The bond between dogs and their humans is historic.
But scientists know very little about where, when, and how ancient dogs and early humans interacted with one another, slowly winning each other's undying affection over generations.
The genomes of 27 ancient dogs could hold crucial clues. In a new study published Thursday in the journal Science, scientists compared how these 27 ancient dogs' DNA match up to similarly ancient human genomes. The findings reveal unprecedented insight into the impact dogs had on how these prehistoric humans lived, and vice versa.
Making these important connections will not only help scientists better understand how dogs evolved and diversified into the myriad breeds we know and love today, but can also help them take a closer look at the day-to-day lives and priorities of ancient humans as well.
Dogs are a diverse bunch. From the sleek and regal Afghan Hound to the hardy Siberian Husky and the feisty Chihuahua, it is hard to fathom how such different looking animals are so closely related.
But while human meddling in dog breed types seems like a purely modern phenomenon, it actually has ancient roots.
Pontus Skoglund is the lead researcher on the study and a geneticist at the Francis Crick Institute. In a video describing the research, he says that when he and his team uncovered the diversity among the ancient dog samples, it was a shock.
"The dog diversity we see today and in the past was present already at least 11,000 years ago," Skoglund explains. "Which has the implication that it must have arisen much earlier than that. Way back in time during the hunter-gatherers Stone Age... way before agriculture."
Essentially, if by 11,000 years ago, very different dog species had already spread through Europe, Asia, the Americas, and Siberia as these findings suggest, then something had to have had a hand in the level of diversification.
To figure that out, Skoglund and his colleagues started to work backwards.
A common ancestor — The theory goes that the domesticated dogs we know today are softer, friendly versions of ancient wild wolves. And looking at the genomes of the 27 different ancient dogs, the researchers behind this study did find that to be the case. But the story appears to be more complicated than that.
Instead of finding that different wolf species were related to different domesticated dog breeds, they found all the different dogs shared one common ancestor — a "single ancient, now-extinct wolf population."
From this common ancestor, the researchers narrowed in on five distinct canine lineages found in different areas of the world:
- Neolithic Levant (modern-day Israel, Jordan, and Palestine)
- Mesolithic Karelia (modern-day Russia)
- Mesolithic Baikal (modern-day Siberia)
- Ancient America
- New Guinea singing dogs
The researchers then compared these five distinct lineage's evolution through time to that of their ancient human contemporaries.
A human connection — Perhaps surprisingly, the analysis did not show a perfect alignment between humans and dogs. But they did identify a number of striking crossovers which offer insights into how our ancestors — and our pets' ancestors — lived their lives together.
One curious finding was that both East Asian dogs and humans are genetically closer to European populations than Near Eastern ones. It's possible that the evolution of dog breeds in that area may have mimicked the "Eurasian" ancestry of the human populations, suggesting humans and animals traveled into certain areas together.
The stomachs of the ancient dogs held more clues. In dogs who lived near agricultural human populations (as opposed to hunter-gatherers), researchers found raised levels of gene responsible for starch digestion. Humans likely developed this gene thousands of years before dogs, but the data sync up with older studies suggesting the gene is a sign of how dogs adapting their diet to human-cultivated food has influenced their evolution. Essentially, ancient humans may have been transforming these dogs from the inside out.
Together, the results suggest that ancient dogs may have moved with certain groups of pioneering humans as they migrated and cultivated the ancient world.
Looking at where the two species' lineages — humans and dogs — diverge revealed interesting threads of the story, too.
"There are instances where [these] two histories differ, suggesting that there are more complex forces at play," Anders Bergström, the study's first author and a postdoc at the Francis Crick Institute, says in the video. Watch the researchers' full explanation here:
Perhaps ancient humans and dogs' relationship went beyond companionship. This may include the selling and trading of ancient dogs across geographical regions, the study suggests.
What's next — It's still too soon to pin down the exact origins of our furry companions. To finally crack this mystery, the researchers hope future studies will look at even older canine and wolf DNA. By analyzing them and pairing the data with other findings from archaeology, anthropology, and ethology, scientists could retrace the paw prints back to the origins of our beloved pets.
"The dog is the oldest domesticated animal," Bergström says. "It has a very long relationship with humans."
"Understanding the history of dogs teaches us not just about their history but about our own history," he adds.
Abstract: Dogs were the first domestic animal, but little is known about their population history and to what extent it was linked to humans. We sequenced 27 ancient dog genomes and found that all dogs share a common ancestry distinct from present-day wolves, with limited gene flow from wolves since domestication but substantial dog-to-wolf gene flow. By 11,000 years ago, at least five major ancestry lineages had diversified, demonstrating a deep genetic history of dogs during the Paleolithic. Coanalysis with human genomes reveals aspects of dog population history that mirror humans, including Levant-related ancestry in Africa and early agricultural Europe. Other aspects differ, including the impacts of steppe pastoralist expansions in West and East Eurasia and a near-complete turnover of Neolithic European dog ancestry.