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How did the donkey spread across the Earth? A genomic analysis has the answer

The scientific team found evidence of a single domestication event in Africa around 5,000 BC.

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A complete genomic analysis of modern and ancient donkeys reveals the origins of this animal and its spread across continents. Domestic donkeys (Equus asinus) have been important to humans for thousands of years, providing a source of work and long-distance transportation for many cultures, particularly in arid and semi-arid regions. (Read Blue Origin’s space rocket crashed in Texas, United States)

However, very little is still known about their history, and when and where they became domesticated is a long-standing scientific mystery. (Read Colombian Ronald García won the Stuart Jay Freedman Prize in nuclear physics)

Now, a new study published in Science reveals that these creatures were domesticated in Africa and spread like wildfire from there, reaching Europe and Asia in just a few centuries. The work is the result of collaboration between more than 30 institutions from various countries and has been led by researchers from the Paul Sabatier University of Toulouse.

Although currently undervalued, probably due to their loss of utility in modern industrialized societies, donkeys remain essential for the development of low- and middle-income communities, particularly in semi-arid environments. Understanding their genetic history is important to assess their contribution to human civilizations, but also to improve their management in the future, the authors write.

Modern and ancient DNA study

The researchers sequenced the genomes of 207 modern and 31 ancient individuals, including 15 wild equids. “To understand genetic change over time, we analyzed the genomes of donkeys that lived in the past in a wide geographical region, from Western Europe to Central Asia,” Evelyn Todd, a researcher at the Center for Anthropobiology and Genomics at Toulouse CAGT and first author of the study.

The scientific team found strong evidence for a single domestication event in East Africa more than 7,000 years ago (about 5,000 BC). This was followed by a series of expansions across Europe and into Eurasia, where subpopulations eventually became isolated and differentiated.

The team estimates that donkeys spread out of Africa at least 4,500 years ago (around 2,500 BC) and spread rapidly both eastward through Asia and westward through Europe in a maximum of 1,000 years.

“The oldest genomes we studied were from West and Central Asia and provide evidence for an early expansion of donkeys out of Africa,” explains Todd.

“Through ancient DNA analysis, we also discovered the existence of a previously unknown genetic lineage in the Levant around 2,000 years ago. Although different from all the other donkeys included in the study, we identified traces of its genetic legacy in modern donkeys throughout Eastern Europe, Central and East Asia,” says Todd. The researchers suggest that this lineage contributed to increasing ancestry towards Asia.

Donkeys in the Roman Empire

The expansion of the donkeys, however, did not follow a single direction and later returned to Africa. Already in Roman times these animals were exchanged between Europe and Africa through the Mediterranean Sea. Although these exchanges continued after the collapse of the Roman Empire, they left the most important genetic imprint on modern West African specimens.

According to the scientists, the breeding of donkeys then implied inbreeding -inbreeding- for the production of giant lineages, at a time when mules were essential for the economy and the army of the Roman Empire.

Mating between these giant donkeys and female horses made it possible to produce sterile mules, which were an important source of animal labor.

Here, the genetic evidence echoes Roman-era texts that describe selective breeding of animals of exceptional stature as already common practice and a lucrative business at the time. “This is the power of ancient DNA: to provide data that allows us to test hypotheses from other classical historical sources”, comments Ludovic Orlando, CAGT researcher and lead author of the research.

This work clarifies global patterns of donkey domestication and movement around the world, but also highlights many directions for future research, the authors write.

“Improving the current African archaeological record will allow us to refine our understanding of the genetic history of these animals and their relationships with humans over time,” Todd concludes.

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Source: Elespectador

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