Which is the lesser of two evils — malaria or DDT? The former kills a million people per year in Africa, many of them infants and children; the latter is the most effective weapon against the virulent disease, but is lethal to fish and wildlife, and thought to be hazardous to humans as well. Two years ago, South Africa opted to fight malaria with DDT — a decision one government official called “a horrible choice” — and infections and fatalities are dropping. Neighboring Mozambique has eschewed DDT, fearing that floods such as those that recently devastated the country could spread the toxic chemical and create worse health problems than the one it is meant to control. In the meantime, though, malaria remains the nation’s leading cause of death for children.