For many of us, there's an intrinsic appeal to the image of a virgin bride -- a pretty concoction of purity in a princess dress.
But for royal families, it's been much more than that: a time-honored manner of ensuring the integrity of their all-important bloodlines.
That is, it seems, until now.
As Kate Middleton and Prince William have thrilled the British public this week with the news of their engagement, there's been barely a whisper about the fact that they've been co-habitating on and off for years.
Contrast that with the engagement of Princess Diana and Prince Charles 29 years ago, in which an uncle of Diana's actually pronounced her a "bona fide virgin" to the press.
"It's amazing how little one has heard about the co-habitation issue," said Deborah Cohen, a professor at Northwestern University who specializes in modern British history. "The modernization of the monarchy has developed very quickly in the last 30-plus years on those sorts of social issues."
Historically, societies began to prize virginity as a marital attribute when they started to develop inherited wealth and social status, said Stephanie Coontz, author of "Marriage, a History: From Obedience to Intimacy or How Love Conquered Marriage."
For commoners in modern times, the idea of saving oneself until marriage was often rooted in religious convictions. For the royals, the motivation was much more pragmatic, said Ms. Coontz, noting that in some royal families it was perfectly acceptable for men and women to have affairs after the birth of legitimate heirs.
"The way that the Ancient Greeks put it is, you want to make sure that when you insert your seed in the ground, another man's seed isn't already there," said Ms. Coontz, who is also a professor of history and family studies at Evergreen State College.
And if a prospective heir to a throne was actually sired by, say, the stable boy, where would that leave the monarchy?
"It was just terrifying to the kings -- the idea that their wife might be impregnated by someone else," Ms. Coontz said.
Controversy over this topic is not unprecedented. In 1660, the man who would be King James II married a very pregnant Anne Hyde.
The wedding was held in secret, amid allegations that the child was not actually sired by the future king.
"What is virginity about?" said Dr. Cohen. "Virginity is about ensuring that the prospective bride, when she delivers a child, is delivering a legitimate heir. The rumors that swirl around whether the heir is legitimate are obviously destabilizing."
In Anne Hyde's case, her first son, Charles, died shortly after childbirth, as did five more of her children. The living heirs, Anne of Great Britain and Mary II of England and Scotland, ruled after James II abdicated the throne during the Glorious Revolution.
These days, of course, DNA tests are a better judge of bloodlines than purported bridal virginity.
But more important, the very essence of royal marriages has changed from that of convenience to companionship. And if royals are now marrying for love, the paternity of the offspring shouldn't really be in doubt.
It's a marked change from even the 1980s. The marriage of Prince Charles and Princess Diana was essentially still an old-fashioned, arranged marriage -- even if Diana might have believed otherwise, Ms. Coontz said.
"They chose for him in a way that would have been perfectly appropriate and accepted for both the male and the female for thousands of years," she said. "They seemed to have ignored the fact that most people, including the young woman, had moved on."
The hubbub over Princess Diana's virginity -- decades after the sexual revolution -- horrified British feminists at the time but seemed still in character for the monarchy.
It wasn't until the unpleasantries following Prince Charles and Princess Diana's marriage and divorce that the royals were really ready to move on, Dr. Cohen said.
Though even now, the royals don't quite play by the same rules as the rest of us. England might be ready to accept Kate Middleton even as a commoner who has been "living in sin" with her Prince Charming.
But if Prince William had fallen in love with someone who had been married before or wanted to adopt an heir, the public and the royal family wouldn't be nearly so accepting.
In some sense, said Ms. Coontz, the royals are just catching up with the rest of us. In the United States, only 15 percent of brides are virgins, she said, speculating that the percentage would be similar in England.
And it's a figure that was likely quite different half a century ago. "Only really in the last 50 or 60 years, not only doesn't it matter whether a bride is a virgin, we no longer need to pretend that it matters," said Ms. Coontz. "Finally, it has trickled up to the royals."
But just because virgin brides are vanishing doesn't mean we can't still have our fairy tales.
"Part of what the Charles and Di story ended up proving is that the arranged marriage of old wasn't as good as the companionate marriage, which is pretty much what the rest of the population had figured out 250 or 300 years before," said Dr. Cohen.
"We have more of an investment in Kate and William being normal than being removed."
Anya Sostek: email@example.com or 412-263-1308.