Domestication Enabled Cats to Rule the World
Using analyses of ancient DNA, for the first time the rapprochement between cats and humans since Neolithic times has been reconstructed spatially and temporally. Two successive waves of cats “conquering the world” were revealed: the first from south-east Asia, and the second from Egypt.
In Egypt, from 1500 before our era, the animal is represented in a domestic context, in a motive called "cat under the chair".
Today, cats have conquered the real world, and also the virtual internet world. This success is closely linked to that of the human species. Thanks to the combination of genetics and archeology, we were able to spatially and temporally reconstitute this common history which has lasted about 10,000 years. We have established that cats conquered the world in two successive phases: the first from South-West Asia and the second from Egypt.
Modern cat genetics reveal the origin of domestic cats and their closeness to wild cats. The comparison of the genomes of wild and domestic cats revealed that only a small number of genes evolved over the domestication of this species, far less than for most other domesticated species, particularly dogs. They are mainly genes involved in the development of a key structure in the embryonic nervous system, the neural crest, which have changed over time.
The origin of the cat itself was found using mitochondrial DNA. This corresponds to a small genome of 16,000 nucleotides present in the mitochondria, an intracellular organelle (*) responsible for the production of energy when cells breathe. This genome is passed down from generation to generation through the mother. Studying it means the geographic origin of the maternal ancestry of these individuals can be found.
BENFICIAL RELATIONSHIP
Around ten years ago, a study of modern cat DNA distinguished the five sub-species of wildcats: Felis silvestris (abreviated to F. s.) silvestris, F. s. lybica, F. s ornata, F. s. cafra and F. s. bieti. Each one is endemic to a specific region: respectively, Europe, North Africa and South-West Asia, Central and Southern Asia, South Africa and North-East Asia. The genetic analysis also revealed that current domestic cats mainly carry the maternal gene of F. s. lybica (the sub-species from North Africa and South-West Asia), also some contributions from other wildcats can be seen, namely from F. s. sylvestris (Europe).
HEARTHS OF PROPAGATION
Map ©D-MAP.com - Muriel Seisser
While the data from this study do not enable the domestication process to be reconstituted further, nor the precise origin of cats to be established, they are compatible with the archaeological data, which indicate a link between this domestication and the invention of agriculture during the Neolithic period. A few cat skeletons found in tombs, show that the relationship between cats and humans started in at least 7,500 B.C. This is suggested by the discovery in 2004 of cat bones in a child’s tomb on the island of Cyprus. A 3,700-year-old tomb discovered in northern Egypt in 2014 also points to this. It contains the remains of six cats of varying ages (two adults - one male and one female about one year old - and four kittens aged from four to five months) (see here and here).
What Brought Cats and Humans Together? It probably began when humans started accumulating grain stores. These would have attracted rodents, fed on by the cats. The bravest cats could have commenced a mutually beneficial relationship with the humans, the cats finding food in large quantities and ridding the humans of the vermin consuming their food stores although excrement remained.
This special relationship can be seen in ancient iconography, especially in the Egypt of the pharaohs. Here again, tombs are a precious indicator of the gradual rapprochement between cats and humans over time. Between 2000 and 1500 B.C., cats were represented in Egyptian tombs as animals to rid them of vermin; for example, a cat can be seen cutting off the head of the demon god Apophis, who was threatening the god Ra during his nocturnal voyage into the underworld. Thanks to the cat, day returns and chaos is avoided.
IN THE MARSCHES
In the second half of the 2nd millennium B.C., representations of cats developed further. It is shown as a hunting companion, especially for birds, in the motif traditionally known as “the cat in the marsh”. It also increasingly appears in a domestic setting. Cats are now installed under the chairs of humans, especially women, in a motif called “the cat under the chair”.
Both discipines, genetics and archaeology, have independently shed light on the rapprochement between cats and humans. Thanks to the recent development of paleogenetics however, which combines data from the latter two disciplines, for the first time we are able to accurately reconstitute the history of the spread of cats across the world, from the origins of their relationship with humans.
To obtain this result, we used a new high-speed sequencing method used to analyse ancient samples of damaged DNA, to study 352 ancient samples and 28 modern samples from wildcats. These samples came from around 9000 B.C. from Europe, South-West Asia and North Africa. More specifically, we analysed the most characteristic short sequences from various groups of feline mitochondrial DNA. By looking for the genetic signature of various sub-species of wildcats in ancient populations of domestic cats, we discovered the geographic structure of these sub-species.
