When news broke in June 2016 that Ari Nagel, a New York community college math professor, had fathered 22 children between 2004 and 2016 with 18 women—all through sperm donation—there were gasps, titters, and more than a few child-support lawsuits from his offspring’s mothers.

Unlike most sperm donors, Nagel had not gone to a sperm bank but had instead found would-be moms on Craigslist. He was apparently eager to please, sleeping with some of the women who sought his services. In other cases, he reportedly spilled his seed into a menstrual cup after a solo interlude in a Dunkin Donuts or Target bathroom. He’s even traveling overseas to help women get pregnant. Media have reported that Nagel regularly sees many of his offspring. Others, however, are complete unknowns.

Investigative journalist Jacqueline Mroz’s eye-opening book, Scattered Seeds: In Search of Family and Identity in the Sperm Donor Generation, looks at families like Nagel’s, that were created by sperm donation. It focuses on several overlapping constituencies with whom she spent considerable time: men who provide sperm altruistically or for a price; the women who use it; and the children they create.

Mroz also assesses the sperm donation industry, a largely unregulated business where, she writes, almost “anything goes.” The book’s blend of compelling personal narratives and commentary about often-unscrupulous practices makes it an engaging and accessible introduction to a complex and morally fraught issue. In fact, sperm donation has a longer history than you might expect, and Mroz does a good job of summarizing the ways the desire to parent has been exploited and sold.

Scientists have long been fascinated by reproduction and, beginning in the 18th century, experimented on enslaved or low-income women. Their goal? To not only understand the mystery of conception, but to manipulate it. Early 20th-century eugenicists took it further and sought to eradicate “feeble-mindedness,” a ridiculously vague concept that included people with mental and physical disabilities and those deemed sexually promiscuous. In the twisted imagination of the eugenics movement, humans could be perfected, and how better to improve society than to increase the birth rate among white, middle- and upper-class professionals?

New technologies developed in tandem with pre-World War II eugenics, with in vitro fertilization and sperm preservation coming to market in the 1930s and 1940s. This “set the stage for sperm banks’ use of frozen sperm to impregnate women. By 1955, four pregnancies from frozen sperm were successful,” Mroz writes.

This achievement followed on the heels of another scientific breakthrough: More than a decade earlier, 10,000 pregnancies had been achieved through artificial insemination, today called assisted reproduction. To a one, the recipients were heterosexual and married; at that time, single women were barred from utilizing reproductive technologies, including contraception. These women who came to their doctors for help were fertile, but their spouses were not. If they were going to conceive and parent, someone else’s sperm would have to be used. Shockingly, in this era it was the doctor, and not the couple themselves, who selected an appropriate donor.

Flash forward to the 1960s, when the technology’s increased availability led to 30,000 babies born through donor insemination each year. In vitro fertilization entered the mix, so to speak, in the 1970s,  and the United States opened its first large-scale assisted reproductive care facility, California Cryobank, in 1977. Its main mission was selling sperm to those who could afford it.

Today’s U.S. fertility industry is estimated to generate up to $4 billion a year, and services are available to any and all—married, single, lesbian and straight—who have enough greenbacks. But “the business of sperm banking,” Mroz writes, “has turned the sale of human genetic material into a commodity, with banks marketing the most popular ‘perfect’ male specimens to their clients, a modern-day eugenics department store.”

For example, Nagel was a healthy, blue-eyed, 6-foot-2 white man with a PhD—and therefore highly sought after, as if intelligence and good looks are as easily purchased as a new car or the right color blouse. And here’s another tidbit to chew on: Mroz writes that the Cryos International Sperm Bank in Denmark—the world’s largest—used to market its Nordic donors as “Vikings” or tall, strapping, blonde He-Men. Meanwhile, many U.S. banks explicitly state that men shorter than 5 feet 6 inches need not apply.

