"'Two peoples never meet,' the American anthropologist Melville J. Herskovits once wrote, 'but they mingle their blood.' Mingling, however, is only one of a range of options when two diverse human populations meet. The minority group may remain distinct for breeding purposes but become integrated into the majority group in all or some other respects (language, religious belief, dress, lifestyle). Alternatively, interbreeding can go on, at least for a time, but one or both of the two groups may nevertheless preserve or even adopt distinct cultural or ethnic identities. Here is an important distinction. Whereas 'race' is a matter of inherited physical characteristics, transmitted from parents to children in DNA, 'ethnicity' is a combination of language, custom and ritual, inculcated in the home, the school and the temple. It is perfectly possible for a genetically intermixed population to split into two or more biologically indistinguishable but culturally differentiated ethnic groups. The process may be voluntary, but it may also be based on coercion - notably where major changes of religious belief are concerned. One or both groups may even opt for residential and other forms of segregation; the majority may insist that the minority lives in a clearly delineated space, or the minority may choose to do so for its own reasons. The two groups may cordially ignore one another, or there may be friction, perhaps leading to civil strife or one-sided massacres. The groups may fight one another or one group may submit to expulsion by the other. Genocide is the extreme case, in which one group attempts to annihilate the other."