Whole-genome sequencing of >200 pathogenic and non-pathogenic species of the Yersinia genus of bacteria has revealed that pathogenic members of the genus — including Yersinia pestis (which causes bubonic plague) and Yersinia enterocolitica (which causes gastroenteritis) — have followed parallel evolutionary paths. Phylogenetic analysis shows that these two species did not share a recent common ancestor, as previously thought, but evolved independently to acquire virulence factors and to lose several metabolic genes on the transitional route to pathogenicity.