What is traditional marriage?
That question lies beneath the surface of the Proposition 8 debate. The measure that bans same-sex marriage in California, which is now being challenged in court, defines the union as between a man and a woman. This, supporters argue, is as religious precepts and social customs demand. It is traditional.
"The proposition is about restoring the traditional definition of marriage," Bishop Jaime Soto, of the Catholic Diocese of Sacramento, has said.
Many agree. Opponents aren't so wedded to that idea. Marriage has been defined in a surprisingly number of ways by different cultures and historical movements.
"Traditional marriage has varied immensely from society to society and time period," said Stephanie Coontz, who teaches history at The Evergreen State College in Olympia, Wash., and is the author of "Marriage, A History."
Coontz said one form of marriage has been supported by more societies prior to the 18th century than any other.
And it's not one man, one woman.
"It's one man, many women," said Coontz, citing examples from the Old Testament.
From polygamy to interracial marriage, the notion of what marriage means – and who can get married – has gone through many permutations, say scholars who have studied the institution.
Consolidating property, building political and military alliances, and bolstering social status were all acceptable reasons for marriage for hundreds of years among the upper classes. Poor people married to expand their labor pool, said Coontz.
Marrying for love became widely practiced in the 18th century.
"There are probably a dozen patterns of marriage," said Glenn Olsen, who teaches history at the University of Utah in Salt Lake City. He said that as Christianity spread, what was then considered the radical notion of monogamy did as well. "The Christians carried their ideas of marriage – monogamy with no divorce – as their religion spread."
What about same-sex marriage?
Coontz said same-sex marriage has been accepted in some cultures. "But those have always been a small minority," said Coontz.
Historians say both sides of the Prop. 8 debate have "overstated" their claims about marriage, said Coontz. "You can't rewrite history to support your moral positions, whatever they are," she said.
The Church of Jesus Christ of Latter-day Saints and its past views on marriage have come under fire since the passage of Prop. 8. Church members reportedly contributed nearly half of the $40 million raised to pass the initiative.
Critics at rallies and in blogs have pointed to the church's past polygamous practices. The church originally practiced polygamy because it wanted to restore biblical ways. The church banned polygamy more than 115 years ago.
"It's behind us. The church is moving on, " said Dennis Holland, spokesman for the Sacramento region.
Mormons believe marriage between a man and a woman is central to the plan of salvation, said Holland. "The traditional unit of man, woman and children is the basic unit for eternity," said Holland. "That's why everything we do in the church is centered around strengthening and building family relationships."
What is unprecedented is that roles in a marriage are now negotiated by the couple, said Coontz. In the 1970s and '80s, states began repealing laws that defined marriage with one set of laws that said spouses had certain obligations.
"There were laws that said a man's job was to support the family and the woman's job was to take care of the home," said Coontz. All this means, say historians, is that marriage will continue to change.
"There was a time when marriage was a property transaction," said Brian Baker, dean of Sacramento's Trinity Cathedral, who voted against Prop. 8. "The notion of marriage we have now is contemporary. This is just another example of the evolution of marriage."
"There's a lot of anxiety having to do with how rapidly marriage is changing," said Coontz. "As a historian I can say that marriage will continue to diversify."