Europeans’ arrival in North America left a mark on the population of people already here. A new study suggests it left a genetic mark as well.
By Nathan Collins
English soldier General John Burgoyne addresses a group of Canadian Natives. (Photo: Hulton Archive/Getty Images)
Of the many devastations Europeans wreaked upon the indigenous people of the “New World,” disease left perhaps the worst impact. According to one recent estimate, around half of the Native American population died as a result of disease. But that’s not all: Researchers report Europeans’ arrival left a genetic mark—one that might help us to understand why diseases like small pox had such a disastrous effect.
“Although the extent of the population decline remains contentious, European-borne epidemics may have disproportionately contributed to the phenomenon,” John Lindo and a team of biologists, archaeologists, and anthropologists write today in Nature Communications. That hypothesis has led scientists to wonder if Native Americans had a particular genetic weakness when it comes to European diseases. Specifically, could their immune systems have been so strongly adapted to local maladies that they were unprepared to fight off novel pathogens?
In short, yes, Lindo and his team report, at least when it comes to the First Nations of the Prince Rupert Harbour region of British Columbia. There, the team collected DNA samples from 25 Metlakatla and Lax Kw’alaams (together known as Coast Tsimshian) individuals and the ancient remains of 25 more people found in archaeological sites in the region. Next, the researchers sequenced each person’s exome, the part of our DNA that contains blueprints for the various proteins we need to live, including those involved in fighting off disease.
The same genes that kept Tsimshian people healthy before European diseases arrived also helped get them sick.
After establishing that the modern and ancient samples (some of which dated as far back as six millennia) were genetically related, the team looked for signs of “positive selection”—that is, that the ancient group might have been particularly well-adapted to their home environment. Typically, that shows up as a lack of genetic diversity, or the prevalence of one particular gene over others.
The researchers found just such a pattern in a gene called HLA-DQA1, part of a family of genes that can help fight off small pox, measles, and tuberculosis. In the ancient samples, there was relatively little variation, suggesting the most common versions of HLA-DQA1 gave carriers a genetic advantage against local diseases.
In the modern samples, however, there was considerably more variation, a sign of what’s called “negative selection”—meaning the most common HLA-DQA1 variants several thousand years ago actually made people more susceptible to European diseases. In other words, the same genes that kept Tsimshian people healthy before European diseases arrived also helped get them sick. Further genetic analysis of the whole exome indicated a 57 percent decline in the Tsimshian population around 175 years ago, when historical documents record a series of epidemics among First Nations people.
“[T]he selection pressure shift could correlate to the European-borne epidemics of the 1800s, suffered in the Northwest Coast region,” the authors write.