How dogs got that way

Rick Weiss/WP Washington Post

Saturday, November 23, 2002

WASHINGTON Research has long indicated that all dogs, from prissy Pekingese to slobbering St. Bernards, are the domesticated descendants of wolves. But scientists have tussled for years over when and where the transition from wild carnivore to man's best friend began - and why, exactly, dogs and humans get along so well.

A new analysis of dog DNA pegs East Asia as the place where wolves and people began their dance of domestication - not Europe or the Middle East, as some have contended. The work also suggests that domestication occurred much more recently than previously thought.

The new findings rewrite the story of how dogs made their remarkable evolutionary journey from wilderness wanderers to their place today in tens of millions of households. It is a story that scientists concede is still far from finished.

Meanwhile, a study published simultaneously Friday helps explain what may be the most enduring canine mystery of all: What is it about dogs that makes them so compatible with people? In the first direct comparison of its kind between dogs and chimpanzees, dogs demonstrated an uncanny ability to interpret human communicative cues - gleaning information from subtle hand gestures and even getting the meaning of a human glance - while the brainy chimps remained clueless to what was going on.

It may not be news to dog owners, but now it can be said with some scientific assurance: Selective breeding over the centuries has created an animal that in some respects, at least, understands us even better than our closest primate cousins do.

"It looks like there's been direct selection for dogs with the ability to read social cues in humans," said Brian Hare, a doctoral candidate in biological anthropology at Harvard, who led the behavior study.

Scientists suspect that wolves hung around primitive human hunter-gatherers long before the first wolf was domesticated, perhaps in the hope of stealing scraps of food. Eventually humans cajoled a few to help with hunting or guarding and began breeding those that proved to be the best companions.

Domestication, of course, is a matter of perspective. Some experts suspect that a few clever wolves initiated the process, recognizing that free food and a warm home beats living in the wild. Either way, scientists would like to know when and where it happened. But that has proved difficult.

Bones from small, doglike animals have been found in human sites dating back 100,000 years or more, but specimens older than about 10,000 years are difficult to identify accurately, said Peter Savolainen of the Royal Institute of Technology in Sweden, who led one of three dog studies that appeared Friday in the journal Science.

Savolainen and his colleagues counted the number of mutations within a stretch of genetic material known as mitochondrial DNA in 654 dogs from Europe, Asia, Africa and Arctic America, and also in wolves. This is the largest such study ever conducted.

Based on the widely accepted assumption that such mutations occur about every 20,000 years, the researchers calculated that domestic dog DNA first appeared about 15,000 years ago - or perhaps 40,000 years ago in the less likely event that domestication started with just one wolf rather than several.

That is much more recent than the 100,000 years ago that scientists had concluded from a smaller DNA study published in 1997. The difference is significant, because dogs were clearly widespread around the world about 9,000 years ago, and such a rapid dispersal over a few thousand years would suggest that dogs were valuable to migrating people and were perhaps widely traded.

Some researchers said they did not trust the new numbers, in part because such calculations depend on many assumptions. "I think it's still an open question," said Robert Wayne, an evolutionary biologist at the University of California at Los Angeles who oversaw the earlier study.

In a second study, scientists present DNA evidence that even New World dogs are the offspring of East Asian wolves and not of native American wolves.

The first dogs in the New World apparently came along as newly domesticated companions when humans migrated from Asia to North America 12,000 to 14,000 years ago.

In a third report, researchers describe several experiments aimed at unveiling the biological and behavioral essence of the human-dog relationship. One experiment presented dogs and chimps with two smell-proof boxes, one empty and the other with a treat. The team tested the animals' ability to read hints from a person as to which box had the food - hints such as tapping on the box or even pointing at the food box and gazing at it.

The dogs usually picked up on the signals and chose the right box, while chimps did not. Hare, who designed the study, acknowledged that chimps performed better than dogs on many kinds of tests. "But in this simple task," he said, "chimpanzees fall flat on their faces."

In a separate series of experiments comparing test performance among human-raised puppies, kennel-raised puppies, dogs and wolves, Hare and his colleagues concluded that this communicative talent was not learned from human interaction during puppyhood and is lacking in wolves. That suggests it has become an innate trait among dogs - the result of individual dogs' having been selected and bred over hundreds or thousands of years on the basis of their ability to "understand" their masters.

Raymond Coppinger, a professor of biology and dog expert at Hampshire College in Amherst, Massachusetts, called the experiments a good start at understanding the dog mind, but he emphasized that such experiments were difficult to design well.

"This argument about cognition and who has it has been going on since Aristotle," Coppinger said. "The thought that one article is going to answer it now for dogs is, well, you fill in the ending."