To log on to Science Connection is to enter a singles site that alternates between quirky and sincere, a niche culture worlds apart from mainstream sites like Lavalife or eHarmony. Its logo is two lab rats, and its introductory blurb reads, "The world is a crowded petri dish, and yet for those of an intellectual bent who happen to be single, it's not easy, especially past university age, to find that certain microbe for a great symbiotic relationship." Ironically, Science Connection boasts no special insight into the science of human reproduction, unlike services such as eHarmony, which claims to have "a scientific approach to match highly compatible singles," using a system based on "29 Key Dimensions of Compatibility," or Chemistry.com, which professes an understanding of core aspects of personality, "even down to the level of brain chemistry." Automated matchmaking based on algorithms "sounds gimmicky to me," says Lambert, who argues that the factors influencing human mate choice are complex and mysterious. "I think we have an exaggerated sense of our own rationality. Most of what goes on psychologically is below the conscious level, including why we like certain people much more than we like other people." She cites experiments in which women were given sweaty T-shirts worn by various men. The women preferred the smell of the shirts worn by men whose immune systems differed most from their own.

Science Connection's sign-up questionnaire is straightforward, as perhaps befits a group of people who are broadly reluctant to divulge intimate information. Lambert notes that scientists are often "rather circumspect. They are not people who can relate to pouring out their hearts on Oprah or to people boasting about themselves in personal ads." Instead, members are asked about their favorite books and music, as well as desirable characteristics in a prospective partner. "I think you can retain your dignity through this process, but it's hard to do if you're being asked personal questions about all your disappointments and past relationships," Lambert says.

A glance through Science Connection's profiles reveals physicists, psychotherapists, microbiologists, geologists, and high school science teachers, among others. Many display a disarming wit and refreshing candor. A physics grad student, "midway between couch potato and running vine," pledges to "try for reasonable unchauvinistic chivalry." "Deeply happy as a hermit," reads another, "but looking for like-minded women . . . with whom to scientifically explore the wilds of the introspective." Exploring the real wilds appears popular: Birding and hiking are commonly cited pursuits. Most members are defiant nonbelievers—not surprising, since a 1998 Nature survey of National Academy of Sciences members found that only 7 percent professed faith in a personal God. "A spiritual but not religious type—disdain dogma and religion," one typical profile proclaims. The most common religion listed on the site is "none," closely followed by atheist and agnostic, with a few Christians, Jews, and an occasional deist, pantheist, or humanist in the mix.

Take Elliot Frank. A 57-year-old high school biology teacher—"I'm on the front lines of the evolution issue," he says—he describes his religion as "Einsteinian/Spinozan," lives surrounded by books, loves dancing and blues guitar, and lists his greatest sources of enjoyment as "kids, thinking clearly and critically, walking in the woods." He tried Science Connection "because I'm overwhelmed with reasonably intelligent people who ask for my sign or recommend homeopathic remedies. I'm tired of being regarded as weird."

Or take Sue Phillips, a 51-year-old divorced math teacher, who says that she feels most comfortable with men "who tend to be structured, analytical, and rational." People in the sciences, she says, "are better at critical thinking, are freethinkers, are healthier, and are interested in environmental conservation." Also, "I love facial hair on men, which is very typical for science types."

Environmental protection and nature conservation are topics that pop up frequently in Science Connection profiles. But the truly dedicated green soul can try another, similarly specialized site, GreenSingles (www.greensingles.com). In a sense, environmentalists and scientists face similar obstacles when it comes to finding partners: They are often uncompromising in their ideals, do not suffer fools gladly, and carve out lives for themselves that may take them to remote spots in which dating options are few. "We're often looked on as strange people, weirdos," says Lee Schulman, founder of GreenSingles, as well as a sister site for vegetarians and vegans, VeggieLove.com. "People don't understand why we're so passionate about these issues. We get ridiculed. It's as if we're wearing a big red X on our foreheads when we talk to people who have no interest. They think they can ride their Hummers and it doesn't affect anything." But GreenSingles members know "that the environment is a fragile thing and live their lives accordingly." On Match.com, an environmentalist might have to scroll through thousands of profiles to find a green soul mate. On GreenSingles, "you start with the same values, and you build the relationship from that," Schulman says.

GreenSingles members are willing to go the extra mile to find other green devotees, as demonstrated by some of the success stories on the site. About 45,000 people have joined GreenSingles since its creation in 1985 as a postal newsletter (it went online in 1996), and Schulman estimates that about 300 members have married partners they met on the site. Chris (a.k.a. "Sealion") writes from an island in British Columbia that a woman he met through the site, "a real heart-stopper," lived "a scant one-hour drive, followed by a seven-hour ferry, followed by another six-hour drive (and another ferry) away. We quickly made a connection, and now we're happily hooked up. She even moved on over to my island and is enjoying the fresh start." A good thing, too: According to the writer, "another lonely winter huddled up alone in my cabin and I fear I would have just embraced the madness . . . and started talking to animals. Actually I still talk to animals, but you get my drift."

Other GreenSingles members choose a less extreme lifestyle—recycling, driving hybrid cars, eating a vegetarian diet—but they aren't prepared to abandon their principles for the sake of love. "I could get lucky with a supermodel—not likely, but a great idea—and then face the prospect of her ordering ham and eggs for breakfast. I couldn't hang with that," says sales manager Jeff Harris, 46. And Douglas Johnson, a 52-year-old scientist who runs Environmental Intelligence, a company that steers clients (including NASA) to new green technologies, says that "at a fundamental level, being green is about loving others—other people, other species."

Divorced since 1999, Johnson is prepared to wait for a while to meet his intellectual and emotional equivalent. "I failed to do this in some of my prior relationships," he says, "and the lesson of the difficulties that ensued stuck with me." It's the same lesson that brought Eric McRae to Science Connection. "There were times in my life when I got into a relationship just to avoid being alone," he says. So he is happily surprised to have found a woman who is compatible with him on so many different levels—a common intellectual curiosity, a mutual attraction, a shared love of singing and nature. Though his new love lives far away in Georgia, they plan to spend the summer together and see a future with each other. "She strikes me as a person who hasn't given up," McRae says, "and neither have I."

Einstein in Love by Dennis Overbye details the romance between Albert Einstein and Mileva Marić. See also Albert Einstein/Mileva Marić: The Love Letters, edited by Jürgen Renn and Robert Schulmann and translated by Shawn Michael Smith.

Also read about women's adventures in science in Space Rocks: The Story of Planetary Geologist Adriana Ocampo by Lorraine Jean Hopping, and Gorilla Mountain: The Story of Wildlife Biologist Amy Vedder by Rene Ebersole.