By Margaret Evans

Recently, genetic research published in the journal Science showed that the Przewalski’s horse, also known as the Mongolian wild horse and the Takhi, was actually not wild as defined by its heritage but descendants of the horses first domesticated by Botai people of Kazakhstan over 5,500 years ago.

It was a shock to just about everyone who has studied the species. And an even greater surprise was that modern domestic horses are not descendants from those early Botai horses as first thought. In fact, the origin of today’s modern domestic horse is still a mystery.

“This was a big surprise,” says the study’s co-author Sandra Olsen, curator-in-charge of the archaeology division of the Biodiversity Institute and Natural History Museum at the University of Kansas who led archaeological work at the Botai villages. “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, Botai horses didn’t give rise to today’s modern domesticated horses. They gave rise to the Przewalski’s horse.”

Normally, scientific discoveries are exciting times. But the sad part about this particular study is that the results indicate there are no truly wild horses left on the planet as defined by their genetic heritage. Exactly when they disappeared is unclear. But it could be that, just as ancient horses completely disappeared from North America at the end of the last Ice Age (after a spectacular evolution on this continent that began 55 million years ago), so wild horses in Europe and Asia also became scarce. It is thought that the driving force for the disappearance of horses and other large mammals in North America was rapid climate change that altered the profile of the landscape changing food and water sources. Likely those same forces reduced equine numbers across Europe and Asia just as, simultaneously, hunter-gatherers were honing their kill skills. 

“It appears, based on the archaeological record, that the end of the Pleistocene [about 11,700 years ago] led to diminished numbers of horses, probably consisting of at least two types, Equus ferus ferus [the Tarpan horse of Europe] and Equus ferus przewalskii, (some biologists separate the two horse groups into different species),” says Olsen. “Small relict populations were sprinkled over their former large range across Eurasia. The most populated area seems to have been northern Europe (northern Germany, Poland, Ukraine, Russia as far east as Kazakhstan, at least). But there were pockets in Turkey, Syria, and other areas even by 7,000 BC. The range of the wild P. type horse is really not settled at this point, but it did split off from E. ferus ferus many thousands of years prior to any domestication event.”

Photo: Canstock/PilipenkoD

According to evolutionary research, the Przewalski-type horse diverged from the horse that would lead to the modern domestic type between 38,000 and 72,000 years ago. Today, Przewalski’s horse has 66 chromosomes compared to the domestic horse with 64, while hybrids of the two have 65.

Przewalski’s horse is named after Colonel Nikolai Mikailovich Przewalski, a renowned explorer who, at the end of the 19th century, reported seeing wild horses during expeditions to Asia by order of Tsar Alexander the Second of Russia. He returned with the skull and hide of a horse which, on examination at the Zoological Museum in St. Petersburg, were confirmed as a wild horse and named in his honour.

But half a century later the population of the wild horse was in catastrophic decline due to hunting and capture for European zoos. The last wild horse was sighted in 1969 in the Dzungarian Gobi. By then, Przewalski’s horses were on display in zoos around the world, descendants from the original founder herd established in the early 1900s. From them, 13 horses were selected to begin a captive breeding program. Decades later, it led to a series of releases of Przewalski’s horses into their ancestral steppe home that began in 1992 with their release into Takhin Tal on the boundary of the Gobi National Park and the Hustain Nuruu Reserve (now the Hustai National Park and certified by UNESCO as a member of the world biosphere network). Despite challenges and some setbacks, the release program was highly successful and today there are about 2,000 reintroduced and native born Przewalski’s horses in Mongolia.

The international team of researchers sequenced the genomes of 20 horses from Botai and 22 horses from across Eurasia spanning the last 5,500 years. Many of the horse bones and teeth that were studied for analysis were those excavated by Olsen at the Botai and Krasnyi Yar sites in Kazakhstan. The genomes of the ancient horses were then compared with existing genomes of 18 ancient and 28 modern horses. From those results, the team theorized that some horses escaped the Botai herds to become the Mongolian wild horse recorded by Przewalski.

Despite the horse’s now apparent ancient domestic heritage, their appearance remains one of a classically wild horse with a stiff upright mane and the dun colour similar to those depicted in the Ice Age cave paintings in France and Spain, some dated to over 30,000 years ago. Their size today is very similar to the size of the Botai horses Olsen and her team excavated.

Complicating the story of the origins of domestic horses is the question of how many times domestication events took place.

“I think it is more likely that there were not more than two or three,” says Olsen. “What seems to be the case is that horse herders were regularly breeding their domestic stallions with wild mares they captured in order to increase their herd sizes as the herders spread out across the steppe.”

