Genetic research has provided a startling insight into the earliest known instance of horse domestication around 5500 years ago, revealing that they were not the ancestors of modern domestic breeds but rather the Przewalski’s horse.
The Przewalski’s horse, or takhi, has long been considered the only surviving horse subspecies never to have been domesticated.
The findings of the research published today change the picture dramatically. Przewalski’s horses are likely to be the feral descendants of the first horses known to be domesticated, and the origin of the modern domestic horse remains shrouded in mystery.
The earliest credible evidence of horse domestication dates back to the Botai culture, who are believed to have tamed horses in northern Kazakhstan around 3500 BC.
Current models suggest that all modern domesticated horses are descended from those first tamed by the Botai people.
But the latest genetic findings by researchers from the French National Center for Scientific Research (CNRS) and Paul Sabatier University in Toulouse, who sequenced their genome, suggest otherwise.
CNRS scientist Ludovic Orlando and his colleagues, writing in the journal Science, described their successful sequencing of the genomes of 20 of these horses, provided a snapshot of biological evolution associated with domestication.
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.
The genomic analysis conducted by Orlando and his fellow scientists yielded unexpected results.
Botai horses did not give rise to today’s domesticated horses, but instead they turn out to be direct ancestors of Przewalski’s horses.
Stunningly, the Przewalski’s horse, commonly thought to be the last true wild horses in existence, are actually the feral descendants of the first horses ever to be domesticated.
The study highlighted certain changes that occurred with this return to a wild state, including the loss of the leopard spotting characteristic of the Botai horse.
The gene variant responsible for this coloration was probably eliminated by natural selection as it also caused night blindness.
The team’s genomic analysis of 22 Eurasian horses, whose lives collectively span the last 4100 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.
The case for horse domestication within the Botai culture around 3500BC, first reported in 2009, involves three independent lines of evidence.
It is firstly based on analysis of horse leg bones showing that Botai horses resembled Bronze Age domestic horses rather than Paleolithic wild horses from the same region. This suggests that people were selecting wild horses for their physical attributes, which were then exaggerated through breeding.
The researchers offered evidence that some Botai horses were bridled, perhaps ridden. They also ran organic-residue tests which they said pointed to the processing of mare’s milk and carcass products in ceramic containers.
The steppe zones, east of the Ural Mountains in northern Kazakhstan, are known to have been a prime habitat for wild horses thousands of years ago. They were a commonly hunted animal.
This, the researchers argued, may have set the stage for horse domestication by providing indigenous cultures with access to plentiful wild herds and the opportunity to gain an intimate knowledge of equine behaviour.
The Przewalski’s horse was once common in Eurasia but hunting and habitat destruction led to its extinction in the wild. This was officially declared in 1969.
China started a breeding program in 1986 using horses brought back from Britain and Germany to repopulate the subspecies. Scores of horses bred through the program have since been released into the wild.
Today, about 2000 Przewalski’s horses survive – making them even rarer than pandas. They are all descendents of only a dozen or so Przewalski’s horses.