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Native Americans’ Siberian ancestry linked through DNA of 12,000-year-old skeleton

DNA of 12,000-year-old skeleton is critical proof in scientific battle

Reuters, AFP-JIJI, AP

The skeleton of a teenage girl who fell down a hole and died more than 12,000 years ago on Mexico’s Yucatan Peninsula shows that migrants from present-day Russia were among the forebears of many of today’s Native Americans, researchers said Thursday.

The girl was among the descendents of Ice Age humans who first crossed into the Americas over a land bridge that formerly linked Siberia and Alaska. Genetic tests on her remains show that this community, not later arrivals, gave rise to 11 percent or more of modern Native Americans.

The girl’s skeleton, dubbed “Naia” by the divers who recovered it, likely lay untouched until its discovery in 2007, the flesh gone but the bones unusually well preserved. It was lying alongside the remains of more than two dozen beasts, including saber-toothed tigers, cave bears, giant ground sloths and a relative of the modern-day elephant called a gomphothere.

Scientists believe the pit was dry when the girl fell into it and filled with water when Ice Age glaciers melted, about 10,000 years ago.

The girl’s cranium was intact. She was petite and slightly built, about 4 feet, 10 inches (147 cm) tall, and researchers believe she was 15 or 16 years old when she died. Her pelvis appears to have broken on impact, suggesting she died quickly, said James Chatters, one of the leaders of the study and an archaeologist and forensic anthropologist.

Measurements of her skull indicate a small, narrow face, wide-set eyes, a prominent forehead and teeth that jutted outward. Her appearance was “about the opposite of what Native Americans look like,” Chatters, who is also owner of the Bothell, Washington-based consultancy Applied Paleoscience, told reporters.

But there was a hidden similarity. Genetic tests on a rib bone and one of her teeth found a genetic marker in her maternally inherited lineage that is the same as that found in many of today’s Native Americans.

The study, led by the Mexican government’s National Institute of Anthropology and History and supported by the National Geographic Society, was published by the journal Science.

It is unclear exactly how the girl died, but she may have ventured into a cave to seek drinking water and plunged to her death into what Chatters called an “inescapable trap” 30 meters deep. The bell-shaped pit is dubbed Hoyo Negro (black hole) in Spanish.

Chatters said the chamber, more than 40 meters below sea level, was “a time capsule of the environment and human life” at the end of the Ice Age.

Naia is the sixth-oldest human found in the Americas, he said.

One of the divers, Alberto Nava, recalled the moment the skeleton was spotted, its skull resting atop a small ledge. “It was a small cranium laying upside down with a perfect set of teeth and dark eye sockets looking back at us,” Nava said.

Tests determined she lived between 12,000 and 13,000 years ago.

Scientists long have debated the origins of the first people of the Americas. Many think these hunter-gatherers crossed a former land bridge called Beringia, now submerged, that connected Asia and Alaska across the Bering Strait, between 18,000 and 26,000 years ago, and subsequently pushed into North and South America perhaps 17,000 years ago.

But the most ancient New World human remains have confused scientists because, like Naia, they have narrower skulls and other features not found in modern Native Americans. This led to speculation that these earliest New World residents might represent an earlier migration from a different part of the world than the true ancestors of Native Americans.

“What this study is presenting for the first time is the evidence that paleo-Americans with those distinctive features can also be directly tied to the same Beringian source population as contemporary Native Americans,” said Deborah Bolnick, an assistant professor at the University of Texas at Austin.

That goes against theories held by some experts that Native Americans were descendants of people who migrated later, perhaps from Europe, southeast Asia or Australia.

Naia provides a crucial link. Her mitochondrial DNA — specifically, mtDNA haplogroup D1 — which is passed down from mother to child and was recovered from one of her molars, contains a distinctive marker found in today’s native peoples, especially those in Chile and Argentina. It is a signature found only in Native Americans and is thought to have arisen among people living in Beringia, the researchers said.

That suggests that the early Americans and contemporary native populations both came from the same ancestral roots in Beringia — not different places, the researchers concluded. The anatomical differences apparently reflect evolution over time in Beringia or the Americas, they said.

“Haplogroup D1 is derived from an Asian lineage but is found only in the Americas today,” explained Bolnick of the University of Texas. “Approximately 11 percent of Native Americans exhibit this genetic lineage. It’s found throughout North, Central and South America and this D1 lineage is especially common in some South American populations.”

Future research will aim to sequence Naia’s nuclear DNA, which should reveal more details about her ancestry.

Dennis O’Rourke, an expert in ancient DNA at the University of Utah who didn’t participate in the work, said the finding is the first to show a genetic link to Beringia in an individual who clearly had the anatomical signs of a very early American. He said he considered the notion of multiple migrations from different places to be “quite unlikely.”

Chatters, the forensic anthropologist, who is best known for his work on Kennewick Man, a 9,800-year-old skull and skeletal remains found in Washington state, said, “I used to be one of those advocates of multiple immigration events.”

He initially believed that Kennewick Man descended from European settlers because his skull did not resemble that of a typical Native American’s. But although the possibility cannot be excluded at this point that other early peoples, known as paleo-Americans, came from places other than Beringia, Chatters said subsequent research, including the DNA analysis on Naia, does not support that theory.

Last February, other researchers reported that DNA from a baby buried in Montana more than 12,000 years ago showed a close genetic relationship to modern-day native peoples, especially those in Central and South America. An author of that study, Mike Waters of Texas A&M University, said the findings based on Naia fit with the remains in Montana.

There are so few such early skeletons from the Americas, he said, that “every single one of them is important.”