Which horse has never been domesticated?

It's difficult to say definitively which horse has *never* been domesticated, as there are many wild horse populations and ongoing research. However, the Przewalski's horse is often considered the only true wild horse species remaining. It was previously thought to be extinct in the wild, but populations were reintroduced in the 20th century.

Here's why it's tricky to definitively say:

* Domestic horses: The domestic horse, *Equus caballus*, is a subspecies that evolved from wild horses. Domestication happened over thousands of years, and there's a lot of genetic mixing.

* Wild horse populations: Many horses living in the wild, like the Mustangs of North America, are actually descended from escaped or abandoned domestic horses. They are not true wild horses.

* Przewalski's horse: While this species is considered the last remaining wild horse, there is still debate about its exact status. Some researchers argue that it might have been domesticated in the past and later escaped.

So, while the Przewalski's horse is the closest we have to a truly wild horse, it's important to acknowledge the complexities of horse domestication and evolution.