4,000 years of partnership: the biological shift that turned wild horses into riding companions
A study published in Science identified a genetic change that helps explain how horses became tame, strong, and rideable, reshaping human mobility, farming, and warfare. The team led by Xuexue Liu and Ludovic Orlando analyzed DNA from a large number of ancient horse remains, focusing on 266 genetic markers linked to coat color, body shape, locomotion, and behavior.
The researchers looked for traces of selection tied to choices made by early breeders. Their analyses found a change in a specific gene - the GSDMC locus - that became more frequent during domestication and was linked to body conformation in horses, as well as spinal anatomy and motor coordination in other mammals. The scientists concluded that a modification of the GSDMC gene could change equine anatomy.
Around 4,750 years ago, horses with the GSDMC mutation were rare, but by roughly 4,200 years ago the mutation became frequent during the domestication bottleneck that reduced genetic diversity. The GSDMC locus showed one of the strongest signals of positive selection during the rise of the modern domesticated horse lineage. This increase preceded the spread of horses from their cradle in the Caucasus steppes across Eurasia, with carriers of the mutation dispersing rapidly.
The mutation affected expression of the Gasdermin C gene, which is present in all mammals and related to cancer biology and immunity. In mice, modifying GSDMC led to a flatter spine and improved motor coordination; in horses it was associated with altered spinal anatomy, superior motor coordination, and stronger front legs. Orlando said the change in the GSDMC gene in horses favored a spinal structure more suitable for riding, enhancing their ability to meet demands of mobility and warfare.
“This genetic change played a decisive role in the emergence of equestrian mobility and horse-riding civilizations, fundamentally reshaping human societies due to its impact on trade, mobility, and war,” EurekAlert reported. Across much of the world, horses served as a primary mode of human transportation until the rise of the combustion engine in the late 19th century. “What is certain is that these first riders kick-started a revolution that changed the world, demonstrating how the immense currents of history can turn on the smallest of biological changes. Although the exact circumstances and the cultural identity of the people who carried out this early intensive breeding remain a mystery, they must have had extraordinary ingenuity, technology, and foresight,” said Laurent Frantz, from Ludwig Maximilian University of Munich.
The study also reconstructed early selection for behavior. During the early stage of domestication, about 5,000 years ago, selective breeding favored a genetic region associated with the ZFPM1 gene, which controlled fear behavior and stress reactions. ZFPM1 regulated anxiety and fear in horses, and its dominant mutation among domestic horses possibly contributed to docility, indicating a likely relationship to tameness and behavior. La Vanguardia reported that the ZFPM1 mutation spread more slowly, suggesting early breeders did not select it as strongly.
The findings contradicted a longstanding hypothesis that humans began domesticating horses by selecting for diverse coloration, as traits like coat color expanded only modestly at first. From the Iron Age onward, breeding practices increasingly emphasized larger body size, tameness, and phenotypes that supported riding or carrying heavier loads. The research identified three genetic variants that increased horse size, with selection beginning 2,700, 2,600, and 1,300 years ago, respectively. This timeline matched the rapid expansion of modern domestic horses from their place of origin in the river basins of the Don and Volga in Russia.
The rapid spread of the GSDMC mutation showed that breeders preferred animals that carried it, and its expansion could not be explained by natural selection alone. According to the authors, selection for a modification of the GSDMC gene by early breeders facilitated mounting and movement. Liu and colleagues showed how human selection shaped horse biology over time.
Horse domestication occurred at least 4,500 years ago, forging a bond that shaped human history as horses aided humans for more than 4,000 years. Early domestication involved selecting less aggressive, easier-to-handle animals for agriculture. Donkeys were domesticated for agricultural purposes before horses. As a result of domestication, horses altered human mobility, farming, and warfare, playing a critical role in shaping society and transforming transportation.
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