Even before the introduction of domesticated horses to Mesopotamia about 4,000 years ago, people there were raising hoofed animals that they used in chariots and plows and used for diplomatic and ceremonial purposes: the so-called congas. However, the genetic origin of these donkey-like animals was previously unclear. DNA analyzes of conga skeletons from Syria now show that the congas were a cross between female domestic donkeys and male wild donkeys. Thus, it is the oldest hybrid species generated by man.
Throughout history, horses and other horses have played a major role in the development of cultures, but also in warfare. A 4,500-year-old Sumerian mosaic shows that the Sumerians were actually using chariots on the battlefield pulled by horse-like animals. However, it was not until about 500 years later that local horses were introduced to this area. Cuneiform clay tablets from that period mention so-called conga, prestigious hoofed animals that cost about six times the cost of domestic donkeys that were in common use at the time. The exact topic of congas has been a topic of debate for a long time.
Ancient DNA of donkeys, horses and relatives
A team led by Andrew Bennett from the University of Paris managed to solve this mystery. To do this, the researchers examined ancient DNA from 25 horse skeletons found in a lavish 4,500-year-old tomb at Tell Umm Marra in northern Syria. While the form of the skeletons was that of horses, it was not in keeping with the horses, donkeys, or wild animals of the area. Paleontologists had previously hypothesized that it could have been an enigmatic conga.
“In order to clarify whether the Tell Umm al-Murra tombs actually contain conga remains of political and symbolic importance and to determine the taxonomic status of these animals, we examined the genomes in samples of these skeletons and compared them with other horse samples,” the researchers explained. They used the genomes of domesticated donkeys and horses as a comparison, and they also sequenced the genomes of extinct wild donkeys that were native to the region at the time. To identify the mother and father of the animals studied, Bennett and colleagues focused on mitochondrial DNA, which is passed down exclusively from the mother, and the Y chromosome that comes from the father.
Combine the advantages of both parents
The result: the conga was a cross between female domestic donkeys and male Syrian wild donkeys that became extinct in the early 20th century. “We thus documented the oldest evidence of hybrid animal breeding,” the researchers wrote. The oldest human-proven hybrid to date was a mule that was bred in Anatolia from around 1000 to 800 BC. Like mules and mules, which result from crossing horses and donkeys, the conga were probably non-reproductive. In order to breed conga, male wild donkeys had to be hunted and mated with female donkeys.
Bones preserved in the tomb indicate that the conga were stronger and faster than donkeys. The Sumerians apparently made use of the advantages of both parent animals through hybrid breeding: the strength and speed of the wild ass, combined with the better controllability of the domestic donkey. However, they did not tame the wild horses that live in the area. About 4000 years ago, native horses were introduced to the region from the Pontic steppes. Since they were easier to breed and displayed similar good properties, they then replaced the conga. In future studies, the researchers plan to examine other equids from similar spatial and temporal contexts in order to better understand the extent of Sumerian hybrid breeding.
Source: Andrew Bennett (University of Paris, France) et al., Science Advances, doi: 10.1126/sciadv.abm0218
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