DNA Shows Ancient Pack Animal Was a Donkey-Wild Ass Hybrid

The kunga, a highly sought-after technological advance in Mesopotamia, may be the oldest known hybrid animal bred by humans.
archaeological excavation showing buried equid skeletons

These 4,500-year-old animals, unearthed at a princely burial site in Syria, are thought to be the mysterious horselike animals known as kungas.

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Charles Q. Choi, Contributor

(Inside Science) -- Ancient DNA may have revealed the genetic identity of the oldest known hybrid animal bred by humans -- the horselike kunga, prized beasts once given as royal gifts and said to pull the vehicles of nobility and gods.

Roughly 5,000 years ago in Mesopotamia, clay tablets and royal seals began depicting the mysterious kunga. Horses had not yet been introduced to the region, but smaller relatives such as donkeys were already present. Ancient texts suggest kungas were valuable, costing up to six times more than a donkey. The size and speed of large male kungas made them desirable for towing four-wheeled war wagons on the battlefield, while smaller males and females found use pulling plows.

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Although the kunga's depictions make it clear it was an equid -- a member of the same family as horses, zebras and donkeys -- its precise nature was a controversy for decades. Previous research suggested one kunga parent was likely a donkey, but the other parent's identity remained uncertain. Potential candidates included Asiatic wild asses (Equus hemionus), also known as hemiones or onagers, which are exceptionally fast but notoriously untamable, and more specifically the subspecies known as the Syrian wild ass (Equus hemionus hemippus), or hemippe, a light swift animal that was the smallest of all modern equids before it went extinct in the early 20th century.

"Hemippes were highly appreciated and described as 'delicious' in the clay tablets of ancient Syro-Mesopotamia," said study co-senior author Eva-Maria Geigl, a paleogeneticist at the Institut Jacques Monod in Paris. According to notes from the director of Vienna's Schönbrunn Zoo, which housed two of the last surviving hemippes, the equids "were extremely fast -- faster than horses -- and aggressive," she added.

In the new study, researchers analyzed DNA from 23 complete male equid skeletons about 4,500 years old unearthed at an ancient royal burial site, Umm el-Marra, in modern-day northern Syria. Men and women there were interred with personal ornaments made of gold, silver, bronze and lapis lazuli, along with silver, bronze and ceramic vessels and bronze weapons and tools.

The size and other features of the bones of these equids differed significantly from those of typical horses, asses and hemiones, leading the scientists to suspect they might have come from hybrids. They were close in size to hemiones but were more robust, and their leg bones suggested they were fast like hemiones.

The hot Syrian climate had wreaked havoc on the DNA in these ancient bones. Still, the researchers successfully analyzed genomes from the mitochondria, inherited from the mothers of the animals, and from the cell nuclei, which possess genetic material from the fathers, and compared them with genomes from horses, asses and hemiones.

The scientists also examined DNA from the Schönbrunn hemippes, and from a roughly 11,000-year-old equid skeleton found at the site Göbekli Tepe in modern-day Turkey. Although the Göbekli Tepe equid was significantly larger than the Schönbrunn hemippes, its DNA confirmed it was a hemippe.

The researchers found the Umm el-Marra equids were likely first-generation hybrids between a female donkey and male hemippe. Although the diminutive size of the Schönbrunn hemippes might suggest these equids were likely not parents of the Umm el-Marra equids, the Göbekli Tepe specimen revealed hemippes could reach larger sizes in ancient times.

All in all, kungas mark the earliest known evidence of hybrid animal, predating the most ancient genetic evidence of a mule by about 1,500 years. "It is very satisfying to be able to show through paleogenomics what these early societies were able to do," Geigl said. 

One implication of these findings "is that the practice of regularly hybridizing domestic donkeys with wild onagers means there was a high level of competence in capturing and raising and breeding wild equids, probably comparable to modern zoos," said zooarchaeologist Benjamin Arbuckle at the University of North Carolina, who did not take part in this research. "Being hybrids, they were probably sterile, so the kunga economy must have had to constantly produce more of these animals. I suspect they were widely used across Syro-Mesopotamia in the fourth millennium B.C." 

Kungas were eventually supplanted by the arrival of domestic horses into Mesopotamia about 4,000 years ago, which were likely easier to breed, the researchers noted. "The story of this technological replacement, perhaps analogous to gas to electric vehicles, is very poorly understood," Arbuckle noted.

Future research can hunt not only for more kunga specimens to study, but for other equid hybrids as well, Arbuckle said. "Horses were just coming down into the Near East in this period, so there must have been an interesting experimental time when equid breeders were seeing what happened when you penned horses and donkeys and onagers together," he noted. "It really shows that ancient people were innovative and experimenters, traits we often associate with the modern world."

The scientists detailed their findings online Jan. 14 in the journal Science Advances

Author Bio & Story Archive

Charles Q. Choi is a science reporter who has written for Scientific American, The New York Times, Wired, Science, Nature, and National Geographic News, among others.