"Dogs participated in this initial migration."
But what was life like before dogs became man's best friend — way, way before? The ancient history of dog domestication is murky, especially when it comes to the arrival of the first dogs in the Americas.
Did dogs arrive with the first humans to the Americas, or did they come later? A new study offers an answer.
What's new — Research published Tuesday in the journal Proceedings of the Royal Society B genetically confirms the oldest dog remains found in the Americas. The femur bone in question is approximately 10,150 years old.
These new results surpass the oldest previously confirmed American dog remains by roughly 240 years.
This finding suggests dogs journeyed with the first humans to the Americas, specifically via a coastal route that followed the Cordilleran Ice Sheet. It began retreating around 17,000 years ago, enabling humans to migrate to the Americas — along with their dogs.
"Our study suggests that dogs participated in this initial migration," co-author Charlotte Lindqvist, an associate professor at the University at Buffalo, tells Inverse.
Previous researchers theorized dogs came to the Americas by a continental route and migrated west to the Pacific Coast. This new study debunks that idea.
How they did it — Researchers analyzed a canine femur bone discovered an Alaskan cave known as Lawyer’s Cave.
The scientists compared these Alaskan remains with data from modern dog breeds, historic Arctic dogs, and pre-contact dogs. These are dogs who lived in the Americas before European colonization.
Cave explorers uncovered these ancient Alaskan remains decades ago. Originally, scientists suspected that the femur bone belonged to a bear, but later research confirmed that it belonged to a dog.
"There are few findings of ancient bone remains from humans, as well as dogs in the New World," Lindqvist says.
Based on limited archaeological findings, some researchers previously hypothesized dogs arrived in the Americas after humans.
"However, based on the relatively little physical evidence we do have, dog remains are no older than around 10,000 years old," Lindqvist explains. This "lags behind the oldest human remains that are older than 12,000 years old, and archaeological artifacts that are even older," she says.
The genetic analysis of ancient Alaskan dog remains — identified in the study as PP-00128 — refutes these previous assumptions.
Ultimately, the team wanted to know when this ancient Alaskan dog genetically diverged from pre-contact dogs. The timing of this genetic divergence can be estimated from DNA data "based on the assumption that genetic changes happen in a clock-like fashion," Lindqvist says.
Digging into the details — The scientists learned the ancient Alaskan dog shared a common ancestor with pre-contact dogs, but the Alaskan animal diverged from that genetic lineage roughly 14,500 years ago. It also diverged from Siberian dogs around 16,000 years ago.
This divergence from Siberian dogs also coincides with the time period when researchers think the Cordilleran Ice Sheet melted, which would have allowed humans — and dogs — to cross into the Americas via the Pacific Coast.
This finding directly contradicts previous research.
"Previous genetic estimates of the split between pre-European American dogs and their Siberian ancestor were younger than the estimates of when the ancestral native American human population diverged from their Siberian ancestors," Lindqvist says. That version of history suggests dogs arrived in later migrations of humans into the Americas.
However, a finding of another ancient human nearby the Alaskan specimen likely confirms this team's hypothesis: Ancient dogs and humans arrived to the Americas together.
The research indicates pre-contact dogs began declining in numbers around 2,000 years ago, coinciding with the arrival of Europeans to the continent. European dog breeds, along with the rise of sled dogs that the Inuit people used, effectively wiped out most pre-contact dog breeds.
Isotope tracing also suggests the ancient Alaskan dog had a diet more closely resembling marine mammals or humans living in Southeast Alaska. The researchers speculate it may have consumed chum salmon — also known as "dog salmon," further illustrating how ancient humans' diets influenced the feeding of dogs.
Why it matters — The scientists do acknowledge these results come with some caveats.
"There is a gap in timing between genetic estimates and the actual physical remains we have from both dogs and humans, also leading to an uncertainty of when humans and dogs first migrated," Lindqvist says.
Despite these uncertainties, the study still provides insight into where and how the first humans migrated to the Americas.
"There has been a long-standing contention about whether the first humans migrated into the Americas south of the ice sheets through a continental corridor between the ice sheet or along the North Pacific coast," Lindqvist says.
It's possible these findings, combined with recent research on ice sheet melting, may resolve this dispute.
"We now have evidence that the coastal edge of the ice sheet started melting at least around 17,000 year ago, whereas the inland corridor was not viable until around 13,000 years ago," Lindqvist says.
"That coastal route for the first Americans seems most likely."
What's next — According to the study, there may be higher amounts of pre-contact dog ancestry in modern dogs than previously thought. Modern dogs are grouped into four major haplotype groups, Lindqvist explains. Pre-contact dogs are haplotype A.
Previously, researchers found a minor genetic overlap between pre-contact dogs and seven modern dogs. In this study, researchers also found an Alaskan Eskimo dog with entirely different precontact ancestry compared to other modern dogs.
The genetic analysis of the ancient Alaskan dog, PP-00128, suggests it "belongs to the pre-contact dog lineage, but its position inside this lineage is at the nexus, or center, of the diversification of most pre-contact dogs," Lindqvist says.
"This suggests it is a closer relative to the pre-contact dog ancestor and belonged to an early lineage of pre-contact dogs."
More research is needed to know for sure. But we do know the story of the Americas is, in a way, a story of dogs. The initial human habitation included canine companionship — and that's a service worthy of some head pats.
Abstract: The oldest confirmed remains of domestic dogs in North America are from mid-continent archeological sites dated approximately 9900 calibrated years before present (cal BP). Although this date suggests that dogs may not have arrived alongside the first Native Americans, the timing and routes for the entrance of New World dogs are unclear. Here, we present a complete mitochondrial genome of a dog from Southeast Alaska, dated to 10 150 ± 260 calBP. We compared this high-coverage genome with data from modern dog breeds, historical Arctic dogs and American precontact dogs (PCDs) from before European arrival. Our analyses demonstrate that the ancient dog shared a common ancestor with PCDs that lived approximately 14 500years ago and diverged from Siberian dogs around 16 000 years ago, coinciding with the minimum suggested date for the opening of the NorthPacific coastal (NPC) route along the Cordilleran Ice Sheet and genetic evidence for the initial peopling of the Americas. This ancient SoutheastAlaskan dog occupies an early branching position within the PCD clade, indicating it represents a close relative of the earliest PCDs that were brought alongside people migrating from eastern Beringia southward along the NPC to the rest of the Americas. The stable isotopeδ13C value of this early dog indicates a marine diet, different from the younger mid-continent PCDs’ terrestrial diet. Although PCDs were largely replaced by modern European dog breeds, our results indicate that their population decline started approximately 2000 years BP, coinciding with the expansion of Inuit peoples, who are associated with traditional sled-dog culture. Our findings suggest that dogs formed part of the initial human habitation of the New World, and provide insights into their replacement by both Arctic and European lineages.