People who instinctively recoil from the idea of genetic engineering tend to forget about Fido. Nobody reached in and hand-tinkered with the DNA of dogs, but the animals that are now thought of as humanity’s sidekick started out as purebred grey wolves. They only turned into our tail-wagging, ball-chasing buddies through selective breeding that gradually dialed down their surly aggression and ramped up their friendliness.
Exactly when and where that transformation began, however, has been a point of scientific contention. East Asia has always been a leading contender, but so have the Middle and Near East—somewhere between Israel and India. As for the timing, bones that are arguably from the earliest dogs—they seem to have the right structure, although the differences between dog and wolf bones aren’t always clear—date back to more than 30,000 years ago. But genetic analysis contradicts that, indicating that dogs and wolves didn’t diverge until about 15,000 years ago.
It is, in short, a very tangled story, but a new report in Science may finally have unraveled it. And the answer is…none of the above. Humans began domesticating dogs somewhere between 18,000 and 32,000 years ago says lead author Olaf Thalmann, a geneticist at Finland’s University of Turku. And it happened in Europe.
Thalmann and his co-authors are quick to acknowledge that this claim shouldn’t be considered definitive. “This is not the end-story in the debate about dog domestication” said Robert Wayne, of UCLA in a statement, “but I think it is a powerful argument opposing other hypotheses of origin.” That’s quite an admission for Wayne, since his previous work pointed to a Middle Eastern origin for dogs. But the new argument is compelling—and it’s in two parts.
The first is genetic: Thalmann, Wayne and their colleagues used mitochondrial DNA (mDNA), which is found outside the nucleus of cells. It isn’t part of animals’ primary genome (mDNA is only inherited from the mother, not from both parents), but it’s more robustly preserved than nuclear DNA. The researchers compared and contrasted mDNA from 18 long-dead canines with mDNA from 77 modern dogs, 49 wolves and four coyotes.
The result: the modern dogs’ distant genetic material most nearly resembled that of an ancient European wolf population that has long since gone extinct. Tracing the relationship back that far at least establishes just who the dog’s wolf ancestors were. As for when the divergence took place, differences between mDNA from ancient dogs and ancient wolves implied that the two species began drifting apart at least 18,000 years ago.
If that’s so, then one piece of conventional wisdom about the origin of dogs might be wrong. The old story is that dogs began to evolve after humans made the shift from a nomadic hunter-gatherer existence to a village-based agrarian society. The abundance of food, goes the argument, would have lured some of the friendlier wolves into town, jump-starting the domestication process. But agriculture didn’t exist 18,000 years ago, so if Thalmann et. al. are correct, wolves were presumably lured into human camps by the leftover carcasses of butchered animals.
This new story clearly upends the old one—but not everyone is prepared to buy it. One objection: mDNA isn’t as reliable a guide to species divergence as DNA from cells’ nuclei. It reflects only,“a small part of the evolutionary history,” Chung-I Wu, of the University of Chicago, who wasn’t involved in the study, told Science. “Two parts of the genome can tell two different stories.” With that, Thalmann agrees: “To make a more solid finding,” he says, “we definitely need nuclear DNA from fossil canines.”
Another problem is that the ancient samples the team used are mostly from Europe, and that, says Peter Savolainen of the Swedish Royal Institute of Technology, who advocates the Asian theory of domestication, skews the results. “It’s not really an objective study,” he told Science. It is, he says, as if you tried to pinpoint human origins without looking at any fossils from Africa.
And again, Thalmann concedes the point. “It’s a red flag,” he admits. “We only had Russian and European samples.” The team would have used samples from the Middle East and Asia as well, but their only fossil from the Middle East yielded no useful data, and, he says “we don’t know of any samples from China older than 13,000 years. What we have is the best we can offer.”
That hardly means the new story Thalmann and the others tell is incorrect, though; it just means they’ll have to keep digging, and that’s what they plan to do. The human-canine cross-species friendship is a long and deep one. How such an unlikely bond came to be is an irresistible question.
(FROM THE ARCHIVES: Sport: Putting on the Dog—Feb. 27, 1928)