Across 70 U.S. cities, in various cafes, bars and nightclubs, tens of thousands of mostly young men and women over the past two years have been signing up for so-called 8MinuteDating events, which the organizers promise are "fast, fun and guaranteed."

Specifically catered to the rat-race, quick-fix demands of modern life, 8MinuteDating.com is just one in a slew of speed-dating options available to America's lonely hearts.

But if the demands of contemporary urban life may be driving the more daring among us to strange, technologically driven encounters of the intimate kind, recent research shows that nature offers up very few paragons of virtue.

Recent advances in genetic testing have proved that several species that were once held up as models of monogamy do in fact indulge in polygamous behaviors that range from mild to voracious. (See Story)

"Be thou like the dunnock," preached the 19th-century clergyman-natural historian Rev. Francis Orpen Morris, extolling his parishioners to display what he believed was the perseverance and fidelity of the tiny hedge sparrow.

But scientists today consider the dunnock — especially the female dunnock — a magnificent example of a species indulging in sex on the sly.

And with seemingly every glossy magazine and pop sexologist citing increased extramarital activities, sex scandals breaking from various quarters of public life, and Web sites offering a gamut of sexual romps — from swingers' club listings to dating services — monogamy, at first sight, seems to be going out of style.

"I think extramarital sex is getting more possible, more culturally acceptable, if not more positive," says Pepper Schwartz, professor of sociology at the University of Washington in Seattle and author of The Lifetime Love and Sex Quiz Book. "People still say it's bad. But it's like overeating — people say it's bad, but how many people do it."

What Humans Do

It's hard to estimate how many people do have extramarital relations, some experts say, in large part because there is a tendency to hide facts. And as Olivia Judson, evolutionary biologist at Imperial College, London, and author of the best-selling book, Dr. Tatiana's Sex Advice to All Creatures, notes, "Getting information on what humans do is difficult because one can't watch how they live — unlike other species."

But a highly regarded 1994 study on American sexual behavior by the National Opinion Research Center found that about 3 percent to 4 percent of currently married people have a sexual partner besides their spouse in a given year. And about 15 percent to 17 percent of people who have been married say they've had a sexual partner other than their spouse while married.

Based on the available information, a 1998 NORC study concluded that "extramarital relations are less prevalent than pop and pseudo-scientific accounts contend."

"I think the state of monogamy is good, it's doing very well," says Helen Fisher, an anthropologist at Rutgers University in New Jersey and author of First Sex. "Monogamy is defined as mono, meaning 'one,' and gamy, 'spouse.' And the tendency to have one spouse is growing because so many people are marrying and remarrying. Ninety-one percent of Americans marry by the age of 49."

And if one were to take into account the traditional reasons for getting married — to raise children — Fisher argues that for many people, there's no apparent reason to marry. "Women are marrying at a later age, there are fewer children, women don't need male help to raise kids, they don't need to marry."

Searching for a Sole Soul Mate

Indeed, many patrons and advocates of speed and online dating services say that for the most part, men and women using high-tech romance-seeking services are looking for a single soul mate.

"My view is that ultimately most people are looking for monogamous relationships," says Tom Jaffee, who founded 8MinuteDating.com in January 2001. "They're looking for a soul mate, or at least someone with whom they can share a strong bond."

Unlike most online dating services, Jaffee notes that with 8MinuteDating, people "meet right away, they can establish right away if they have enjoyed meeting and based on what they can establish in eight minutes, they can decide if they want to learn more. So the second date has no nasty surprises."

While most conventional forms of online dating have the perks of anonymity and mystery, they also have a built-in propensity for springing unpleasant surprises when the words on a computer screen don't match the real thing.

Earlier this month, the romantic hopes of some 50 women in the United States and Canada were crushed when the news media broke the story of a married U.S. Army colonel who had proposed to a number of unsuspecting women he had met on a slew of dating sites while he was posted in Afghanistan. (See Story)

The Army is investigating the incidents, although it is unclear at this point whether the cyber Lothario's alleged actions violate either criminal law or military regulations.

Danger Zones of Marital Infidelity

But the incident highlighted what experts such as Shirley Glass, a Baltimore psychologist and author of Not Just Friends, call the "new danger zones" of marital infidelity: the workplace and the Internet.

"For sure technology has contributed to infidelity," says Schwartz. "The fact that with cars and planes you can be in another city, there are cell phones as opposed to work and home phones, and with the Internet you can find people without moving out — it creates an environment where extramarital affairs are possible."

By all accounts, experts say the infidelity rate is higher among couples dating and living together — including those in long-term relationships — than among married couples. But even if technology has made cheating easy, some experts say there is little evidence of a rise in serial cheats, although there are numerous signs that serial monogamy is on the rise.

In serial monogamy, a couple will remain faithful for as long as their relationship endures. But when a monogamous relationship dissolves, each person is likely to look for a new permanent partner rather than multiple romances.

"There is a trend toward serial monogamy everywhere in the world due to higher divorce rates," says Fisher. "And the main reason for that is working women all over the world who are economically independent and so bad marriages can end."

Despite increasing divorce rates, Fisher's verdict for the marriages that survive is bright. "There's every reason to believe marriages are getting a bit better," she says. "Women can walk out of marriages because they have enough money to walk out of marriages."

Between a Chimp and a Gorilla

But in what Samuel Johnson famously called "a triumph of hope over experience," the vast majority of divorced Americans ultimately remarry, according to Fisher.

The popularity of serial monogamy, Fisher says, boils down to what she calls the three brain circuits in the biochemistry of love. "The first is the sex drive, the second, romantic love and the need for elation, and the third is the need for attachment, calm and unity. With this circuitry in place, we're going to keep marrying," she says.

Culture, according to Schwartz, plays a large part in the overriding tendency to keep trying at marriage. "In a culture where self-worth is bound up in monogamy, it's hard for people to break out of it and even if they do, they do feel bad about it because they're breaking the rules."

While stressing that it's hard to predict human behavior in an unlegislated state without the baggage of cultural expectations, Judson believes that humans are, for the most part, "fairly monogamous."

"It's difficult to say what would happen if humans were placed on an island, but it's not obvious to me that there will necessarily be a sexual free-for-all," she says. "There are species that have a number of sexual partners, there are other species that have a small number of partners and there are a small number that are entirely monogamous.

"I think humans are fairly monogamous," she says. "Humans are nowhere near as promiscuous as chimpanzees, but a human female has more sex than the female gorilla."