The phenomenon known as "passing as white" is difficult to explain in other countries or to foreign students. Typical questions are: "Shouldn't Americans say that a person who is passing as white is white, or nearly all white, and has previously been passing as black?" or "To be consistent, shouldn't you say that someone who is one-eighth white is passing as black?" ... A person who is one-fourth or less American Indian or Korean or Filipino is not regarded as passing if he or she intermarries with and joins fully the life of the dominant community, so the minority ancestry need not be hidden. ... It is often suggested that the key reason for this is that the physical differences between these other groups and whites are less pronounced than the physical differences between African blacks and whites, and therefore are less threatening to whites. ... [W]hen ancestry in one of these racial minority groups does not exceed one-fourth, a person is not defined solely as a member of that group.

A person is not a member of a racial minority if ancetry does not what?