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From a single domestication, donkeys helped build empires around the world

Donkeys may lack the popularity and prestige of horses, but these diminutive equines played an outsize role in human history. Now, an extensive analysis of the genomes of both modern and ancient donkeys reveals they were domesticated only once, in East Africa around 5000 B.C.E. Soon after, they rapidly spread throughout Eurasia and became distinctive populations, with limited mixing between them. That likely helped donkeys adapt to serve as critical pack animals for transporting water, belongings, and goods across a variety of environments.

“This is the story of the donkeys … and the detail is amazing,” says Greger Larson, an evolutionary biologist at the University of Oxford who was not involved with the work. The new work clarifies a debate over how many times donkeys were tamed, he says, and reveals that donkeys never became inbred in the way that horses have been.

Improvements in the sequencing of both modern and ancient DNA have shed light on the domestication of horses, dogs, maize, goats, and microbes. But relatively little work has been done on donkey domestication, in part because they are not central to life in industrialized countries today, says Fiona Marshall, an anthropologist at Washington University in St. Louis who was not involved with the work. That’s an oversight, she says. “Their domestication transformed society. They were the first land-based transport.” In many parts of the world, they still serve that role.

To better understand the origins of these humble beasts of burden, evolutionary biologist Ludovic Orlando from Paul Sabatier University—who has spent years working out the domestication history of horses—turned to donkeys. Working with Evelyn Todd in his lab and colleagues from 37 laboratories, they evaluated the genomes of 207 modern donkeys from around the world and sequenced DNA from the skeletons of 31 early donkeys, some dating as far back as 4000 years. “They made a remarkable effort to sequence the worldwide diversity,” says Eva-Maria Geigl, a paleogeneticist at the French national research agency, CNRS, at the University Paris-Cité who was not involved with the work.

The genomes of donkeys (Equus asinus) from different areas proved quite distinct. These differences “[record] a lot about the domestication, not just when it started but also how it spread,” Orlando says.  

A previous study, analyzing a relatively small amount of modern DNA from hundreds of donkeys, had suggested the equines had been domesticated twice, in Asia and in Africa. Those researchers teamed up with Orlando and Todd to reanalyze their findings in light of the new, much larger data set. They used computer models to crunch the donkeys’ genetic and geographic data to estimate how they related to one another. They concluded the donkey was domesticated just once, more than 7000 years ago, when herders in Kenya and the Horn of Africa began to tame wild African asses, the researchers report today in Science. By 5000 years ago, domestication was in full gallop. The earliest donkeys were traded northward and westward to Egypt and Sudan. Within 2500 years they had spread throughout Europe and Asia, where they developed into distinct regional populations.   

Nine of the early donkey genomes came from an archaeological site in northeastern France that was the site of a Roman villa between 200 and 500 C.E., which seems to have housed a donkey breeding center. The new genetic data show Romans interbred African and European donkeys to create giant donkeys 155 centimeters tall—about 25 centimeters taller than a typical donkey.

Geigl still wonders whether donkeys may have been domesticated more than once. She thinks it will take even more ancient and modern genomes to verify that and to positively identify the wild ancestor of donkeys. However, “Even if several research questions remain in the shade, the paper sheds light in an unprecedented manner on the history of a very important societal asset.”

And, Larson says, “I’m pleased to see the donkey finally getting his day.”

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