The history of the powerful genetic publishing technique, which was this year recognised with the Nobel Prize for Chemistry and which may in the near future be the solution to many diseases that are now incurable, began more than 3 billion years ago when the first bacteria and bacteriophages, the viruses that are their predators, appeared. These viruses can help us to tackle the very serious problem of bacterial resistance to antibiotics. This is the fourth episode of the “Brave New World”. Statements by Joana Azeredo, biological engineer of the School of Engineering of University of Minho.