Or referred to as the one-drop rule states that those who had at least one ancestor of African descent were identified as Black. This developed by “scientific” communities developed this idea and "determined” that Blacks were inherently and genetically inferior to whites. They stated that any mixing between “pure” white blood and “tainted” Black blood would contaminant and dilute the purity of whiteness. This lead to exclusive boundaries of white identity and it was incorporated into American political institutions, (including the courts, state legislatures, U.S. Congress, and other bureaucratic institutions.) These institutions created and maintained laws based on racial pseudoscience for most of America’s history.
Significance: This continues to shapes racial boundaries. Some Americans and new immigrants to the United States have challenged the notion of the “one drop,” because it requires one to identify as black based on their ancestors and it lumps all black people together, failing to capture the social heritage of individuals whose cultures and identities were not formed in the American context of slavery, discrimination, and segregation.