One problem with these assignments is admixture. Many people have a highly varied ancestry. For example, in the United States, colonial and early federal history were periods of numerous interracial relationships, both outside and inside slavery. This has resulted in a majority of people who identify as African American having some European ancestors. Similarly, many people who identify as white have some African ancestors. In a survey in a northeastern U.S. university of college students who identified as "white", about 30% were estimated to have up to 10% African ancestry.
When were periods of numerous interracial relationships in the U.S.?
colonial and early federal history