Genetically Speaking, Americans Really Are a Melting Pot of Diversity

In the outstanding science fiction novel, Lathe of Heaven, racism is solved by turning everyone’s skin color to the same light gray shade. It turns out that if we peel away the skin and pay attention to just the DNA, we might not need this magical solution. At the DNA level, people in the U.S. are more similar than their outward appearance might suggest.

That is the conclusion of a new study that used genetics to trace the ancestry of over 160,000 U.S. customers of 23andMe, a personal genomics company located in Mountain View, CA. The researchers found that most people who self-identified as European-American, Latino or African -American actually had DNA from the one or both of the other groups as well.

For example, people who self-identify as African-American had, on average, 24% European and 0.8% Native American ancestry. And people who self-identify as Latino had, on average, 6.2% African, 18% Native American and 65% European ancestry. Although the numbers were not as large for those who report themselves to be European-American, they still had on average around 0.2% African and 0.2% Native American heritage.

This doesn’t sound like a lot but if we extrapolate the results with European Americans to the U.S. population, it means that more than 6 million of these folks carry some African ancestry and over 5 million carry some Native American ancestry. We are all way more similar than our cultural labels might imply.

Of course, this doesn’t mean the labels are totally wrong. Another finding is that self-reporting lined up very well with the majority of people’s ancestry. For example, if you are mostly of African ancestry, odds are you have self-identified as such.

This last result does not change the fact that scientists can see in people’s DNA there has been a whole lot of mixing since Europeans and Africans came to the U.S. The U.S. really has been and still is a great melting pot.

Moms Not Dads

Scientists are able to tease out how much of a certain ancestry came from mom’s side of the family and how much from dad’s by comparing a person’s X chromosome with his or her other chromosomes. Remember, men have an X and a Y chromosome and women have two X’s.

By doing such an analysis, the scientists in this study concluded that the non-European ancestry tended to come more from mom’s side of the family. For example, European-Americans might have ten times as many female Native American ancestors as male ones. And African-Americans have four times as many.

There are a couple of possible explanations for this. One obvious one is exploitation. European men may have taken advantage of Native American women meaning that Native American ancestry would flow in from the maternal side of the family.

Another possible explanation has to do with there being more men than women on the frontier. In that situation, many of these men needed to turn to Native American women if they wanted a partner. We can see the results of their successful searches in modern DNA.

Digging Deeper

As companies like 23andMe and AncestryDNA amass more and more genomes in their database, they will be able to parse out everyone’s genomes more and more precisely. For example, in this study the researchers were able to see that the European part of the ancestry of Latinos tended to come from Spain and Portugal as we might expect.

They were also able to see that most of the mixing we see in the U.S. population happened over the last 500 years or so. They are not seeing some ancient mixing of African and European populations back in the Old World. No, they are seeing the results of everyone coming together in the New World.

There is lots more in this study too that you can peruse at your leisure (it is open access which means anyone can read it.) And these sorts of studies are just a start. I can’t wait to learn even more about our ancestry in the future.