Single people wishing to have biological children are creating a new sort of family. Colin Weil had a daughter in a partnership with her mother. Evan Sung for The New York Times

Rachel Hope is 1.75 meters tall and likes yoga, dance and martial arts. A real estate developer and freelance writer in Los Angeles, Ms. Hope, 41, is seeking a man who lives near her, is healthy and fit, and "has his financial stuff together," she said. Parker Williams, the 42-year-old founder of QTheory, a charity auction company, would seem like a good candidate. A 1.9-meters-tall former model who loves animals, Mr. Williams is athletic, easygoing, compassionate and organized.

Neither Ms. Hope nor Mr. Williams is interested in a romantic liaison. But they both want a child, and they"re in serious discussions about having, and raising, one together. Never mind that Mr. Williams is gay and that the two did not know of each other"s existence until last October, when they met on Modamily.com, a Web site for people looking to share parenting arrangements.

Mr. Williams and Ms. Hope are among a new breed of online daters, looking not for love but rather a partner with whom to build a non-nuclear family. And several social networks, including PollenTree.com, Coparents.com, Co-ParentMatch.com, and MyAlternativeFamily.com, as well as Modamily, have sprung up over the past few years to help them.

"While some people have chosen to be a single parent, many more people look at scheduling and the financial pressures and the lack of an emotional partner and decide that single parenting is too daunting and wouldn"t be good for them or the child," said Darren Spedale, the founder of Family by Design, a partnership site. "If you can share the support and the ups and downs with someone, it makes it a much more interesting parenting option."

The sites present what can seem like a compelling alternative to surrogacy, adoption or simple sperm donation.

Manly matters?

"I"ve met so many women in this same situation, who aren"t married and feel like they missed the boat," said Dawn Pieke, 43, a sales and marketing manager in Omaha, Nebraska, whose daughter, Indigo, was born in October. Ms. Pieke met Indigo"s father, Fabian Blue, on a Facebook page for Co-parents.net in June 2011. She feared having a child alone because, she said, "I didn"t grow up with my dad." She wanted someone to share the financial and emotional stresses of child rearing.

Mr. Blue had wanted to be a father since 2006. He had considered adoption, but "figured no one would let a single gay male adopt a child," he said.

Ms. Pieke and Mr. Blue first met in person on Thanksgiving 2011.Theyfollowed up by reading each other"s medical charts and undergoing fertility tests. He moved into a separate bedroom in her home, and, she said, four weeks later, "he handed me a semen sample, we hugged, and I went into my bedroom and inseminated myself."

The two never drafted a legal agreement, which they agree was unwise. "There were so many things I didn"t anticipate - like, how much should I be responsible financially? What happens if I lose a job? What happens if he does? It"s not a marriage," she said.

A history of hair?

The laws on parenting partnerships vary from state to state. In 2008, a New Mexico court ruled against a sperm donor who had agreed to pay some child support but refused when the amount rose. Last year, a court in California ruled in favor of a Texas sperm donor who was sued for child support.

Even a legal document is not necessarily binding. "Courts will operate on the basis of what is in the best interest of the child," said Bill Singer, a lawyer in Belle Mead, New Jersey.

Colin Weil and the mother of his 2-year-old daughter, Stella, drew up a contract before she got pregnant. Mr. Weil, 46, who is gay, met Stella"s mother, who asked that her name not be used, in October 2009 through a mutual friend. Stella now spends one night a week with Mr. Weil and they plan to work up to more.

"When you think about the concept of the village, and how the village was part of child rearing for so many cultures for so many thousands of years, it makes total sense," he said. "The idea that two people - let alone one person - would do it without the village is really nutty."

But Elizabeth Marquardt, director of the Center for Marriage and Families at the Institute for American Values, a nonpartisan advocacy group in New York, disagrees.

"It"s a terrible idea, deliberately consigning a child to be raised in two different worlds, with parents who did not even attempt to form a loving bond with one another," she wrote in an e-mail. "As children of divorce will tell you, it"s very difficult to grow up in two different worlds, with your parents each pursuing separate love lives that can be increasingly complex over the course of a childhood."

Others say parenting partnerships spare a child the future pain of divorce.

"Certainly, from a research standpoint, I don"t think having a romantic relationship is necessary to have a good co-parenting relationship," said Sarah J. Schoppe-Sullivan, an associate professor at Ohio State University.

These types of partnerships also encourage people to strategize on a philosophy of child rearing ahead of time, which many traditional couples don"t do.

Ms. Hope, who already has two children ages 22 and 4 from previous co-parenting relationships, said she had only met "desirable, accomplished men" while seeking her third. Regarding her next partner, she said: "It"s about whether we can relate to each other, but also about being shrewd and making a really logical, rational decision for my future unborn children."

The New York Times