Marriage a trois (or more)

Marriage as we know it now is not the timeless, immutable institution it has often been made out to be. For much of human history, wedded unions were matters of commerce as much as anything; the modern idea that people should pair off with romantic partners is only a few centuries old, and even today isn't universal.
Forty years ago, however, many believed that by now, there would be a lot more choices on the Western matrimony menu, starting with polygamy.