Scientists have completed the first comprehensive comparison of the genes of domesticated dog breeds.
The analysis of 85 common types—including the Pekingese, Great Dane, Border collie, and dachshund—found fascinating clues about how dog breeds are related to one another, and how they may have descended from ancestral dogs in different parts of the globe. Those clues, in turn, could increase understanding about early human migration.
The findings, reported in tomorrow's edition of the research journal, Science, may also offer the first way to determine the breed of a dog based on a genetic sample. The majority of breeds tested have a unique DNA signature, despite the fact that many breeds were created only within the last few centuries.
"Since the formation of breed clubs and official breed standards only happened in the 1800s, it's really surprising that we've found such a high degree of distinction between different breeds," said geneticist Leonid Kruglyak of the Fred Hutchinson Cancer Research Center. Based in Seattle, Washington, Kruglyak is a co-author of the study.
Explosion of Breeds
The distinction found between breeds is much higher than the distinction between human populations on different continents, Kruglyak said. The variation is large enough that an individual dog's breed can be distinguished using its genetic sequence alone, he added.
"It's remarkable to find such differentiation, since the vast majority of the explosion of breeds we see today have a recent origin," commented Robert Wayne, evolutionary biologist and expert on dog genetics at the University of California, Los Angeles.
Most previous research using a different, less-sensitive type of genetic technique had not been able to detect great differences between different breeds, Wayne said.
To collect data, graduate student Heidi Parker, geneticist Elaine Ostrander—both of the Hutchinson center—and other team members contacted breed clubs across the U.S. They also scouted numerous dog shows to take cheek-swab DNA samples from five purebred dogs of each of the 85 common breeds they tested.
Over two years of focused work, with the assistance of the American Kennel Club, the team collected and analyzed DNA from 414 dogs.
The results revealed that an unexpected and geographically diverse cluster of breeds—including the Siberian husky, the Afghan hound, Africa's basenji, China's chow chow, Japan's akita, and Egypt's saluki—are most closely related to dog's ancient wolflike ancestors. "Dogs from these breeds may be the best living representatives of the ancestral dog gene pool," the researchers wrote.
The finding may back up claims by some experts that dogs originated in Asia and migrated with nomadic humans both south to Africa and north to the Arctic.
The ability to link these diverse African and Asian breeds to a common ancestor reveals an interesting correlation with patterns of human movement, commented Melinda Zeder. Zeder is curator of Old World archaeology at the Smithsonian Institution in Washington, D.C., and expert on animal domestication. "In this way, these modern breeds provide a map of human migration," she said.
The data also confirm the idea that dogs moved with humans from Asia into the New World and were not domesticated from scratch with wolves in North America, said Zeder. Zeder is also a member of the National Geographic Society's Committee for Research and Exploration.
Another surprise for dog lovers is that some purportedly ancient breeds—such as the Ibizan hound, the pharaoh hound, and the Norwegian elkhound—are not included in this ancestral group. "Breeds like the pharaoh hound have long been thought to be quite ancient, descended from ancient breeds pictured in wall art in [5,000-year-old] Egyptian tombs," Zeder said.
These dogs may in fact have been recreated in modern times from European stock to resemble these ancient breeds, Kruglyak said. Or they might have undergone so much mixing with other breeds that it has masked their ancient origins.
The large majority of breeds, however, likely have recent, European origins, according to the authors. A second cluster of dogs consists of mastiff-like breeds, including the bulldog, rottweiler, and boxer. A third group includes ancestors and descendents of herding-type dogs, such as the Irish wolfhound, the collie, the greyhound, and the Saint Bernard. The final cluster includes scent hounds, terriers, spaniels, and retrievers.
Human Health Benefits
The initial motivation for the study was to use dogs as genetic models to study the bases of human diseases like heart disease, epilepsy, or cancer, Kruglyak said.
At least half of the 300 or so known inherited illnesses in dogs are shared by humans, and many of these illnesses are more prevalent in some breeds than others. For example, kidney cancer is common in German shepherds, and eye problems are common in border collies.
Researchers of human diseases often focus on small groups of people known to share a common ancestry. Focusing on each of 400 or more isolated breeds of dogs will help researchers find disease genes far more easily, Kruglyak said, ultimately benefiting humans as well as dogs.