By David Brown
Washington Post Staff Writer
Friday, June 29, 2007
Your hunch is correct. Your cat decided to live with you, not the other way around. The sad truth is, it may not be a final decision.
But don't take this feline diffidence personally. It runs in the family. And it goes back a long way -- about 12,000 years, actually.
Those are among the inescapable conclusions of a genetic study of the origins of the domestic cat, being published today in the journal Science.
The findings, drawn from an analysis of nearly 1,000 cats around the world, suggest that the ancestors of today's tabbies, Persians and Siamese wandered into Near Eastern settlements at the dawn of agriculture. They were looking for food, not friendship.
They found what they were seeking in the form of rodents feeding on stored grain. They stayed for 12 millennia, although not without wandering off now and again to consort with their wild cousins.
The story is quite different from that of other domesticated animals: cattle, sheep, goats, horses -- and dogs, cats' main rivals for human affection. It may even provide insight on the behavior of the animal that, if not man's best friend, is certainly his most inscrutable.
"It is a story about one of the more important biological experiments ever undertaken," said Stephen J. O'Brien, a molecular geneticist at the National Cancer Institute's laboratory in Frederick, Md., and one of the supervisors of the project.
"We think what happened is that cats sort of domesticated themselves," said Carlos A. Driscoll, the University of Oxford graduate student who did the work, which required him, among other things, to befriend feral cats on the Mongolian steppes.
Today, there are 37 species in the family Felidae, ranging from lions through ocelots down to little Mittens. All domestic cats are descended from the species Felis sylvestris ("cat of the woods"), which goes by the common name "wildcat."
The species is indigenous to Europe, the Middle East and East Asia. The New World, Japan and Oceania lack wildcats. North America's closest counterpart is the lynx.
There are five subspecies of wildcats, and they look very much like many pet cats, particularly non-pedigree ones. The Scottish wildcat, for example, is indistinguishable from a barn cat with a mackerel tabby coat. These animals, however, are a true wild species. They are not escaped pets that have become feral, or reverted to the wild.
Driscoll and his collaborators, who included Oxford zoologist David Macdonald, took blood samples and ear punch biopsies from all wildcat subspecies as well as from fancy-breed cats, non-pedigree pet cats and feral cats. They analyzed two kinds of genetic fingerprints: nuclear DNA, which carries nearly all of an animal's genes and reflects inheritance from both parents, and mitochondrial DNA, which exists outside the cell nucleus, carries only a few genes and descends through the generations only from mothers.
Both fingerprints showed that domesticated cats around the world are most closely related to the wildcat subspecies (called lybica) that lives in the Near East. (War prevented the sampling of Iraqi wildcats, but the researchers believe those animals are of the same species as animals they collected samples from in Israel and on the Arabian Peninsula.)
One might think that people in each region would have domesticated their local wildcats. In that case, European pet cats today would genetically most closely resemble European wildcats and Chinese cats would be descended from East Asian wildcats. But that isn't the case.
Genetics can't answer the question, but history and archaeology can provide a good guess.
Large-scale grain agriculture began in the Near East's Fertile Crescent. With the storage of surplus grain came mice, which fed on it and contaminated it.
Settled farming communities with dense rodent populations were a new habitat. Wildcats came out of the woods and grasslands to exploit it. They may have lived close to man -- but not petting-close -- for centuries.
Eventually, though, natural selection favored individual animals whose genetic makeup by chance made them tolerant of human contact. Such behavior provided them with things -- a night indoors, the occasional bowl of milk -- that allowed them to out-compete their scaredy-cat relatives.
For people, it was a great package -- agriculture, food surplus (and all the civilizing effects that came with it), with domesticated cats thrown in to protect the wealth by eating the mice.
"When that technology was transferred to other cultures, so were the cats," said Robert Wayne, an evolutionary biologist at the University of California in Los Angeles. Therein lies the reason other cultures didn't domesticate local wildcats, he said. "Why reinvent the wheel?"
This is not true with other acts of animal domestication.
Genetic studies have shown that cattle, goats, sheep, pigs and water buffalo were all domesticated at least twice in independent events. With horses, it happened many times.
The consequence of one other feline behavior -- the average cat's uncertainty about whether it wants to be indoors or out -- was also written in the genes Driscoll studied.
He found that a significant fraction of wildcats in Europe, southern Africa and central Asia were hybrids. They carried genetic evidence of having tomcatted around from time to time with their domesticated relatives.