Monogamy - Is it normal?

I consider myself a one-on-one, type of gal. I never quite understood polygamy or polyamourous relationships, at least not from a practical stand point. I mean, sure, maybe it would be nice to be like Empress Nympho from "History of the World, Part 1" and have my pick of manliness on any given evening. And, I'm sure that there are quite a few men out there love having their pick of women any given night. I'm sure that there are many doing so right now. But once the fantasy and the pleasure of the moment is over, then what? Back to the reality of emotions, diseases and unwanted pregnancies.

But in this world where monogamy is the social standard, I keep hearing time and time again that monogamy simply isn't normal. That's why men and women cheat. They are just giving in to human nature.

That got me to thinking. If it is our human nature to have more than one partner at a time, just where did the idea of monogamy come from? Is it more of a religious thing that we have just over time have socially accepted as law?