Donkeys once heehawed out of Africa
African wild asses were probably tamed not once, but twice, in locations far apart to become the willing donkeys that carry loads the world over, an international team of researchers says.
The researchers' study of donkey DNA, published in today's issue of the journal Science, suggests that two separate female wild asses were the ancestors of today's domesticated donkeys.
The domestication of asses and horses was an important milestone in human history. It marked a major cultural shift from a sedentary lifestyle to more movement and trade.
"Sparse archeological evidence from Egypt suggests that donkeys, like horses, were domesticated about 5000 years ago," wrote Albano Beja-Pereira, of the French research institute CNRS in Grenoble, and colleagues.
"Exactly where this occurred is still unclear."
The researchers used an increasingly popular method called a genetic clock, in which genetic mutations can be calculated for each generation, and then generations of two separate species can be counted back to a theoretical common ancestor.
"We assessed domestic donkey origins by sampling donkeys from 52 countries across the Old World and sequencing 479 base pairs of the mitochondrial DNA control region," they wrote.
They also examined the DNA of Asian wild half-asses and wild African asses.
"Our data suggest two separate maternal origins of the domestic donkey from two distinct wild populations," they wrote. They date back to more than 10,000 years ago, before any livestock was domesticated.
This means two wild females, living far apart geographically, were the ancestors of virtually all donkeys living today.
"The African wild asses are ... the likely progenitors," they wrote.
This can shed light on the movement and development of early humans, they said.
"If both lineages arose in Africa, it suggests that the donkey is the only ungulate domesticated solely in Africa," they wrote.
"Moreover, this study demonstrates that the practice of animal domestication, which first emerged in the Near East, reappeared in Northeastern Africa. It provides insight into the role that this region may have played in population expansion and trade across the Old World," they said.
"Domestication of the donkey may have been driven by the response of pastoralists and other societies in Northeastern Africa to the desertification of the Sahara around 5000 to 7000 years ago."