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New research overturns a long-held assumption that Przewalski’s horses (Equus ferus przewalskii), a rare and endangered animal native to the steppes of central Asia, are the last wild horse species. Instead, phylogenetic analysis shows Przewalski’s horses are the feral descendants of horses herded by the Botai people of northern Kazakhstan and not truly wild horses. Further, the study finds that the Botai didn’t give rise to today’s equines, an assumption previously held by many scientists.
Some of the Botai horses were found to carry genetic variants causing white and leopard coat spotting patterns. Image credit: Ludovic Orlando / Sean Goddard / Alan Outram.
“Our findings literally turn current population models of horse origins upside-down: what we used to understand as the last wild horse on the planet is in fact the descendant of the earliest domestic horses, which simply escaped human pressure and became feral during the last few millennia,” said Professor Ludovic Orlando, from the University of Copenhagen, Denmark, and the French National Center for Scientific Research.
“This was a big surprise,” added Dr. Sandra Olsen, of the Biodiversity Institute and Natural History Museum at the University of Kansas.
“I was confident soon after we started excavating Botai sites in 1993 that we had found the earliest domesticated horses. We went about trying to prove it, but based on DNA results Botai horses didn’t give rise to today’s modern domesticated horses — they gave rise to the Przewalski’s horse.”
For the study, Professor Orlando, Dr. Olsen and co-authors sequenced the genomes of 20 horses from the Botai and 22 horses from across Eurasia that spanned the last 5,500 years.
They compared these ancient horse genomes with already published genomes of 18 ancient and 28 modern horses.
The analysis found that many of the earliest Przewalski’s horses had white, spotty Dalmatian-style coats.
These horses once roamed freely along the Mongolian-China border and have recently been reintroduced to the region after having been saved from extinction in captivity.
Thousands of years ago a surprisingly large number were bred to have the Dalmation-style coloring, possibly because it looked attractive.
“Ironically, we used to think that the endangered population of Przewalski’s horses should be preserved as the last wild horses on the planet,” said Charleen Gaunitz, a Ph.D. student at the Natural History Museum of Denmark.
“We now find that they must be preserved as the closest descent of the earliest domestic horses.”
“We carried out archaeological excavations on the Botai culture for decades and have found communities living there thousands of years ago had horses who wore bits and were harnessed. They also milked their horses and ate horse meat,” the researchers said.
“New excavations show Botai people built corrals to keep horses in numbers, close to their habitations.”
“We found a corral that contained high levels of nitrogen and sodium from manure and urine. It was very concentrated within that corral,” Dr. Olsen said.
“The final smoking gun was finding residues of mares’ milk in the pottery. It’s commonplace today in Mongolia and Kazakhstan to milk horses — when it’s fermented it has considerable nutritional value and is very high in vitamins.”
“There is a lot of evidence in the archaeological record demonstrating that Botai horses were husbanded. It is not just horse meat that Botai people consumed, but also mare’s milk,” added Professor Alan Outram, from the University of Exeter.
“It was essential to Botai people to manage the horse resource as it provided the basis of their subsistence strategy. Probably horses were even first domesticated at Botai because horse riding somehow facilitated horse hunting.”
The team’s results were published online February 22, 2018 in the journal Science.
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Charleen Gaunitz et al. Ancient genomes revisit the ancestry of domestic and Przewalski’s horses. Science, published online February 22, 2018; doi: 10.1126/science.aao3297
