Virtually all African Americans have some detectable European genetic admixture. Some carry few Euro DNA markers and some have many; but overall, about 17 percent of the collective African-American gene pool comes from Europe. What fraction of that 17 percent comes from European females? Can DNA tell? The short answer is “no”. Let’s see why not.
The question arises because it is fraught with ethno-political implication. Many Americans see Blacks and Whites as mutually hostile groups. About half of those who see “races” as adversarial blame Whites for the challenges facing the African-American community, challenges such as gaps in net worth, test-scores, and criminality. They attribute these challenges to White-on-Black racism past and present. The other half blames Blacks for their own plight, attributing it to an oppositional culture that idolizes victimization and disdains diligence. The former ideology sees the European genetic contribution as resulting from the rape of Black female slaves by White male slaveowners. If much of the European DNA in the African-American genetic enclave were to actually come from European females, it would weaken this ideology.
Unfortunately, how much of the European contribution to the African-American gene pool came from which sex may not be answerable via DNA studies. First, let’s look at autosomal markers. Then we shall consider paternal and maternal haplotype lineages.
Some autosomal DNA markers are more common in west Africa or in Europe, enabling laboratories to estimate your continent-of-ancestry admixture ratios. So you can say with some confidence that the mean subsaharan admixture among self-identified White Americans is under 5 percent and the mean Euro admixture among self-identified Black Americans is about 17 percent. See this for yourself in the following scatter diagram.
In the diagram, each point (representing one individual) is plotted vertically to depict Afro-European genetic admixture (100 percent European at the top) and horizontally into four groups representing ethnicity. The groups, from left to right, are: 147 self-identified White Americans, 264 self-identified Black Americans, 135 individuals from Zaire (formerly Congo), and 159 individuals from Nigeria.
But the autosomal markers that reveal each person’s ratio of European to African DNA (which determine each dot’s vertical position on the graph) are silent as to whether any particular marker came from a male ancestor or a female. The markers are sexless. There is no way to tell how much of the European contribution to the African-American gene pool came from which sex using autosomal ancestry-informative markers.
Matrilineal (mtDNA) and patrilineal (Y) haplotypes are also continent-unique, so they show whether your paternal lineage came from this continent or that, and the same for you maternal lineage. But this looks at only two out of the 1,000 ancestors that you had in the year 1800. The other 998 ancestors may have had completely different origin. Using haplotype ratios to estimate European genetic contribution yields at best an extremely crude and unpersuasive estimate. Nevertheless, crude or not, what do the lineage haplotypes tell us?
In February of 2006, Richard Willing of USA Today quoted Dr. Rick Kittles, then with Howard University, as saying that 30 percent of the clients of a DNA lab he helped found had Euro paternal lineage and “almost all” had Afro maternal lineage.[i] This is reasonable in light of three formal studies:
Parra (2001) examined 90 residents of Columbia SC and found that 2.6 percent had Euro maternal lineage and 24.1 percent had Euro paternal lineage.[ii](2) In other words, ten percent of the Euro lineages in this group were maternal.
Kayser (2003) examined samples of from 49 to 146 individuals and found that 9-to-15 percent of them had Euro maternal lineage and 28-to-34 percent had Euro paternal lineage.[iii] In other words, from 21 to 35 percent of the Euro lineages were maternal.
Parra (1998) examined 47 persons in Detroit and found that none had Euro maternal lineage and 30.33 percent had Euro paternal lineage. Hence, none of the Euro lineages in this group were maternal. The same study also looked at 100 people in Houston and found that 6.8 percent had Euro maternal lineage and 8.55 percent had Euro paternal lineage.[iv] In other words, 44 percent of this group’s Euro lineages were maternal.
