Ancient DNA points to the origins of modern domestic horses


A herd of horses in the steppes of Inner Mongolia.Credit: Ludovic Orlando

Archaeologists have used ancient DNA samples to identify the genetic homeland of modern horses, where animals were first domesticated about 4,200 years ago. According to a study published in Nature October 201, modern domestic horses probably originated in the steppes around the Volga and Don rivers, which are now part of Russia, before spreading across Eurasia, eventually replacing all pre-existing horse lineages.

“This study solved a huge mystery and also fundamentally altered our view of some of the most important human migrations in prehistory,” says Alan Outram, bioarchaeologist at the University of Exeter, UK, and co-author of the book.

Horses have shaped much of human development, revolutionizing transportation, communications, and warfare. But the origins of domestic horses have long been debated because, unlike other farm animals, such as cattle, it is difficult to say whether the bones and other remains belong to domestic or wild horses. “Previous work had to be built on circumstantial evidence, such as killing patterns, tooth damage, traces of mare’s milk consumption, symbolic evidence and more,” says lead author Ludovic Orlando , molecular archaeologist at Paul Sabatier University in Toulouse, France.

Over the past 5 years, Orlando and his team have collected pieces of bone and teeth from ancient horses – amassing over 2,000 samples from places where domestic horses might have originated, including the Iberian Peninsula, the Anatolia, the steppes of Western Eurasia and Central Asia.

The researchers were able to obtain complete genome sequences from a subset of about 270 samples. They used radiocarbon dating to determine the age of the samples and collected information from field archeology for cultural context. This allowed them to track various populations of horses before, during and after domestication. They discovered that until about 4,200 years ago, many distinct horse populations inhabited various parts of Eurasia.

“As these populations were genetically differentiated, we could then identify the line from which the genetic variation present in modern domestic horses developed,” says Orlando.

The analysis revealed that horses with the modern domestic DNA profile lived in the western Eurasian steppes, particularly the Volga-Don region, from the sixth to the third millennium. Before Christ. “Modern-ancestry domestic horse populations were marginal at best elsewhere,” says Orlando.

Around 2200-2000 Before Christ, these horses had appeared outside the western Eurasian steppes – first reaching Anatolia, the Lower Danube, Bohemia and Central Asia, then spreading through Eurasia, replacing all other local horse populations with about 1500 to 1000 Before Christ. “We discovered that about 4,200 years ago, horses’ breeding grounds had enlarged considerably, indicating that this is when ancient breeders began to breed these horses in large numbers. to meet the growing demand for horse-based mobility, ”says Orlando. Humans probably rode on horseback before the invention of horse-drawn vehicles: the first chariots with spoked wheels emerged around 2000-1800 Before Christ.

Human migration

The results also challenge popular beliefs about the role of horses in some early human migrations. Analyzes of ancient human genomes have revealed massive migrations from the western Eurasian steppes to Europe during the third millennium Before Christ, associated with a culture known as Yamnaya. These people are believed to have helped spread Indo-European languages ​​to Europe and were often believed to have ridden horses. “If these many people came with so many horses, then we should expect an equivalent change in the pedigree profile of the horses,” said Orlando. But analysis suggests that at that time there were few ancestors of domestic horses outside of the steppes of Western Eurasia. This would exclude scenarios in which horses played a role in the Yamnaya migration and the initial spread of Indo-European languages.

“It radically changes our understanding of mass human movements from the steppe to Western Europe in the Bronze Age,” Outram explains. “It appears that these migrations were not, as it was commonly believed, facilitated by domestic horses.”

The research “addresses long-standing controversies regarding the role of the domestic horse in the human expansions of the Bronze Age,” says Eske Willerslev, an evolutionary geneticist at the University of Copenhagen, Denmark.

The Orlando team also studied genetic variants that became common in modern domesticated horses from the end of the third millennium. Before Christ. The remarkable gene was GSDMC, which in humans may have mutations associated with hardening of the spinal discs – a condition that can cause chronic back pain and pain when walking. Another important gene was ZFPM1, which is essential for the development of neurons involved in regulating mood and aggressiveness. Inactivation of ZFPM1 in mice causes anxiety and fear.

“Two variants of GSDMC and ZFPM1 the genes were selected early in the domestication process, probably making taming easier, increasing resistance to stress and giving horses a stronger back, ”says Orlando. “These qualities may explain why the new type of horse has been so successful around the world.”

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