Despite transforming history as beasts of burden essential for transporting goods and people, the humble donkey has long been woefully understudied.
But scientists on Thursday took a big step towards clarifying the species’ origins with a comprehensive genomic analysis of 238 ancient and modern donkeys, finding they were likely domesticated in a single event in eastern Africa some 7,000 years ago.
The paper, published in the journal Science, was the result of an international collaboration led by Evelyn Todd at the Centre for Anthropobiology and Genomics of Toulouse, France.
“Donkeys subsequently spread into Eurasia from ~2500 BCE, and Central and Eastern Asian subpopulations differentiated ~2000 to 1000 BCE,” the team wrote.
Eventually, lineages from Europe and the Near East backbred into western African donkey populations.
Horses, their equid cousins, are believed on the other hand to have been domesticated twice — the first time around 6,000 years ago in the western Eurasian steppes.
The donkey DNA study included three jennies (females) and six jacks (males) from an ancient Roman site in France who were closely interbred.
The authors suggest that Romans bred improved donkey bloodlines to produce mules that were essential to sustaining the military and economic might of the empire.
Donkeys were vital to the development of ancient societies and remain important in middle and lower income countries, but lost their status and utility in modern industrial societies, perhaps explaining why they were neglected by science.
DNA has great potential for unraveling humankindās shared history with our animal companions. In 2021, Orlando and his colleagues used DNA from the bones of horses to track their domestication to the Eurasian steppes, in whatās now southwestern Russia, more than 4,200 years ago (SN: 10/20/21).
But the history of donkeys (Equus asinus) had remained murky. Today, domesticated donkeys are found all over the globe. A dwindling number of wild asses in Asia and Africa ā the closest wild relatives of donkeys ā pointed toward one of those continents as the likely donkey homeland.
Archaeological evidence ā including a 5,000-year-old Egyptian tablet depicting marching asses, sheep and cattle ā zeroed in on Africa as the most probable contender. But genetic studies attempting to pin down when and where donkeys were domesticated have been largely inconclusive.
This was probably because scientists were lacking donkey DNA from many regions of the world, Orlando says. For example, to date, there have been no published genomes from donkeys living south of the equator in Africa. To get a broader diversity of DNA, Orlando and his colleagues gathered 207 genomes from donkeys living in 31 countries, ranging from Brazil to China, along with DNA belonging to 31 donkeys that lived between 4,000 and about 100 years ago.
By comparing these genomes with those of wild asses, the researchers found that all donkeys could trace their lineage back to a single domestication event in East Africa, perhaps in the Horn of Africa, around 5000 B.C. From there, domesticated donkeys spread to the rest of the continent and into Europe and Asia, where they formed genetically distinct groups based on region. Humans have now brought donkeys to nearly every continent on Earth, carrying their genetic legacy with them.
These results add new clarity to the story of donkey domestication, says Emily Clark, a livestock geneticist at the Roslin Institute at the University of Edinburgh. āDonkeys are extraordinary working animals that are essential to the livelihoods of millions of people around the globe,ā she says. āAs humans, we owe a debt of gratitude to the domestic donkey for the role they play and have played in shaping society.ā