The Przewalski’s horses that dot the plains of Mongolia have long been considered the last wild horses in the world. While wild horses like the American mustangs in the western United States and the horses on the Shackleford Banks in North Carolina are actually feral horses descended from ancestors that were once domesticated, scientists thought the Przewalski’s horse had never been tamed. A new genomic study, however, is forcing us to rethink our assumptions.
In a paper published Thursday in the journal Science, an international team of researchers describe the findings of their genetic analysis of these seemingly undomesticated horses. In the study, they investigated the genomes of 88 modern and ancient horses to find out how similar the horses that were raised by the Eneolithic Botai people over 5,000 years ago in modern-day Kazakhstan are to the horses that are around today.
Przewalski’s horses, they discovered, are most likely the feral descendants of the horses that the Botai society domesticated prior to 3,000 B.C.E. In other words, their findings suggest there hasn’t been such a thing as a truly “wild horse” on Earth for thousands of years.
To conduct this research, the team, led by Ph.D. students Charleen Gaunitz of the Natural History Museum of Denmark and Antoine Fages of the University of Copenhagen and University of Toulouse, collected and sequenced 42 samples of ancient horse DNA from archaeological sites around Europe and Asia, including 20 from Botai sites. By comparing these horses’ genomes to 46 previously published modern and ancient horse genomes, the researchers concluded that the Przewalski’s horses are descendent of the Botai’s domesticated herds.
Complicating the picture, they found that horse DNA samples from within the last 4,000 years do not share many similarities — only about 2.7 percent ancestry — to the Botai horses. This suggests that other societies that domesticated horses did so by capturing and breaking horses from a different horse population.
It’s possible that future studies incorporating larger sample sizes could make the picture clearer, especially with regards to the origins of all other domestic horses.
“Future work must focus on identifying the main source of the domestic horse stock and investigating how the multiple human cultures managed the available genetic variation to forge the many horse types known in history,” write the study’s authors.
Abstract: The Eneolithic Botai culture of the Central Asian steppes provides the earliest archaeological evidence for horse husbandry, ~5,500 ya, but the exact nature of early horse domestication remains controversial. We generated 42 ancient horse genomes, including 20 from Botai. Compared to 46 published ancient and modern horse genomes, our data indicate that Przewalski’s horses are the feral descendants of horses herded at Botai and not truly wild horses. All domestic horses dated from ~4,000 ya to present only show ~2.7% of Botai-related ancestry. This indicates that a massive genomic turnover underpins the expansion of the horse stock that gave rise to modern domesticates, which coincides with large-scale human population expansions during the Early Bronze Age.