I'm not sure what the show was called, but it was interesting how they connected the points. I was hoping someone could say how plausible this point could be and hopefully someone saw this show and can add points too.
hi! can I take a guess that this was a tv doc based on Jared Diamond's book Guns, Germs, and Steel? If so, I'll let the experts reply to your specific question about horses, but for general opinions on this book, see this section of the FAQ