AIDS is now the leading cause of death in Africa, where twenty-eight million people are HIV-positive, and where some twelve million children have lost one or both parents to AIDS. In Zimbabwe, 45 percent of children under the age of five are HIV-positive, and the epidemic has shortened life expectancy by twenty-two years. A fifteen-year-old in Botswana or South Africa has a one-in-two chance of dying of AIDS. AIDS deaths are so widespread in sub-Saharan...