(CN) – The ancient genomes of the Tsimshian indigenous people reveal their population was on a gradual decline at least 6,000 years ago, according to a new study that is the first population-level nuclear DNA analysis of a Native American group – ancient or modern.
“The finding contradicts a popular notion,” said lead author John Lindo, a geneticist at Emory University. “There is this idea that after Native Americans came in through the Bering Strait that they were all expanding in population size until Europeans showed up.
“At least for this one population, we've shown that was not the case.”
The discovery is the byproduct of improvements in next-generation DNA sequencing technology, which have enabled the exploration of the evolutionary history of different populations.
“Ancient nuclear DNA analysis is a relatively new field," Lindo said. "Not until recently have we had methods to sequence an entire genome quickly and inexpensively.”
Nuclear DNA reveals information on an individual’s lineages dating back hundreds of thousands of years. Lindo is one of the few geneticists examining ancient whole genomes of Native Americans, and is particularly focused on determining how the genomes of their different populations evolved over time.
“Their evolutionary histories are radically different,” he said. “Over thousands of years, various Native American populations have adapted to living in every ecology throughout North and South America, from the Arctic to the Amazon.”
“That's about as an extreme as you can get for differences in environments.”
The Tsimshian people historically lived in longhouses in southern Alaska and coastal British Columbia, harvesting the abundant sea life. Lindo and his team sequenced the genomes of 25 living Tsimshian people and 25 ancient individuals who populated the same region between 6,000 and 500 years ago, and verified they were a continuous population.
In a previous report that used the same data set, the researchers noticed a dramatic shift between the two time periods in a class of genes connected to the immune system, suggesting a significant evolutionary pressure on the population to adapt to pathogens.
A demographic model indicated a crash in the Tsimshian population size of roughly 57 percent during the early- to mid-19th century. That discovery matched historical accounts of how smallpox, introduced by European colonists, ravaged the Tsimshian during two epidemics within this period.
The new study probes broader genetic variations between the ancient and modern DNA. An analysis showed how the variation declined steadily in the ancient population before the collapse, but has since rebounded.
“After a population collapse, only a subset of the genetic diversity remains,” said Lindo. “We find a more nuanced story, that despite the population collapse, the genetic diversity of modern Tsimshian people varies significantly.”
Intermarriage with other Native American groups and non-native populations expanded the genetic diversity of some of the modern-day Tsimshian people, placing it near the levels prior to their population collapse, according to the study.
“A population with relatively high genetic diversity has a greater potential to fight off pathogens and avoid recessive traits,” Lindo said. “It exemplifies the benefits of gene flow between populations, especially following catastrophic events such as the smallpox epidemics that the Tsimshian endured.”
One of Lindo’s other projects is focused on genetic fluctuations, which can explain ancient adaptations in various Native American populations. He is currently working with 10 tribes across North America.
“I listen to their stories and how they are working to keep their cultures alive,” he said. “One elder from a southwestern tribe told me that his grandfather was taken away in the early 1900s because he was a shaman and Christianity was swelling through the area.”
Most ancient DNA analyses occur in Europe, where such labs are often based and cold temperatures help preserve specimens.
Lindo hopes to bring some of the insights people of European ancestry have gained about their past to Native Americans.
“I'd like to disentangle this idea that Native Americans are part of a singular race,” he said. “I want to help Native American tribes to reclaim knowledge of their very ancient evolutionary histories – histories that have been largely wiped away because of colonialism.”
The study was published Monday in the American Journal of Human Genetics.
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