Wouldn't it be great if scientists could genetically engineer mosquitoes to be immune to the malaria parasite, thus protecting people from that disease? How about restoring the effectiveness of a pesticide by eliminating resistance genes in weeds and insect pests? Or altering genomes to eradicate a pesky invasive species? These are exactly the sorts of things that a brand new biotechnological tool could do, and it's got some people worried. Reason Science Correspondent Ronald Bailey looks into how "gene drives" can be used safely to manage wild ecosystems.