The relationships between human populations, as calculated from H. pylori found in stomachs and from mitochondrial DNA data. (a) Relationships between modern subpopulations of H. pylori . Each subpopulation is represented by a circle with a diameter proportional to the genetic diversity within it. The centres of the circles are joined by a phylogenetic tree showing the relationships between the four subpopulations. Bacteria in each subpopulation are found predominantly in people who originate from the regions shown. (b) A population-level phylogenetic tree of the H. pylori geographic subpopulations shown in (a). (c) A median-joining network of human populations derived from mitochondrial DNA . Such a network shows alternative potential evolutionary relationships between clusters. Each circle represents a cluster of mitochondrial types with a diameter proportional to the frequency of that type within the subpopulations. All non-African populations are derived from one African lineage; the network of relationships within this lineage is magnified (top). (a,b) Adapted from ; (c) adapted from .