Apropos of my comment about sex & civilization, a reader brought up Sparta, and over @ 2 Blowhards there's a nice post, Case Studies in State Formation - Sparta:
There was an extreme egalitarianism on the surface in Sparta, where all men ate in messes and dressed identically until getting married in middle age. Indeed, the Spartans called themselves the homoioi, those who are alike. While egalitarianism was a very strong trend throughout the Greek world during the archaic and classical eras, in Sparta the appearance of egalitarianism was deceptive, at least in a politically. Spartan egalitarianism was the result of military necessity rather than an expression of the economic or social equality. The Spartan aristocracy never surrendered political control of Spartan politics.