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by the selection of mere external differences, and that they have not been long exposed to uniform conditions of life. Nor should it be forgotten that long-continued domestication apparently tends to eliminate sterility, and is therefore little likely to induce this same quality. Independently of the question of fertility, in all other respects there is the closest general resemblance between hybrids and mongrels, in their variability, in their power of absorbing each other by repeated crosses, and in their inheritance of characters from both parent-forms. Finally, then, although we are profoundly ignorant of the precise cause of the sterility of first crosses and of hybrids, the facts given in this chapter do not seem to me opposed to the belief that varieties and species are not fundamentally different.
by the selection of mere external differences, and not of differences in the reproductive system. In all other respects, excluding fertility, there is a close general resemblance between hybrids and mongrels. Finally, then, the facts briefly given in this chapter do not seem to me opposed to, but even rather to support the view, that there is no fundamental distinction between species and varieties.