World, meet Naia. She's from the Yucatan Peninsula and is the oldest teenager you'll meet—about 13,000 years old—but her skeleton, skull, and DNA are intact. And, as the journal Science reports, she might provide us with some of the most concrete clues about how humans spread through the Americas.
You're familiar with the basics: Most scientists believe that somewhere between 26,000 and 18,000 years ago, hunter-gatherers crossed from northeast Asia to what's now Canada via a land bridge over the Bering Strait—known as Beringia—that was formed during the end of the most recent ice age. These humans spread through North America as the Pleistocene period came to a close.
Until now, scientists have had trouble connecting these early American settlers with subsequent Native Americans.
"Individuals from 9,000 or more years ago have morphological attributes—physical form and structure—distinctive from later Native American peoples," says Penn State archeologist and study co-author Douglas Kennett.
Enter Naia. "What we have here is the unique combination of an adolescent Paleoamerican skeleton with a Native American DNA haplotype," Kennett says. She's the missing link scientists have been searching for.
Divers found Naia's remains 130 feet below sea level in Hoyo Negro—Spanish for "black hole"—a water-filled pit the size of a professional basketball arena that's a part of the Sac Actun cave system on Mexico's Yucatan Peninsula. Scientists think Naia fell to her death while searching for water. Naia's remnants include most of the body's major bones, as well as an intact cranium and set of teeth, making her the most complete skeleton older than 12,000 years found in North America.
"The discoveries are extremely significant," says Pilar Luna, director of underwater archaeology at Mexico's National Institute of Anthropology and History. "Not only do they shed light on the origins of modern Americans, they clearly demonstrate the paleontological potential of the Yucatan Peninsula and the importance of conserving Mexico's unique heritage."
Naia's skeleton sheds light on the archaeological discrepancies between the earliest Americans and later Native Americans. "Modern Native Americans closely resemble people of China, Korea, and Japan, but the older American skeletons do not," says James Chatters, the study's lead author. "This has led to speculation that perhaps the first Americans and Native Americans came from different homelands, or migrated from Asia at different stages in their evolution."
This explanation could be flawed, however, according to the information Chatters's team extracted from Naia's mitochondrial DNA. Despite differences in craniofacial form—basically, the shape of the face and head—Naia had key genes in common with modern Native Americans. Rather than representing separate waves of migration from Eurasia, Paleoamericans and later Native Americans may have diverged from a single population after it crossed the Bering Strait.
The find is remarkable in its own right. Early Americans were highly nomadic and often cremated their dead, making their skeletons rare. And to discover Naia, scientists had to go on a fairly intrepid quest.
"Only technical divers can reach the bottom" of Hoyo Negro, Chatters says. "First they must climb down a 30-foot ladder in a nearby sinkhole, then they swim along 200 feet of tunnel to the pit rim before making a final 100-foot drop. The divers are the astronauts of this project; we scientists are their mission control."