When "we" accquired souls? When God contacted man? (I thought he created man ), polygamy = no soul?
Accidentally, yes, widespread polygamy was linked with an absence of human soul. Here's the picture: some primates gradually get smarter and begin to stand up, and at some point (I don't know when) God makes them human, a categorical change which brings with it eternal human souls. From this point, humans are divine beings, the same as we are today, and are called to monogamy. Cgannon's question was whether it was immediately immoral to be polygamous, which seems counterintuitive given the instantaneous nature of the change. He doesn't mean that polygamous people now lose their souls, but that monogamy, as part of human identity, was instituted at the same time as human souls entered beasts and made them men.
You talk about beasts and brute instincts as if they're a bad thing. Why strive against them, clinging painfully to some moral code that has failed to make men happy for two thousand years? I'll take curiosity and the spirit of inquiry and self-understanding over a hard slab of laws any day.
A "beast" is just a locomotive creature that isn't human. I kept my language neutral and just presented the options in order to show that the question is pointless. You clearly prefer materialism, and think that men simply do what they want to do, so why not act on the most basic of the wants. Fine, I'm not going to try to change your mind. But then, as I said, the question is a trivial one-- humans are generally monogamous, because they want to be, but sometimes they want even more to act on urges to promiscuity. Then it's not a question about what's "natural", because there is no nature to investigate, but about what people do-- simple empirical data. And incidentally: 1) a thing called a "moral code" is of a nature to be followed, so if it is really a moral code, that very fact answers the question of why we should follow it. 2) this particular moral code has on balance contributed an immense amount to happiness, both in this world and the next, even if it sometimes is difficult for an individual to follow it.
To me the latter seems entirely superior. And in the end it will trump the former.
Okay, but on your materialist account, it doesn't really matter. If men obey their lower instincts, it's because they want to, and it couldn't be otherwise. Ditto if they refer to culture in favour of their urges. If people do in fact act based on the influence of their culture, telling them they should instead obey their instincts is insensible, because it amounts to telling them they should want something else. We'll just have to see how things go, and maybe it will be interesting, but the result is not of moral import on your account: whichever people will have wanted more, that's what they'll have done. Luckily, your account is wrong, and we will achieve transcendent happiness in the end, but even without agreeing with that, you should be able to see why your position isn't one from which you can say X or Y should not be.