Lessee, what were we talking about?
Somewhere in this wilderness of a thread, a brave soul tried to get back on track by suggesting that polygamy might work in special circumstances. I think that person (sorry, can't find the post or the poster's name) has put his finger on it.* There are at least two societies, the Todas of central India and the upper class of Tibet, that practice multiple marriage, i.e., men have more than one wife and wives have more than one husband. Both are nomadic or at least bi-local societies, which means that homesteads are left husbandless for part of each year.
Among the Todas, a married man is obliged to leave his wife at home while he takes the cattle to distant pastures (much the same situation obtains, or used to obtain, in Tibet, at least among people who were well enough off to own large herds). The household he leaves behind includes various unmarried or otherwise unsupervised men, brothers, uncles, fathers, etc. The most practical answer is to formalize the couplings that will inevitably develop in these circumstances. A Toda woman marries not just her husband but also his brothers and father - and it's not pro-forma marriage, it's the real thing. Further, a Toda woman is expected to have a lover or series of lovers, and again this is a recognized institution; for example, the lover has a ritual part to play at a married woman's funeral.
Some Indians have observed that the Todas are just an uncommonly honest people: they do openly what everybody else does by stealth. But I'm of the opinion that their uncommon marital arrangements are forced on them by the peculiar circumstances of their economic life.
Right there we have the answer as to why polyamory doesn't work too well in uni-local societies like ours: hubby isn't off to the high pastures from May to October; everybody lives under everybody else's eye, and normal human possessiveness causes friction and the heat that comes from friction. Maybe someday our institutions will expand to include multiple spouses, if our living conditions change sufficiently.
* 1intoChrist: You keep your dirty mind off that figure of speech. Shame on you.
