The first humans to populate the Americas arrived from Siberia via the Bering land bridge around 16,000 years ago. Man’s best friend, the domesticated dog, didn’t arrive for another 6,000 years or so, crossing over just in time to avoid the land bridge’s collapse, but archaeological evidence suggests that the two species lived in harmony for thousands of years—at least until 1492, the year Columbus sailed the ocean blue.
According to a study published in Science on Thursday, “pre-contact” American dogs possessed a unique genetic signature derived not from the North American wolf, as previously thought, but from domesticated Siberian ancestors. Today, that singular genome has all but disappeared, eradicated by the 15th-century arrival of European settlers and their canine companions.
National Geographic’s Maya Wei-Haas explains that European dogs, like their human owners, probably carried diseases that pre-contact dogs were unequipped to fend off. The colonists preferred European breeds and discouraged their pets from mating with the native dogs, which study co-author Angela Perri, a zooarchaeologist at Durham University, says were viewed as “wild” and “vicious.”
“This study demonstrates that the history of humans is mirrored in our domestic animals,” Greger Larson, director of the Palaeo-BARN at Oxford and senior author of the study, said in a statement. “People in Europe and the Americas were genetically distinct, and so were their dogs. And just as indigenous people in the Americas were displaced by European colonists, the same is true of their dogs.”
To trace the story of these pre-contact dogs, researchers studied DNA found in the mitochondria of 71 North American and Siberian dog bones. The remains, which date from roughly 10,000 to 1,000 years ago, included those of the Koster dogs, a group of four domesticated canines discovered at a burial site in western Illinois during the 1970s. (A second study, newly published in pre-print server Biorxiv, further discusses these early dogs.) As Science’s David Grimm notes, the Koster pups lived about 10,000 years ago, making them the oldest known dogs in the Americas. Perri, referencing the animals’ small, slender stature, tells Grimm that “it wouldn’t be surprising if they were all used as hunting dogs.”
DNA analysis allowed the scientists to identify pre-contact dogs’ closest relatives: a group of dogs native to Zhokhov Island, a frigid Arctic site situated about 300 miles north of the Russian mainland. The Atlantic’s Ed Yong writes that these dogs were the first to be bred for a specific purpose, namely pulling their humans’ sleds.
In addition to shedding light on the first American dogs’ origins, the study offers insights on pre-contact dogs’ connections—or rather, lack of connections—with modern dogs. Researchers compared the 71 ancient genomes with DNA from more than 5,000 modern dogs, including breeds like chihuahuas and Carolina dogs, which are commonly thought to be descended from indigenous populations. The highest level of pre-contact DNA conclusively found in any of the modern dogs was four percent, a negligible result, the New York Times’ James Gorman reports.
The team’s findings suggest that modern American dogs are descended solely from Eurasian breeds introduced by European settlers. Perri tells Wei-Haas that the scientists expected to find evidence of interbreeding between the pre-contact pups and the new arrivals. Instead, they realized that the native dogs had virtually vanished.
“It is fascinating that a population of dogs that inhabited many parts of the Americas for thousands of years, and that was an integral part of so many Native American cultures, could have disappeared so rapidly,” Laurent Frantz, study co-author and evolutionary geneticist at Queen Mary University of London, said in a statement.
Oddly enough, scientists found that the closest surviving trace of pre-contact dogs’ DNA is found in a sexually transmitted canine cancer. The Los Angeles Times’ Deborah Netburn writes that the disease, known as canine transmissible venereal tumor, stems from the genetic mutation of a single North American dog that lived up to 8,225 years ago. The tumor cells spread through mating and carry a copy of that original DNA, allowing researchers to paint a clear picture of the “founding dog,” or patient zero.
Elaine Ostrander, chief of the cancer genetics and comparative genomics branch at the National Human Genome Research Institute, tells Wei-Haas, “It's the world’s oldest continuously propagated cell line, which is really, really remarkable.”