Photo by Gao Erqiang/China Daily

The research was done as a joint effort between the academy and Washington University in St. Louis. Hu, whose research focuses on the relationship between humans and domesticated animals, joined the team to look for evidence of the contribution of millet agriculture to the domestication of animals.

"It is very interesting for us to find the consumption of millet-based foods by the cats" since this kind of evidence had long been missing, Hu explains.

Since cats usually eat meat, such a diet would be unexpected, unless the cats were being fed by people, the study argues.

The researchers also found that one of the cats survived to reach old age, implying that it had a safe place to live and enough to eat. Taken with the other evidence, that shows a well cared for animal, the study suggests.

Why the farmers wanted to keep cats nearby-or make them "pets"-could be answered by other evidence. Chinese archaeologists found ceramic storage containers in the village that were specifically designed to keep out rodents-a vermin that cats, being notorious rodent hunters, could certainly have helped with.

The simplified theory is that rats were attracted to the food of farmers, and so were harmful to farmers. Cats were attracted to the rats, and so farmers formed a mutually beneficial relationship with cats, taking care of them in return for pest control.

Despite all the evidence, one big mystery remains-where did the cats in the study come from? That, the study says, will take further research to figure out.