Polygny/polygamy is merely a human subsistance strategy. As is polyandry. In small communities, where land is limited, but populations continue to grow, polygamy and polyandry allow distribution of land/wealth to occur on a more consitent basis. Imagine a father with four sons (the four were needed to work the land) who dies. Who gets the land? There are some possibilities: the eldest, it's split up, etc. In a polyandry society, the brothers marry the same woman, and she becomes the matriarch, the land stays in the family as a whole piece. This works best for smaller parcels of land. In a polygamy society, the land stays in the family, but the brothers each marry multiple women, producing several offspring each who become laborers for the land. This works best in situations where land is abundant and far too large to be worked by a father and a couple sons. Perhaps as in Utah. The situation is not infinite, because the land does eventually become split among the sons, though not at a necessarily fast rate. Christianity has little to do with polygamy, other than some christians in the past needed laborers for their flocks/land. Marrying multiple women was a sure way to increase your workforce. But then, there are many such traditions and even taboos in Judeo-Christian mythology that have social origins, not religious ones. The taboo against eating swine, for instance, probably had to do with the fact that pigs are direct competitors with humans for sustinence. They eat pretty much what we do. Ovicaprids (sheep, goats, etc.), on the other hand, eat vegetation like grass & shrubbery.
