Submitted: Apr 12, 2008 - On the HBO drama "Big Love," Bill Paxton plays a man with three wives. But polygamy isn't just fictional fodder for TV shows, as evidenced by recent news about a polygamist religious sect in Texas. How prevalent is it?

Today, most Americans think of monogamy as the "normal" form of marriage. But as it turns out, strictly monogamous practices are in the minority. In fact, cultures that…