Ancient DNA pushes back timing of the origin of dogs

Some friendships go way back. New genetic evidence suggests that the relationship between humans and dogs may have been forged as long as 40,000 years ago.

DNA analysis of an ancient wolf calibrates the split between dogs and wolves to 27,000 to 40,000 years ago. Researchers had previously calculated that the divergence happened about 11,000 to 16,000 years ago. The new dates, reported online May 21 in Current Biology, may mean that dogs were domesticated during the last Ice Age.

Paleogeneticist Love Dalén of the Swedish Museum of Natural History in Stockholm brought the ancient wolf’s bones back from a 2010 expedition to Russia’s Taimyr Peninsula in northern Siberia. The wolf roamed the Ice Age tundra about 35,000 years ago. Dalén and colleagues extracted DNA from a rib bone and deciphered the animal’s entire genetic makeup, its genome.

Using the wolf’s DNA as a time stamp, the researchers calculated the mutation rate for dogs and wolves. “We find that mutations occur half as fast as people previously assumed,” says lead author Pontus Skoglund, an evolutionary geneticist at the Broad Institute of Harvard and MIT. Scientists had assumed that, each generation, dogs and wolves pick up one mutation in every 100 million DNA bases. The new calculation puts the per-generation rate at 0.4 mutations in 100 million DNA bases. If the calculation is correct, researchers would need to about double previous estimates of when dogs and wolves went their separate ways.

“The slower mutation rate wasn’t expected,” says evolutionary biologist Adam Boyko of Cornell University. “That’s at the lower end for mammals.” He and some other scientists say they aren’t ready to sign off on the mutation rate until they check the data themselves.

Geneticists in general have struggled to pinpoint mutation rates, says Laurent Frantz, an evolutionary geneticist at the University of Oxford. Additional ancient wolf genomes might verify the calculations. But he’s satisfied that the new estimate is solid. “The analysis is sophisticated and really sound,” he says.

Researchers usually assume that the genetic split between dogs and wolves indicates when dogs were domesticated. But “we don’t know that these ancestors of domestic dogs were tame and lived with humans,” Skoglund says. Wolves that eventually became dogs may have followed human hunter-gatherers, or the animals they hunted, for centuries before becoming human companions, he suggests.

That’s a reasonable scenario, agrees Robert Wayne, an evolutionary biologist at UCLA. Wolf groups with different habits can become genetically different, perhaps even forming new species, he says. For instance Arctic wolves that follow caribou herds rarely breed with territorial wolves that live in forests. As a result, the groups have become genetically distinguishable from each other.

Like Skoglund, Wayne says that dog domestication was probably gradual, adding that “the weight of the evidence suggests a very ancient domestication event.” 

The ancient wolf is about equally related to present-day gray wolves and dogs, the researchers found. That means that several genetically distinct groups of wolves, including the Taimyr wolf’s group, probably existed at about the time when the dog ancestor first appeared. A previous study suggested that dogs evolved from an extinct wolf (SN: 7/13/13, p. 14). The new discovery that different groups of ancient wolves existed at the same time supports the idea that one type morphed into dogs, while another became today’s gray wolves.

Some present-day dog breeds, particularly northern breeds, can trace part of their ancestry to the Taimyr wolf’s line, the researchers found. For instance, Greenland sledge dogs inherited between 1.4 and 27.3 percent of their DNA from Taimyr wolves. That genetic inheritance was probably passed down when the ancient wolves bred with dog ancestors.