DNA reveals that cows were almost impossible to domesticate

By | April 6, 2012

Breeding of Iranian Aurochs resulted in all modern cattle.  Image: Modern breed of Aurochs, “rebred” to the original

 

Cows are quite possibly the most important domesticated animal in human history, providing vast quantities of meat, dairy products, leather, and let’s not forget manure for fertilizer. And yet DNA analysis reveals ancient humans almost didn’t succeed in domesticating cows at all.

There are about 1.3 billion cows in the world today. That makes just a bit of a change from 10,500 years ago, when the first population of domesticated cattle was likely just eighty head. That’s the new finding from a team of British, French, and German researchers, who extracted DNA from cow bones found at an Iranian archaeological site that dates to not long after the domestication of cows.

They discovered that the differences between these ancient DNA sequences and those of modern cattle were so minute that the only way to explain them would be if the original cattle population was extremely small, with about 80 cattle the most likely number. As the researchers explain in Molecular Biology and Evolution, since the domestication process was spread out over a thousand or so years, that’s the equivalent of only adding two new cattle each generation.

That’s a recipe for astoundingly low genetic diversity — and yet it seems that pretty much every living cow can claim ancestry to those eighty cows and no others. It’s a testament to how skilled ancient humans must have been at breeding cattle that the population survived and thrived the way it did, as these cows were effectively domesticated into an instant population bottleneck.

To put it in perspective, one of their wild counterparts, the American bison, almost went extinct in the late 19th century, and its population never dipped below about 750, nearly ten times the founding cattle population. There are recent examples of species whose population fell below 80 — the European bison and northern elephant seal both dropped to just 30 — and even as their numbers slowly recover, they continue to teeter on the brink of extinction.

Eighty initial cattle would have given their human breeders pretty much no margin for error in terms of maintaining genetic diversity, and yet the billion cows alive today reveal just how remarkably well they succeeded in growing the population. The fact that all cattle seemingly descend from a single domestication event is also unusual — for most other domesticated animals like horses or dogs, there’s good evidence to support multiple domestication events, even if some lineages ultimately died out. But we know from the analysis of the ancient Iranian cattle bones that all cows throughout history likely only came from this one population.

The reason for all this is likely that the wild ancestors of cows, known as aurochs, were nearly too wild to domesticate at all. Though the archaeological record makes it clear that aurochs roamed throughout Europe and Asia, it seems that either most domestication attempts failed or most people just thought the better of trying to tame these creatures. …

via DNA reveals that cows were almost impossible to domesticate.

Domestication of the aurochs began in the southern Caucasus and northern Mesopotamia from about the 6th millennium BC, while genetic evidence suggests that aurochs were independently domesticated in northern Africa and in India. Domestication caused dramatic changes to the physiology of the creatures, to the extent that domestic cattle must now be regarded as a separate species.

Genetic analysis has provided many insights about the aurochs. Though aurochs became extinct in Britain during the Bronze age, analysis of bones from aurochs that lived contemporaneously with domesticated cattle there showed no genetic contribution to modern breeds. So modern European cattle are thought to be descended directly from the Near East domestication event. Indian cattle (zebu), although domesticated eight to ten thousand years ago, are related to aurochs which diverged from the Near Eastern ones some 200,000 years ago. The African cattle are thought to descend from aurochs more closely related to the Near Eastern ones. The Near East and African aurochs groups are thought to have split some 25,000 years ago, probably 15,000 years before domestication. The “Turano-Mongolian” type of cattle now found in Northern China, Mongolia, Korea and Japan may represent a fourth domestication event (and a third event among Bos taurus–type aurochs). This group may have diverged from the Near East group some 35,000 years ago. Whether these separate genetic populations would have equated to separate subspecies is unclear.

The original range of the aurochs was from the British Isles, to Africa, the Middle East, India and central Asia. By the 13th century A.D., the aurochs’ range was restricted to Poland, Lithuania and East Prussia. The right to hunt large animals on any land was restricted to nobles and gradually to the royal household. As the population of aurochs declined, hunting ceased but the royal court still required gamekeepers to provide open fields for the aurochs to graze in. The gamekeepers were exempted from local taxes in exchange for their service and a decree made poaching an aurochs punishable by

death. In 1564, the gamekeepers knew of only 38 animals, according to the royal survey. The last recorded live aurochs (female) died in 1627 in the Jaktorów Forest, Poland.

In the 1920s two German zookeepers, the brothers Heinz and Lutz Heck, attempted to breed the aurochs back into existence (see breeding back) from the domestic cattle that were their descendants. Their plan was based on the conception that a species is not extinct as long as all its genes are still present in a living population. The result is the breed called Heck Cattle, ‘Recreated Aurochs’, or ‘Heck Aurochs’, which bears an incomplete resemblance to what is known about the physiology of the wild aurochs.

via SheppardSoftware

This gives ancient stories of men fighting bulls (Gilgamesh, for example) new meaning. The bulls back then were way more powerful and fierce than any bulls we know today.

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