How Humans Created Cats

Following the invention of agriculture, one thing led to another, and ta da: the world's most popular pet.

A Persian kitten being examined by a referee during an international feline beauty competition in Bucharest, Romania, Saturday, Sept. 29, 2012. (Vadim Ghirda / AP)

Why do people keep cats?

As a non-cat person, I have long been perplexed by this state of affairs, in which millions and millions of humans around the world have wound up sharing a home with these odd (and—fine—kind of cute) creatures. How did this come to be?

For a long time, archaeologists have hunted for early evidence of this relationship between humans and cats. They've found a wildcat buried near a human on Cyprus from about 9,500 years ago, a proximity suggesting some sort of relationship between the two species. And from ancient Egypt there are paintings, about 4,000 years old, that depict cats, often sitting beneath the chairs of women.

But these bits of history did little to reveal how man and cat first reached, paw to hand, across that species divide.

Now, new archaeological evidence from China, published today in the Proceedings of the National Academy of Sciences, documents for the first time a chain of events that forged the relationship between human and feline.

The story begins with agriculture. About 5,560-5,280 years ago in the Shaanxi region of central China, humans were experiencing an agricultural boom. "It's early, but it's not the earliest farming in China," the paper's co-author, Fiona B. Marshall of Washington University, told me. "It's from the time when farming really took off, when it was successful."

They had small villages, with clusters of homes, cemeteries, and communal areas. They kept pigs and dogs and grew crops, primarily millet but a bit of rice, too, which they kept in ceramic vessels.

Now, these farmers had a bit of a problem: rodents. Archaeologists at the village of Quanhucun found an ancient rodent burrow that led right into an ancient grain storage pit. Storage vessels found at the village feature angles and slippery surfaces, design elements that seem to indicate an intention to protect the contents from thieving zokors. Rodent bones from the site contain evidence of millet consumption. "Clearly those rodents were eating the farmers' grains," Marshall said.

But the farmers had some help in their battle against the rodents: cats.

Archaeologists found eight cat bones in pits across the sites. When they looked at isotopes in the bones, they could detect traces of what those cats had eaten, and wouldn't you know it, the cats had been eating animals that had been feasting on human grain.

Four of the bones from the Quanhucun site, including
in (A) a left mandible with teeth that indicates a more
aged feline (PNAS)

Marshall explained to me, "There are different photosynthesis pathways for plants in different places. If it's hotter or closer to the tropics, they more often have what we call a C4 pathway, whereas if it's cooler, they are more likely to have a C3 pathway. Where Quanhucun is, it's an area where the vegetation would be C3. The deer were clearly eating C3 plants. But the people and the pigs and the dogs, they were all eating C4 plants, and C4 had to come from the millet, which was cultivated and brought into that region. So it had a special signature of its own." The rodents and the cats all showed signs of that C4 pathway, indicating a path from human cultivation, to rodent, to cat.

And, soon enough, to pet: It could not have been long before farmers realized the utility of keeping the cats around, which would have led them to support the cat population, "by a) not killing them, and by b) even helping them in various ways—letting them stay in the warmth, providing foods," Marshall said. Unfortunately, though, there is not much evidence of that phase of the process. One solitary clue: One of the bones includes teeth that appear to be from a much older cat, suggesting "at the very least that it was doing well in that environment."

Marshall says the evidence is "terribly exciting" because scientists have never before seen documentation this old of the pathway through which wildcats stepped over the threshold and into the home.

"It's very hard to find, archaeologically, exactly what relationship caused domestication," she said. "Usually we can find the time or the place. It's been speculated that for modern cat behavior that cats were attracted to early farmers, but it wasn't known for sure. But what this shows us is, yes, there was food for ancient cats in ancient farming villages, and that they helped the farmers out, making it a mutualistic relationship, by eating rodents."

Cats, Marshall explained, are very hard to find archaeologically, in part because humans do not tend to eat them. "What we mostly excavate from ancient homes and villages is the garbage. And we're just not going to find many cats," she said. Furthermore, it was a surprise to come across cat bones in China, as most of the existing evidence shows early cats in Egypt and around the eastern Mediterranean. Furthermore, modern genetics has shown that today's house cats are more closely to related to Middle Eastern wildcats than any other. Research is still being done on the DNA of the Shaanxi cat bones to determine whether there is any relationship, perhaps via an early trans-Asian trade route, between these ancient cats and the popular pet.

Whether they are related or not, Marshall agrees that the whole chain of events, from agriculture to rodents to cats to pets, is so unprompted, so self-starting, that it makes sense that it would have happened in many places at many points in time, anywhere there was both agriculture and wildcats. "It probably happened this way, everywhere," she told me.

Because cat domestication was a response to agricultural development, house cats are a much more recent creation than domesticated dogs, which first started hanging around hunter-gatherer hunting sites, long before agriculture. Wild wolves were likely attracted to the meat that humans hunted and, then, "people found them useful either to give alarm or to help in hunting." This may have happened as many as 10,000 or even 20,000 years ago, Marshall says.

But, as for cats, this process is what scientists call a "commensal" pathway to domestication. Unlike cows or sheep, which evolved from wild animals that humans hunted, dogs and cats came into a mutually beneficial relationship with humans through food. Nothing about the process was intentional; no human set out to try to domesticate a cat or a dog and make it into a pet, but a chain reaction was set off by a human practice, and one thing led to another, and our pets today are the result.

Alexis C. Madrigal

Is domestication, then, in a sense, natural? Marshall says that the modern understanding of domestication complicates any sense of a stark line between domesticated and wild. "The idea of domestication comes out of 19th-century thinking," she told me. "At that point, Darwin was thinking about Victorian animal breeding, which was very much: You take a male, you take a female, you breed intensively, and you change the animal very intentionally."

But that's not what happened with cats nor dogs. There are animal responses to humans, and human responses to animals. There is a relationship, centered around food, in which both species—human and feline—react and adapt over time.

The resulting system is one in which "the humans are changing everything," Marshall says, "but some of it is intentional and some of it is not."

To me, at least, it sounds pretty familiar.