Przewalski horse

Przewalski's horse (pronounced /(p)ʃəˈvɑːlskiz/ or /preɪəˈvælskiz/; Polish: ), Equus przewalskii or Equus ferus przewalskii, also called the Mongolian wild horse or Dzungarian horse, is a rare and endangered horse native to the steppes of central Asia. At one time extinct in the wild, it has been reintroduced to its native habitat in Mongolia at the Khustain Nuruu National Park, Takhin Tal Nature Reserve, and Khomiin Tal. The taxonomic position is still debated, with some taxonomists treating Przewalski's horse as a species, E. przewalskii, others as a subspecies of wild horse (E. ferus przewalskii) or a feral variety of the domesticated horse (E. f. caballus). Common names for this equine include takhi, Asian wild horse, and Mongolian wild horse. The horse is named after the Russian geographer and explorer Nikołaj Przewalski. Most wild horses today, such as the American mustang or the Australian brumby, are actually feral horses descended from domesticated animals that escaped and adapted to life in the wild. Przewalski's horse has long been considered the only 'true' wild horse extant in the world today, never having been domesticated. However, a 2018 DNA study suggested that modern Przewalski's horses may descend from the domesticated horses of the Botai. Przewalski's horse was described in 1881 by L. S. Poliakov, although the taxonomic position of Przewalski's horse remains controversial and no consensus exists whether it is a full species (Equus przewalskii), a subspecies of the wild horse (Equus ferus przewalskii, along with the other subspecies, domesticated horse E. f. caballus, and the extinct tarpan E. f. ferus)), or even a subpopulation of the domestic horse. Early sequencing studies of DNA revealed several genetic characteristics of Przewalski's horse that differ from what is seen in modern domestic horses, indicating neither is ancestor of the other, and supporting the status of Przewalski horses as a remnant wild population not derived from domestic horses. The evolutionary divergence of the two populations was estimated to have occurred about 45,000 YBP, while the archaeological record places the first horse domestication about 5,500 YBP by the Botai culture. The two lineages thus split well before domestication, probably due to climate, topography, or other environmental changes. Several subsequent DNA studies produced partially contradictory results. A 2009 molecular analysis using ancient DNA recovered from archaeological sites placed Przewalski's horse in the middle of the domesticated horses, but a 2011 mitochondrial DNA analysis suggested that Przewalski's and modern domestic horses diverged some 160,000 years ago. An analysis based on whole genome sequencing and calibration with DNA from old horse bones gave a divergence date of 38–72 thousand years ago. A new analysis in 2018 involved genomic sequencing of ancient DNA from mid-fourth-millennium B.C. Botai domestic horses, as well as domestic horses from more recent archaeological sites, and comparison of these genomes with those of modern domestic and Przewalski's horses. The study revealed that Przewalski's horses not only belong to the same genetic lineage as those from the Botai culture, but were the feral descendants of these ancient domestic animals, rather than representing a surviving population of never-domesticated horses. The Botai horses were found to have made only negligible genetic contribution to any of the other ancient or modern domestic horses studied, which must then have arisen from an independent domestication involving a different wild horse population. The karyotype of Przewalski's horse differs from that of the domestic horse by an extra chromosome pair because of the fission of domestic horse chromosome 5 to produce the Przewalski's horse chromosomes 23 and 24. In comparison, the chromosomal differences between domestic horses and zebras include numerous translocations, fusions, inversions and centromere repositioning. This gives Przewalski's horse the highest diploid chromosome number among all equine species. They can interbreed with the domestic horse and produce fertile offspring (65 chromosomes).