Ancient humans bred horses to make them more "rideable" 4,200 years ago, study suggests

Many of the most successful conquests in history — such as Genghis Khan’s infamous and brutal invasions — were only made successful on the back of horses. These powerful animals could single-hoofedly spell the difference between the winner and loser of a clash, typically swaying the victory towards the combatant on horseback. But in order to get horses to a spot where it was actually comfortable enough to ride the beasts into battle, it took a hefty bit of work, scientists have found.

By analysing ancient DNA samples extracted from fossil remains from the Eurasian continent dating back tens of thousands of years, researchers have pieced together a comprehensive narrative of horse evolution, even discovering a previously unknown lineage of ancient horses that existed alongside their modern counterparts.

To understand how we came to rear horses, the researchers honed in on three pivotal indicators of early horse husbandry: the initial spread of modern domestic horse progenitors beyond their native steppes, demographic changes in horses throughout the third millennium BCE, and signs of deliberate breeding practices that extended horse reproductive lifespans. This breeding was aimed at enhancing the horses' physical characteristics, making them more suitable for riding and other forms of work.

In fact, the analysis of 475 ancient horse genomes revealed that, around 4,200 years ago, many domestic horses suddenly began to sport a genetic mutation that changed the shape of their back. This likely made it easier for humans to ride them. This concerted effort to breed horses for rideability led to significant changes in their anatomy and behaviour.

This period marks the true onset of horse-based mobility, a transformation that revolutionised transportation and communication across vast distances, facilitating trade and cultural exchanges that had profound impacts on human societies.

“We saw this genetic type spreading almost everywhere in Eurasia — clearly this horse type that was local became global very fast," explains study author Ludovic Orlando. The researchers speculate that this mass-adoption of the new type of horse was because Bronze Age communities were beginning to use the animals to help expand their territories.

Furthermore, the study challenges long-standing assumptions about the geographic origins of modern horses. Contrary to prevailing theories that suggest horses were domesticated in a single region, such as the Eurasian steppe, the research suggests a more complex pattern of domestication involving multiple horse populations across different continents.

"Humans changed the horse genome stunningly quickly, perhaps because we already had experience dealing with animals," notes genetics expert Laurent Frantz. "It shows the special place of horses in human societies."

The findings of this study have been published in Nature and can be accessed here.