The beast of burden probably best known for its bray can now trace its ancestry well beyond the first days of its partnership with humans. By studying DNA from hundreds of Old World donkeys, molecular biologists have established that domesticated donkeys have their roots in Africa and that Africans domesticated these animals only twice.
For decades, archaeologists and anthropologists have debated the origins of the first donkeys, as well as where domestication occurred. The Bible, Koran, and Talmud all mention donkeys and until Napoleon's day they helped transport wartime supplies. They are still used by some traders and farmers for heavy lifting. Given this rich history, Albano Beja-Pereira of the University of Joseph Fourier in Grenoble, France, decided to bring genetics to bear on the debate.
Beja-Pereira and his colleagues collected mitochondrial DNA from 256 donkeys from 52 countries in Europe, Africa, and Asia. They sequenced about 500 bases from each animal, studied the differences, and firmly established that the donkey family tree has two branches; one in Asia and the other in Africa. Although it's not yet certain which branch is older, the first domesticated donkeys clearly came from Africa, the researchers report in the 18 June issue of Science.
Further DNA comparisons revealed that the African branch of the donkey family tree is itself split in two. One sub-branch, the Nubian wild donkeys, live in Sudan and southern Egypt. The other, the Somali asses, hail from what are today Ethiopia, Somalia, and Eritrea. These two populations began evolving independently as early as 800,000 years ago and were already distinct subspecies by the time humans harnessed them a mere 6000 years ago. When Beja-Pereira and his colleagues looked at the data closely, they discovered that the two subspecies of African donkeys were domesticated independently.
The study "brings an important new part to our knowledge about the origin of domestic animals," says Jean-Denis Vigne of the National Museum of Natural History in Paris. The finding stands out because most animals were domesticated in the Middle East, says Carles Vilà of Uppsala University in Sweden. Yet, as with other livestock, donkey domestication occurred relatively few times.