Resistance is useless

Evolutionary theory may help to fight a fatal diseaseLIKE many other activities, global health has fashions. For the past couple of decades AIDS has captured both the imagination and the research dollars. Recently, though, the focus has shifted towards malaria, which kills a million people a year, most of them children, and debilitates hundreds of millions more. Insecticide-impregnated bednets designed to stop people being bitten by infected mosquitoes are being scattered throughout Africa. New drugs based on a Chinese herb called Artemisia have been introduced. And researchers are vying with one another to be the first to devise an effective vaccine. But the traditional first line of attack on malaria, killing the mosquitoes themselves, has yet to have a serious makeover.One reason is that time and again chemical insecticides have produced the same dreary pattern. They prove wonderfully effective at first, only to dwindle into uselessness. This is because evolution quickly throws up resistant strains. Indeed, spraying campaigns, which generally aim to kill mosquitoes before they can breed, might have been devised as textbook examples of how to provoke an evolutionary response. With their competitors all dead, the progeny of a mosquito carrying a mutation that can neutralise the insecticide in question have the world to themselves. ...