Nevertheless, we cannot use those numbers to argue that no females contributed to the European component of Detroit’s African-American gene pool. Nor can we say that females contributed 44 percent of the European component of Houston’s African-American gene pool. This is because the paternal and maternal lineages are an infinitesimal fraction of the gene pool. As already mentioned, looking back to the year 1800, this method examines only two ancestors out of every thousand. And the farther back you look, the worse it gets. In 1607, when the first colony in British North America was founded, the lineage haplotypes examine just two out of every million ancestors—a hopelessly inadequate sample.
To grasp the unreliability of small sample size, examine the idea of confidence interval. How confident can you be in the results of a sampling? It depends on the size of the sample and the percentage of the phenomenon measured. The standard formula for computing the 95-percent confidence interval is as follows: likely error = 1.96*SQRT(r*(1-r)/(2*n)), where “r” is the measured percentage and “n” is the sample size. This formula yields an error span such that the chances are 95 out of a 100 that the real answer lies within its range.
With this in mind, what is the likely error span of determining your overall ancestry by looking at the haplotype lineages of just two of the ancestors you had in the year 1800? Measured sample results ranged from 2.6 percent (Parra 2001 Columbia) to 44 percent (Parra 1998 Houston). Applying the formula for a sample size of 2 yields a likely error of 15.6 percent for the former and 48.65 percent for the latter. In other words, the actual female contribution to European DNA among Columbia’s African Americans is most likely to fall between negligible and 18 percent. And the actual female contribution to European DNA among Houston’s African Americans is most likely to fall between negligible and 93 percent.
What can we conclude from that? Nothing much. To say that a fraction of anything might fall between negligible and 93 percent is to say nothing very persuasive.
There are other problems as well. In addition to the unsuitability of haplotype lineages for estimating genetic contribution, three unexamined assumptions lurk in the original question about rape by slaveowners.
It assumes that all mating between Euro males and Afro females was rape. In fact, although intermarriage was illegal in most states during the 50 Jim Crow years, it was not uncommon in the Deep South before 1850.[v] It was common before the color line was invented in 1691.[vi] And in Boston of the 1860s, it was very popular indeed.[vii]
It assumes that all slaveowners were White. In fact, many slaveowners in South Carolina and the Gulf Coast were biracial. In 1830, one out of every 25 Louisiana slaves,[viii] and one out of every hundred South Carolina slaves was owned by a biracial slave master.[ix] In 1839, 41 percent of the Coloured households of New Orleans owned at least one slave.[x]
It assumes that all slaves were Black. In fact, tens of thousands of biracial slaves were considered White, due to their appearance and descent from Europeans. The one-drop rule of invisible Blackness was unknown in the antebellum South.[xi]
In conclusion, it is not safe to put any number on the female share of the Euro contribution to the African-American gene pool. The most that you can say is that there exists an odd contrast between, on the one hand, the remarkable stability of the 65-35 male imbalance in legal B/W intermarriages over the past two centuries and, on the other hand, the fact that more African Americans carry European patrilineal haplotypes than carry European matrilineal haplotypes.
[ii] E.J. Parra and others, “Ancestral Proportions and Admixture Dynamics in Geographically Defined African Americans Living in South Carolina,” American Journal of Physical Anthropology 114 (2001): 18-29, table 3.
[iii] Manfred Kayser and others, “Y Chromosome STR Haplotypes and the Genetic Structure of U.S. Populations of African, European and Hispanic Ancestry,” Genome Research 13 (2003): 624-34, 631.
[iv] Esteban J. Parra and others, “Estimating African American Admixture Proportions by Use of Population-Specific Alleles,”American Journal of Human Genetics 63 (1998): 1839-51, table 6
[v] Frank W. Sweet, Legal History of the Color Line: The Rise and Triumph of the One-Drop Rule (Palm Coast FL: Backintyme, 2005), 260.
[vi] Ibid., 120.
[vii] Ibid., 251.
[viii] Ibid., 210.
[ix] Ibid., 189-190.
[x] Ibid., 210.
[xi] Ibid., Chapter 7, “The Antebellum South Rejects the One-Drop Rule”.
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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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