But this is not
the real evidence which genetics offers. The evidence is of numerous
kinds, and several lines might be destroyed without impairing the
validity of the remainder. It is impossible to review the whole body of
evidence here, but some of the various 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.
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