Analysis of ancient teeth questions theory that Native Americans originated from Japan

Native Americans may not have originated in Japan as previous archaeological evidence has suggested, according to a new study of ancient teeth. 

For years, archaeologists had predicted that the first people to live in North America descended directly from a group called the Jomon, who occupied ancient Japan about 15,000 years ago, the same time people arrived in North America around 15,000 years ago via the Bering Land Bridge, a strip of land that previously connected Russia to North America before sea levels rose above it. This theory is based on archaeological similarities in stone tools, especially projectile weapons, found in Native American and Jomon settlements.

However, the authors of the new study say this scenario is highly unlikely because the biological evidence "simply does not match up" with the archaeological findings, according to a statement from the researchers. 

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"The Jomon were not directly ancestral to Native Americans," lead author G. Richard Scott, an anthropologist at the University of Nevada, Reno, told Live Science. "They [the Jomon] are more aligned with Southeast Asian and Pacific groups than with East Asian and Native American groups."

Instead, the researchers suspect that Native Americans descended from a different group living somewhere in East Asia, although a lot of uncertainty remains about exactly where and when those ancestors lived.

An archaeological theory 

 Scott and his colleagues began their study because they were unconvinced by the main argument linking Native Americans with the Jomon — the stone tool similarities, they said. 

"The artifact similarities between ancient Jomon and at least some of the earliest known Native American sites lie in the stemmed projectile points," co-author John Hoffecker, an archaeologist at the Institute of Arctic and Alpine Research at the University of Colorado Boulder, told Live Science. These similarities led previous researchers to suspect that the knowledge to make those tools had been passed down from one culture to the other, he added. 

The study researchers said this evidence was not compelling enough to make a conclusion. "Cultural parallels are not unusual," Scott said. "People can borrow ideas from others or independently come up with similar solutions to the same problems."

Instead, the researchers turned to genetic analysis to uncover the origins of Native Americans.

"I think paleo-genetics adds a tremendous amount of information to reconstructions of population history," Scott said. "It does not supplant archaeology but has become an important adjunct method that can address issues archaeologists cannot get at."

Teeth analysis 

To look at the genetic links between the two groups, the researchers turned to teeth, which can provide a wealth of genetic information.

"Tooth crown and root morphology has been studied intensively in twins and families, and there is no question they are under strong genetic control," Scott said. Unlike other genetic traits, such as blood type, which are controlled by a single gene, dental morphology is polygenic, meaning it is influenced by a combination of many different genes, he added.

For example, in another recent study one version of a gene, known as EDAR V370A, was recently found to alter the shape of shovel-shaped incisors by around 20% in people who have it, which would make that gene very easy to identify and track through time using dental records, Scott said.

This means the shape of teeth (and their roots) can provide researchers with a lot of information about a person's genetic origins and how closely related two individuals are compared to others. Additionally, teeth shapes are rarely influenced by environmental factors, which makes them a reliable way of looking at ancestry. 

"A change in the environment does not trigger a change in dental morphology," Scott said. "You can invent similar artifact styles, but you cannot invent your dental morphology."

In this study, Scott and his team compared 25 dental morphology traits in around 1,500 sets of ancient teeth from Native American and Jomon people dating back over 10,000 years, as well as other ancient groups from East Asia, Southeast Asia and the Pacific.

This analysis of tooth traits and DNA within the teeth revealed that the Native Americans were not closely related enough to the Jomon people to consider them ancestors but that they may have descended from another unknown group from East Asia, Scott said.

"The authors make a convincing argument for eliminating Japan's Jomon people as direct ancestors of the first Native Americans," Brian Fagan, an archaeologist at the University of California, Santa Barbara who was not involved with the study, told Live Science. "It is a major advance in our knowledge of the first Americans."

Uncertain origin  

Although the study suggests Native Americans did not descend directly from the Jomon people as previously thought, the two groups would have shared a much older common ancestor, Scott said.

"The common ancestor of Jomon and Native Americans could go back many millennia [more than 30,000 years], while the common ancestor of East Asians and Native Americans would be more recent [less than 30,000 years ago]," Scott said.

However, it is unclear exactly who the Native Americans' East Asian ancestors were. The "most likely point of origins is what many call Greater Beringia," a region of Northeast Asia that connected to the Bering Land Bridge and is now within modern-day Siberia, Scott said. But "at this time, there are limited remains from this area, so it's hard to be more precise," he added.

The researchers also think the Native Americans would have lived in isolation for multiple generations before they migrated to North America — another factor that makes it harder to determine their exact genetic origins.

"Ancestors of Native Americans were likely stalled out in Beringia during the late Pleistocene [when ice sheets and glaciers would have trapped them] until conditions improved enough to allow travel down the west coast of North America," Scott said. "And during this period of isolation, they differentiated from ancestral populations in East Asia."

However, recent findings, including the discovery of footprints in New Mexico dating as far back as 23,000 years, have called into question exactly when people arrived in North America, Live Science previously reported.

"Unfortunately, we cannot address this issue with the data at hand," Scott said.

The study was published online Oct. 13 in the journal PaleoAmerica.

Originally published on Live Science.