A growing body of evidence shows that far from being an invasive species, the horse originated in North America some 53 million years ago and traveled over the Bering Land Bridge, dispersing into Asia 800,000 to 1 million years ago.
Fossil evidence had long supported the idea that horses, once leaving the Americas, evolved into a new species, and so the horses which Spanish explorers brought to the New World were unfamiliar to this land.
Advances in molecular genetics, however, have proven otherwise: the horse completed its last adaptation in North America before its absence (for what was ostensibly a short-term blip on the scale of geologic time), and so when the Spanish and then early European settlers brought horses to this new land, these horses from which today’s wild horses have descended – Equus caballus– were, in fact, returning home.