Viruses have a secret, altruistic social life

Researchers are beginning to understand the ways in which viruses strategically manipulate and cooperate with one another. Social organisms come in all shapes and sizes, from the obviously gregarious ones like mammals and birds down to the more cryptic socializers like bacteria. Evolutionary biologists often puzzle over altruistic behaviors among them, because self-sacrificing individuals would at first seem to be at a severe disadvantage under natural selection. William D. Hamilton, one of the 20th century’s most prominent evolutionary theorists, developed a mathematical theory to explain the evolution of altruism through kin selection — for instance, why most individual ants, bees and wasps forgo the ability to reproduce and instead pour all their efforts into raising their siblings. Bacteriologists developed game-theory models to explain why bacteria in groups produce metabolites for their neighbors, even though some cheaters take advantage of the situation. But until recently, no one had considered that simple viruses, too, have...