Essays on the Color Line and the One-Drop Rule
by Frank W Sweet
September 6, 2008
olecular anthropologists are often asked if DNA markers can tell what “race” you are. The short answer is “no.” Mitochondrial DNA and Y haplogroups can tell from which continent your matrilineal and patrilineal ancestors came. And if you live in the Americas, autosomal mapping can tell what fraction of your ancestors came from Africa as slaves, what fraction came from Europe as colonists, and what fraction were Native Americans. But no DNA can tell your “race.”
Oddly, there is no contradiction between saying, “DNA cannot tell what race you are,” and saying, “DNA can tell where your ancestors came from.” To see why, consider one by one, mitochondrial DNA markers, Y chromosome markers, and autosomal markers.
Mitchondrial markers (mtDNA haplogroups) were discovered first and have been well studied. Everyone carries them. They descend through the maternal line, passing from mother to daughter. Men get theirs from their mothers but cannot pass them on. It reminds you of the clan system of the Native American tribes of the U.S. southeast, so mtDNA haplogroups are often called “clans.” The map shows prehistoric migrations of mothers who, over tens of thousands of years, carried the different mtDNA markers around the globe. Here are three examples: If your mtDNA is “H” then you descend from mammoth hunters who moved into Europe about 45 millennia ago. If your mtDNA is “B,” then you either descend from Native Americans or from their ancestors who remained in Asia about 22 millennia ago. If your mtDNA is L3, then you descend from east Africans.
Why does this not tell your “race”? Because ten generations ago (around the year 1800) you had a thousand ancestors, only one of whom (your mother’s, mother’s, mother’s …. mother) had that particular mtDNA. Your other 999 ancestors might all have had totally different ancestry. For example, my own mtDNA is “A” (Native American) and yet I am northern European in appearance and my family has no tradition of having any Native American ancestry at all. Hence, my mtDNA may be Native American, but my “race” in most people’s eyes is not.
Y chromsome markers (Y haplogroups) are more recent but are also well understood. Only males carry them. They descend through the paternal line, passing from father to son. It reminds you of the way surnames work in the Western world, so Y haplogroups are often used by genealogists pursuing surname ancestry. The map shows prehistoric migrations of fathers who, over the past tens of thousands of years, carried the different Y markers around the globe. If your Y is “R1b” then your ancestors arrived in Europe before the ice ages. If your Y is “Q,” then you either descend from Native Americans or from their ancestors who remained in Asia. If your Y is ExE3b, then you descend from west Africans.
Why does this not tell your “race”? Again, it is because only one man, out of your thousand ancestors from 1800, carried your Y haplogroup. The other 999 might have had totally different ancestry. For example, my own Y is R1* (from Cameroon in west Africa). And yet, as already mentioned, I have a northern European appearance and no credible family tradition of sub-Saharan ancestry. Hence, the “race” that most people see in me matches neither my mtDNA nor my Y.
Autosomal markers are different from mtDNA or Y haplogroups in that they measure the average continent-of-ancestry admixture in your entire DNA. The technique of autosomal mapping is more recent that either mtDNA or Y, and it is constantly being refined. It was originally devised for New World inhabitants, to measure what fraction of their ancestry came from each of the three demographic sources: Africa, Europe, and Native America. Autosomal mapping comes closer to identifying “race” than the other two. With a couple of exceptions, if your DNA admixture is overwhelmingly of European origin you are likely to be seen as White. And if it is of mostly African origin you will probably be considered Black.
The exceptions are because most of the population of the Americas is mixed to some extent. Virtually all African Americans have some European DNA admixture, about one-third of White Americans show detectable African admixture, and all Latin Americans are blended in proportions matching each region’s colonial population.
It often happens that an American who looks White and is seen as White actually has significant African DNA, and one who looks Black and is seen as Black has more than half European DNA. But most importantly, Hispanics are usually seen (and see themselves) as a third “race,” no matter what their DNA admixture shows.
In conclusion, neither mtDNA nor Y DNA can give any hint as to your “racial” membership in U.S. society. Autosomal DNA, if very lopsided to one continent or another, can suggest what you look like. But this does not work for those African Americans who choose to self-identify as Black despite having mostly European DNA, nor for White Americans unaware of their African DNA, nor for Hispanics, whose “racial” membership is determined by their culture, not by their genes.
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Frank W. Sweet is the author of Legal History of the Color Line (ISBN 9780939479238), an analysis of the nearly 300 appealed cases that determined Americans’ “racial” identity over the centuries. It is the most thorough study of the legal history of this topic yet published. He was accepted to Ph.D. candidacy in history with a minor in molecular anthropology at the University of Florida in 2003 and has completed all but his dissertation defense. He earned an M.A. in History from American Military University in 2001. He is also the author of several state park historical booklets and published historical essays. He was a member of the editorial board of the magazine Interracial Voice, and is a regular lecturer and panelist at historical and genealogical conferences. To send email, click here.
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