Gene research suggests tamed dogs have existed for more than 100,000 years. Tim Cornwell spoke to the researchers and their critics

Modern man is about 100,000 years old, archaeologists say. But early Fido may be up to 135,000 years old, University of California researchers have concluded.

No one claims to pinpoint the moment when man's best friend joined him at the camp fire, and earned the title Canis Familiaris. But the earliest date offered until now comes from the remains of a dog found in a Palaeolithic grave at Oberkassel, Germany, estimated at about 14,000 years old.

Carles Vila and Robert Wayne, evolutionary biologists at the university in Los Angeles, took a different approach. By analysing gene samples from 140 dogs across 67 breeds, and working backwards, they concluded that dogs were tamed far earlier than anyone thought.

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For their research they collected blood and tissue samples from breeds including bulldogs, Irish setters and rottweilers. They also analysed the blood of 162 wolves from more than 12 countries and from animals killed on the road.

Their findings confirm what was widely thought: that dogs evolved from wolves, rather than from jackals or coyotes, who split from the wolf as much as one million years ago. Somewhere in the distant past, the wolf was tamed. The dog, it is widely thought, was the first animal to be domesticated, cats probably the last.

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The level of genetic diversity found in dogs, with 26 different DNA sequences among them, was far greater than could have developed over a mere 14,000 years, the UCLA team concluded. The first domestic dog might be 100,000 or more years old, they calculated, with 135,000 the outside figure.

"In some groups of dogs we have variability that has to be older than 14,000 years. We can't be sure about 135,000. But much older than 14,000," says Dr Vila. It is likely that remains of older dogs have simply failed to turn up. "I hope they will", he adds. "We believe that the fossil remains that we do have are too incomplete to show anything about what's going on."

But there are critics of this controversial research. James Serpell, a British animal behaviour expert at the University of Pennsylvania, regards the findings as "barely credible".

Part of the controversy is rooted in the complex relationships between the wolf, Canis Lupus, and the dog, Canis Familiaris. They can interbreed, though with different oestral cycles - twice a year for the dog, to the wolf's one - that can be difficult. When it comes to identifying archaeological remains, a dog has smaller teeth, jaw and bones, characteristics that are a byproduct of the relationship with humans. "Wolves have more powerful muscles and more powerful bones to hold the muscles," says Vila. "With domestication, the muscles and the skull decreased in size, because the need to hunt or kill the prey was gone."

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Most modern breeds were developed less than 300 years ago. Four breeds are thought to be considerably older: the dingo, the New Guinea singing dog, the African basenji, and the greyhound. But the UCLA scientists assert that after domesticated dogs separated from wolves they remained physically indistinguishable from them for thousands of years. They only began to look like dogs, they argue, when their human masters began to lead a settled existence, from about 15,000 years ago.

Serpell disagrees. An animal living in a group of people is immediately subject to different selection pressures, he says. The first thing primitive "owners" had to select would be tameness. "Wolves are never as tameable as dogs," he says, but instead show traits valued in the wild, such as extreme caution and fearfulness. Studies in the former Soviet Union where farmed foxes were selected for tameness found the animals rapidly changed their appearance, acquiring drooping ears, curly tails, piebald colours, and in some cases the double oestral cycle.