An accidental underwater discovery made by a group of recreational scuba divers in a remote cave in Mexico’s Yucatán Peninsula has yielded the oldest intact human skeleton ever found in the Americas, a find which holds important clues in the debate about the origins of the first Americans, according to a new research paper published Thursday in the journal Science. Divers discovered the nearly complete skeleton of a teenage girl from the Late Pleistocene age in an underwater cave, Hoyo Negro, just outside Tulum. An international team of scientists and divers has determined that Naia, as she has been nicknamed, is 12,000 to 13,000 years old. What’s more, Naia’s skull and facial characteristics are different from those of modern Native Americans and has characteristics more in common with people from Africa and Australia. But after a rigorous genetic analysis of the enamel on her teeth and the minerals found in her bones, the scientists discovered that although she was found in Mexico, Naia shares certain genetic characteristics with the earliest hunter-gatherers thought to have crossed the Bering land bridge from northeastern Asia into the Americas 18,000 to 26,000 years ago. “Thus Naia, one of the earliest occupants of the Americas yet encountered, suggests that the paleo-Americans [the earliest Americans] do not represent an early migration from a part of the world different than that of Native Americans,” archaeologist James Chatters, the lead author of the study, said in a release. “Rather, paleo-Americans and Native Americans descended from the same Beringian source.” Because modern Native Americans have different genetic characteristics from those Beringian ancestors, some scientists think multiple groups migrated from Eurasia to the Americas, Chatters told Al Jazeera. But others insisted it was one group that spread southward and that the differences between them and modern Native Americans evolved later. Naia marks the first time that scientists have been able to match an early American skeleton with DNA linked to the Beringian hunter-gatherers, supporting the single-migration theory and suggesting they may have spread much farther across the Americas than previously thought. “It’s good, strong evidence,” Chatters said, but with the caveat that it’s just one skeleton. “It’s still a powerful step in that direction.”

A team effort

That Naia was found submerged in a cave filled with chemically neutral water that was sealed off from oxygen for at least 8,000 years helped conserve the bones, Chatters said. The scientists say that people and animals likely fell into this cave and became trapped and that about 10,000 years ago the climate began to warm and glaciers melted, filling the cave with water. Chatters said finding a nearly complete skeleton more than 12,000 years old is extremely rare. Other specimens he has examined through the years, such as the Kennewick man, discovered in the state of Washington in 1996, were not more than 10,000 years old, and they’re often just fragments, making it difficult to analyze their DNA. “Part of it was a political reason,” he said, referring an eight-year legal battle he fought with Native American tribes in Washington, who as part of their burial rituals wanted to rebury the Kennewick man. “Part of it’s the practicality that we didn’t have the methods to extract the DNA effectively from poorly preserved material,” he said, “and part of it is the extreme rarity of the skeletons.” “But now,” he said, “we are getting the ability to get nuclear genetic material in small quantities. We’ve got the computers doing the job for us. And all of a sudden, the field is just moving at 100 miles per hour.” So far, they’ve used photography, videography, 3-D modeling and minimal sampling to study the cave, starting with the human skeleton. Determining Naia’s age, Chatter said, was a group effort. Three research institutions did radiocarbon dating of the enamel from her teeth, and he and other scientists decided that uranium-thorium dating could be used to analyze the mineral deposits in her bones. In addition to that, they analyzed the water levels and considered the types of animals also found in the cave and were able to determine that she was 12,000 to 13,000 years old.

‘Discovery of our lifetimes’