Domestic dogs can become, and again and again do become, wild, even consorting with wolves, interbreeding with them, assuming their gregarious habits, and changing the characteristic bark into a dismal wolf-like howl.

Between some of the non-human species (horses and camels, for instance) instinctive mutual hatred, as distinguished from fear, does seem to exist, but nowhere, as far as I know, is it found between varieties so nearly related to each other and so readily interbreeding as the various human races.

The teeth of these two kinds of bears show a marked and uniform difference, proving conclusively that there is no interbreeding between the species.

For the moment we shrink from the interbreeding of races, but we do so in spite of some conspicuous examples of successful interbreeding in the past, and largely because of our complete ignorance of the conditions on which success depends.

For the moment we shrink from the interbreeding of races, but we do so in spite of some conspicuous examples of successful interbreeding in the past, and largely because of our complete ignorance of the conditions on which success depends.