Race is an artificial concept designed to divide us. "Mixing" therefore is irrelevant.
The idea that humankind is a mammalian animal
species is unacceptable to some, thus the substitute designation, "race." But use of the word
race when referring to the taxonomic divisions within the human species becomes awkward when the concept of a human "race" arises. I must ask, do I belong to the Caucasian "race" or to the Human "race?" That simple equation summarily dismisses the validity and usefulness of the word
race with regard to divisions within the human species.
The simple reality is we humans are another species of animal and, as is it within other animal types, our species is divided into recognizable
sub-species, each manifesting its own uniquely distinguishable physical and behavioral characteristics.
Another commonly used term for
sub-species when referring to varying types within a "lesser" animal category is,
breed -- as in, "Another
breed of cat."