Baku, December 17 (AZERTAC). Discovery of the 5,300-year-old bones fills an enormous gap in experts' understanding of cat domestication, but the location is a surprise. Archaeologists in China have unearthed the first clear evidence of cats living among humans as semi-domesticated mousers about 5,300 years ago, a heretofore missing link in the history of the world's most popular pet, experts say.

The evidence, published Monday in the Proceedings of the National Academy of Sciences, supports the long-held view that cats began their symbiotic relationship with people following the advent of agriculture, many thousands of years after dogs were tamed by nomadic hunter-gatherers.

The discovery fills in an enormous gap in experts' understanding of cat domestication, but it has also thrown them for a curve. In some ways, an ancient Chinese village is the last place researchers expected to find such evidence.

"This was a very unexpected find," said study coauthor Fiona Marshall, a zooarchaeologist at Washington University in St. Louis.

Today, every domestic cat in the world — whether it's howling in a back alley, starring in a YouTube video or climbing into an empty box in your living room — is descended from a single subspecies of Middle Eastern wildcat known as Felis silvestris lybica.

Marshall and her colleagues note that the ancient village of Quanhucun, in central China's Shaanxi province, is far beyond F. s. lybica's natural range, and raises the question of just how the cats got there.

Were they imported from the Middle East as novelties, or even food? Were the Quanhucun kitties descended from an Asian subspecies of wildcat, Felis silvestris ornata, and later displaced or wiped out?

Marshall and her colleagues hope upcoming DNA analysis will clarify matters. In the meantime, experts have been left to wonder.

"The question everyone has is, what cat is this and where did it come from?" said biologist and cat lineage expert Carlos Driscoll, who is based at the National Institutes of Health and was not involved in the study. "The key ingredient that's missing here is DNA evidence."

The discovery reported in PNAS consisted of eight fossilized bones from at least two felines that were found in ancient trash pits along with other animal remains, pottery shards and tools. The bones in the pits accumulated over about 200 years, they wrote.

Researchers emphasized several factors that suggest the remains belonged to cats that had developed a unique relationship with long-ago farmers.

The bones are comparable in size to those of European house cats but smaller than those of European wildcats, they reported. A partial jawbone from one of the Quanhucun cats has very worn teeth, suggesting that it was quite old and would have needed help to survive to such a ripe age, they added.

Other indications come in the form of isotope analysis. By examining the ratio of carbon and nitrogen isotopes in bone collagen, scientists can determine where an animal fell in the food chain and whether its diet consisted mostly of plants or of meat.

Tests showed that one of the Chinese cats appeared to eat more millet than would be expected of a carnivore living in the wild, raising "the possibility that this cat was unable to hunt and scavenged for discarded human food or that it was looked after and fed by people," the study authors wrote.

Scientists have long speculated that the process of cat domestication was related to agriculture. Wildcats, they surmised, were probably drawn to farming settlements by the promise of food scraps and a ready supply of rats and mice. Prehistoric humans probably tolerated the cats for their vermin-hunting prowess and allowed them to stick around.

The hypothesis makes sense, but proving it has been difficult — and the aloof nature of cats hasn't helped.

"The impact of domestication is difficult to tell from archaeological remains. Actually, it's hard to tell when you have the living damn cat, because they retain so much of their native behaviors," said Melinda Zeder, an archaeobiologist and expert on animal domestication at the Smithsonian Institution's National Museum of Natural History in Washington.

Yet Zeder, who was not involved in the study, said it appeared to be the first to demonstrate a synergistic relationship between cats and humans and was therefore significant.

The oldest evidence of a special bond between the two species dates back 9,500 years to the island of Cyprus. There, archaeologists discovered the full skeleton of a wildcat buried near a human. The proximity of the two skeletons suggests the cat might have been tamed, experts say.

Until now, the next-oldest record of cats living with people came from ancient Egypt, where 4,000-year-old tomb paintings and writings described cats being kept as pets in the homes of the wealthy.

Unlike the Egyptian cats, which were often depicted sitting under chairs, the cats of Quanhucun were hardly house cats. They were probably more akin to the cats that populate today's parking garages: creatures wary of people but also reliant on them for an occasional handout or carelessly dropped garbage.

"There's nothing to show us that there was anything more than an alley cat type of relationship in this village," Marshall said.

In fact, although many experts say cats were attracted to early agricultural settlements by the rats and mice that raided grain stores, Driscoll said he believes trash was the bigger draw. Once people gave up their wandering, hunter-gatherer ways, their agricultural settlements became virtual buffets for cats.

"Cats are dumpster divers par excellence," he said.