DNA tells tale of how cats conquered the world | Science News for Students

DNA tells tale of how cats conquered the world

Analyzing 9,000 years of cat remains points to two waves of feline migration
Jul 10, 2017 — 7:05 am EST
cat grass

Caption: 

Before cats achieved world dominion, they spread in two waves, a DNA study suggests. Early Middle Eastern farmers probably brought kitties and agriculture to Europe over land. Egyptian cats may have been transported by boat to far-reaching parts of Europe, Africa and Asia.

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Astrid860/iStockphoto

Before cats achieved world dominion, they spread in two waves, a DNA study suggests. Early Middle Eastern farmers probably brought kitties and agriculture to Europe over land. Egyptian cats may have been transported by boat to far-reaching parts of Europe, Africa and Asia.

Astrid860/iStockphoto

When it comes to revealing when and how wild felines became couch kitties, the cat is starting to come out of the bag. Cats were likely first tamed in the Middle East. Later, they spread — first by land, then by sea — to the rest of the world, researchers now report.

Early farmers brought cats with them to Europe from the Middle East by 6,400 years ago. That’s the conclusion from looking at DNA from 352 ancient cats. A second wave of migration, perhaps by ship, appears to have occurred some 5,000 years later. That’s when Egyptian cats quickly colonized Europe and the Middle East.

Researchers describe how they came to these dates in a new study. It was published June 19 in Nature Ecology & Evolution.

Domestication (Doh-MES-ti-kay-shun) is the long and slow process by which people have adapted wild animals or plants to be tame and useful. Wolves became dogs, for instance. Wild ox became cattle. And wildcats became house cats.

Exactly where and when this happened to cats, though, has been a matter of great debate. Researchers had only the DNA from modern cats to work with. These data showed that house cats had been tamed from African wildcats. What was not clear was when domesticated cats began to spread around the world. Now, new ways of studying ancient DNA are pointing to some answers.

Eva-Maria Geigl and Thierry Grange are behind this deepest dive yet into the genetic history of cats. They are molecular biologists. Both work at the Institute Jacques Monod in Paris, France. Mitochondria (My-tow-KON-dree-uh) are tiny energy-producing structures inside cells. They contain a bit of DNA. Only mothers, not fathers, pass mitochondria (and its DNA) to their offspring. Scientists use slightly different varieties of mitochondrial DNA, called mitotypes, to track the female side of families.

Geigl, Grange and their colleagues collected mitochondrial DNA from 352 ancient cats and 28 modern wildcats. These felines spanned 9,000 years. They came from regions stretching across Europe, Africa and Southwest Asia.

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Egyptian cat
Ancient Egyptians often depicted cats in paintings and statues. Cats were frequently first portrayed as hunters killing snakes. Later, they showed felines curled up under chairs (like this cat from a copy of a wall painting in the private tomb of a man named Nakht in Thebes). That progression may mirror the cat’s transformation from a solitary, wild hunter that captured vermin around ancient farmers’ grain stores to a sociable house pet, say researchers involved in a new study.
ANNA (NINA) MACPHERSON DAVIES © ASHMOLEAN MUSEUM/UNIVERSITY OF OXFORD

About 10,000 to 9,500 years ago, African wildcats (Felis silvestris lybica) may have tamed themselves. They would have hunted rodents and scavenged scraps from the homes of early farmers in the Middle East. People probably encouraged the cats to hang around as a way for these farmers to control mice, rats, snakes and other vermin. The arrangement would have been “mutually profitable for both sides,” explains Grange.

No one really knows how friendly people and cats were with each other at the beginning of cat domestication. Some people may have been very close to their pet cats. Indeed, one person on the Mediterranean island of Cyprus, 9,500 years ago, was buried with a cat. Says Geigl, this suggests that some people, back then, already had close ties to cats.

Before early farmers started migrating from the Middle East to Europe, European wildcats (Felis silvestris silvestris) carried one mitotype. It’s called clade I. A 6,400-year-old Bulgarian cat and a 5,200-year-old Romanian cat had a different type of mitochondrial DNA. They both had mitotype IV-A*. That mitotype was previously seen only in domesticated cats from what is now Turkey.

Cats are territorial and usually don’t roam far. This suggests people must have transported cats to Europe.

