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.”
No comments:
Post a Comment