By combining full-genome sequencing and ‘evolutionary replay’ experiments to dissect the origin of aerobic citrate use in an experimental Escherichia coli population over 40,000 generations and 2 decades, the authors unveil a 3-step process in which potentiation makes a trait possible, actualization makes the trait manifest and refinement makes it effective.

The crystal structure of an influenza antibody that recognizes a small, conserved site in the variable receptor-binding domain of HA is described; this antibody shows broad neutralization across multiple subtypes of influenza A virus through an antibody–antigen interaction dominated by a single heavy-chain complementarity-determining region 3 loop.