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cat patterns
Wildcats and early domestic cats all looked the same with tiger-striped, mackerel coat patterns. Now, though, about 80 percent of modern domestic cats carry a mutation that gives a cat a blotched tabby coat pattern. New genetic data suggest this mutation first popped up in Southwest Asia during the Middle Ages. (Boxes in chart represent ancient cats sampled as part of a DNA study. Blue indicates mackerel coats and red the blotched tabby pattern.) The blotched look may have spread rapidly because it helped people distinguish their kitties from all the mackerel look-alikes.
C. OTTONI ET AL/NATURE ECOLOGY & EVOLUTION 2017

Mummies (and more) tell another story

Domesticated cats in Africa — including three cat mummies from Egypt — had yet another mitotype. It’s known as IV-C. Until about 2,800 years ago, that type was found mostly in Egypt. But then it began showing up in Europe and the Middle East. And between 1,600 and 700 years ago, it spread far and fast. By then, seven of nine of the ancient European cats the researchers tested now carried this Egyptian type of DNA. Among them was a 1,300- to 1,400-year-old cat from a Viking port far to the north, on the Baltic Sea.

Thirty-two of 70 cats from Southwest Asia also had that mitotype. That rapid spread may indicate that sailors traveled with cats, some of which could have jumped ship to find a new home.

The speedy spread of the Egyptian cats’ DNA could mean that something made these animals especially attractive to people, Geigl and Grange say. House cats aren’t much different from wildcats. The big difference is that domestic cats tolerate people. And the Egyptian cats may have been particularly friendly. They may have more resembled the type of purring pet found in homes today, the researchers speculate. Earlier house cats might have been more comfortable with people than wildcats were, but still have qualified as scaredy cats.

There’s not enough evidence to say that, counters Carlos Driscoll of the National Institutes of Health in Bethesda, Md. Working at its Laboratory of Comparative Behavioral Genomics, he studies the genetic bases of some behavioral traits. And Driscoll now suggests another reason why Egyptian cats got popular so fast: They may have lived along shipping and trade routes. That would have made hopping a boat to some new port easy, especially if they offered to work as mousers on the ship.

Earlier cats may have been just as popular, Driscoll says, but moving them would have been harder. Those early cats, he says, would have been “dependent on somebody putting a bunch of kittens in a basket and walking across a desert with them.”

Power Words

cattle     Also known as bovines (because they’re members of the subfamily known as Bovinae), these are breeds of livestock raised as a source of milk and meat. Adult females are known as cows and the males as bulls.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells.

clade      The entire group of living and extinct species that all descend from some common ancient ancestor.

colleague     Someone who works with another; a co-worker or team member.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions.

domestication     (v. domesticate) A process of producing a tame version of an animal from a wild one, which can take thousands of years. A domesticated animal is one that has been bred in captivity.

ecology     A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

evolution     (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. 

feline     Adjective for something having to do with cats (wild or domestic) or their behaviors.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

mackerel      An oily, oceanic fish harvested as a human food. It has wavy patterns on its back. Or a term for such wavy markings as they appear on other animals, such as cats.

migration     (v. migrate) Movement from one region or habitat to another, especially regularly (and according to the seasons) or to cope with some driving force (such as climate or war). One that makes this move is known as a migrant.

mitochondria     (sing. mitochondrion ) Structures in all cells (except bacteria and archaea) that break down nutrients, converting them into a form of energy known as ATP.

mitochondrial DNA     DNA passed on to offspring, almost always by their female parent. Housed in mitochondria, this DNA is double-stranded but circular. It’s also very small, only possessing a small share of the genes found in the main package of DNA, the material found in a cell’s nucleus.

mitotype     A group of DNA variations in mitochondria (also known as a haplotype), that tend to occur — and become inherited — as a set.

molecular biology    The branch of biology that deals with the structure and function of molecules essential to life. Scientists who work in this field are called molecular biologists.

mutation    (v. mutate) Some change that occurs to a gene in an organism’s DNA. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet. A gene with this change is referred to as a mutant.

National Institutes of Health (or NIH)    This is the largest biomedical research organization in the world. A part of the U.S. government, it consists of 21 separate institutes — such as the National Cancer Institute and the National Human Genome Research Institute — and six additional centers. Most are located on a 300 acre facility in Bethesda, Md., a campus containing 75 buildings. The institutes employ nearly 6,000 scientists and provide research funding to more than 300,000 additional researchers working at more than 2,500 other institutions around the world.

ox     A cow or bull (although normally a castrated male) raised for meat or as a draft animal on a farm.

rodent     A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

territorial     (in biology) An adjective for organisms that try to keep others of their species away from an area they control.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

vermin     Pest animals that people find noxious or disgusting — such as flies, lice, bedbugs, roaches, mice and rats. Owing to their size, speed and ability to reproduce quickly, these animals can be hard to control. Many also can spread disease.

Citation

Journal:​ ​​C. Ottoni et al. The palaeogenetics of cat dispersal in the ancient world. Nature Ecology & Evolution. Vol. 1, June 19, 2017, p. 1. doi: 10.1038/s41559-017-0139.