Low-income women—no matter how desperately they want a child—are also derailed. As Mroz reports, “a vial of standard donor sperm [currently] costs between $600 and $800,” and most women opt to purchase a few in case the first effort fails. They may also want extra so that they can give their firstborn a genetically similar sibling when the time is right. “Plus,” she continues, “there’s the cost of storing the sperm—about $70 per month, per vial, or $475 if you pay by the year.”

This likely explains the Craigslist ads and the subsequent solicitation of child support in Nagel’s case, something people using sperm banks typically promise not to do.

But money aside, those born through purchased sperm often want to know something about their biological dads and relatives. And since there is no regulation on how often men can donate and there are no limits on how many different banks they can service, the possibility of half-siblings has raised concerns about extended family ties.

In fact, these concerns prompted Wendy Kramer and her now-adult donor-conceived son, Ryan, to create the online Donor Sibling Registry (DSR) in 2000. Thanks to this database, children who know their donor number—in most cases, they do not have a name since donation was supposed to be anonymous—can find one another. A site offshoot allows donors to post messages affirming their willingness to be contacted by their children.

Scattered Seeds documents numerous reunions and, as you’d expect, they run the gamut. Some half-siblings seem to bond almost instantaneously while others do not. The same is true of father-child encounters. While many children are delighted to meet their biological dad, learn medical and paternal family history, find out what prompted their dad to donate sperm, and even get to know their cousins and grandparents, others have a harder time connecting with a person they’ve known only as a number.

More disturbing, some have been overwhelmed to discover that their half-siblings number in the hundreds. Yes, hundreds.

Take donor B155A, for example. This man—known to have spawned at least 150 children—donated to a sperm bank in Fairfax, Virginia. He was 6-foot-2, blue-eyed, and blonde. He was also highly educated, worked in a profession that demanded skill and precision, and was an avid rugby player; in short, he was the epitome of brain and brawn. His swimmers were big sellers in England, Israel, and the United States.

For Mroz, cases like this illustrate why donations should be limited and regulated. The American Society for Reproductive Medicine agrees, recommending that donors be restricted to 25 births per population of 800,000.

But even this step, Mroz adds, would be insufficient “since sperm is shipped all over the country—and world—it’s easy to get around this standard.” Additionally, there is what she calls a “gray market,” in which women sell or give extra vials of sperm to other women once they no longer want or need them.

Anonymity is another big issue. Despite promises to the contrary, sperm banks cannot truly assure donor privacy, since websites like the Donor Sibling Registry can link donor-conceived children to their siblings or parents. Wendy and Ryan Kramer, the DSR’s creators, want an industry that is both more regulated and transparent. They believe that any healthy man (meaning free of communicable or infectious diseases) should be able to donate. But their vision also includes less anonymity; at minimum, they advocate for any offspring’s right to know their donor’s identity when they turn age 18, which is not the case now—as individual donors get to choose if they want to be known donors.

It’s certainly a policy change worth considering. Then again, the whole subject of assisted reproduction, and the potential creation of designer babies, needs a good airing.

Scattered Seeds opens the door to a clear and nuanced understanding of the pluses and minuses of assisted reproductive technologies. Assisted reproduction allows lesbians, single heterosexual women, and those experiencing infertility to have and raise the children they desire. On the negative side, this market for sperm reinforces class and racial biases that tend to favor those who already get a lot of privilege in this society: well-educated, tall, white, blue-eyed athletes.

There’s more to be said, of course, on all these topics. There’s also more to be said about families that include dozens—or hundreds—of genetically linked half-siblings. It’s a brave new world writ large, but, as Mroz reports, the fact that more than one million Americans were conceived via donor sperm ensures that the “market” will continue and likely expand.

“This is the dawn of a challenging moment in time for assisted reproduction,” Mroz concludes. “With technology evolving rapidly, it’s time for legislators and policymakers to start acknowledging these changes and examine the consequences of an unregulated industry.”

I’d say it’s long overdue.