In 2013, some 200 million humans suffered from malaria, and an estimated 584,000 of them died, 90 percent in Africa. The vast majority of those killed were children under age 5. Decades of research have fallen short of a vaccine for this scourge. A powerful new technique that allows scientists to selectively edit entire genomes could provide a solution, but it also poses risks—and ethical questions science is only beginning to address.

The technique relies on a tool called a gene drive, something scientists have discussed since 2003 but which has only recently become possible. A gene drive greatly increases the odds that a particular gene will be inherited by all future generations. Genes occasionally evolve the ability naturally, but if we could engineer it deliberately, small interventions could have enormous impact, giving scientists the power to eradicate diseases, remove invasive species, and wholly remake the natural landscape.

One proposed use of a gene drive would alter the genetic code of a few mosquitoes that carry the malaria parasite, ensuring that the ‘Y’ chromosome would always be passed on. The...