Monogamy and alcohol together serve to keep lower ranking males content, and less likely to overturn their ruling class. This system works very well in areas with an entrenched and stable group of wealthy and powerful who want to keep it that way. Sex and alcohol is spread out among the lower ranking males to placate them, and keep their ambitions from heating up too much. (Though the wealthy and powerful often have provisions for themselves to have access to multiple females in these systems, despite the official monogamy. )

Polygamy is less stable unless there is a lot of war in the area, and there is a large surplus of women. In which case polygamy helps stabilize society by ensuring the surplus women are provided for. If there is a roughly equal birth rate and not a lot of war, it is a very unstable system, and would be selected against unless they can pawn off their excess males by expulsion onto other groups. Perhaps these groups tend to limit alcohol consumption because alcohol would have less of a placating effect on young men who had no mate, and little chance of acquiring one by means other than unseating someone with a harem.

In spite of the vineyards and barley fields
the hunter/gatherers use to have…