There are also practical obstacles. Like any operation, circumcision presents a risk of infection. Much of Africa lacks the equipment and personnel to perform the procedure on a large scale. But similar arguments were made against the possibility of AIDS treatment. A concerted American and international commitment proved that pessimism to be unjustified.

The main problem with circumcision is that it is only partially protective. If a newly circumcised male stops using condoms or increases his number of partners out of a false sense of invulnerability, his risk of getting AIDS rises, along with the risk of giving it. The Uganda and Kenya studies found no increase in risky sexual behavior after circumcision. But clearly health education will be required. "People will still need to use condoms consistently," Bailey says, "still need to reduce their partners, still need to practice faithfulness."

As circumcision scales up, the reductions in overall infection rates will be gradual. But the implications for the individual man in Africa are dramatic. A $40 or $50 procedure can cut his risk of HIV infection in half. Giving him that option is a matter of moral urgency.

That begins with African governments. Both routine infant circumcision and adult circumcision must be considered, especially in the areas of highest infection. International donors need to aggressively support African circumcision programs with new resources. And European governments, which have refused to deal with this issue, need to start respecting the data and lend their support.

Circumcision has played a mixed role in history. During the worst days of the India-Pakistan partition in the 1940s, Muslims ambushed trains and murdered every uncircumcised male, knowing they were Hindus. Hindus used the same method to identify Muslims.

Today this source of division is becoming a source of hope that could eventually save many lives. When it comes to AIDS, circumcision is the kindest cut.