Horses originated in North America roughly 55 million years ago. Their earliest ancestors were small, multi-toed creatures that looked nothing like the animals we know today. Over tens of millions of years, horses evolved across the North American continent, migrated to other parts of the world, went extinct in their homeland, and were eventually domesticated thousands of miles away on the grasslands of modern-day Russia and Ukraine.
The First Horses Appeared in North America
The oldest known horse, called Hyracotherium, lived between 55 and 45 million years ago during the Eocene epoch. Fossils have been found at many sites across the western United States and in Europe. This animal was roughly the size of a dog, with a short face and low-crowned teeth that already showed the beginnings of the ridged molars horses still have today. It had four toes on its front feet and three on its back feet, each tipped with a small hoof and supported by a soft footpad, similar to what you’d see on a modern tapir.
Hyracotherium was a browser, feeding on leaves and soft plants in warm, forested environments. Artists have historically depicted it with a striped coat, reflecting a life spent in dappled forest light rather than open plains.
From Forest Browsers to Open-Plains Runners
Over the next 50 million years, horses underwent a dramatic physical transformation driven largely by changes in their environment. As North America’s dense forests gave way to expanding grasslands, horses adapted in three key ways: they got bigger, their teeth grew taller and harder to handle tough grasses, and their feet changed radically.
The shift from multiple toes to a single hoof happened in stages. Early horses stood on padded feet with three functional toes, a posture similar to modern rhinos and tapirs. As grasslands spread, horses transitioned to standing on the tip of a single enlarged toe, enclosed in a large hoof. This change was once thought to be purely about increasing galloping speed by lightening the foot, but it likely also improved general locomotion efficiency at slower gaits like the trot. A single wider hoof distributed weight over a larger surface, reducing the chance of sinking into soft ground and lowering the risk of injury. By the time horses in the genus Equus appeared, they had reached a body mass of around 200 kilograms and were fully single-hoofed.
Migration Out of North America
Horses didn’t stay put. Starting around 1 million to 800,000 years ago, populations of horses in North America diverged from those that had crossed into Eurasia. The route was the Bering Land Bridge, the strip of land that periodically connected present-day Alaska to Siberia when sea levels dropped during ice ages.
This wasn’t a one-time event. Genetic analysis of ancient horse DNA has identified at least two rounds of movement in both directions across the land bridge: once between roughly 875,000 and 625,000 years ago, and again between about 200,000 and 50,000 years ago. Gene flow between the North American and Eurasian populations remained low overall, meaning these were relatively brief windows of contact rather than sustained mixing. Once in Eurasia, horses spread across the continent and into Africa, diversifying into the various species of wild horses, zebras, and asses that would eventually populate the Old World.
Extinction in Their Homeland
Despite thriving in North America for over 50 million years, horses disappeared from the continent around 13,000 years ago, near the end of the last ice age. They were part of a massive wave of megafauna extinctions that also claimed mammoths, giant ground sloths, and saber-toothed cats.
The extinction didn’t happen uniformly. In eastern Beringia (unglaciated parts of Alaska and the Yukon), some horse populations vanished as early as 31,000 years ago during a relatively mild warm period, well before humans arrived in the region. Farther south, below the continental ice sheets, horses held on until roughly 13,000 years ago. This staggered timeline suggests that different populations responded to different pressures depending on where they lived. The near-simultaneous final disappearance of multiple horse species across North America points to shared causes, likely some combination of rapid climate change, habitat loss, and possibly human hunting, though the exact balance of factors remains debated.
Domestication on the Eurasian Steppe
For thousands of years after horses went extinct in North America, wild horses continued to roam the grasslands of Europe and Asia. The question of where and when people first domesticated them has been one of the most contested debates in archaeology.
For years, the leading candidate was the Botai culture in northern Kazakhstan, dating to around 3500 BCE. Researchers pointed to apparent wear marks on horse teeth as evidence of bridle use. But more recent analysis, comparing those teeth carefully with fossils of wild Pleistocene horses, found that the marks were likely caused by natural dental development and wear, not bits. The Botai sites now appear to represent organized hunting of wild horses rather than early domestication.
The true origin of all modern domestic horses has been traced through genomic analysis to the steppes of the lower Don and Volga rivers, in what is now southern Russia. Between roughly 2700 and 2200 BCE, a specific horse lineage known to geneticists as DOM2 underwent intense selective breeding. This involved close reproductive control, shortened generation times, and a severe population bottleneck, hallmarks of deliberate human management. Starting around 2200 BCE, these domesticated horses exploded outward across Eurasia, replacing nearly every local horse population they encountered. Every domestic horse alive today descends from that single DOM2 lineage.
Horses Return to the Americas
After roughly 10,000 years of absence, horses set foot in the Western Hemisphere again in 1493, when Columbus brought a herd of 25 on his second voyage. Spanish colonists continued importing horses over the following decades, and the animals spread rapidly through trade, theft, escape, and deliberate breeding by Indigenous peoples. Within a few centuries, wild and semi-wild horse herds roamed from Patagonia to the Great Plains. The mustangs of the American West, often thought of as wild horses, are technically feral descendants of these Spanish imports.
Przewalski’s Horse: The Last Wild Relative
Przewalski’s horse, native to the steppes of Central Asia, is often called the last truly wild horse. Its lineage diverged from domestic horses tens of thousands of years ago, and it carries a different number of chromosomes: 33 pairs versus 32 in domestic horses. This distinction arose from a chromosomal rearrangement, and it means the two can interbreed but produce offspring with odd chromosome counts.
Przewalski’s horses went extinct in the wild in the 1960s due to habitat loss, harsh winters, hunting, and some interbreeding with domestic horses. Every Przewalski’s horse alive today descends from just 12 wild-caught individuals and a handful of domestic horses used in early breeding programs. Conservation efforts have since reintroduced small populations to Mongolia and China, but the species remains endangered.