Langridge et al. characterized the evolution of a single lineage of Salmonella enterica subsp. enterica, a primary cause of foodborne gastroenteritis. This lineage comprises closely related members that exhibit differential host range, including host generalists (S. enterica serovar Enteritidis), as well as host specialists (S. Gallinarum and S. Dublin, which infect galiforme birds and cattle, respectively). The authors sequenced the whole genomes of 60 Salmonella isolates, which were selected to represent a range of serovar, sequence and geographical diversity, and reconstructed the phylogeny and evolutionary history of this Salmonella lineage. They tracked the order of adaptive events and pseudogene formation that resulted in differentially host-adapted pathogens. In particular, they found a degradation of common metabolic pathways in members showing host restriction rather than generalism, and confirmed the functional impact of gene loss with phenotyping assays. They identified a new clade within S. Enteritidis, which was demonstrated to show intermediate levels of pathogenicity between ancestral S. Enteritidis and S. Gallinarum in an avian model of infection. The authors suggest that this represents an intermediate stage in the evolution of host adaptation.