By James Gorman, The New York Times, May 22, 2012
|The Saluki has less mixed DNA than many other dogs.|
Photo credit: Alen Popov
As scientific puzzles go, the origin of dogs may not be as important as the origin of the universe. But it strikes closer to home, and it almost seems harder to answer.
Cosmologists seem to have settled on the idea that 13.7 billion years ago the universe appeared with a bang (the big one) from nothing — albeit a kind of nothing that included the laws of physics.
With dogs, the consensus is that they came from wolves. Beyond that, there are varying claims. It seems dogs appeared sometime between 15,000 and 100,000 years ago, in Asia or Africa or multiple times in multiple places.
There is a reason for this confusion, according to Greger Larson at the University of Durham in England. In a new research paper, he argues that the DNA of modern dogs is so mixed up that it is useless in figuring out when and where dogs originated. “With the amount of DNA we’ve sequenced so far,” Dr. Larson said, “we’re lucky to get back a hundred years, max.” He says that only with the analysis of DNA from fossil dogs, now being done, will answers along this line emerge.
Dr. Larson, the first of 20 authors on a paper about the origin of dogs published Monday in The Proceedings of the National Academy of Sciences, argues that genetic study of modern breeds does not “get us any closer to understanding where and when and how dogs were domesticated.”
Adam Boyko of Cornell University, who has worked in the field of dog genetics but was not involved in the study, said that Dr. Larson’s group had a “fantastic data set,” and laid out clearly the current difficulties in nailing down the details of dog domestication. Dr. Larson and his colleagues analyzed 49,024 locations on dog DNA where the genetic code varies, so called SNPs (pronounced snips, for single nucleotide polymorphisms). They took the DNA from 1,375 dogs of 121 breeds, and 19 wolves.
What they found was that all the so-called modern breeds had been so mixed that their deep genetic history was obscured.
They also found six breeds that they called basal, meaning that their DNA was less mixed — the basenji, shar-pei, Saluki, Akita, Finnish spitz and Eurasier.
When they added these to eight breeds deemed ancient (older than 500 years) in other studies, what they found was that the dogs that were most genetically distinct were not from the places where the oldest archaeological and fossil evidence had been found. Dr. Larson said that the expectation was that if these breeds were closer genetically to the first domesticated dogs, they would be geographically closer as well, more likely to be found near the sites of early dog fossils, or archaeological records of ancient breeds.
Instead, the more genetically distinct dogs had been geographically isolated relatively recently in the history of domestication. For example, dingoes, basenjis and New Guinea singing dogs came from Southeast Asia and southern Africa, where dogs did not arrive until 3,500 and 1,400 years ago, respectively. Their distinctive genes were indications of relatively recent isolation.
But, he said, all is not lost. Humans have buried their dogs for a long time, and as a result there are fossils of truly ancient dogs, in the neighborhood of 15,000 years old, from which DNA can be extracted. Just as DNA from Neanderthals has helped illuminate the origins of modern humans, DNA from ancient dog fossils should help illuminate the story of early dog domestication in the next few years.
“Let’s step back,” he said. “Let’s take a breath. We’re not a million miles away” from figuring out when and where dogs appeared. “We’re close.”