The Botai people disappeared from their roots in Botai and Krasni Yar. Along with other Bronze Age people they were on the move across the Eurasian steppe. According to Olsen, if the Botai people migrated eastward they would most likely have taken their horses with them and perhaps capitalized on other wild mares with which to breed their stallions.

“We knew the Botai either moved out of northern Kazakhstan when Bronze Age people moved in or were assimilated,” she says. “This finding suggests they moved eastward with their horses.”

The migration of Bronze Age people across a great swath of Eurasia could have led to other as yet undiscovered domestications. Much of that could be still hidden in DNA samples from between 4,000 and 5,000 years ago that are still being studied for more details of migration and population patterns.

Finding ground zero for today’s domestic horse remains perplexing.

Przewalski’s horses in the Chernobyl exclusion zone around the site of the 1986 Chernobyl nuclear reactor disaster. Photo: Shutterstock/Maryna Shkvyria

“What's interesting is that we have two different domestication events from slightly different species, or separate sub-species,” says Olsen. “It's thought that [perhaps] modern-day domesticated horses came from Equus ferus, the extinct European wild horse [or Tarpan]. The problem is they were thought to have existed until the early 1900s. But, the remains of two individuals in St. Petersburg, Russia, are probably feral or at least probably had some domesticated genes. Wild horses may have vanished a very long time ago, having been outcompeted, hunted, and eaten to extinction.”

The genetic study revealing that today’s Przewalski’s horses are descendants of captive Botai horses gives rise to a very modern question and a potential dilemma. The entire captive breeding and reintroduction program for Przewalski’s horse has been based on its indigenous wild status. It is still ranked Endangered by the IUCN Red List of Threatened Species. But does this study change the direction of future funding for the management of the horse?

“The EU has strict laws prohibiting the release of domestic herds into nature preserves like those in Mongolia, so that could halt funding for that program for the P. horse,” says Olsen. “That would be terrible! The biologists on our team tested and tested their results for a year, realizing it could have a big impact. In the end, the science has to come out but it is a shocker and rather sad.”

However, working in the horses’ favour are the conservation and management programs in China where, according to the Red List, the Wild Horse Breeding Centre in Xinjiang Province has a large captive population. Since 2001, horses have been released into the nearby Kalamaili Nature Reserve and one harem group roams free on the Chinese side of the Dzungarian Gobi. Another herd roams free during summer but is contained in an acclimatization pen during winter. The Gansu Endangered Species Research Centre has a captive breeding program with successful releases and winter feeding management programs.

In the long run, it may be that the Mongolian herders themselves will be the horses’ protectors. Today, Przewalski’s horses roaming the Gobi steppe are highly valued. Before their extirpation from native ranges, wild horses were driven from prime grasslands which were reserved for domestic sheep and cattle. That made access to winter ranges difficult for the horses.

But a study done by researchers at the University of Veterinary Medicine, Vienna, and published in Scientific Reports found that, today, Przewalski’s horses have access to high-quality grass year-round. The researchers were able to study the diet of historic and contemporary horses from chemical analysis of tail hairs, the historical samples (some 120 years old) being provided by researchers at museums in St. Petersburg and Moscow. The isotope ratios provided information on the animal’s water and nutrition intake and its habitat.

“The wild horses can now feed on grass throughout the year because humans allow it,” says lead author Petra Kaczensky, wildlife biologist.

Przewalski’s horses are protected by local communities because they are worshipped today as “holy animals” in the Gobi Desert. Kaczensky writes that it is a profound shift in human attitude that is key to the species’ survival. Perhaps it is even more vital if changes result from the DNA study and yield less funding for management programs in the future.

Meanwhile, Olsen says that the genetic study has given rise to a new scientific quest: locating the real origins of today’s domestic horses.

Really, it’s hard to let go of the image of the Mongolian wild horse as the last truly wild horse on the planet. In a time when so many species are at risk, the idea that the horse is no longer genetically wild is almost a betrayal of the species. That focus was not lost on the multidisciplinary research team.

“It is so great that molecular biologists, archaeologists and paleontologists are coordinating their efforts,” says Olsen. “It is key that the biologists get meaningful samples to analyze and the archaeologists and paleontologists can provide those. Then, how the DNA results are interpreted and explained becomes more trustworthy when all the scientists from the different disciplines weigh in on it. That is the stage we are in now and, while it may disrupt the status quo, we can answer questions we never dreamed possible. In my opinion, the Przewalski’s horse may be even more remarkable than we previously thought. It represents a very early, if not the earliest, lineage of domesticated horses that needs to be preserved for historical reasons.”

Main article photo: Canstock/PilipenkoD