Richard Collins: Primordial horse of the steppe is gone forever

Hunited for its meat on the steppes of Central Asia, the horse seems to have been domesticated by the Botai people of Kazakhstan five and a half millennia ago. The noble beast was revered even then; horse skulls were buried with their snouts facing the rising sun, writes Richard Collins.

A thousand years later, working animals were brought to the Middle East; a Mesopotamian depiction of one with a rider dates from that time. Over the centuries, quadrillions of tonnes of soil were turned by horse-drawn ploughs. Horses helped us build civilisation, explore the world and fight wars. Until steam-trains arrived, they offered the fastest means of transport. What became of their wild ancestor? Experts speculated that it might be still alive, but a paper just published suggests that it isn’t.

Horses were depicted on the walls of the Chauvet Cave about 31,000 years ago. The 17,000-year-old Lascaux paintings include 364 images of horses. Similar illustrations at Altamira are 15,000 years old. The free-roaming white herds of the Camargue, however, are not direct descendants of these ancient beasts; they derive from Celtic and Roman domesticated ones. Likewise, the wild mustangs of the American West, protected by the US Bureau of Land Management, are feral animals of colonial Spanish origin.

The great German naturalist Gmelin described a horse he saw in Russia in 1769. Its local name, “tarpan”, means “wild horse” in old Turkish. Driven into extinction in the 19th century, the last tarpan died on a Russian estate in 1909. The jury is still out as to its evolutionary status.

In 1881, the Russian geographer Nikolai Przewalski led an expedition to Mongolia. He described a type of horse living wild there which, it seemed, had never been tamed. Twenty years later, Przewalski horses were captured and taken to the West for a breeding programme. There were 31 in captivity by 1945. No Przewalski has been seen in the wild since 1966. In 1992, 12 captive-bred animals were returned to the steppes. Following further releases in Mongolia, and on the fringes of the Gobi Desert, the reintroduced horses prospered; there are now over 300 in the wild. Their IUCN designation “extinct in the wild” has been changed to “endangered”.

However, is the Przewalski a truly wild horse? Is it the primeval ancestor of all breeds alive today? Are its genes unsullied by domestication? A 47-member research team, drawn from 28 institutions worldwide, generated 42 ancient horse genomes, including 20 Botai ones. Forty-six published genomes were also examined. The results, appearing in the journal Science, show that the Przewalski is not, alas, a true wild horse. It’s a descendant of those herded by the Botai people. Even its appearance has changed; the genes show that the Przewalski’s coat used to have leopard-like spots but natural selection eliminated them over the centuries.

The origins of modern horses turn out to be much more diverse than was thought.

“All domestic horses dated from 4,000 years to the present only show 2.7% Botai- related ancestry. This indicates that a massive genomic turnover underpins the expansion of the horse stock that gave rise to modern domesticates,” say the scientists.

It “coincides with large-scale human population expansion during the Early Bronze Age”.

Like the auroch, whose domestic cattle descendants are the most successful large mammals in the world today, the primordial horse is gone forever. This result is a blow to Przewalski enthusiasts. With further DNA analysis, researchers may eventually uncover the horse’s true family tree.

Charleen Gaunitz et al. Ancient genomes revisit the ancestry of domestic and Przewalski’s horses. Science. February 2018.

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