Donkeys are well known for being beasts of burden. However, in some parts of the world it has been associated, perhaps unfairly, with terms of insult or derision. But in a French village, some 174 miles (280 kilometers) east of Paris, archaeologists have made a discovery that is helping to rewrite much of what we know about donkeys.
At the site of a former Roman villa in the village of Boinville-en-Woëvre, a team unearthed the remains of several donkeys that would have dwarfed most species we are familiar with today. “They were giant donkeys”, says Ludovic Orlando, director of the Toulouse Center for Anthropobiology and Genomics, at the Purpan Faculty of Medicine in Toulouse, France. “These specimens, which were genetically linked to donkeys in Africa, were also larger than some types of horse”.
Orlando has been leading a project that sequenced the DNA of donkey skeletons. It was part of a much larger study to trace the origin of donkey domestication and its subsequent spread to other parts of the world. Research is providing surprising insights into the very history of our species through our relationship with these highly versatile animals.
According to Orlando, donkeys raised at the Roman villa of Boinville-en-Woëvre measured 155 centimeters from ground to withers (a ridge between the shoulder blades). The average height of donkeys today is 130 centimeters. The only modern donkey that comes close is the American mammoth donkey, also known as the jack mammoth, a species where males are unusually large and often used for breeding.
Giant donkeys like those found at Boinville-en-Woëvre may have played an important but underappreciated role in the expansion of the Roman Empire and its subsequent attempts to hold on to this territory, Orlando says. “Between the 2nd and 5th centuries, the Romans bred donkeys to produce mules, resulting from crossbreeding with horses, and which played a key role in transporting military equipment and goods”, he says. “Although they were in Europe, they mixed with donkeys that came from West Africa”.
But the changes in the fate of the Roman Empire were probably instrumental in making this giant breed of donkey disappear as well. “If you do not have an empire of thousands of miles wide around, you will not need an animal that transports goods over long distances”, says Orlando. “There was no economic incentive to continue producing mules”.
A trace of thousands of years ago
To trace how donkeys have played their role throughout human history, an international team of 49 scientists from 37 laboratories sequenced the genomes of 31 ancient and 207 modern donkeys from around the world. Using genetic modeling techniques, they were able to track changes in the donkey population over time. They found that donkeys were possibly first domesticated from wild donkeys, probably by herders, around 7,000 years ago in Kenya and the Horn of Africa, in East Africa.
While this is a bit earlier than first thought, perhaps most surprisingly, the researchers also concluded that all modern donkeys living today appear to have descended from this single domestication event. Even so, there are previous studies that suggest that there may be other attempts to domesticate donkeys in Yemen.
Interestingly, this first donkey domestication in East Africa coincided with the aridity of a once-green Sahara. An abrupt weakening of the monsoon around 8,200 years ago, combined with increased human activity in the form of grazing and burning, led to decreased rainfall and gradual expansion of the desert and Sahel region.
Domesticated donkeys may have been crucial in adapting to this increasingly harsh environment. “We think that due to climate changes, local (human) populations had to adapt”, says Orlando. “As for the donkeys, they may have taken advantage of their strength and this essential service of transporting large amounts of loads over long distances and difficult landscapes”.
They also noticed that the donkey population apparently suffered a drastic decline after being domesticated and then rose sharply again. “This is something very typical of domestication and is seen in almost all domesticated species at any given time”, says Evelyn Todd, a population geneticist at the Center for Anthropobiology and Genomics in Toulouse, who was also involved in the study. The decline is the result of selecting a specific stock of donkeys to domesticate and then purposely breed, which contributed to their sharp increase.
These analyzes suggest that donkeys appear to have originated in East Africa, being traded in northwestern Sudan and then Egypt, where remains of donkeys have been found at archaeological sites dating back 6,500 years. Over the next 2,500 years, this new domesticated species spread across Europe and Asia, developing the lineages found today.
They were buried in their own right
According to archaeologist Laerke Recht of the University of Graz in Austria, donkeys made a huge difference in humanity’s ability to transport goods over long distances over land due to their stamina and capacity.
“While rivers like the Euphrates and Tigris in Mesopotamia and the Nile in Egypt could be used for transporting heavy and/or bulk goods, donkeys meant a massive increase and intensification of contacts overland”, he says. Recht recounts that this coincided with the increased use of bronze during the third millennium BC. “Donkeys could carry heavy copper over long distances and to areas where it did not occur naturally (or only in very small amounts), including Mesopotamia”.
Donkeys and other equids also changed the art of warfare during the same time. “We started to see them in front of wheeled vehicles engaging in battle, as well as providing transportation for supplies needed by an invading army”, says Recht. Donkeys were so appreciated that they even appeared in important rituals. “Both in Egypt and Mesopotamia, they were considered important enough to be buried with humans. In some cases, even with kings or rulers”, says Recth. “There are also examples of buried donkeys in their own right”.
He adds that in the second millennium BC donkeys were also slaughtered for so-called foundation or construction deposits; that is to say, the holes excavated in specific points of buildings or temples where ceremonial objects were placed to avoid the ruin of the place. They were also used as part of rituals in the signing of treaties.
A constant companion
The oldest sample studied by Orlando and his colleagues were three Bronze Age donkeys in Turkey. “Radiocarbon analysis dates them to about 4,500 years old and they have a similar genetic makeup to modern Asian subpopulations”, says Todd. This suggests that the Asian subpopulation of the domesticated donkey diverged from other lineages around this time.
The research also confirms that donkeys have been a much more constant companion to humans than their equine relatives, horses. “Modern domesticated horses, which were domesticated around 4,200 years ago, have had a huge impact on human history. Now, our study reveals that the impact of donkeys extends even further”, says Orlando.
The animal’s enduring utility is in stark contrast to the attention it has received compared to horses and dogs. Although donkeys are overlooked in many parts of the world today, in some other places they are still as important as they have been throughout history. “The donkey is an important animal in the daily lives of millions of people around the world”, says Todd. “Its population increases by 1% every year. Although donkeys are not used in daily life in developed countries, in many developing communities in areas such as Africa and the Arabian Peninsula, people still rely on donkeys to transport people and goods”. He adds that understanding the genetic makeup of donkeys could also help improve their breeding and management in the future.
Its fellow wild species
A key question that the researchers hope to address in future studies is finding a close relative of the domesticated donkey in the wild. Orlando, Todd and their colleagues were able to identify 3 candidates. “We know that the donkey is a descendant of the African wild ass”, says Todd. «We know about 3 sub-species: one of them became extinct in the year 200 AD, in Roman times; the second was probably extinct in the wild; and the third is critically endangered”.
However, more work is needed to find out if there were or are any as yet unidentified sub-species of the African wild ass which would help to further improve our understanding of the donkey’s genetic history and perhaps reveal more about the important role it has played in our own history.