Mar 19, 2021 - Research

DNA Reveals America’s Mixed-Race History

Hands Together

By Elliot Aguilar, Ph.D.*

For nearly all its existence, America has not only been a multiracial nation but a nation of mixed-race people.  

It’s a truth that is still rarely acknowledged, despite the evidence being easy to find. In the nineteenth century, famed antebellum diarist Mary Chesnut remarked on the mixed-race children in “everybody’s household,” while her contemporary, Fanny Kemble, made note of some enslaved children who bore striking resemblance to the white overseer of her husband’s plantation. From 1850 to 1920, the category of “Mulatto” appeared in multiple US Censuses. 

And there are many other examples from old newspaper advertisements for ‘bright mulatto’ runaway slaves to popular songs like The Yellow Rose of Texas, that celebrate the pivotal role of a mixed-race woman in the fight for Texan independence. Each is a testament to the truth of our country’s history. 


History is Personal

While the historical evidence can tell us that racial mixing happened, the advent of DNA testing from 23andMe and other companies has helped to bring to light America’s complicated racial history on an individual level. The science of population genetics now allows us to quantify—and appreciate—the scale of past mixing and its effect on the ancestry of contemporary Americans. 

My own family’s recent origins are in Central and South America where racial mixing is a more openly acknowledged fact of our history.  As a population biologist and a first-generation American, I am fascinated by how science can teach all Americans about our shared, intertwined history.

However, this history will come as no surprise to many African Americans, whose family lore often retains the memory of interracial unions, as well as the often traumatic circumstances that gave rise to them. Even then, science is illuminating and validating those family histories. As poet Caroline Randall Williams, the author of the acclaimed NYT op-ed, My Body is a Confederate Monument, has put it, “the science has made it easier to…claim and reframe” those family traditions. 

DNA Reveals

A 2015 study by 23andMe senior scientist and population geneticist Kasia Bryc and colleagues in the American Journal of Human Genetics, found that, on average, self-reported African Americans in a dataset of 23andMe customers, had about a quarter European ancestry.  Another study — this one by researchers at McGill University published two years later — showed a lower, but still very significant average level of European ancestry, about 17 percent. 

But both studies vividly illustrated not just the historical intermixing of people of African, European, and Native American ancestry, but also the regional differences of that mixing within the United States. Both studies also found a measurable number of self-identified European Americans had one percent or more African ancestry. Though far lower than the European contribution to African American genomes, these findings show that the direction of genes flowing between the groups was not exclusively one-way.

Another telling finding in both of these studies is that African Americans’ European ancestry was more often than not traceable to Northern Europe, the source of most early European settlers in colonial America. This finding points to intermixing from our nation’s earliest history.  It is also a testament to the centuries-long residence of African Americans in this country, stretching back long before the founding in 1776.

What that Means

The levels of European ancestry among African Americans can give us some idea of how often interracial unions — whether forced, coerced, or consensual — occurred. Using estimates from computer simulations of African American population history by anthropologist Jessica Gross based on genetic data and historical records, I calculated that an African American, randomly selected from any point in American history, had a nearly 17 percent chance of having at least one white grandparent.

A photo of the writer Elliot Aguilar.

Elliot Aguilar, Ph.D.

Put another way, if you could travel to any time between 1619 and today, and poll an African American person at random, there would be a one in six chance that he or she had at least one white grandparent. And this number is likely an underestimate as Gross’s models assumed that the European contribution per generation to the African American gene pool has been constant throughout American history. It was likely significantly higher during the time of slavery when some Americans held total dominion over the bodies of others.

Out of Many, One

The findings from these studies, and the results of individual genetic ancestry tests, undermine the long-held binary classifications of black and white.  This notion is the legacy of the so-called ‘one-drop rule,’ by which a person with a single known ancestor of African descent was considered black. This rule had its earliest origins in colonial-era legislation, but it wasn’t until the Jim Crow era that it became a fixed legal and social reality. The fact that race has been assigned according to laws and social definitions, as opposed to one’s actual ancestry, underlines the fact that race is a social construct and not a biological reality.

Ever since the 2000 US census allowed Americans to select multiple races, a lot of articles have been written about the increase of the country’s mixed-race population.  As the evidence above demonstrates, we have always been a nation with a sizable mixed-race population. What is new is that Americans can now claim their multiple ancestries without shame or discrimination. 

America has endured centuries of social division based on race, despite our shared genetic ties. The challenge of our future is to make our famous motto ‘E Pluribus Unum’— out of many one — a social reality, just as it has been a genetic reality all along.

*This post comes to us from a friend of 23andMe. Elliot is a scientific advisor for the Africa Center in New York City. He has an undergraduate degree in physics from Harvard and a Ph.D. in Evolutionary Biology from City University of New York. He did post-graduate work in mathematical biology at the University of Pennsylvania. Elliot’s day job is as a data scientist with an e-commerce company.

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