Fidelity isn't natural, but jealousy is. Hence the one-spouse rule. One isn't the number of people you want to sleep with. It's the number of people you want your spouse to sleep with.
"What is historically odd is that as gay marriage is gaining acceptance, the resistance to polygamy is much more powerful."
But when you factor in jealousy, the oddity disappears. Women shared husbands because they had to. The alternative was poverty. As women gained power, they began to choose what they really wanted. And what they really wanted was the same fidelity that men