Moonstruck partners pledging eternal love may be the current definition of marriage, but this starry-eyed picture has relatively modern origins.
Though marriage has ancient roots, until recently love had little to do with it.
"What marriage had in common was that it really was not about the relationship between the man and the woman," said Stephanie Coontz, the author of "Marriage, a History: How Love Conquered Marriage," (Penguin Books, 2006). "It was a way of getting in-laws, of making alliances and expanding the family labor force."
But as family plots of land gave way to market economies and Kings ceded power to democracies, the notion of marriage transformed. Now, most Americans see marriage as a bond between equals that's all about love and companionship.
That changing definition has paved the way for same-sex marriage and Wednesday's (June 26) Supreme Court rulings, which struck down the Defense of Marriage Act (DOMA) and dismissed a case concerning Proposition 8.
From polygamy to same-sex marriage, here are 13 milestones in the history of marriage.
1. Arranged alliances
Marriage is a truly ancient institution that predates recorded history. But early marriage was seen as a strategic alliance between families, with the youngsters often having no say in the matter. In some cultures, parents even married one child to the spirit of a deceased child in order to strengthen familial bonds, Coontz said.
2. Family ties
Keeping alliances within the family was also quite common. In the Bible, the forefathers Isaac and Jacob married cousins and Abraham married his half-sister. Cousin marriages remain common throughout the world, particularly in the Middle East. In fact, Rutgers anthropologist Robin Fox has estimated that the majority of all marriages throughout history were between first and second cousins.
Related: Why marrying your cousin may pay off
3. Polygamy preferred
Monogamy may seem central to marriage now, but in fact, polygamy was common throughout history. From Jacob, to Kings David and Solomon, Biblical men often had anywhere from two to thousands of wives. (Of course, though polygamy may have been an ideal that high-status men aspired to, for purely mathematical reasons most men likely had at most one wife). In a few cultures, one woman married multiple men, and there have even been some rare instances of group marriages.
4. Babies optional
In many early cultures, men could dissolve a marriage or take another wife if a woman was infertile. However, the early Christian church was a trailblazer in arguing that marriage was not contingent on producing offspring.
"The early Christian church held the position that if you can procreate you must not refuse to procreate. But they always took the position that they would annul a marriage if a man could not have sex with his wife, but not if they could not conceive," Coontz told LiveScience.
5. Monogamy established
Monogamy became the guiding principle for Western marriages sometime between the sixth and the ninth centuries, Coontz said.
"There was a protracted battle between the Catholic Church and the old nobility and kings who wanted to say 'I can take a second wife,'" Coontz said.
The Church eventually prevailed, with monogamy becoming central to the notion of marriage by the ninth century.
6. Monogamy lite
Still, monogamous marriage was very different from the modern conception of mutual fidelity. Though marriage was legally or sacramentally recognized between just one man and one woman, until the 19th century, men had wide latitude to engage in extramarital affairs, Coontz said. Any children resulting from those trysts, however, would be illegitimate, with no claim to the man's inheritance.
"Men's promiscuity was quite protected by the dual laws of legal monogamy but tolerance — basically enabling — of informal promiscuity," Coontz said.
Women caught stepping out, by contrast, faced serious risk and censure.
7. State or church?
Marriages in the West were originally contracts between the families of two partners, with the Catholic Church and the state staying out of it. In 1215, the Catholic Church decreed that partners had to publicly post banns, or notices of an impending marriage in a local parish, to cut down on the frequency of invalid marriages (the Church eliminated that requirement in the 1980s). Still, until the 1500s, the Church accepted a couple's word that they had exchanged marriage vows, with no witnesses or corroborating evidence needed.
8. Civil marriage
In the last several hundred years, the state has played a greater role in marriage. For instance, Massachusetts began requiring marriage licenses in 1639, and by the 19th-century marriage licenses were common in the United States.
9. Love matches
By about 250 years ago, the notion of love matches gained traction, Coontz said, meaning marriage was based on love and possibly sexual desire. But mutual attraction in marriage wasn't important until about a century ago. In fact, in Victorian England, many held that women didn't have strong sexual urges at all, Coontz said.
10. Market economics
Around the world, family-arranged alliances have gradually given way to love matches, and a transition from an agricultural to a market economy plays a big role in that transition, Coontz said.
Parents historically controlled access to inheritance of agricultural land. But with the spread of a market economy, "it's less important for people to have permission of their parents to wait to give them an inheritance or to work on their parents' land," Coontz said. "So it's more possible for young people to say, 'heck, I'm going to marry who I want.'"
Modern markets also allow women to play a greater economic role, which lead to their greater independence. And the expansion of democracy, with its emphasis on liberty and individual choice, may also have stacked the deck for love matches.
11. Different spheres
Still, marriage wasn't about equality until about 50 years ago. At that time, women and men had unique rights and responsibilities within marriage. For instance, in the United States, marital rape was legal in many states until the 1970s, and women often could not open credit cards in their own names, Coontz said. Women were entitled to support from their husbands, but didn't have the right to decide on the distribution of community property. And if a wife was injured or killed, a man could sue the responsible party for depriving him of "services around the home," whereas women didn't have the same option, Coontz said.
12. Partnership of equals
By about 50 years ago, the notion that men and women had identical obligations within marriage began to take root. Instead of being about unique, gender-based roles, most partners conceived of their unions in terms of flexible divisions of labor, companionship, and mutual sexual attraction.
13. Gay marriage gains ground
Changes in straight marriage paved the way for gay marriage. Once marriage was not legally based on complementary, gender-based roles, gay marriage seemed like a logical next step.
"One of the reasons for the stunningly rapid increase in acceptance of same sex marriage is because heterosexuals have completely changed their notion of what marriage is between a man and a woman," Coontz said. "We now believe it is based on love, mutual sexual attraction, equality and a flexible division of labor."
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Tia is the managing editor and was previously a senior writer for Live Science. Her work has appeared in Scientific American, Wired.com and other outlets. She holds a master's degree in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor's degree in mechanical engineering from the University of Texas at Austin. Tia was part of a team at the Milwaukee Journal Sentinel that published the Empty Cradles series on preterm births, which won multiple awards, including the 2012 Casey Medal for Meritorious Journalism.