Recent research that mapped the genome of a 700,000-year-old extinct species of horse may also help settle a debate over the status of the Przewalski’s horse.

The debate has centred on whether the Mongolian equine is really wild and not domesticated, like all other horse breeds.

In one camp are the experts who consider the Przewalski’s horse to be a separate species and the last true wild horse.

Others believe they are subspecies, a wild offshoot of domestic horses.

The Danish researcher who mapped the genome of the ancient extinct horse, taken from a piece of bone removed from permafrost in the Yukon, Canada, compared the genome with that of a pre-domestication horse, a modern donkey, five modern domestic samples and one modern Przewalski’s horse.

The researchers found all contemporary horses, zebras and donkeys originated 4 million 4.5 million years ago – twice the conventionally accepted time to the most recent common ancestor of genus Equus.

The study also showed that many demographic fluctuations occurred in horse populations in the past two million years, especially during the period of major climatic changes.

The study suggested that the Przewalski and domestic horse populations diverged 38,000 to 72,000 years ago, and there has been no cross-breeding between the two types of horses.

Przewalski”s horse foals at San Diego Zoo.

Przewalski’s horse foals at San Diego Zoo. © Ken Bohn / The Zoological Society of San Diego

These findings provide evidence that the Przewalski does indeed represent the last survivor of wild horses, a view supported by striking physical differences compared to domesticated horses, as well as an extra pair of chromosomes.

The team also found the evidence supporting the continuous selection of the immune system and the sense of smell throughout horse evolution, and dozens of genomic regions that are likely to be taken as genetic markers during the domestication.

The Przewalski’s horse was named after a Russian colonel who led an expedition into their nature rangelands in 1881.

They were extinct in the wild for decades until a captive breeding program reintroduced them to Mongolia in the mid-1990s.

Given their truly wild origins, the researchers found wide genetic diversity in the genome compared with the domestic horses, which is good news for conservation efforts, given the limited numbers that survive.