Dogs tagged along with the first humans to venture into the Americas, according to a recent study that analyzed existing collections of canine and human DNA. The results suggest that people domesticated dogs sometime before 23,000 years ago in Siberia, where isolated groups of wolves and people were struggling to survive the Last Glacial Maximum.
A tail of two species
Researchers generally agree on how dogs evolved (more on that below), but the when and where have remained more elusive. Durham University archaeologist Angela Perri and her colleagues used genetics to try to narrow it down.
Because genomes collect small, random mutations at a predictable rate, geneticists can compare genome sequences and tell how long ago two animals last shared a common ancestor. Perri and her colleagues used already-sequenced genomes from ancient and modern dogs to calculate when populations had split or interbred, and then they repeated the process with human genomes.
Their results suggest that people in northern Siberia domesticated the first dogs sometime before 23,000 years ago.
Like several other recent genetic studies have recognized, Perri and her colleagues noticed that dog and human groups tended to split or merge in roughly the same times and places, creating a genetic map of our species’ shared journey. The timing of one of those splits, around 16,000 years ago, strongly suggests that the first people to enter the Americas brought dogs with them.
Did someone say W-A-L-K?
A major split in both dog and human populations happened between 16,000 and 15,000 years ago. Archaeological evidence tells us that at this time, people were making their way south along the Pacific coast of North America, traveling past the edges of the massive ice sheets that still covered most of the continent.
At the same time, a new branch of dogs split off from the Arctic dog population, which includes modern Siberian huskies. The branch is called haplogroup A2b, and it’s the maternal lineage of all indigenous North American dogs. Mitochondrial DNA from ancient and modern dogs suggests that the dogs of haplogroup A2b last shared a common ancestor with Siberian huskies around 16,400 years ago—about the time the first people were crossing the Bering land bridge and moving into North America. “The time frame is remarkably consistent with that of the first peopling of the Americas,” wrote Perri and her colleagues.
Sadly, you won’t find many dogs from haplogroup A2b in the Americas today.
“There are some dogs that have small amounts of those lineages, such as the Carolina Dog, or some Chihuahuas, but most dogs in the Americas today all genetically look like European breeds,” coauthor Kelsey Witt Dillon, a molecular biologist at Brown University, told Ars. “Similar to how many Native Americans were killed by Europeans through warfare and disease, their dogs were likely also targeted by European colonizers and died from diseases from European dogs,” she said. “And when Europeans brought their dogs with them in large numbers, European breeds eventually replaced a lot of the genetic lineages we see in these ancient dogs.”
However, the mitochondrial DNA of ancient dogs tells us that when the first Americans ventured across the narrow strip of Beringia and into a new continent, they brought their dogs along. And just as dogs helped people with hunting, tracking, and protecting themselves in Eurasia, they probably helped the first Indigenous people in the Americas survive as well.
“Dogs were part of a larger cultural repertoire that may have assisted humans in rapidly dispersing into and throughout the Northern Hemisphere,” wrote Perri and her colleagues.
We finally know who let the dogs out (probably)
For a few thousand years before migrating to the Americas, however, those intrepid explorers and their dogs lived in Ice Age Siberia. There, genetic evidence suggests, they were mostly cut off from everyone else in the world. DNA from ancient human remains tells us that several genetically distinct groups of people lived in Siberia at the time, but they apparently stopped swapping genes (which was definitely what all the hip young people called it back then) a few thousand years before people first ventured into Beringia.
Paleogeneticists call this period the Beringian Standstill. If the eventual first Americans (population geneticists now call them Ancestral Native Americans because we’ll never know what they called themselves) had dogs, they probably had them before the Beringian Standstill started. Estimates of how long the Beringian Standstill lasted vary because nuclear DNA, Y-chromosome DNA, and mitochondrial DNA all tell us slightly different things, but it was probably somewhere between 2,400 and 9,000 years ago.
Before it set in, though, the ancestors of indigenous North Americans had, ahem, swapped occasional DNA with another group of people called Ancient Northern Siberians. In fact, the two groups of people had a long history; Ancestral Native Americans branched off from the Ancient Northern Siberian population around 24,000 years ago, but from that time until the Beringian Standstill set in, the two groups kept mingling occasionally.
Meanwhile, ancient dog genomes tell us that dog haplogroup A2—the branch that includes the American haplogroup A2b as well as Siberian huskies—split off from the dog family tree around 22,800 years ago, right around the time of the human population split and the onset of Ice Age isolation.
Here’s what Perri and her colleagues suggest all of this evidence points to: Ancient North Siberians domesticated dogs sometime before 23,000 years ago. When Ancestral North Americans branched off to become their own population, they took their dogs with them. A few thousand years later, the descendants of those dogs and their people walked into North America together.
It’s a testable hypothesis: remains of ancient dogs like one from the Afontova Gora site in Siberia could hold ancient mitochondrial DNA that could fill in some of the blanks in canine history. “Regarding next steps, right now we’re hoping to sequence additional dog genomes, especially those from Siberia and near Beringia, to try to narrow the timing of dog domestication and clarify when dogs came to the Americas,” Witt Dillon told Ars.
One more piece of evidence points to the Ancient Northern Siberians as the people who first domesticated dogs. Like Ancestral Native Americans, groups of people in Western Eurasia also got in on the gene-swapping with the Ancient Northern Siberians. Those interactions could help explain how dogs also reached central Europe at around the same time they reached the Americas.
“I say this based on long, yet utterly unscientific experience as a dog person: they will run off! So even if the humans’ interaction was brief, I can easily see a dog or dogs deciding to go trotting after the kids in the group they just met when they take their leave,” co-author David Meltzer, an archaeologist at Southern Methodist University, told Ars.
Bow wow how? Survival of the friendliest
Siberian archaeological sites dating to the Last Glacial Maximum are few and far between, and they mostly reveal people living in small, isolated groups. The Ice Age landscape wouldn’t have supported large groups of people in any one place, and long-distance travel needed to keep far-flung groups connected would have been nearly impossible once the Beringian Standstill set in.
Based on genetic, archaeological, and paleoclimate evidence, it seems likely that in the harsh conditions of the Last Glacial Maximum, most groups of people in Siberia were clustered in small areas called refugia: places where the terrain and the local climate made survival a little easier. Refugia would have sheltered some edible plants, which attracted the game species people relied on for food, clothing, and tools.
“Climatic conditions may have brought human and wolf populations into close proximity within refugial areas, given their attraction to the same prey species,” wrote Perri and her colleagues. That put wolves and humans in relatively close quarters, both struggling to survive. Canine cognition researcher Brian Hare describes what happened next as “survival of the friendliest.”
People and wolves probably scavenged each others’ kills, and some brave wolves probably hung out around the edges of human camps, scavenging scraps. No group of hunter-gatherers armed with spears would have tolerated aggressive predators lurking around their fires, however. Wolves that tried to attack people instead of just stealing their garbage probably didn’t live very long.
Over thousands of years, that meant that wolves who were brave enough to venture near human camps, and friendly enough not to bite the hands that fed them, survived. And they started to live very different lives from wolves that avoided humans altogether. Eventually, sometime before 23,000 years ago, those friendly wolves evolved into something new.
Hare and other researchers have found that as wild species like wolves, foxes, and even cattle and pigs undergo domestication, their appearance also changes. Spots, floppy ears, and curved tails all seem to be part of the genetic package, along with curiosity and friendliness toward humans. That’s why modern dogs look so much friendlier than Ice Age wolves.
PNAS, 2021 DOI: 10.1073/pnas.2010083118 (About DOIs).