Sometime toward the end of the last ice age, a group of humans armed with stone-tipped spears stalked their prey in the bitter cold of northeastern Siberia, tracking bison and woolly mammoths across a vast, grassy landscape. Beside them ran wolflike creatures, more docile than their ancestors and remarkably willing to help their primate companions hunt down prey and drag it back to camp. These were the world’s first dogs. Their descendants flowed both west and east, populating Eurasia as well as accompanying the ancestors of Native Americans as they spread into the Americas.
That’s the scenario laid out in a new study combining DNA data from ancient dogs and humans. The analysis, published today in the Proceedings of the National Academy of Sciences, aims to end years of debate about where and when dogs were domesticated. It may even explain how wary wolves were transformed into faithful companions in the first place.
“I love this study,” says Jennifer Raff, an anthropological geneticist at the University of Kansas, Lawrence, and an expert on ancient people in the Americas. More genomes from ancient dogs and people will be needed to confirm the findings, she says, but already, “It’s amazing to see how the dog story and the human story match up.”
The research started over beers in evolutionary biologist Greger Larson’s office at the University of Oxford. He was chatting with Angela Perri, a zooarchaeologist at Durham University, about a canine conundrum: the origins of ancient dogs in North America, where genetic and archaeological evidence suggests they have lived for at least 10,000 years.
Archaeologist David Meltzer, visiting from Southern Methodist University, chimed in to suggest comparing ancient DNA from dogs and humans. “Dave started talking about how and when people branched out into different groups first when they were in Siberia and then after they reached North America,” Perri recalls. If dog DNA showed similar patterns, that could reveal when the dog and human stories began to match up. “We went to a giant whiteboard and started scribbling arrows in all different directions. It was a hot mess, but it spelled out the story of dog domestication.”
To refine their doodling, the researchers analyzed previously sequenced mitochondrial genomes of more than 200 dogs from all over the world, some dating back 10,000 years. The mitochondrial DNA—short sequences that are more abundant in fossils than nuclear DNA—showed all ancient American dogs carried a genetic signature—dubbed A2b—and that they splintered into four groups about 15,000 years ago as they populated different parts of North America.
The timing and location of those splits mirror those of ancient Native American groups, the team found. All of these people are descendants of a group scientists call ancestral Native Americans, who arose in Siberia about 21,000 years ago. Those humans must have brought dogs with them when they entered the Americas about 16,000 years ago, the team concluded. (The ancient American dogs eventually vanished. When Europeans came to the Americas, their canines may have simply taken over.)
Going even deeper into the genetic past, the team found that the A2b dogs descended from a canine ancestor that lived in Siberia about 23,000 years ago. That ancestral dog probably lived with people who belonged to a genetic grouping known as the ancient north Siberians, the team speculates. The group, which appeared more than 31,000 years ago, lived in a relatively temperate part of northeastern Siberia for thousands of years, barred by a harsh climate from moving too far east or west. They shared this oasis with the gray wolf, the direct ancestor of today’s dogs.
“These people were probably sleeping on the ground in furs, roasting fresh kills on the fire,” Meltzer says. “If you’re a hungry carnivore and you smell a mammoth barbecue, you’re going to check it out.”
The leading theory of dog domestication holds that gray wolves inched closer and closer to human campsites to scavenge food, with the least timid ones evolving over hundreds or thousands of years into the gentle pups we know today. The idea doesn’t work if humans travel so far and wide that they’re always encountering new populations of wolves. But if the team’s findings are correct, both species were in relatively close quarters in Siberia for millennia, Perri says.
What’s more, genetic evidence suggests the ancient north Siberians mingled with the ancestral Native Americans before they migrated to the Americas. The ancient dog breeders might have traded animals to the lineage that became Native Americans, as well as to other groups of people, including those traveling farther west into Eurasia. That could explain why dogs appeared in both Europe and North America about 15,000 years ago, a puzzle that had previously led scientists to speculate that dogs were domesticated more than once. Instead, all dogs descend from the 23,000-year-old Siberian pups, the team argues.
Peter Savolainen, a geneticist at the Royal Institute of Technology in Stockholm who has long argued that dogs were domesticated in Southeast Asia, is more dismissive. He says the A2b signature that the team claims is exclusive to the Americas has been found elsewhere in the world. This invalidates the entire genetic analysis, he argues, and the new study “can’t say anything” about dog domestication.
But based on everything she knows about ancient people in the Americas, Raff says the study’s basic story “rings true.” Still, she notes, mitochondrial DNA represents only a tiny fraction of an animal’s genome. “You can’t fill in the full picture without nuclear DNA,” she says.
The same could be said for the Native American ancestors who may have first spread dogs to the far corners of the Americas. “This work represents some really clear progress,” says Justin Lund, a Ph.D. student in anthropology at the University of Oklahoma and a member of the Navajo Nation who has worked to include Native American perspectives in genomic studies. “But these narratives are never really complete until we start incorporating the knowledge that was present in the Americas prior to colonization.”