May 16, 2014
Most Complete Ancient Skeleton From New World Sheds New Light On Human Migration
Lawrence LeBlond for redOrbit.com - Your Universe Online
An international team of scientists have uncovered the most genetically complete human skeleton from the New World yet, dating back more than 12,000 years. The skeleton, discovered in an underwater cave system in the Yucatan Peninsula, is that of a 12-year-old girl who fell into the once dry open pit, breaking her pelvis and likely killing her instantly from the 190-foot fall, according to researchers.
Publishing the study in the journal Science, the team, led by archaeologist James Chatters, owner of the forensics firm Applied Paleoscience and a Research Associate in the Office of Graduate Studies, Research, and Continuing Education at Central Washington University, said this is the single biggest piece of the puzzle to date, as the skeleton contains both the craniofacial features of ancient Paleoamericans and the mitochondrial DNA possessed by latter-day Native Americans.
AN ANCIENT PUZZLE
Anthropologists have long puzzled over why Native Americans do not look more like their ancient ancestors, who migrated into the Americas during the Pleistocene, the epoch that encompassed the last Ice Age, which ended about 12,000 years ago.
“The ancient skulls are larger, their faces are narrower and more forward-projecting, and they more closely resemble native peoples of Africa, Australia, and the southern Pacific Rim than they do their supposed American descendants,” wrote Glen Hodges of National Geographic. “Were those differences the product of evolutionary changes in the founding populations? Or were the Paleoamericans, the first arrivals to the Americas, displaced by later migrations of people with features more like those of Native Americans?”
With the newest discovery now in their hands, scientists can better understand who the first Americans likely were. The prevailing theories point to all Native Americans descending from ancient Siberians who moved across the Beringia land bridge that spanned Asia and North America between 26,000 and 18,000 years ago. As time continued, these people likely spread southward, giving rise to the Native American populations encountered by European settlers centuries ago.
However, something doesn’t add up, according to Chatters.
"Modern Native Americans closely resemble people of China, Korea, and Japan… but the oldest American skeletons do not," Chatters said, as cited by the Smithsonian's Mohi Kumar.
Most early American specimens discovered to date have much smaller and shorter faces and longer and narrower skulls than later Native Americans, more closely resembling the modern people of Africa, Australia, and the South Pacific. "This has led to speculation that perhaps the first Americans and Native Americans came from different homelands," Chatters continued, "or migrated from Asia at different stages in their evolution."
So, the newly discovered skeleton, which has been named Naia (Greek for water) by the divers who made the discovery of the teenage girl, should help solve this puzzle.
Though Naia’s skull is shaped like those of other early Americans, she shares a DNA sequence with modern Native Americans, indicating she is likely a genetic “great-aunt” to indigenous people currently found in the Americas.
To make a solid conclusion of this hypothesis, the scientists had to first determine the girl’s age.
Helping the team was the fact that the cave where the skeleton was discovered – a submerged chamber called “Hoyo Negro” (Spanish for black hole) of the Sac Atun cave system – was also littered with fossils of saber-toothed tigers, giant ground sloths, cave bears and even an elephant-like creature known as a gomphothere, which would have last walked the Earth thousands of years ago during the last ice age.
But this wasn’t good enough for the team. So they took a closer look at the regional sea-level data to get a minimum age at which the cave filled with water. Based on their analysis, the site, which is now 130 feet below sea level, was submerged between 9,700 and 10,200 years ago. This indicates that Naia had to have fallen in the cave before this time.
TEETH TELL THE TALE
Unlike previous skeletal remains found, Naia’s included her teeth. Douglas Kennett, a professor of environmental archaeology at the Pennsylvania State University, co-led a team that radiocarbon dated the girl’s tooth enamel to 12,900 years ago.
However, because the skeleton was exposed to sea water within the limestone caves, her bones were mineralized.
"Unfortunately, we can't rule out that the tooth enamel is contaminated with secondary carbonates from the cave system,” Kennett explained in a statement.
But this didn’t deter the team in determining the age. They looked even more closely at the bones and found something very interesting: they were spotted with rosette-looking mineral deposits. Before the cave was submerged, water dripping from the roof of the cave created a mineral deposit on the bones that dried into floret patterns.
"Because the florets grew on the human bones, we knew that dating them would give us a minimum age for the bones," explained Victor Polyak, a research scientist at the University of New Mexico’s Department of Earth and Planetary Sciences, as cited by the Smithsonian. "And again, given that Hoyo Negro pit was dry when Naia made her way to the bottom, the florets had to have grown between the time of her death and 10,000 years ago when the bottom of the pit became submerged by brackish water because of rising sea level. Therefore, the oldest pieces of florets provided the oldest minimum age."
The analysis of the florets concurred with other findings that Naia fell into the cave no earlier than 12,000 years ago.
Now that the age was established, the team’s commenced to determine if they could extract DNA from Naia’s molars.
"We tried a DNA extraction on the outside chance some fragments might remain," said Chatters, according to the Smithsonian. "I was shocked when we actually got intact DNA."
The team focused on mitochondrial DNA (mtDNA), which is more abundant than DNA found in a cell’s nucleus. The team focused their attention specifically on haplotypes, which are sequences of genes that mutate more slowly than the rest of the mtDNA. The analysis showed that Naia’s mtDNA contains a haplotype that occurs in modern Native Americans and is only found in the Americas; scientists surmise that it evolved in Beringia.
“We were able to identify her genetic lineage with high certainty," said Ripan Malhi, a professor of anthropology at the University of Illinois. "This shows that living Native Americans and these ancient remains of the girl we analyzed all came from the same source population during the initial peopling of the Americas."
Naia’s mtDNA proves that migrations from Beringia made it to southern Mexico. But as for why her skull was so different from modern Native Americans, coauthor Deborah Bolnick, assistant professor of anthropology at the University of Texas at Austin, explained: “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.”
The studies of Naia – namely the fact that she is a genetic forerunner to modern Native Americans – ironically raises interesting questions about whether scientists will be able to get access and extract the remains of other early Americans that have yet to be uncovered.
As an example, Chatters could not further analyze the remains of the 9,000-year-old Kennewick Man in 1996 after discovering the scientific importance of his remains. This was because the local tribes claimed the body as an ancestor under the Native American Graves Protection and Repatriation Act (NAGPRA), passed in 1990. That decision was overturned in 2004 by a Circuit Court of Appeals judge, ruling that the remains could not be defined as “Native American” under NAGPRA law, allowing studies on the body to resume.
The discovery of Naia could open the door to similar struggles in the future.
Chatters, however, dismisses that idea, noting in the current study, “We’re not looking at an ancestor-descendent relationship here necessarily. We’re simply looking at a common heritage.”
This study was led by Mexico’s National Institute of Anthropology and History, and coordinated by Chatters. The Hoyo Negro expedition will be featured in National Geographic magazine and will be on a National Geographic Television program airing on the PBS series “Nova” in 2015.
Image 2 (below): Cave diver Alexandro Alvarez inspects the newly-discovered skull of Naia, the 12,000-13,000 year-old human skeleton discovered in a submerged cave on the Yucatan peninsula of Mexico. An international team of researchers detailed their analysis of what is the oldest most complete, genetically intact human skeleton in the New World in a paper published today in the journal Science. (SEE FULL IMAGE) Credit: Photo by Daniel Riordan Araujo