But in all these cases there has been rigid selection by
which the weak or the infertile have been eliminated, and with such
selection there is no doubt that the ill effects of close interbreeding
can be prevented for a long time; but this by no means proves that no
ill effects are produced. Mr. Huth himself quotes M. Allie, M. Aube,
Stephens, Giblett, Sir John Sebright, Youatt, Druce, Lord Weston, and
other eminent breeders, as finding from experience that close
interbreeding _does_ produce bad effects; and it cannot be supposed that
there would be such a consensus of opinion on this point if the evil
were altogether imaginary. Mr. Huth argues, that the evil results which
do occur do not depend on the close interbreeding itself, but on the
tendency it has to perpetuate any constitutional weakness or other
hereditary taints; and he attempts to prove this by the argument that
"if crosses act by virtue of being a cross, and not by virtue of
removing an hereditary taint, then the greater the difference between
the two animals crossed the more beneficial will that act be.
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