Exactly How 'Black' Is Black America?

100 Amazing Facts About the Negro: Find out the percentage of African ancestry in black Americans.

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Are You Mixed? Admixture Tells Us 

What exactly is admixture? I asked a few prominent geneticists to define it for this article. Dr. George Church, a professor at the Harvard Medical School and a pioneer in the mapping of the human genome, defines it this way: "Genetic admixture is the breeding between two or more previously isolated populations." 

Dr. Joanna Mountain, the senior director of research for 23andme.com, defines admixture this way: "Every one of us has the story of our ancestry hidden in our DNA. Any section of DNA -- say, one piece of chromosome 3 -- can be linked with people who lived in a particular geographic location thousands of years ago. By adding up the fractions of DNA from each location, we can determine the percentage of a person's ancestors who lived in each location."

She also stresses the fact that it is very important to use regional or geographic categories in genetic ancestry-tracing, rather than the standard four or five so-called "racial" divisions that have been employed in the West since the 18th century, which is one reason why her company now uses 17 categories of "Ancestry Composition," and will soon expand that number to 24. All of the other companies mentioned in this article now use between nine and 20 such categories. However, for convenience sake, I'll be presenting the admixture results in three large regional summaries: sub-Saharan African, European and Native American.

Dr. Nathan Pearson, the principal genome scientist at Ingenuity, tells us that "interbreeding has occurred throughout history, and notably leaves telltale traces in our genomes that hint strongly at who came together, and when." In conclusion, he says, "the ingredients in your genome track which regional populations mingle in your family tree, and in what proportions," revealing "the mix of recent continental origins among your ancestors." Think of admixture, he says, "as gene mingling."

So what do the collective genomes of the African-American community reveal about the mix of ancestral populations -- of mingled genes -- that we have inherited? Here are the surprising results from five DNA companies.

Exactly How "Black" Are Black Americans? 

* According to Ancestry.com, the average African American is 65 percent sub-Saharan African, 29 percent European and 2 percent Native American.

* According to 23andme.com, the average African American is 75 percent sub-Saharan African, 22 percent European and only 0.6 percent Native American. 

* According to Family Tree DNA.com, the average African American is 72.95 percent sub-Saharan African, 22.83 percent European and 1.7 percent Native American.

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