Wired for Monogamy

I was having a discussion about Ayn Rand yesterday with a Christian friend, who is reading Atlas Shrugged. He argued that we are "divinely wired for monogamy." Ayn Rand promoted adultery in Atlas Shrugged and herself carried on an extramarital affair with her student, Nathaniel Branden. And yet, my friend argued, the adulterous characters in Rand's book don't like the prospect of being cheated on. And Rand herself was disturbed when Branden was sleeping with another woman.

We also see this sort of thing in the movie, Reds, in which Warren Beatty and Diane Keaton play Communists in the early twentieth century. Part of their ideology was free love, and yet Diane Keaton didn't like it when Warren Beatty was cheating on her.

Moving into an ancient Near Eastern culture, the Hebrew Bible presents problems with polygamy. If a man has two wives, both wives fight over their husband's affections. I think here of Jacob, Leah, and Rachel.

But there are exceptions to the rule. There are wife-swappers. There are women who don't mind when their boyfriend cheats, and they cheat themselves. What are we to make of exceptions? Do exceptions invalidate the rule that we are wired for monogamy? Or are the exceptions examples of sick people?