By Sean Elder, WebMD Feature Reviewed by Amal Chakraburtty, MD, MD Once it was simple. You got married, had kids, worked the land, and stayed married whether you could stand each other or not. The concept of "a happy marriage" was no more relevant than the idea of "a pretty tractor." "That has changed over time as marriage has become more independent," says Steven Nock, a professor of sociology who studies marriage at the University of Virginia and author of Marriage in Men's Lives. "Couples don't need each other for quite as many things as they once did. If you're running a farm with someone, it doesn't matter if you're pissed at her or not. You need her labor as much as she needs yours. The couple is more or less equally dependent on each other." Chances are, though, if you are reading this, you are not running a farm with your mate. And if you are, you are probably doing it out of choice, not necessity. As a recent Washingt...