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

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.

Until a few years ago the two were interbred, but disputes as to their essential differences led the Kennel Club to intervene and the types have since been kept rigidly apart, the smart little bat-eared Bulldogs of France receiving recognition under the breed name of Bouledogues Francais.

The two varieties are much interbred, and several litters in consequence include representatives of both; and not only this, but it is quite a frequent occurrence to get a smooth puppy from wire-hair parents, although for some generations neither of the parents may have had any smooth cross in their pedigrees.

The different varieties of Toy Spaniels have been so much interbred that a litter has been reputed to contain the four kinds, but this would be of very rare occurrence.

The Willoughby Pug was duller in colour than the Morrison, which was of a brighter, ruddier hue, but the two varieties have since been so much interbred that they are now undistinguishable, and the fact that they were ever familiarly recognised as either Willoughbys or Morrisons is almost entirely forgotten.

Every age is an age of transition, of minglings, of the breaking up of old, narrow cultures, and the breaking down of barriers, of spiritual and often of actual interbreeding.

The general fact of variability;the patent fact, that all species vary more or less; that domesticated plants and animals, being in conditions favorable to the production and preservation of varieties, are apt to vary widely; and that by interbreeding, any variety may be fixed into a race, that is, into a variety which comes true from seed.

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.

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.

The big red wolf of the South American plains is not closely related to the northern wolves; and it was to me unexpected to find it interbreeding with ordinary domestic dogs.