Domesticated Horses' Unknown History

Unsaddling Old Theory on Origin of Horses

CNRS, Paris, February 22, 2018 -- Botai horses were tamed in Kazakhstan 5,500 years ago and thought to be the ancestors of today's domesticated horses . . . until a team led by researchers from the CNRS and Université Toulouse III–Paul Sabatier sequenced their genome. Their findings published on 22 February 2018 in Science are startling: these equids are the progenitors not of the modern domesticated horse, but rather of Przewalski's horses—previously presumed wild!

The earliest proof of equine domestication points to the steppes of Central Asia roughly 5,500 years ago. Current models suggest that all modern domesticated horses living now descend from those first tamed in Botai, in the north of present-day Kazakhstan. For CNRS scientist Ludovic Orlando—from the Anthropologie Moléculaire et Imagerie de Synthèse research lab (CNRS / Université Toulouse III – Paul Sabatier / Paris Descartes University)—and his team, sequencing the genomes of 20 of these horses provided a snapshot of biological evolution associated with domestication. Indeed, it is nearly impossible to uncover the earliest stages of domestication through analysis of modern horse genomes, which have been considerably transformed by humans through selective horse breeding.

Yet this genomic analysis yielded unexpected results. Though Botai horses did not give rise to today's domesticated horses, they turn out to be direct ancestors of Przewalski's horses. Thus the latter, commonly thought to be the last wild horses on our planet, are actually the feral descendants of the first horses ever to have been domesticated. The study highlighted certain changes that occurred with this return to a wild state, including the loss of leopard spotting characteristic of the Botai horse. The allele responsible for this coloration was probably eliminated by natural selection as it also caused night blindness.

The team's genomic analysis of twenty-two Eurasian horses, whose lives collectively span the last 4,100 years, has revealed that none are related to the Botai horse. So the origin of modern domestic horses must be sought elsewhere. The researchers are now focusing on other candidate locations in Central Asia as well as on the Pontic-Caspian steppe of southern Russia, in Anatolia, and at various European sites that are refuges for these animals.

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