Do Dogs "Read" Humans to Find Food?
for National Geographic News
|November 21, 2002|
As every dog-lover knows, canines can sense a meal a mile away. Now, scientific findings suggest that dogs' chow-time cunning could be the oldest trick in the bookand one the animals mastered on their own.
The ability to find hidden food by reading cues in humans' gestures may be precisely what separated the earliest domesticated dogs from their wild kin, according to Brian Hare.
"If you can figure out how to [find food while] stay[ing] out of the humans' way, you can more successfully get garbage out of the heap," Hare said. By "you," of course, he means an ancient dog-wolf, looking to freeload off the throwaway scraps of people living nearby. Domesticated dogs arose from wolves that somehow became accustomed to living among people.
Hare, a graduate student at Harvard University and a researcher for the Max Planck Institute in Germany, and colleagues conducted a series of experiments that tested the cue-reading abilities of dogs, wolves, and chimpanzees. In each test, an animal was allowed to enter a room after food had been concealed inside one of two identical opaque containers. The only clue the animals got as to the hidden meal's whereabouts came from a human experimenter in the room, who stared at, pointed at, or tapped one of the containers.
One could be excused for expecting chimps, as humans' closest animal relatives, to perform best. In fact, dogs consistently outperformed both chimps and their own closest relatives, wolves, regardless of which clues the experimenters provided.
Born To Be Tame?
Interestingly, even young, kennel-reared dogs with little past experience of people displayed this unusual perceptiveness toward human gestures.
At first, said Hare, "we assumed they were learning. It turned out young dogs could do it just as well." That suggests the dogs' ability is inborn, not learned, Hare said.
Now "we're trying to figure out the origin of this ability," he continued. "It's not enough just to say it occurred during domestication."
He speculates that dogs' understanding of human gestures may have evolved thanks to natural selection. Thousands of years ago, semi-wild wolves that could figure out where food was by watching humans gesture to each other might have obtained more food than gesture-illiterate pack mates.
Such selection pressure could have made it "important for dogs to adapt to human societies," said Peter Savolainen, a biologist at the Royal Institute of Technology in Stockholm, Sweden. "There should have been some sort of behavioral evolution."
To test that possibility, Hare plans to travel to Siberia this summer to study a rare animal known as Belyaev's silver fox. These foxes are products of a unique experiment in domestication that wouldn't have favored the cue-reading ability Hare has found in dogs. If the silver foxes can read human gestures anyway, Hare said, it will imply that dogs' capacity to interpret gestures was simply a chance byproduct of their domestication.
Hare also hopes that focusing attention on these unique animals will save them from disappearing. There are only about 200 Belyaev's foxes, and the money currently set aside to breed and care for them is rapidly running out.
East Was Eden
While Hare's work hints at how man's best friend became domesticated, other studies are honing in on where and when the dog parted ways with the wolf.
It happened in East Asia, about 15,000 years ago, figures Savolainen.
Savolainen and colleagues in Sweden, Germany, and China reached this conclusion after examining variations in the DNA each dog inherits from its mother. They compared the genetic sequences of 654 dogs representing the gamut of the world's breeds.
Virtually all dogs can trace their maternal lineages to one of three females that lived between 15,000 and 40,000 years ago. Savolainen thinks these prehistoric individuals belonged to a pack that was in the process of giving up its wild wolf-like ways and settling down to live among people.
He made his best guess about the date of domestication based on a compromise with archaeological evidence that suggests wolves were tamed a little more than 12,000 years ago.
Savolainen found the greatest amount of genetic variation among dogs from East Asia, flagging that region as the likeliest site of domestication. Genetic anthropologists used a similar technique years ago to show that humans' last common maternal ancestor, dubbed Eve, lived in Africa close to 200,000 years ago.
The small number of canine progenitors suggests that domestication occurred just once for dogs, Savolainen said. Subsequent trade or human migration with dogs in tow probably spread the domesticated animals to the rest of the world.
That diaspora apparently took just a few thousand years. Jennifer Leonard, a geneticist with the Smithsonian Institution in Washington, D.C., has evidence that domestic dogs came to the New World with early settlers from Asia some time before 9,000 years ago.
Leonard and her colleagues mined DNA from fossils of more than 50 ancient dogs found in Alaska and Latin America.
The fossil dogs they studied were more closely related to Old World wolves than New World wolves, indicating that they had not been independently domesticated from indigenous packs by early Native Americans.
"It fits in very well," Savolainen said, in relating Leonard's discovery to his own. "That's exactly what I would have expected."
All three studies appear in the November 22 issue of the journal Science.
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