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Earlier research in 2021, led by Ludovic Orlando, a molecular archaeologist at the Centre for Anthropobiology and Genomics of Toulouse, France, traced the origins of modern horses to southwestern Russia about 4,200 years ago.

But while the time and place were clear, one big question remained: What exactly changed in horse DNA that allowed them to be tamed and ridden?

Orlando, working with scientists from China and Switzerland, studied the genomes of 71 horses representing various breeds and time periods. They focused on 266 points in horse DNA that showed evidence of change during domestication.

The results? Nine genes showed strong signs of selection, indicating that their traits were likely deliberately selected by early humans.
 

The second gene, GSDMC, began showing major changes between 4,700 and 4,200 years ago. In humans, mutations in this region are associated with back problems and chronic pain. In horses, however, changes here affected the body-to-height ratio, influencing load-bearing ability.

Knockout experiments in mice showed straighter spines and stronger forelegs, clear signs that this gene plays a key role in shaping the ideal riding-horse posture.

Not long after, the GSDMC variant spread at lightning speed. Within just a few hundred years, it went from nearly undetectable to present in almost all domestic horses.

“When you see a genetic shift that dramatic, it means humans were actively spreading the mutation. Horses carrying this trait had about 20% more offspring, which means it was truly a game-changer,” Orlando explained.

While ZPFM1 and GSDMC are central pieces of the puzzle, Orlando emphasizes that other genes—or even cultural practices invisible in DNA—likely played a role in domestication. For example, the ways humans interacted with and trained horses may have been just as crucial.

Today, Orlando’s team is analyzing horse DNA from Steppe empires in Mongolia and China to better understand how great civilizations bred and developed their prized horses.