The malaria parasite has been responsible for half of all human deaths since the Stone Age

One in 14 modern humans carry genes that first arose to help protect people from its ravages. Today, it sickens 300 million people every year, and kills nearly 1 million, despite the fact that doctors and scientists have known how to cure it (with parasite-killing drugs) and prevent it (by avoiding mosquito bites) for over a century.