Most powerful new technologies are double-edged. Cars are a vast improvement on horses as a means of transportation, but they also kill more than three thousand people a day and they are a major source of pollution.

So here comes another double-edged technology, and its edges are very sharp. Gene drives can spread an engineered mutation through an entire species with amazing speed, which means that you could, for example, make the breeds of mosquitoes that transmit the malaria parasite to human being immune to the parasite themselves. (You could also just wipe those species of mosquito out, but then a lot of birds and bats would starve.)

The idea of a gene drive was first suggested 12 years ago by Austin Burt, an evolutionary geneticist at Imperial College in London. What drew his attention were certain naturally occurring "selfish" genes, known as homing endonuclease genes, that can get themselves passed on to the next generation more than the usual fifty percent of the time.