Mapping Native Americans’ roots


It’s a basic lesson in biology: DNA is the “blueprint of life,” the genetic code that manifests itself in traits like the shape of our nose or color of our hair. But anthropologist Theodore Schurr has shown he can also transform DNA into a lesson in history.

For more than two decades, Schurr, an associate professor in Penn’s Department of Anthropology, has been analyzing DNA to tell the story of early humans. He has a particular interest in uncovering the ancestry of the first people to settle the Americas.

“The inherent complexity of the question [of Native American origins] is very attractive intellectually,” says Schurr. “From a historical standpoint, it’s a question people have been asking since Europeans came to the New World.”

Based on linguistic, archaeological, and genetic evidence, anthropologists have long been confident that Native Americans can trace their origins to Asia. As the theory goes, people living in Siberia 20,000 to 25,000 years ago made their way into the northeast reaches of Asia and eventually crossed over the Bering landmass into the region that today is Alaska.

What researchers weren’t certain of, however, was where the predecessors of those land-bridge crossers were living before they migrated to the frozen taiga.

In a recent article published in the American Journal of Human Genetics, Schurr and colleagues, including Penn graduate student Matthew Dulik, fill gaps in this period of human prehistory. Their work has revealed that a small, mountainous area of south-central Siberia called the Altai Republic may have been the homeland of ancestral Native Americans.

With abundant freshwater sources and plenty of wildlife, the Altai “is an area that has been hospitable for archaic humans and earlier versions of modern humans,” says Schurr. Archaeologists have uncovered remains of Neanderthals in the region and, in 2010, discovered the finger bone of a female proto-human that is believed to be more than 40,000 years old.

Today, the Altai region is home to several indigenous groups. To collect data needed for his latest study, Schurr collaborated with Russian colleagues to visit the area and collect blood samples from 750 residents.

These samples provided a basis for comparison with 2,500 DNA samples Schurr has collected from indigenous people living across the Americas, from arctic Canada to Mexico, as part of his work with the National Geographic Society’s Genographic Project. That project aims to sequence the complete genomes of 100,000 indigenous and traditional people worldwide.

For each sample, Schurr and his team examined specific sequences in mitochondrial DNA, which is inherited down the maternal line, and Y chromosome DNA, which is passed from father to son.

In both cases, the researchers identified unique genetic signatures shared between Altaians and Native Americans. Their calculations place the most recent common ancestor between the two groups as living a little more than 20,000 years ago—perhaps when pioneering humans left the Altai Mountains and headed northeast toward the Bering Strait.

On a broad scale, the discovery clarifies ancient human migrations. But on a personal level, it also gives the study participants insight into their own genealogy. “That’s why many people get involved in the research,” Schurr says. “Our goal is always to go back to the communities we work with, whether it’s in the U.S. or Canada or Mexico or Siberia, and give them back the results and then help to piece together their stories.”

An added benefit of the research may lie in the biomedical field. With a large pool of genomes from varied locations around the world, Schurr and his colleagues hope to identify genetic factors responsible for biological differences between ethnic groups they’ve studied. Such differences could reflect adaptations to local conditions, including an ability to fight off locally prevalent infections, metabolize certain diets, or even withstand a cold climate. These revelations could help explain, for instance, why some native populations develop health problems when switching from a traditional to a more Westernized diet.

Although Schurr says he has had some difficulty keeping up his work in Russia due to political constraints, he hopes to return soon to continue collecting samples and resume his partnership with the local people.

“You get to meet the people and see how things look for yourself from a geographic standpoint. You get to talk about the histories with your Russian colleagues,” he says. “You can’t come away from Siberia without being terribly impressed with how tough people are to be able to live there and sustain themselves for a long, long time. That’s the part that brings the anthropology and the genetics together for me.”

Originally published on February 16, 2012