NEW YORK – A new genetic analysis has shed additional light on how the history of dogs and humans has long been intertwined.
While it is not clear when, where, or how often dogs were domesticated, dogs have enjoyed a long association with people, dating to between 20,000 and 40,000 years ago, by many estimates.
By sequencing the genomes of more than two dozen ancient dogs, an international team of researchers examined their relationships with wolves and people to piece together a picture of how they spread. As they reported on Thursday in Science, the researchers found that dogs share a common ancestry with present-day wolves and established five major lineages by about 11,000 years ago. They further noted that the population history of dogs broadly mirrors that of humans.
"Dogs are our oldest and closest animal partner," co-author Greger Larson from the University of Oxford said in a statement. "Using DNA from ancient dogs is showing us just how far back our shared history goes and will ultimately help us understand when and where this deep relationship began."
He and his colleagues sequenced the genomes of 27 ancient dogs that lived up to 10,900 years ago to a median 1.5-fold coverage. They then used that data to model the genetic history of dogs, which indicated that the five major ancestry groups — Neolithic Levant, Mesolithic Karelia, Mesolithic Baikal, ancient America, and New Guinea singing dogs — were established by about 10,900 years ago.
Previous studies have suggested that, as dogs and modern-day Eurasian gray wolves are monophyletic, wolf lineages likely contributed to the early diversity of dogs. But the new study found little evidence of gene flow from wolves into dogs. Instead, the researchers found unidirectional gene flow from dogs to wolves was common, with evidence of dog-to-wolf gene flow in nearly all the wolf populations they analyzed. This, they noted, differs from the wild introgression that is observed in other domesticated animals like pigs, horses, or cattle.
As dogs have close relationships with people, the researchers also investigated just how closely tied their population histories are. They examined 17 sets of human genome-wide data matched to the age, geographic location, and cultures of their dog samples. Broadly, they found that the population structures of the two species resembled one another, suggesting that as people migrated across the globe, they brought their dogs with them.
However, there are exceptions. For instance, in Neolithic and Chalcolithic Iran, while the human population remained the same, the local dog population was replaced by Levantine dogs, while in Neolithic Germany and Neolithic Ireland, incoming Anatolian farmers adopted local dogs.
While early European dogs had diverse ancestry, much of that has been lost. A single dog from a 5,000-year-old site in southwestern Sweden can be modeled as a single-source proxy for 90 percent to 100 percent of the ancestry of most modern dogs. Additionally, the modern European dog has now spread globally and is a major contributor to the ancestry of most dogs.
"If we look back more than four or five thousand years ago, we can see that Europe was a very diverse place when it came to dogs," lead author Anders Bergström, a postdoc at the Francis Crick Institute, said in a statement. "Although the European dogs we see today come in such an extraordinary array of shapes and forms, genetically they derive from only a very narrow subset of the diversity that used to exist."
While the researchers added that their data are consistent with a single origin for dogs, where that domestication occurred remains to be determined.
In a related commentary in Science, Pavlos Pavlidis from the Foundation for Research and Technology Hellas and the Middle East Technical University's Mehmet Somel added that they expect "genetic analyses of early dog-like fossils from Eurasia may help to resolve the longstanding debate surrounding the origins of dog domestication."