of their conduct, save that
they inherited a certain temperament from their sire? Yet the
inheritance of temperament is one of the things which certain
psychologists most "view with alarm." If it is proved in other animals,
can it be considered wholly impossible in man?

2. _The segregation of mental traits._ When an insane, or epileptic, or
feeble-minded person mates with a normal individual, in whose family no
taint is found, the offspring (generally speaking) will be mentally
sound, even though one parent is not. On the other hand, if two people
from tainted stocks marry, although neither one may be personally
defective, part of their offspring will be affected.

This production of sound children from an unsound parent, in the first
case, and unsound children from two apparently sound parents in the
second case, is exactly the opposite of what one would expect if the
child gets his unsoundness merely by imitation or "contagion." The
difference can not reasonably be explained by any difference in
environment or external stimuli. Heredity offers a satisfactory
explanation, for some forms of feeble-mindedness and epilepsy, and some
of the diseases known as insanity, behave as recessives and segregate in
just the way mentioned. There are abundant analogies in the inheritance
of other traits in man, lower animals and plants, that behave in exactly
the same manner.

If mental defects are inherited, then it is wort