[yad]

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Its worth mentioning though that Jared Diamond's Guns, Germs, and Steel claims that the presence or absence of large domesticatable animals like horses is one of the main factors that shaped the rapidity with which civilizations advanced in the north and south of the globe. It turns out that there really aren't that many candidates for this kind of thing. If you took away oxen and camels too, we might still be in the bronze age.

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he's right too. there are a remarkable number of characteristics that are required for an animal to be suitable for domestication, and there really aren't that many animals that fit the bill at all. certainly zebras are totally unsuitable, i think because of certain characteristics of their genetic system. i think elephants are also pretty tough. camels and llamas have major drawbacks compared to horses (much harder to train -- I don't think a "cavalry charge" with camels would ever be possible).

of course without the horse other developments would eventually ahve filled the gap, but especially given the horse's role in warfare and hence its role in stimulating military technology, I don't think it's unreasonable that many aspects of "civilization" would have been set back hundreds or thousands of years without htem.