New research on horse genomes indicates the domestic verison may have originated in the Russian Ukraine and spread from there, with lots of interbreeidng with wild horses along the way:
(BBC) — Dr Vera Warmuth from the Department of Zoology at Cambridge said: “It shows that horse domestication originated in the western part of the Steppes and that the spread of domestication involved lots of integration of wild horses.
“The theory explains why evidence from mitochondrial DNA – which contains genes inherited solely from the mother – suggests horses were domesticated many times, in different places.
In fact, it appears that wild mares were used to re-stock herds of existing domesticated horses, perhaps because they did not breed easily in captivity. This is the case with Przewalski’s horse, which is the closest wild relative of modern horses.
I bet they spread alright. If riding horses didn’t spread by interbreeding, I’d wager they spread fast enough by marauder on horseback running down opposing defenders brave enough to bear the brunt of the first cavalry charges!
Well, I don’t know if that happened often or not. But the first horse-riding culture would surely have had a big advantage over competitors in many ways including warfare. In fact I’m not sure but it seems I remember the common root of Indo-European language spoken throughout most of Eurasia and the New World also originated near the same epicenter. Maybe that culture had a big leg up and their language spread with their horses. It’s fascinating to speculate anyway.