Prehistoric teenager's preserved skeleton offers clues to origins of Americas' first inhabitants

Divers explore the Hoyo Negro, or "black hole", where the 12,000 year old remains of a teenage girl were found. (Credit: Roberto Chavez-Arce/Science)

Friday, May 16, 2014, 1:47 PM - Exploring a dark, submerged cave along the Yucatan Peninsula in 2007, a team of divers discovered a treasure trove of ancient preserved bones, including the remains of a teenage girl who lived over 12,000 years ago. After years of study, these bones are now providing scientists with valuable clues about the origins of the people who first lived in North and South America.

Modern Native Americans and First Nation peoples are descended from people who migrated from Asia, residing in Beringia - the land mass between Siberia and Alaska - for some time before continuing on to settle in North America. However, they were preceded by the Paleoamericans (the Clovis people, for example), who arrived in the Americas towards the end of the Pleistocene epoch. The physical differences between Paleoamericans and modern Native Americans are quite striking, so it has always been a mystery as to how these different peoples may be related to one another. 

According to a study published in the journal Science on Thursday, the remains of a girl, perhaps 15 to 16 years old, found in the side-chamber of a dark, water-filled cave in Mexico, called Hoyo Negro (or "black hole") holds at least some of the keys to solving this mystery. The skull of this girl, which the scientists named 'Naia' - meaning 'water nymph' in Greek - has physical features common to the ancient Paleoamerican people. However, extracting one of the teeth from the skull revealed that she also shares mitochondrial DNA with current day Native Americans. 

Unlike the DNA that is found in the nucleus of a cell, which comes from both parents, mitochondrial DNA (or mtDNA) is passed down only from mother to child. Although analysing both nuclear DNA and mitochondrial DNA gives the best look at a person's complete genome, analysis of mtDNA allows scientists to trace direct lineage back along maternal lines. 

"This is the first time that we have genetic data from a skeleton that exhibits these distinctive skull and facial features," study co-author Deborah Bolnick, an anthropological geneticist at the University of Texas at Austin, told National Geographic.

In a UT press release, Bolnick added: "The Hoyo Negro girl was related to living Native Americans and has ancestry from the same Beringian population. This study therefore provides no support for the hypothesis that Paleoamericans migrated from Southeast Asia, Australia or Europe. Instead, it shows that Paleoamericans could have come from Beringia, like contemporary Native Americans, even though they exhibit some distinctive skull and facial features. The physical differences between Paleoamericans and Native Americans today are more likely due to changes that occurred in Beringia and the Americas over the last 9,000 years."

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Although fully submerged now, the cave were Naia was found would have been dry 12,000 years ago, since water levels were much lower in those times. The researchers speculate that she was very likely searching for water when she fell over 30 meters to her death at the bottom of the cave. The reason why her bones were so perfectly preserved, along with those of another 26 different animal species - including cave bears, giant ground sloths and even sabre-tooth tigers - was that the cave was submerged sometime between 10,000 and 4,000 years ago, and mineralization from the water strengthened the skeletons.

According to National Geographic, American forensic anthropologist and palaeontologist Jim Chatters, who led the research team, called Hoyo Negro "a mini La Brea Tar Pits, only without the tar and considerably better preservation."

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