Cats

 

                                                                

Sometime around the invention of agriculture, the cats came crawling. It was mice and rats, probably, that attracted the wild felines. The rats came because of stores of grain, made possible by human agriculture. And so cats and humans began their millennia-long coexistence.

This relationship has been good for us of course—formerly because cats caught the disease-carrying pests stealing our food and presently because cleaning up their hairballs somehow gives purpose to our modern lives.

But this relationship has been great for cats as species, too. From their native home in the Middle East, the first tamed cats followed humans out on ships and expeditions to take over the world—settling on six continents  with even the occasional foray to Antarctica.

Domestication has been a fantastically successful evolutionary strategy for cats. A comprehensive new study of DNA from ancient cat skeletons and mummies spanning 9,000 years traces the spread of cats from the Middle East to the rest of the world. The whole study, from conception to publication, took about 10 years—not least because of the work it took to find ancient cat remains.

“Cat remains are scarce,” says Eva-Maria Geigl, a paleogeneticist at Institut Jacques Monod and an author on the study. We don’t eat cats for food, so their bones don’t end up in ancient trash piles the way pig or chicken bones do. Geigl and her colleagues, especially Wim Van Neer, wrote to museums and collections asking to sample cat remains found in archeological digs.

The team ultimately got bone, teeth, or hair from 352 ancient cats—including Egyptian cat mummies at the British Museum. Not all of the remains yielded DNA. The Middle East environment is hot. In Egyptian tombs, where the cat mummies came from, it was also humid.

“This is really a disaster for DNA,” says Geigl. The very act of extracting DNA can damage it, too. So to protect the DNA from heat released when bones and teeth are ground, the grinding process happens in a liquid nitrogen bath. Ultimately, the team was able to get DNA from 209 of the cats. This large number of samples painted a fairly detailed picture of how cats followed humans on trade routes.

Modern domestic cats appear to have all originated in one of two places.  The first was Anatolia, which roughly corresponds to modern-day Turkey. These cats spread to Europe as early as 4,400 B.C.E. A second domesticated lineage appears to have begun in Egypt and then later spread through the Mediterranean. And wherever the cats followed humans, they also interbred with the native wildcats already there.

This DNA exchange went both directions along the trade routes, too. That led to what, at first, seemed like baffling results in the ancient DNA. For example, a 2,000-year-old cat in Egypt had DNA sequences typical of wildcats in India.  Claudio Ottoni, another member of the research team now at the University of Oslo, remembers thinking it was a mistake when he first got the sequences back on his laptop.

In fact, that cat was found in an ancient Roman port city called Berenike, which was directly connected to trade routes in the Indian Ocean. Humans brought cats onto ships to catch mice and, in the process, spread cats all around the world. Compared to many other animals, cats have also changed very little in the domestication process.

Behaviorally, they’ve become more tolerant of humans. Physically, though, they’re still about the same size and shape. They still like to pounce on small prey. “Cats have done since before they were domesticated what we needed them to do,” says Leslie Lyons, a feline geneticist at the University of Missouri.

In other words, unlike dogs that herd sheep or hunt badgers, cats didn’t need humans to breed them to become good mouse hunters. But wildcats and pet cats do look differently in a small but obvious way to humans: Domestic cats come in a great variety of colors and coat patterns. From the ancient DNA, Geigl and her colleagues determined that the tabby pattern first emerged in the Middle Ages based on a single letter mutation in the Taqpep gene.

This was the only coat gene Geigl and her colleagues investigated. For the most part, their analysis focused on DNA in a part of the cell called mitochondria, which is more abundant than DNA in chromosomes but accounts for only a tiny fraction of genes.

This is a good start, says Greger Larson, a paleogenomicist at Oxford, and it sets the stage for using ancient chromosomal DNA to further refine the story of ancient cats. Larson has done similar work with ancient dog DNA. “It’s great that cats are the getting same long deserved treatment,” he says of the new paper. “It’s kind of strange it’s taken this long given the general interest in cats.”

The dog days of ancient cat DNA are over.

-Sarah Zhang is a staff writer at The Atlantic.