UNDER THE MICROSCOPE:THE DOMESTIC cat may be the most popular pet, with more than 600 million in homes worldwide. The cat was a cult animal in ancient Egypt and until recently it was believed it was first domesticated there about 3,600 years ago. However, recent research indicates that domestication of the cat began about 10,000 years ago when agriculture was beginning. The story is told by CA Driscoll, J Clutton Brock, A Kitchener and SJ O'Brien in Scientific American, June 2009.
It was long suspected that all varieties of domestic cat are descended from the wild-cat species Felis silvestris, which is scattered throughout the Old World. Researchers (Driscoll, O'Brien and others) recently analysed DNA from wildcats and domestic cats across the Old World to determine which subspecies of Felis silvestris gave rise to the house cat. The DNA clustered into five groups, each coming from a specific region – Europe, central Asia, southern Africa, China and Middle East. Domestic cats grouped only with Felis sylvestris lybica, the Middle Eastern wildcat, showing that all house cats are descended from Fs lybicaalone.
When was the house cat domesticated? In 2004 the National Museum of Natural History in Paris reported that adult human remains were found in a shallow 9,500-year-old grave in Cyprus and 40cm away in its own little grave was an eight-month-old cat whose body was oriented in the same direction as the human. Cats are not native to most Mediterranean islands and must have been taken there by boat. Together with the archaeological data, this indicates that people had developed a special relationship with cats almost 10,000 years ago, about the time agriculture was beginning in the Middle East.
There is good reason to wonder why cats and humans developed a special relationship. Driscoll and colleagues point out that cats are unlikely candidates for domestication for a number of reasons. First, other wild animals were domesticated to supply humans with food, clothing or labour, but cats contribute neither sustenance nor work to humans. Second, cats would be difficult to domesticate. The ancestors of most domesticated animals lived in herds with hierarchical structures. Humans simply supplanted the dominant herd individual. Cats, however, are solitary hunters that defend their territory. They are obligatory carnivores and cannot be fed on easily available plant foods. And cats certainly do not take well to instruction. It is therefore highly likely that cats chose humans rather than the other way around as with other domesticates.
Settlements at the dawn of agriculture about 10,000 years ago provided new opportunities for animals capable of exploiting them, for example the house mouse who moved indoors to feed on stores of wild grain. These mice attracted cats, as did trash heaps on the outskirts of settlements. Natural selection favoured the survival of those cats capable of collaboration with humans.
Cats would have appeared attractive to humans since they got rid of mice and snakes. Also, wildcats have “cute” features – snub face, large eyes and high rounded forehead – known to elicit nurturing feelings in humans. The authors explain that as agriculture spread out from the Fertile Crescent, so too did the now tame Fs lybica, occupying the same niche everywhere they went, thereby preventing the local wildcat population from fulfilling that role.
The high-point of the domestic cat came during Egypt’s golden era, which began 3,600 years ago. Paintings from that period show that cats were fully domesticated. The cat became the “official deity” of Egypt in the form of the goddess Bastet. Egypt banned the export of cats for centuries, but by 2,500 years ago cats had reached Greece, from where they spread throughout the Roman Empire.
Cats spread to the east about 2,000 years ago along trade routes. These cats evolved along their own trajectory in the absence of native wildcats with whom to interbreed. Isolated groups of oriental domestic cats developed distinctive coat colours and other mutations through a process called genetic drift, leading to the emergence of “natural breeds” such as the Siamese cat. The Mayflower brought cats to the US and cats reached Australia with European explorers in the 1600s.
Serious efforts to produce novel breeds of cat did not begin until relatively recently. Nearly 60 breeds of domestic cat are now recognised. Genetic differences between domestic cat breeds are slight, comparable to that between adjacent human populations such as French and Italians.
We do not see the wide variety of size, shape and temperaments in cats as we do in dogs, eg Great Dane and chihuahua. Humans have selectively bred dogs since prehistoric times to do useful things such as herding, guarding, hunting and so on, but cats show no inclination to do tasks that are useful to humans and consequently were never subjected to much selective breeding pressures.
William Reville is UCC’s associate professor of biochemistry and public awareness of science officer
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