Actually, we _do_ see this in Europe too. They don't have castes in Europe, by that name, but they did have the feudal system, with a clear division between com

Actually, we _do_ see this in Europe too. They don't have castes in Europe, by that name, but they did have the feudal system, with a clear division between commoners and aristocrats. One big difference was that it was possible for a commoner to be given a title and hence promoted, so there was some fresh blood coming in, but you still saw things like the serious genetic diseases of the Habsburgs.