Ancient Skeleton In Mexico Sheds Light On Americas Settlement

May 16, 2014
Originally published on August 28, 2014 1:40 pm

The nearly complete skeleton of a teenage girl who died some 12,000 to 13,000 years ago in a cave in the Yucatan Peninsula, has yielded DNA clues linking her to Native Americans living today.

The connection bolsters the prevailing theory that the sole route of human migration into North America took place over a Siberia-Alaska land bridge known as Beringia, starting 15,000 to 20,000 years ago.

NPR Science Correspondent Joe Palca says the skeleton of the girl, who died at age 15 to 16, was discovered in 2007 amid a complex of flooded caverns in Mexico known as Hoyo Negro, or "Black Hole."

Scientific American says, "She lies in a collapsed chamber together with the remains of 26 other large mammals, including a saber-toothed tiger, 600 meters from the nearest sinkhole. Most of the mammals became extinct around 13,000 years ago."

"It was impossible to safely recover the body from the cave location, so the research team dove to the cave and made bone measurements in situ. They placed Naia's skull on a rotating tripod, and set a camera on a second tripod next to it. Turning the skull slowly, they snapped pictures every 20 degrees. Later the team used the photographs to reconstruct a three-dimensional image."

James Chatters of Applied Paleoscience in Bothell, Wash., led the study and published the results in the journal Science.

Chatters says the skeleton, known as Naia after the water nymphs of Greek mythology, doesn't look much like modern Native Americans who have narrower faces, different teeth and a different palate.

"I could tell from the shape of the palette and some other aspects of the skull that she was similar to some of the other earliest Americans I'd seen," Chatters says. "So many differences that it seemed they must come from somewhere else."

But the DNA told a different story.

The University of Texas at Austin's Deborah Bolnick, an expert in extracting ancient DNA from fossilized teeth and bones got a sample of Naia's mitochondrial DNA, which is inherited exclusively from the mother.

Bolnick found a lineage known as D-1 that's found in Northeast Asia (including Siberia) and also very common in Native Americans.

What that suggests, Bolnick says, is that the girl is indeed descended from the first humans to cross the land bridge and not some later migration from somewhere else.

That means the physical differences between the first "Paleoamericans" and Native Americans of today are the result of evolution since the great migration out of Asia.

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One day, about 12,000 years ago, a girl was walking around in cave. This was on the Yucatan Peninsula in what we now know as Mexico. She fell into a deep pit, fractured several bones in her pelvis and died. Today, that cave is underwater but the girl's remains were found by divers. And now her DNA is helping scientists understand where the earliest Americans came from.

NPR science correspondent Joe Palca has the story.

JOE PALCA, BYLINE: A few years ago, archeologist and paleontologist James Chatters was at a scientific meeting when a colleague showed him a picture. It was taken by divers at the bottom of cave on the Yucatan Peninsula. The cave had flooded sometime in the last 12,000 years or so. In the picture there was a human skull.

JAMES CHATTERS: I could tell from the shape of the palette and some other aspects of the skull that she was similar to the other earliest Americans I'd seen.

PALCA: Along with a variety of colleagues from around the United States and Mexico, Chatters began an intensive investigation of the girl's skull and other bones. The first fruits of their labors appear in today's edition of the journal Science. They estimate the girl was 15 or 16 years old when she died and that she'd been dead for between 12 and 13,000 years.

But it's the girl's DNA that proved most intriguing. That's because there's been a big debate about whether modern Native Americans are related to the very first people who came to the Americas, like the young girl, or to people who came in a more recent migration. The reason there's a question about that is the first people who came to the Americas, like this young girl, don't look very much like modern Native Americans. Chatters says modern Native Americans have narrower faces, different teeth, different palette

CHATTERS: Oh, so many differences, that it seem like they must come from somewhere else.

PALCA: But girl's DNA tells a different story. Deborah Bolnick is from the University of Texas Austin. She's an expert in extracting ancient DNA from fossilized teeth and bones.

DEBORAH BOLNICK: A lot of my work is focused on trying to using genetics to help us understand more recent population history in the Americas.

PALCA: Bolnick studied the girl's mitochondrial DNA, a type of DNA you inherit exclusively from your mother. What she found was the girl had a mitochondrial DNA inheritance pattern that's quite common in Native Americans alive today. So despite the differences in appearance Bolnick says the new results suggests that modern Native Americans are, indeed, descended from the very first humans to reach the Americas and not some more recent migration.

By studying more of the girl's DNA, scientists are hoping to get clues about which genes were responsible for the changes in appearance.

Joe Palca, NPR News, Washington. Transcript provided by NPR, Copyright NPR.