The multiracial idea has at least two versions. One is that multiracial people are of mixed blood or mixed genetic material. The other is that multiracial people are those with parents of different recognizable races. On examination, both of these positions present problems. The first is most blatantly tied to the racist science of the nineteenth century. It suggests that a person with both black and white ancestry is not adequately or accurately described as black (or white). This assertion rests on the discredited biological model. To sustain this position, one would have to show not only that bloodlines or genes are the appropriate foundations upon which to classify races, but also that bloodlines or genetic indicators are clear. Stated more strongly, this view implies that pure blood-lines—people who are uniracial—define the current racial categories.
Many of the proponents of new multiracial categories are politically left of center and reject the overt racism of nineteenth-century biology. Yet, a number of the assumptions adopted by these advocates end up relying, unwittingly, on the same discredited science, one of the main assertions of which was that race and racial categories were based on blood or genes. Supposed racial difference cannot be sustained on this basis, however; the majority of white Americans have African ancestry, the majority of blacks have white ancestry, and a substantial number of each have American Indian ancestry. Indeed, under the old hypodescent or “one drop” rule, which asserts that “white blood” is pure and therefore contaminated by even one drop of “black blood,” most white Americans are, in fact, African American.
john a. powell, Racing to Justice: Transforming Our Conceptions of Self and Other to Build an Inclusive Society, (Bloomington: Indiana University Press, 2012), 39.