[sam h]

I think it would have set humanity back some, but not as much as you think. Camels or oxen would probably have been pressed into service by most of the civilizations on the Eurasian landmass.

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.