For thousands of years, we humans have lovingly mutilated our children. We give birth to them, swaddle them, and then cut their genitals. Some people condemn these rituals; others defend them. Now reports from Africa are shaking assumptions on both sides. Our mutilation of girls may be killing them. Our mutilation of boys may be saving their lives.

According to UNICEF, at least 100 million women, largely in Africa, have been genitally disfigured. Two months ago, the World Health Organization reported that these women, compared to their uncut peers, were up to 69 percent more likely to hemorrhage after childbirth and up to 55 percent more likely to deliver a dead or dying baby. For every 100 deliveries, the WHO estimates that female genital mutilation kills one or two extra kids.

Fortunately, the world is mobilizing against this practice. More than 50 African nations have signed a protocol against female mutilation. Last year, two reports found it was declining across the continent. The governments of Djibouti and Mauritania have campaigned against it; public support has diminished in Egypt, Ethiopia, and Senegal. Last year, practitioners in Ivory Coast renounced the trade and gave up their instruments. Three weeks ago, colleagues in Sierra Leone followed suit. Britain and are cracking down on immigrants who try to import it.

But why stop with girls? Why not rescue boys, too? That's the argument of the anti-circumcision movement, whose constituencies—groups such as Mothers Against Circumcision, Jews Against Circumcision, and Catholics Against Circumcision — are flooding the Internet. There's a site for intactivists and another for foreskin restoration. There's a gallery of naked men, literally uncut. Some groups troll for personal injury plaintiffs; others promote marches on Washington to honor Genital Integrity Awareness Week.

To its credit, the movement has challenged custom and inertia. It has pleaded for scientific research and an "open mind" and doctors have listened. Seven years ago, the American Academy of Pediatrics concluded that evidence of potential benefits was "not sufficient to recommend routine neonatal circumcision." The American Medical Association agreed. Fewer boys are being circumcised today than in 1970, and more medical residency programs that teach circumcision are including anesthesia.

But scientific rebellions against religion have a nasty habit of becoming religions themselves. First come the myths. Last month, Dan Bollinger, director of the International Coalition for Genital Integrity, launched Project: OUCH!, a "collection of first hand accounts" by victims of genital mutilation. The first account, written by Bollinger, described a recurring "flashback of my circumcision when I was three days old." It was a moving story. But according to brain researchers, such memories at that age are biologically impossible.

Then comes the ideology. Foreskin advocates say uncut men are "intact, natural and normal." Circumcised men, by implication, aren't. Technically, according to Doctors Opposing Circumcision, it's up to you whether to "go through life with incomplete genitalia." But what kind of man would choose that?

Half the time, anti-circumcision activists talk like anti-abortion activists. They're pushing federal legislation to impose a jail sentence of up to 14 years on anyone who "cuts or mutilates the whole or any part" of the foreskin of a boy younger than 18. (Call it the "partial bris" bill.) They're fighting to end public funding of circumcisions on the grounds that this procedure, like elective abortion, is "nontherapeutic" and "not health care." They're planning lawsuits to intimidate doctors and ban infant circumcision through the courts.

The rest of the time, they talk like radical feminists. They're outraged that we deplore female mutilation but tolerate male circumcision. They call this sex discrimination and a violation of the Constitution's equal protection clause. Their founding declaration opposes, in the same breath, "foreskin, clitoral, or labial amputation." The ICGI has even proposed an international legal code equating removal of the foreskin with removal of the clitoris.

Have these people lost their heads?

The stakes in that question are becoming deadly serious. Of the 5 million people who contracted HIV last year, two-thirds lived in sub-Saharan Africa. In Swaziland, more than one-third of adults have the virus. In South Africa, nearly 30 percent of pregnant women are carrying it. Four years ago, an analysis of 38 studies by the U.S. Agency for International Development, mostly in Africa, concluded that circumcised men were less than half as likely as uncircumcised men to get HIV, apparently because of the susceptibility of foreskin. Last fall, reporting on a randomized controlled trial in South Africa, scientists found that circumcision reduced female-to-male transmission by 60 percent. "Male circumcision provides a degree of protection against acquiring HIV infection, equivalent to what a vaccine of high efficacy would have achieved," they wrote. It was, they observed, "the first experimental study demonstrating that surgery can be used to prevent an infectious disease."

Think about that: surgery as a vaccine. Drug researchers would kill for an HIV vaccine half as effective as circumcision. Condoms and abstinence often aren't effective because they require diligence. Circumcision works more reliably for the same reason foreskin enthusiasts hate it: It lasts forever. In the parlance of AIDS doctors, it's a "one-off intervention." Using the new data, scientists estimate that over the next 20 years, circumcision in sub-Saharan Africa could prevent 6 million infections and 3 million deaths.

What do you do when mutilation turns out to save lives? Anti-circumcisionists can't bear it. Years ago, they denied the HIV-prevention effect. When evidence from Africa defied them, they changed the subject to Europe. When evidence from Europe defied them, they changed the subject again. Some say a link between circumcision and HIV can never be proved. Others ignore it. Others insist it's unethical and false. It can't be true. It's heresy.

The strongest argument against circumcising babies to prevent HIV is that they're too young to consent, and they won't be at risk for the virus till they're grown. But we vaccinate babies all the time. Should we treat circumcision like a vaccine? At clinics across southern Africa, men are lining up, pleading, and nearly rioting to be circumcised. They want protection. Can we assume their sons would want the same thing?

Next weekend in Seattle, critics of genital mutilation are convening an international symposium on circumcision. The program lists 40 sessions. Not one mentions AIDS or male circumcision in Africa. Something's sorely missing from this conversation, and it ain't foreskin.

A version of this piece appears in the Washington Post Outlook section.