Five thousand years ago, in North Africa, humans formed an alliance with the wild ancestors of the donkey, twice.
This was no insignificant feat; domestication of the donkey's ancestors helped these ancient cattle herders become more mobile and adapt as the Sahara Desert expanded. Donkeys also expanded over-land trade and contributed to the growth in the early Egypt state.
New research answers, and raises, questions about who these wild animals were and how humans brought them into the fold.
Donkey family tree:
Modern donkeys can be divided into two, genetically distinct groups, leading scientists to believe that they have two ancestors, which were believed to be the Somali wild ass and the Nubian wild ass, both subspecies of the African wild ass.
In new research, scientists analyzed mitochondrial DNA, or that contained in the energy-producing centers of cells, taken from archeological sites, museum collections and live animals.
Their results showed that the Somali wild ass, or a close relative of this subspecies, was not one of the two ancestors. It is possible this unknown ancestor came from an extinct population of wild ass or from another region, the researchers suggest.