I was reading this morning's post about non-Africans as slaves. I could not find a good way to fit this into original question, but I wanted to ask. I have always been a fan of Twain, and I have wondered if the plot device was realistic. The plot involves a female slave who is 1/16th African and has a son by her master. The master's wife dies in childbirth at about the same time as the slave's child is born, and the slave ends up taking care of both children. She decides to switch them so that her son will grow up free. The book is a scathing criticism of slavery and prejudice.
I did a search but didn't find much to answer this question.
EDIT: I did some addition reading on the book. I was wrong about the ratio. The child was 1/32nd African. The mother was 1/16. The basic point still stands because the doctrine was that one drop of African blood was all that was needed to be a slave.
Hopefully this is helpful:
Since Negroes were presumed to be slaves and whites were presumed to be free, the southern states found it essential in cases of mixed ancestry to decide who were to be treated as Negroes and who as whites. No state adopted the principle that "a single drop of Negro blood" made a person legally a member of the "inferior race." Each state prescribed the proportion of Negro ancestry which excluded a person from the privileges enjoyed by white men.
In Virginia, according to the code of 1849, "Every person who has one-fourth part or more of negro blood shall be deemed a mulatto, and the word 'negro' ... shall be construed to mean mulatto as well as negro." In Alabama a "mulatto" was "a person of mixed blood, descended, on the part of the mother or father, from negro ancestors, to the third generation inclusive, though one ancestor of each generation may have been a white person." In other southern states also the term mulatto was defined loosely, so as to include as a rule persons with one Negro grandparent (quadroon) or great grandparent (octoroon); such persons were treated in law as Negroes. Only in South Carolina did the statutes refer to "negroes, mulattoes and persons of color" without defining these terms. The Court of Appeals, however, refused to infer from this that all persons "of any mixture of negro blood" were legally Negroes. Rather, it ruled that there must be a "visible mixture" and that much depended upon a person's "reputation" among his neighbors.
Any person with Negro ancestors too remote to cause him to be classified as a mulatto was by law a white man. While such a person could be held as a slave, the burden of proof was placed upon the putative master. In Kentucky, affirmed the Court of Appeals, "it has been well settled that ... having less than a fourth of African blood, is prima facie evidence of freedom." A Virginia jury having found that a woman suing for her freedom was white, it was incumbent upon her master to prove that she "was descended in the maternal line from a slave. Having not proved it, she and her children must be considered free."
Some slaveholders preferred to use "bright mulattoes" as domestics; a few paid premium prices for light-skinned females to be used as concubines or prostitutes. But most masters saw the inconvenience of owning slaves who were nearly white: the presumption of freedom in their favor, and the greater ease with which they could escape. One former bondsman, a "white man with blue eyes," recalled his master's repeated attempts to sell him, always unsuccessful. A Kentucky slave, "owing to his being almost white, and to the consequent facilities of escape," was adjudged to be worth only "half as much as other slaves of the ordinary color and capacities." Here was convincing evidence of the importance of racial visibility of keeping the Negro in bondage.
Source: The Peculiar Institution.