Extinctions to order: Gene-ocide.

IN A competition to find the world’s least-loved animal, the mosquito would be hard to beat. Only a few species of the insect carry the parasites that cause human diseases such as West Nile virus, dengue and yellow fever, but the harm they cause is enormous. Malaria kills more than 400,000 people, mostly children, every year. Zika has spread to dozens of countries (see article). If species such as Anopheles gambiae and Aedes aegypti could be eradicated, the world would surely be a better place.; ; Genetic engineers have already taken some steps in that direction: male A. aegypti mosquitoes that have been modified to become sterile have been released in Brazil, for example. Such approaches, controversial though they are among some greens, are limited in their impact and geographical range. A nascent technique called a “gene drive”, which could make it far easier to wipe out species, raises harder questions.