Arctic find confirms ancient
origin of dogs
For 6 weeks in the summer of 2010, a hardy band of scientists
floated down a river on the Taymyr Peninsula, a bare hump of
Siberia that juts out into the Arctic Ocean. They were on a hunt
for ice age treasures: animal bones that had tumbled from the
melting permafrost along the riverbank. There, among
mammoth tusks and other remains, Love Dalén spotted what he
thought was a reindeer rib. But when the evolutionary geneticist
analyzed it back at the Swedish Museum of Natural History in
Stockholm, he realized that the 5-cm-long specimen belonged
instead to a wolf—one that could shed new light on the history
of dog domestication. “This will be one of the critical pieces,”
says Robert Wayne, an evolutionary biologist at the University
of California, Los Angeles, who was not involved with the work.
Humans domesticated dogs long before any other animal, yet
researchers don’t agree on where or when this happened. One
study of the DNA of modern dogs and wolves suggests that
dogs arose less than 16,000 years ago in Southeast Asia, but
another genetic analysis of ancient dogs and wolves pegs the
event to Europe as long as 32,000 years ago. Archaeological
studies have been similarly contentious, with some groups
claiming that Russian and Belgian skulls dated to about 30,000
years ago represent the world’s first dogs, whereas others
argue that the oldest definitive dog skulls are 16,000-year-old
craniums found in Russia and Germany.
Dalén hopes the new study will put some of the debate to rest.
When he and his colleagues dated the small Taymyr bone and
sequenced its genome, they discovered that the specimen
belonged to a male wolf that lived about 35,000 years ago. The
DNA, when compared with that of modern and ancient dogs
and wolves, indicated that this individual lived during a critical
period in canine history, when an ancient population of wolves
divided into lineages that would eventually give rise to the
Taymyr wolf, modern gray wolves, and today’s dogs.
“It looks like a three-way split that all happened around the
same time,” says lead author Pontus Skoglund, a postdoc at
Harvard University. According to the genetic mutation rate the
researchers calculated by comparing the DNA of the Taymyr
wolf with that of dogs and other wolves, the lineage that gave
rise to today’s dogs arose somewhere between 27,000 and
40,000 years ago, the team reports online today in Current
Biology.
“I like that time period,” says Wayne, whose own work
indicates that dogs arose in Europe about this time. “That’s
when modern humans first entered Europe and began
encountering wolves that became the raw material for dogs,”
he says, referring to the older end of the time frame. “It’s a
good paper,” agrees Peter Savolainen, a geneticist at the Royal
Institute of Technology in Stockholm, who was not involved
with the work. His team’s analysis of modern dog and wolf
DNA suggests that the wolf and dog lineages split off from
each other about 32,000 years ago. “It’s really nice that the
modern and ancient DNA matches up,” he says.
Still, neither Savolainen nor Wayne—who have argued over
whether dogs arose in Asia or Europe—thinks the study
provides clarity on that debate or whether dogs were
domesticated multiple times, as some scientists have proposed.
“There’s still a lot of open questions,” Skoglund agrees.
Also unclear is whether Siberian huskies and Greenland sledge
dogs—both considered ancient breeds—were among the first
types of dogs. When Skoglund, Dalén, and their colleagues
compared the DNA of the Taymyr wolf with that of 48 dog
breeds, they found that Greenland sledge dogs and Siberian
huskies shared more ancestry with the Taymyr wolf than did any
other breed. That could mean that these two breeds arose soon
after dogs split from wolves. But it could also be a genetic red
herring, especially if these breeds mated with descendants of
the Taymyr wolf in recent history. Still, Dalén says, “my hunch
is that both are a fairly early form of dog.”