Back then, doctors extracted women’s eggs surgically under general anesthesia. The risks of infection, organ damage and even death from the procedure may have been justifiable for an infertile woman going through I.V.F., but not for a donor. So early researchers borrowed a trick from animal husbandry: when the donor ovulated, she was inseminated with the recipient’s husband’s sperm, the embryo formed in her body and, four to six days later, was flushed out of the uterus and transferred to the intended mother. This adapted procedure “was problematic in many ways,” said Dr. Richard Paulson, chief of reproductive endocrinology and infertility at the University of Southern California’s Keck School of Medicine in Los Angeles and a pioneer in the development of egg donation. For one thing, if the doctors missed the embryo, the donor could wind up pregnant.

By the late ’80s, though, European researchers perfected a new method of retrieving eggs by using a thin needle, guided by ultrasound and inserted through the vaginal wall. The procedure took 10 minutes and required only light anesthesia. As Liza Mundy writes in her book “Everything Conceivable,” this technique would revolutionize — or, you could even argue, create — the fertility industry by unhooking clinics from their dependence on hospital operating rooms. Suddenly, any doc with a lab and the right equipment could set up his own shop. Using that advance, Paulson and his team made a breakthrough of their own: some of their patients had aged past 40, which was considered the outer limit for medical intervention, while waiting for donors. Would it be possible, Paulson wondered, to push that threshold? He tried transferring multiple embryos created from a young woman’s eggs into the body of a 40-year-old . . . and she became pregnant. In 1990, Paulson published an article in The New England Journal of Medicine announcing that as long as the eggs were young, the age of the recipient appeared immaterial. And just like that, the market for donor eggs was born.

One day this spring, Becky, who is 38, met me at the airy loft in a sketchy neighborhood of Oakland, Calif., where she works in the music industry. She is a tiny woman — just over five feet tall — with dark blond ringlets pulled back in a ponytail and three earrings ascending one ear. A wedding photo on her desk, taken last summer, showed her tucked beneath the arm of her husband, Russell, a public-school teacher who is a more than a foot taller than she and who asked that I use only his middle name. Next to the photo was a clutch of supplements and prenatal vitamins that she was downing to prepare her body for pregnancy. Behind those sat a small statue of Ganesha, the pachyderm-faced Hindu deity, lord of both obstacles and beginnings.

Becky, who asked me to use a nickname, sat down and began scrolling through pictures on the Web site of Ova the Rainbow, one of the (regrettably named) agency sites she browsed last fall during her search for an egg donor. “When I first started doing this it was really emotional for me,” she said. “I kept thinking about that kids’ book, ‘Are You My Mother?’ I’m looking through these pictures of young women and feeling like: ‘Oh, my God! Is this the mother of my future child? Is this the mother of my future child?’ ”

I stood behind her, watching the young women go by. Each was accompanied by an assortment of photos: girls in caps and gowns graduating from high school, sunburned and smiling on family vacations, as preschoolers in princess frocks, sporting supermodel pouts in shopping-mall glamour portraits. Sperm banks rarely provide such visuals, which is just one disparity in the packaging and treatment of male and female donors, according to a study published last month in The American Sociological Review. Egg donors are often thanked with presents and notes by recipients for their generous “gift.” Sperm donors are reminded that they’re doing a “job,” providing a “sample,” and performing an act they’d presumably do anyway — which may be why many men in the study were rattled when told a pregnancy had actually occurred. And although the men could admit they were in it for the cash, ovum donors were expected to express at least a smidge of altruism.

It was weird to look at these pictures with Becky. I inevitably objectified the young women in them, evaluating their component parts; it made me feel strangely like a guy. Becky clicked on a photo of a 22-year-old brunette with a toothy grin. Each profile listed the donor’s age (many agencies consider donors to be over the hill by 30), hair color (there seemed to be a preponderance of blondes), eye color, weight, ethnicity, marital status, education level, high school or college G.P.A.’s, college major, evidence of “proved” fertility (having children of their own or previous successful cycles). Some agencies include blood type for recipients who don’t plan to tell their child about his conception. Others include bust size and favorite movies, foods and TV shows. One newly pregnant woman told me she picked her donor because the woman liked “The Princess Bride.” “Some donors chose ‘Pulp Fiction,’ and their favorite color was black,” she said. “That’s just not me. If I have the choice between someone who likes ‘The Princess Bride’ or someone who likes ‘Pulp Fiction,’ everything else being equal, I’m going for ‘Princess Bride.’ ”

Obviously, a penchant for romantic comedy is not an inherited trait. Nor, for that matter, will appearance or intelligence necessarily be passed along, though they are the first things most prospective parents look for in a donor. It’s a curious paradox: couples who conceive a baby this way believe that relationships, not genes, make a family, yet in their search for a donor, they romanticize the potential of DNA. And why not? The culture itself is in conflict over how much genes shape us, even as science and the media claim they determine, or predetermine, more than ever. Consider the schmaltzy news stories of reunions between adopted children and their “real” mothers, or tales of identical twins reared apart who are eerily alike. The notion that blood is thicker than water, that we can pass on our best — or someone else’s best — characteristics (but somehow not our worst) is a powerful one, even though anyone who has biogenetic children will tell you that they can be as different from one another, and from their parents, as strangers.