Seattle ? From Yorkshire terriers the size of a teacup to Irish wolfhounds near the size of a small pony, all dogs originated from a single species, probably an East Asian wolf seeking the warmth of the human hearth and an easy meal.

“We think there was a series of domestication events in East Asia,” said Norine E. Noonan, a dog researcher at the College of Charleston in South Carolina. “It happened a lot longer ago than anybody once thought — at least 100,000 years ago.”

There likely was a set of “dog Eves,” a central proto-dog that adopted humans as a protector, provider and best friend. In return, the early wolflike animals helped humans hunt, Noonan said Friday.

She and other scientists gave a report on the status of dog research at the national meeting of the American Association for the Advancement of Science.

Based on genetic research, said Deborah Lynch of the Canine Studies Institute in Aurora, Ohio, “there were only about a half-dozen domestication events in East Asia.”

After that, dogs followed where humans went, migrating to the Americas, for instance, when people did.

“Domesticated dogs are much older than we once thought,” Lynch said. “They literally walked out of the caves with us.”

Somewhere along the way, humans learned they could breed dogs for particular jobs. Mating two fast dogs produced young that were also fast. The same was true for dogs that could dig, herd animals, hunt or attack humans.

Eventually, the experts said, the dog became the most variable animal on Earth in terms of shape, size and color. There are now more than 300 recognized species, ranging from the very small Japanese Chin to the monster St. Bernard.

The various breeds have certain appearances because sometime in the distant past humans wanted a dog for specific service to people, Lynch said.