Black American's DNA at Center of Discovery

His Y chromosome may show that humanity's common male ancestor lived far earlier than previously thought.

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(The Root) -- An African-American family is at the center of a discovery that researchers say pushes back previous estimates of how deep the roots of the human family tree are. Analyzing DNA provided by the kin of a man from South Carolina, they estimate that the most recent common ancestor of all humans with a Y chromosome lived about 338,000 years ago in Africa. The fossil record goes back only about 200,000 years.

"We happened to match this individual's Y chromosome to 11 men that lived in western Cameroon," one of the researchers, University of Arizona professor Michael Hammer, told The Root. The Y chromosome had an extremely rare mutation, a characteristic that belied its ancient origins. "Africans today, as well as African Americans, carry more diversity in their genome than people from other continents," explained Hammer, a condition that fits the "out of Africa" model that says all humans descend from common African ancestors.

Further explanation is provided by a University of Arizona announcement: "Unlike the other human chromosomes, the majority of the Y chromosome does not exchange genetic material with other chromosomes, which makes it simpler to trace ancestral relationships among contemporary lineages. If two Y chromosomes carry the same mutation, it is because they share a common paternal ancestor at some point in the past. The more mutations that differ between two Y chromosomes, the farther back in time the common ancestor lived."

While African Americans have, on average, 20 percent non-African ancestry, testing ruled out any other region as a source of the chromosome, said Hammer. "There's no doubt about it that it's an African Y chromosome, it came over with the Atlantic slave trade in the last 500 years and it came from a part of Africa ... where we know the slave trade was very active -- probably from the interior of Africa. And it makes perfect sense that today it's surviving in this group called the Mbo from western Cameroon."

The report, "An African American Paternal Lineage Adds an Extremely Ancient Root to the Human Y Chromosome Phylogenetic Tree," came out of research that was done in conjunction with Family Tree DNA. The report thanks Family Tree DNA customer "Jacqueline Johnson and her male cousins, the descendants of Albert Perry," of South Carolina.

Read more about it on the University of Arizona website.

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