In particular, we looked at the sub-species F. s. lybica, which includes five genetic variations belonging to five regions of the world; cats are territorial animals that migrate very rarely. These variations were named A, B, C, D and E. Two of the five variations are very present: variation A, characteristic of Anatolia, and variation C, from Egypt. By following them we were able to retrace the evolution of the spatial distribution of F. s. lybica over time.
SHEEP, PIGS, CATTLE
Before and at the start of the Neolithic era, the situation was simple; a specific sub-group of DNA can be found in each geographical region. Then, around 6,500 years ago, cats bearing the genetic variation A arrived in Europe. This corresponds to what is known of human history at the time. Agriculture was invented a little over 10,000 years ago in the Fertile Crescent, a region in the Near-East passing through the current states of Israel, Palestine (not a state!!), Jordan, Syria, Lebanon, Turkey (south-east), Iraq (north and east) and Iran (the western edge). In the same region, it was followed by the domestication of goats, sheep, pigs and cattle. These first farmers then migrated to Europe in around 6000 or 7000 B.C. bringing with them their inventions... and their cats. Indeed, they could not have arrived under their own steam; the strait of the Bosphorus was under water at the time.
Cats spread mainly via the sea; this was established for the first time thanks to remains found in the port of Berenike, located on the Red Sea and founded in 260 BCE. We found the DNA signature of F. s. ornata, a wildcat living in India. Archaeologists have established that this was a country that traded a lot with Egypt. Cats played a key role on ships; hunting rodents, a risk to the food and other rope and leather items on a ship. The vital role of cats on ships continued into modern times, as their presence was mandatory in the British navy until the 20th century.
At the same time, the C variation, corresponding to Egyptian cats, spread across Europe, supplanting the Anatolian variation. Between 800 and 1300 BCE, it was highly successful; more than half the cats in Anatolia carried this genetic signature at the end of this period. In addition, these cats travel over great distances. For example, all the cats identified in a Viking port on the Baltic sea around the 6th century carry the Egyptian origin signature. Why So Successful? Maybe because they were more sociable. From a genetic standpoint, few differences can be observed between wildcats and domestic cats, with the exception of some genes involved in brain structure, and which could act on behaviour and sociability. This would explain why humans were attracted to these cats, although this hypothesis remains to be confirmed.
ONE-OFF MUTATION
Final part of our paleogenetic analysis; following a genetic marker responsible for a variation in the cat’s coat, changing it from tiger-striped to marbled. This coat is particularly well represented in current domestic populations. It results from a one-off mutation whose appearance and spread we followed over time. It seems to have originated in South-West Asia. It first developed during the Ottoman Empire before spreading to Europe, probably due to its popularity. In terms of timing, it was late, as it occurred after the year 1000. All the more so if we compare it to changes that have been observed in other domestic animals. From this point of view, the example of the horse is significant; in horses, changes in coat came with the start of domestication, several thousands of years earlier.
Only in the 19th century during the genetic selection frenzy on farm animals and pets, did the cat’s genome evolve more rapidly. This phenomenon was accentuated by growing urbanisation and the gradual disappearance of wildcats’ habitat, leading to a recent separation between the populations of wildcats and domestic cats. This separation limits genetic flows between them and accelerates their divergence. The relationship of subordination arising from this domestication is so recent that it could explain how cats have retained a large part of their deep-seated independence, which among other characteristics, contributes to their great success on the web.
(*) An organelle is a specialist structure contained in a cell’s cytoplasm
NATURAL RAPPROCHEMENT
Late selection of a genetic variation (**) should be placed in parallel with the small number of genes selected in the cat during domestication. Cats probably accomplished the tasks that humans expected of them, naturally and early on without asking for much attention and without the need for protection from them. It was therefore not necessary to improve their genome. It is even conceivable that the changes in behaviour revealed by genomics were selected without the direct intervention of humans. In other words, the less ferocious genetic variants, more compatible with closeness to humans, moved closer to dwellings and prospered, thanks to the regular supply of food that this proximity brought.
(**) A genetic variant is an individual of a species that has a slight mutation in its genome.
>AUTHORS
Thierry Grange and Eva-Maria Geigl
Geneticists
Thierry Grange and Eva-Maria Geigl, CNRS research directors, jointly manage the Epigenome and Paleogenome team at the Institut Jacques Monod in Paris. They are studying the evolution of genomes, the hereditary material of living organisms, by analysing the DNA preserved in ancient biological remains.
